RC Boat Tips

The tips presented below are the result of our experience and from other R/C boaters from Brazil and other countries. Collected from personal conversations, reading R/C books and from web sites specializing on the hobby, mainly Jim's R/C Boat Dock Page (link on link section). We do not intend these tips to be original, but only to be useful.

General

Using your equipment on salt water

Special care should be taken if you run your boat in salt water. At the end of the day's activities, wash the hull and all metallic parts with plenty of fresh water and neutral soap. Protect the carb inlet and use a lot of water. If you have access to a air compressor, use it, if not use rags and brushes. Remove the flex cable, prop shaft, prop and all other removable parts, grease everything in the drive system with nautical grease. Take off the radio box lid, check for humidity on the electronics and dry it carefully. Leave the box open to evaporate any remaining moisture. Now, apply spray oil to all metallic parts you can see and even on that ones you can't see but you know are there. Don�t forget to oil the rudder pivot.

With proper care and knowing that all our boats use stainless steel, aluminum and brass hardware, your boat is well protected. By the way, when assembling a engine we substitute all the original steel screws with stainless steel ones. It takes roughly 40 screws and insures much better durability.

Before putting your boat on water

Check the tightness of all screws, mainly the ones that mount the engine, the rudders and propeller. On sail boats check, specifically, the mast and rudder screw. The worst enemy of your electronics is water, mainly salt water. It's just impossible to make a completely sealed radio box - too many holes for antenna, accelerator and rudder cables/rods, wires, etc. Make those holes with the small diameter possible; close with silicone when possible. For the ones where this is not possible - rudder and carburetor cables, use rubber boots for protection. Keep the receiver inside plastic bags - make a small hole for the antenna wire and close the bag - including the small hole - with plastic straps.

Flotation

It is of utmost importance that your boat floats when - and this will happen sooner or later - it turns upside down on the water. Either from aggressive driving or because you faced a big wave or too strong a wind. Sooner or later you will be on the shore, looking at a boat that, hopefully, floats with the bottom end up. The best, cheapest and most effective floatation you can use is an empty plastic soda bottle. Take the cap off, squeeze the bottle and insert as many as you can under the bow. Blow them to their original shape and securely tighten the cap. More over, and as this trick can only be used at the bow, and to prevent your boat to become a buoy when submersed, fix to the hull's open portion as many pools noodles as you can.

Getting rid of ingested water

It happened. Your boat is upside down in the middle of the lake. Of course it was not your fault... But the important thing to know is what to do. As you followed the above tip about flotation � I hope - your boat will be (hopefully) floating and not sunken. After using all your stock of bad words, it's time to recover your boat and fix the damage:

Empty the gas tank and fuel lines. Take off the spark plug, flip the engine over. Let the water drain. Spray a lot of WD-40 into the spark plug hole and into the carb bore. Connect the ignition coil to the spark plug. Ground it, otherwise your can damage your coil. Pull the starter many times. While there is a brown liquid going out from the hole, there is water inside. More WD-40, more pulls of the starter. When only oil comes out, put the spark plug in place, fill the gas tank with new fuel and start the engine. You must use some kind of refrigeration to cool the engine. See below how to make one. Start the engine a few times, to be sure everything is OK. It is a good idea to take your engine out of the boat and disassemble, dry, clean and oil the starter. The return coil has a bad habit of rusting with water. Take off the plug again. Fill the cylinder with the same oil you mix to gas. Pull the starter slowly. Let the oil go down to the case. The next time you start the engine, you will need to get rid of the excess oil in the case. At that time, take the plug off, put the engine upside down and pull the starter until the excess oil has came out. About the electronics, look below how to repair a wet receiver.

