1.01 cmb burning holes in pistons

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steve wood

Well-Known Member
Joined
Dec 6, 2004
Messages
1,773
i would like to start a new conversation that will hopefully let us find out what is causing the 1.01,in particular,to burn holes in pistons,and how to permanently find a solution to the problem.

i don't run this motor,although i have worked on many of them.

i have only talked to 1 person that has not holed a piston,and i don't know why he has not.he is running the stock button,i think.

i have heard: it's too lean.it's got too much compression,it's got too small a pipe,it's got too large a pipe,pipe is too short,pipe is too long,wrong pipe,piston crown too thin,piston material no good(burns holes in high silicone bar stock material also).you name it i've heard it,but i have not heard of a real solution to fix it.

i'm just gonna throw this out there,i don't think it's compression or pipe,i think it's a lean or fuel flow problem.

i know there are people that insist on running the water to the lower chamber in the water jacket.i think that this is a bad idea.i think that the upper chamber provides more than enough water to cool the engine,maybe too much.i think we may be overcooling all our motors.

ok lets get the ball rolling
 
Been running 1.0 and 1.01 for a long time on stock head buttons. Water in the lower chamber or not. Found that head clearance is the main casue................IMHO.
 
Look at the VAC.91 and then look at the RS.91-1.01 real close you will see the answer.

It is right in front of your eyes.

David
 
I think there are a few issues with the motors in stock form that are causing folks to hurt them, but the MAIN thing is fuel flow. The holes are from a LEAN condition!

I personal saw a big difference with simply adding additional length to the fuel line going from the needle to the carb.

The motors I won twin class with at Hobart this year were ran HARD for 11 months and are still ready for more. There are plenty of videos on youtube of it running all season with the same pair of motors AND these are the factory pistons. They can be made to last and run well for a long time.
 
Most of the pistons I've holed and the few I've seen others hole where done going thru the corners on the course!?!
 
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these engines need alot of fuel. I use cooling on the bottom and top chamber theres not a issue there i ran my engine for almost 1 1/2 years with no problems at all. LEAN CONDITIONS these engines are not 21's

I agree with Buckshot
 
Anyone who has damaged 101 pistons and sleeves that wants to donate them to science send them my way!! All the ones that I have seen and repaired were burned dead nuts in the center . The one that I holed was one that I had been running for a year , had burned out a few plugs along the way and then I changed to a different head button and did not richen it up enough apparently . I did hear it sag a tad but didn't let off ( X Mono ) and down she went . I have been using the same tank and needle system for years and it needles great with little fuss . I would have to say that a lean condition causes abnormal combustion (pre-ignition - detonation ) that eventually causes such a hotspot that it melts through in an instant .

those that have found the HOLY GRAIL expound on your findings . Buck are you saying that your longer fuel lines have in effect acted as a RESERVOIR or FUEL PLENUM in front of the carb , after the needle ?

Chuck , head clearance , expound .

David for those of us that don't have every species of engine scattered ....expound ??
 
I think so Tom.

I believe I was "sucking the needle dry" even with 5/32" tank tubes and large fuel lines.

Why did no one ever hurt the old 1.0's and now all of a sudden hole after hole after hole with the 1.01's??!!??!! I'm positive CMB changed piston material.
 
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The fuel system in the Seaducer has about 4 " to the needle and about 3 " to the carb. Now after the incident I drilled the spraybar to .095 " at the advice of Jeff Lutz but I also put a .91 piston and sleeve in it so this will be a new test for me with a 101 P/S now .
 
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The fuel system in the Seaducer has about 4 " to the needle and about 3 " to the carb. Now after the incident I drilled the spraybar to .095 " at the advice of Jeff Lutz but I also put a .91 piston and sleeve in it so this will be a new test for me with a 101 P/S now .
An increase in spray bar ID is a MUST on the RS motors!
 
well the ones i have seen burned thru the center. I can normally walk up on the boat and find the problem if it has not been disturbed. The things i have found, Cracked fuel lines (lean condition) dried busted header orings