Note: About grounding the spark plug, lets see what my friend William has to say: "If you pull start your engine without grounding the spark plug you will have, at the plug's terminal, an infinite resistance. Without a path to discharge the spark, the high voltage generated at the coil will try to jump trough the coil wires, destroying the isolation and the coil"

Running the engine out of water

Although the final adjustment of the engine just can be done with the boat on water, during normal use, the first adjustments are always made out of water. This requires some sort of cooling, without cooling the engine will overheat with possible damage to it. A cheap and efficient system cam be made at marginal expense using a plastic soda bottle, a few feet of aquarium line, a plastic valve also used on aquariums and a piece of wire. Make a hole in the bottle's cap and epoxy the line in the cap, so the tip of the line barely passes the bottle's neck. Insert the other end of the line onto the valve. On the valve outlet fasten a 5 inch piece of the plastic line. Make a hole on the bottle's bottom, that will double as a ventilation and filling device and also as a support for the wire, that should be bent in a hook fashion. When out of water, fill the bottle with water by the bottom hole, closing the valve. Hang the bottle anywhere higher than your boat, take off one of the original water inlet lines at the water jacket and insert the line from the plastic valve. Open the valve and adjust the water flow, to maintain the normal operating temperature for the running engine - that is, the water jacket should be warm but not so warm that cannot be touched with your bare hands. Presto: you have all the time you need to adjust your engine. REMEMBER: When out of water the engine reaches higher RPM�s than recommended. Take care with the accelerator under these circumstances. The prop shaft�s thrust washers and bushings are lubricated and cooled by water when the boat is moving. Don't run the engine more than 2 minutes out of water.

Hull

Trim Tabs

Inner trim tabs are the ones closer to the keel. Besides adjusting the boat's attitude on water, they may be used to correct torque roll, the tendency the hull has to lean to the right as a reaction to the engine torque. In this instance, the right part - starboard - should be opened, lifting the hull's right side. As a consequence, the bow gets deep in the water. Eventually, closing the left trim tab - port side - could be a better alternative. attitude on water, they may be used to correct torque roll, the tendency the hull has to lean to the right as a reaction to the engine torque. In this instance, the right part - starboard - should be opened, lifting the hull's right side. As a consequence, the bow gets deep in the water. Eventually, closing the left trim tab - port side - could be a better alternative.

The outer trim tabs - far from the keel - are used to adjust boat's attitude on turns. The bigger the angle the more the transom lifting at that side, the deeper the bow and the sharper the turns. outer trim tabs - far from the keel - are used to adjust boat's attitude on turns. The bigger the angle the more the transom lifting at that side, the deeper the bow and the sharper the turns.

There is also a consensus that the trim tabs would not be lined with the hull bottom. 1/8" looks like a good distance. With this, unwanted drag is prevented and the tabs acting as a hull extension is minimized.

I seldom, if ever, use trim tabs. So, I hardly qualify as an expert on this issue. But they are sometimes necessary and answering a post at his board Jim Nissen got to the point. That was the question:

"Is there a rule of thumb that dictates how far the inner edge of the inboard trim tabs should be from the centerline of the keel on a mono? I have read or heard numbers from 7/8" to 1-1/2". Is it important that the inner edge of the trim tab be positioned so that it is outside the prop diameter?"

And the answer:

"Yeah it really depends on the angle of the mono or deep vee as well as the diameter of the prop. I have setup monos normally with the tabs just to the outside of the prop's diameter. If the hull is rather wide you can get away with a second set of tab's on the outside. The best race setup's typically will use one wide tab per side but then split it in the middle to produce inside and outside tabs.

I would not recommend putting them in any closer to the keel than the outer prop diameter. The closer they are to the keel line the more shallow the prop will surface and less water it will have to work with. This can be a good thing in low power setup's but be very bad for higher output motors.

Oh and remember the most important aspect of tabs. They tend to act like a hull extension. The boat will have more lift the closer they are to the keel line. Move them outside and the hull will be allowed to ride lower in the water. There is a limit though to the amount of lowering the hull will be allowed to do. The limit is the hull design itself."

Bellow, a pic of a Ron Frank's boat with out and inner trim tabs.

Turn Fin

Should be installed at the chine line parallel to the keel and perpendicular to the hull. In a way that, when the boat leans at the turn it should be in a vertical position to the water surface or slightly tilted toward the keel. Only when turning, as the hull rolls into the turn, are they supposed to dip the water. When traveling in a straight line they should not touch the water, this is to avoid drag

Hull porposing (up and down oscillation of the bow, when traveling in a straight line)

Normally occurs on monos with surface drive, when the prop is too far from the transom. To correct, bring the prop closer to the transom. Adjust half an inch each time, until the oscillation ceases. After correction, adjust the strut angle to determine the bow height when running.

What makes a high lift hull?

Strakes that run back pretty far and/or are also pretty sharp

A very rounded keel

As Jim Nissen says:

"The strakes are flat riding surfaces that limit the water from spilling off to the sides. As a result they act like ski's. They tend to make the hull ride on top of the water opposed to cutting through it. The further back toward the transom the strakes extend then the bigger the ski (surface area for this to occur). All high speed hulls eliminate the strakes several inches ahead of the transom or eliminate them completely. This allows the hull to lift up to the point where the strakes end. The rounded keel doesn't help much either. As Don says - it's like a rounded ride pad.
A sharp keel cuts through the water and will limit lift. Even sharp keels have limitations. Ride pads integrated into the hull bottom have to be used once you hit speeds in the upper 50-60 MPH range. At this kind of speed even a sharp strake less keel can provide enough lift to cause chine walking. Trim tabs can help but your really fighting against the physics involved and mother nature will win this one! "

Bellow, a picture of a ride pad on Ron Frank's boat

Rudders: Don Betz is a big fan of Speedmaster rudders. His choice for gas boats is a 65/90 single water pick-up, with the gas bracket (longest) and the water passage drilled to 1/8.

Engine

Breaking in

Although some engine makers - Zenoah included - say that their engines don't need any special break-in procedures, some precautions should be taken until your engine has used at least ½ of a gallon of fuel.

Oil. Increase the amount of oil mixed to gas. We like to use 25:1 on engines already broken in, which comes to be more oil than the Zenoah suggestion of 32:1. During the first tanks this mix should be 20:1, for easier setting of the rings.

Adjusting the engine. During this same period, open the needle 1/8 turn above the normal adjustment.

Look for the color of the spark plug ceramic.

Light gray: too lean, adjust immediately. Turn the needles counter clockwise.

Brown, from light to middle dark: OK. During break in it's desirably that the element be on the darker side

Black: too rich. Turn the needles clockwise.

For all those adjustments turn the needles 1/8 each time

Needles

A tip from Mike Hoffmeister:

Just cut two pieces of medium blue silicone hose, about 1/4" long, and slide them up on the shank of the needle valves. The pieces interfere with each other just enough to damp vibrations and keep the needles from falling out (especially the low-speed needle). The only concern is to make sure that when you adjust one, it does not cause the other to rotate!

The picture bellow show how this work. Simple and efficient.

Water pump

A boat without a water pump relies on it's forward movement to push water through the water jacket. If your boat has a clutch, a water pump, which works even with a stationary boat is mandatory.

Gas oil mixture

A 2 stroke engine runs on a gas/oil mix. Period. It's unbelievable the number of engines that need reworking because the happy owner forgot this little detail. The result is an engine that will need a complete tear down and new piston and rings and maybe the cylinder itself. The engine makers recommend a 32/1 to 50/1 ratio mixture for their engines what means that, for each 32 (or 50) parts of gas you should add 1 part of oil. FORGET IT! This mixture is good for a engine running on a weed eater between 4 - 5000 RPM. Not on a boat, with a hopped up engine. It will be much happier with 25:1 mixture. Translating the math, each gallon of mixture should have 5 - 8oz of first grade 2 stroke oil. Don't try to save on fuel: it's the cheapest item of your equipment. Bellow, some recommendations from experimented boaters:

Amsoil
Blendzall Racing Castor
Golden spectrol
Honda HP-2 synthetic racing oil
Klotz Super Techniplate 80% synthetic 20% racing castor oil
Quicksilver, Mercury Outboard
Redline 2 cycle Racing
Silkolene Pro2. 100% synthetic

Old mixture

Mix just the amount of gas you intend to use in one or two weeks. Aged gas, especially if mixed with oil, looses its combustive properties and evaporates away part of its chemical components. This causes hard starting and low power.

Gas tank placement

Put your gas tank as close the CG of your boat as possible. Like this, you reduce the CG alteration when running your boat. Besides, the fuel line will be shorter - witch is always better.

Tank ventilation

Make a coil from 1.5 foot of gas line, coil it and connect to the gas vent outlet. In the event of a roll over, fill the tank by the return line until gas is expelled from the ventilation coil, and all water in the lines will be expelled.

Auxiliary tank

Connect a 2 ounce auxiliary tank to the vent line. Connect the main tank to the auxiliary tank with a fuel line and a brass tube that reaches the center of the auxiliary tank. The vent tube must be at the top of the tank, so, if water enters the system through the auxiliary tank, the main will not be affected. Position the auxiliary tank in a way it can be easily removed and any water removed. Look bellow. Using a film canister instead of the auxiliary tank is also a tip that have more than few users.

Ultimate gas tank setup

This is a tip that Ron Frank posted at Jim's board. Not being enough, he posted also pics about it..

"After running an IV bag fuel tank for a year I finally came up with the best of both worlds.

A plastic tank is easy to fill and vent BUT will pickup water in a flip/blow over.

The "bladder" or IV tank needs no vent and will not pickup any water in a flip/blow over BUT is a pain to fill & get the air bubbles out, Especially in the confined space of a mono when the bag is under the motor..

SOLUTION: A hybrid setup using a standard tank BUT the vent goes to a 250ML IV bag. It's filled thru the return line (WA-167 or any carb with a primer bulb), A Quick-Fill valve or a separate sealable fill line(WT-257 or other carb without a primer bulb}. The vent is a sealed system so no water can enter the tank.

It's worked well with a plastic tank /IV hybred and an IV/IV setup. On the IV/IV I mount the primary (500ML )bag under the motor, run 1 feed line to the carb & a vent line to the 250ML bag mounted in the bow. The vent bag is elevated so the air flows into it when refilling. No need to worry about air in the primary bag, Just gas & go..

As Mel Gibson said in "Lethal Weapon", "Works for me"

Good luck
Ron"

IV Bags

To the best of my knowledge, Don Betz (db) was the first one to come with the idea of using an IV bag as a gas tank. The pros are so many that this setup is quickly becoming a unanimity between us. Here, he explains how to install one:

"Supersimple.
1L I.V. Bag
Position:
Outputs facing aft, end of the bag about even with the output side of motor, span the rails at forward side of bag with zip-ties and loop them through the hanging hole in bag.
Hookup:
Different bags have different line configurations but you'll get the idea. Go to the auto-parts store and get a barbed plastic "T" fitting (vacuum, or windshield washer fittings). Stick one of the tops of the "T" into the output line in the bag. Attach large Tygon to the other top of the "T" and run that to an inline filter then to the carb. The other part of the "T" is your filler line, you just attach another several inch long piece of Tygon that you can just plug and unplug to add fuel.
Usage:
Fill the tank, once nearly full lift the aft end of the boat and pump the air out of the tank. Unplug the filler and replace the plug in the boat filler line.
Supersimple.

LOW center of gravity.
Changing weight very near the fore-aft C of G.
Closed system, NO water contamination potential.
Supersimple.

The main reason I came up with this idea was to get the changing weight near the C of G. Think about it, with a normal tank mounted in front of the motor the bow of the boat gets lighter as it runs lower on fuel. This is also interestingly enough around the same time that the race water is getting really churned up, right?

I still can't seem to finish races but Oh well. Hopefully the L45 will get me to the finish this season
db
dbetz@fuse.net"

Wayne Rathbun, from Jim's site, posted this pic that perfectly illustrates how to fix fuel lines to an IV bag:

Fuel lines

The Walbro 167A carb uses 2 fuel lines, both connected to the fuel tank. The first one is the feeding line, the second is the return line. As the carb works on any position, I suggest using the primer (clear plastic bulb) up. This makes priming the fuel a lot easier. In this arrangement, the return line is the one by the primer, the supply line is at the opposite side. If you are using a quick fill valve, look at the drawing bellow to connect the lines.

Return line blocking

Matthew Waldron, from MD Designs, uses to block the primer exit to the tank. He states that, under some circumstances, vibrations from the engine may cause problems on the diaphragm or valve. It never happened to me, but Matthew is a very experienced boater and his advises must be taken in consideration. I quote him, when answering a question posted on Jim's Board:

"We observed that while running the motor at some speeds the vibrations were enough to make the diaphragm or valve open up in the primer bulb and lose fuel out the fitting, after blocking it off the motors were easier to set the needles and the ran better with out have to adjust for different fuel flow rates. All we do now is prime the carb and put a cap on the exit fitting from the carb.

Fuel line length

The shorter, the best. Don�t use a fuel line longer than 1 foot, place your fuel tank near the engine. By the way, the close the tank to the engine the less the CG will change when the tank empties.

Needles settings

Carburetor WT-257, engine QD 25 or Zenoah: low side: 2 to 2.50
high : .75 to 1.25

Zenoah engine, modified: low side: 3/4 to 1
high : 2 to 2-1/4

Premium gas

Well, I was maybe the last one to be convinced about this matter. I read a lot about it, and now things make sense. High octane gas has additives to SLOW the burning time, as to prevent detonation on high compression ratio engines. Our 2 stroke engines are LOW compression engines, so this kind of gas is not necessary and even undesirable because they tend to burn - part of it - into the tuned pipe, making no useful power over the piston. I have a very good reason to taking so much time to see the light: Brazilian gas has a lower octane rating when compared to USA pump gas. In Brazil I do use - and recommend - special gas, which has the same octane rating as regular on USA. Thanks to Mike H., Ron Frank and other that showed me, with facts, that I was wrong.

Clearance between the coil and flywheel:

0.015 - 0.016 inches( 0.38/0.4 mm). This allows a good spark and, at the same time, avoids the coil touching the flywheel which cause drag, loss of power and radio interference. If necessary, to adjust the clearance, file the mounting holes of the coil.

Jim asked Zenoah about specifications for the manufacturers coils. That's the response:

RED Coil: Secondary voltage Ignition Timing
@1.000 rpm 16KV @ 7.000 rpm 30 BTDC
@7.000 rpm 28KV @10.000 rpm 28 BTDC

GRAY Coil: @1.000 rpm 20KV @ 7.000 rpm 28 BTDC
@7.000 rpm 20KV @10.000 rpm 25 BTDC

"As you maybe know, the gray coil has good performance at low (idle-7.000rpm) and the red coil has good performance at high (over 7.000rpm) range."

"This difference is set up according to the engine purpose, red coil (G230PUH/PUM is for high power at high rpm range, gray coil G230PU) is for easy starting by propeller flipping and good power at mid (7.000)rpm range."

Komatsu said the coil/flywheel gap should be .3mm, and .2mm if you can get it. The smaller gap the hotter the fire.

Not a word on the mysterious black coil.

Additional information from the 260 Zenoah Manual

Source Coil 1160-71211:
Between Coil core and Red wire = infinite resistance (open)
Between Coil core and Black wire = 185 ohms

Source Coil 2629-71210:
Between Coil core and Red wire = infinite resistance (open)
Between Coil core and Black wire = 255 ohms

How big is a big bore Walbro?

There is a lot of discussion about how big is a Walbro carb. You can do one of two things to discover: look at the 11 pounds Walbro Service Manual (if you can find one) or do what Mike T. says:

"On a Walbro, there is a number in a small circle at the air inlet. That denotes the venturi (the small part) diameter in 64ths of an inch. A WA-167 has the number 28, which is 28/64. That fraction reduces to 7/16th of an inch. A wee bit less than a half inch. About 11mm. "

Intake manifold for big bore carbs:

Jeff Thompson offered this tip on how to make an intake manifold for a big bore carb, using the stock one as a starting point. This guy knows what he says:

I have seen a few Big bore intakes on the market and here's a tip for the new guy's ,it will save you some buck's, I have used this trick for a while and it work's, and I get asked this a lot so here goes, Take your stock intake off and JB weld up the vacuum port's and the other void area's, let it dry and lay out some 180 or 220 sand paper on a good flat surface then sand it just enough to take off the excess epoxy, Then measure your throat on the carb and drill out the intake to match the big bore carb. word to the wise when you start to drill it out go in about 1/8" on both side's then drill all the way threw, Best to use a drill press. OK now that you have that. To operate the carb correctly take out the big screw on the top of your carb, you will see a beefy raised area on there by the screw hole on the cover plate drill it out and tap it using a 10/32 tap and install a nipple. and put the cover back on the carb, next install a nipple in your case on the side or in the crank cover, make up new intake gasket's and run a 5/32 vacuum hose from the case to the nipple on the carb.

A tip from Paul Govostes

The Walbro (WYK-33 Barrel Carbs), have just the (one H-Jet) needle visible. The Low Jet is a tiny screw which is hidden under a very small plastic cover. These Walbro Carbs come standard on the 35cc QuickDraw Engines and they are great carbs.

Quick-Fill valve installation

A Quick-Fill valve makes easy filling and, mainly, emptying the tank, witch is mandatory at the end of the day, when there is some fuel left. The drawing bellow shows how to make the connections to a carb with primer bulb. If you carb doesn't have a primer, just ignore that specific connection.

Fuel filter/filler valve

This is a tip from Jim Jellison, replacing, at the same time, the line filter and the quick fill valve.

"This is a KJS fuel filter. The part number is 419,T Type Clear Fuel Filter. There is a filter screen in the body of the unit at the end facing the fuel line shutoff clip. This end of the filter goes to the carb. The other horizontal barb is connected to the fuel tank. The barb facing the tape measure is the fuel filler/drain barb. Just put the filter in line between the tank and carb, and then install a filler/drain line on the 3rd barb that is long enough to get over the side of the boat and connect to your fuel jug outside the boat. No mess, No fuss, No leakage. Nothing to break. In addition you need a fuel line plug for the filler line. I have found the fuel line shutoff clip is not necessary, as the carb never gets flooded during the fueling process. Of course you drain the fuel tank through the same line. Works great. Price $3.50 per filter"

Coil test

Testing the coil is not a easy task. First, because the small gap at the plug, the spark at the spark plug, when out of the engine, is not a secure indication that the coil is in good shape. Out of the cylinder, and having not to overcome the resistance of the compressed mixture, even a defective coil may produce a spark. Second, the spark gap makes a very small and hard to see spark. Solution? You may improvise, with leftover material, a very effective tester for your plug. Look the picture bellow.

Basically, what we have is a metal shaft with a conical tip, fixed to a metallic base, electrically isolated from the base by a nylon or similar material bushing, soldered to a piece of spark plug wire. At the other end, a screw that can came close to the conical tip. This screw is not isolated from the metal base. Fixed to the base, making electrical contact with it, a wire with a alligator clip.
Utilization: First, establish the maximum distance from what the coil is able to produce a spark. Connect the alligator clip to a good ground at the engine. Take of the plug and connect the two plug wires together - the one from the engine to the one from the tester. Separate the screw from the conical tip ant pull the starter. The spark will be easily seen. Continue the process, until there is no spark anymore. Go back with the screw to get the spark back. You have just discovered the maximum gap your coil is capable of making a spark jump. Register the information. From now on, whenever you need to check the coil, connect it to the tester and check the distance you have a spark. If much less than the registered, you have a defective coil. Believe me, it's easy to use and works.

Carb fuel inlet

Sometimes, you would like having the carb inlet in a different angle. Don't force it. It's plastic and breaks half the times you try it. Larry has a better option:

Pull the fitting out, take the bottom off the carb. The hole is the right size for a 10/32 tap, thread the hole and then you can put any kind of fitting you want. Blow out the hole and put the bottom back on the carb. you can find straight or angel fittings so you can point the fitting any direction you wish.

Larry Ingelson

Fuel filter

Always use at least one filter between the tank and the carb. Whenever possible, use another one between the fuel line/quick valve and the tank.

Water lines connections

The water cooling system of your boat includes the water pickup, water pump (optional), water inlets and outlets at the water jacket, header and coupler water cooled or not. The pictures bellow show how to connect the lines on each one of those systems. We always recommend 2 pickups, if one of them clogs, the other will take care of the cooling. If the water pickup has only 1 inlet, use a Y to connect both pickups to the engine. The water pump is normally only used on engines with a clutch. If this is not the case for you, just ignore the pump at the pics. I like, whenever possible, having all the water inlets coming to the engine water jacket - it's the most critical part of the system, if something fails an expensive engine may be lost. From this basic setup. you may adjust your connections. On a system where neither the header nor the coupler are cooled, the engine outlet(s) conduct the water to the outside of the boat. One last word: use the lower connections as inlets - outlets at the higher ones. This way, the cooling water has to travel trough the entire system before leaving.

The letters at the pics are:

A: pickups
B: water pump
C: water inlets at the engine
D: water outlets at the engine
E: water inlet at the header
F: water outlet at the header
G: water inlet at the coupler
H: water outlet at the coupler

Lines without connections are the outlets from the boat.

System 1: Engine with 2 inlets and 2 outlets, cooled header and coupler.

System 2: Engine with 2 inlets and 2 outlets, cooled header and no cooled coupler.

System 3: Engine with 1 inlet and 2 outlets, cooled header and coupler.

System 4: Engine with 1 inlet and 2 outlets, cooled header and no cooled coupler.

System 5: Engine with 1 inlet and 1 outlet, cooled header and coupler.

System 6: Engine with 1 inlet and 1 outlet, cooled header and no cooled coupler.

Checking compression

Checking the engine compression is an excellent indicator of it's health. While new or in good conditions, check and register the compression. This number will be a parameter whenever you need to check the engine condition after some time of using it (months, years, any time you feel it necessary). The pics bellow show how simple is the operation. Use a gauge from automotive line, that reads, at least, 200 PSI. They are trustful and accurate instruments.

As compression must be measured with a fully open carb, if you are operating alone it's easy to take the carb off.

If you have someone helping you, you may skip taking off the carb. At the pic, the engine is fixed to a mount we use for this purpose. A very simple one, just a very strong wood base, with 2 aluminum rails on rubber mounts, set apart 5 inches, and with holes for different engines. Take off the spark plug, thread the instrument in place and pull the starter a few times, up to the needle stops. This is your engine compression. Take note and keep for future reference.

Homelite - Taking off the crankshaft

Homelite engines, beside being very popular have a point in common: all use bearings of the worst quality available at the market, that can't stand with the additional effort of a hopping-up. Replace bearings is not too hard - the most complicate part is taking off the crankshaft. Pics bellow show how to do this, using a press, to prevent damaging the crankshaft with a hammer. The part # are 6001 - front and 6201 rear.

Take the opportunity and replace also the oil seals.

Finally, the totally disassembled engine

Homelite insulator block

Homelite dealers have an insulator block that allows for a straight pull carb installation. On hobby shops it can costs as many as ten times the US$ 2.00 price tag at the dealers. Part # 06445

Aeromarine motor mounts

David, from Dallas RC Thunderboats, likes the Aeromarine mounts, for the 6 isolators in line with the crankshaft e for strength. Nevertheless, taking the engine out is a lot of work:

The solution came from the old Hyper Torque mounts, simple and efficient.

Exhaust pipes

Fixing a tuned pipe to a McCulloch engine:

Some engines, after water cooled, loose the pipe fixing points. Tom Olejownik discovered a clever way to solve the problem, as the pics bellow show:

First step: making two 1/4" dowel pins

Following, drill and tap the pins for 8/32 screws

Prepare the cylinder to accept the pins

The 3 last remaining fins will hold the dowel pins

Inserting the dowel pins

Everything in place, the exhaust flange is hold by the screws.

Drive Train

Improving the propeller:

(This one is a post from Jim Nissen himself on his board. As he says, was not tested, but makes a lot of sense)

A tip I read about and have yet to try!

Spray machinist die on the props. Run the boat several laps and bring it in. Look at the color of the die on the props. The areas that have the die removed are doing the most work. The dark areas are areas that improvement can be made and/or material can be removed. The ideal prop would have a nice even area of die removed. This would indicate that the entire blade surface is working together to move the water.
Also will show if one blade is working harder than the other.

I hear the big boys are using this technique with great success.

Compensation for prop walk

If sharpening is not enough to eliminate prop walk, you should adjust the side to side angle of your strut. Seen from back, the prop shaft must be angled 2-4� to the left. That way, the prop will tend to push the stern to the right, diverting the bow to the left, offsetting the natural tendency to the right. Use washers to do this so you can return easily to the original setup, if necessary. Use the least angle that corrects the problem. As a alternative, the rudder trim could be adjusted a little to the left (1 or 2 clicks on transmitter trim). More than this and excessive drag will occur, with a resulting performance loss. A wider or deeper rudder can also be tried.

Two and three blades props

The props normally used in R/C boating have 2 or 3 blades. More blades = more area = more pushing force but also more drag and more power demands on the engine. Three bladed props are more often used on cats and hydros, because they produce more lift. A two blade prop is normally faster. A three blade prop is equivalent to a 2 blade prop with 1 or 2 mm larger diameter - with the same pitch.

Wedge type rudder:

As stated on Assembling your R/C boat segment, the wedge type rudder is the best one. However, commercially available wedge rudders, probably because of production facility, are not of a true wedge design. Don Betz showed a very interesting drawing on how they are and how they should be. It's requires some work to fix them, but certainly it worth.

Rudder to servo rod

Stainless steel wheels spokes can be used as neat rudder to servo rods. If you have a 4-40 die, fix the non-threaded tip to the servo arm and cut the other (threaded) tip to the right length and use the die to make another thread. If happens that you don't have the tool, save the threaded tip, cut the other to the length and make a Z bend to fix it to the servo arm.

Stuffing Tube

Sometimes, it is necessary to elongate the stuffing tube, because you change engines or because you want to change the C.G. of the boat. If the stuffing tube is fiber glassed to the hull, taking it off, replace it and fixing the new one is a hard task. An easier and quicker alternative: use a tube with a diameter just a bit bigger than the s.t. fixed to the hull, solder inside it a piece of tube with the same diameter as the s.t. and long enough to achieve the desired length and solder the support tube to the s.t. Look at the picture bellow.

Releasing a set screw from the ferrule

If you already tried Corrosion X, heat, all the bad words you know and even a few others that you didn't remember you knew, that is the ultimate solution: a Dremel, emery-stone and there goes the set screw AND the ferrule.

And now, a much better tip: don't ever, never, forget to disassemble the flex cable at the end of the day, mainly if you are running in salt water. No need to ask how I know, right?

Electronics

Batteries

The battery/receiver connectors are fragile and offer no resistance against salt water. On all our packs we use Dean connectors, much more strong and recoverable when corroded. Look at the pics bellow:

Fail safe

A dangerous situation occurs when you lose contact between the transmitter and the receiver. The immediate consequence is a total loss of control of the boat. It's hardly fun. Futaba solved the problem designing what they call a Fail Safe. It's a little electronic device linked between the receiver and the accelerator servo that closes the carb and kills the engine as soon as the receiver looses the transmitter signal. Very effective, but Futaba charges US$ 69,00 for it (plus S/H) in the USA. In Brazil you could expect to pay as much as twice this for it. For that reason, our electronic engineer and handy man developed a similar device, as effective as the one from Futaba, that costs a fraction of the price. But this was not enough. The fail safe depends on battery power to be effective. And if the battery is discharged or disconnected? The new device takes care of this: used together with the fail safe, it cuts the engine if the battery disconnects from the receiver or discharges. Total protection. The second picture compares it to the existent fail safe. And the third one shows the all new one, that incorporates the new device in a single piece. The 5th generations Shark Racing Fail Safe incorporates those devices:

a. monitor for the radio signal;
b. relay to kill the engine if the battery is discharged or disconnected;
c. a LED that indicates the receiver battery charge;
d. a sensor that kills the engine if the carb servo disconnects from the receiver.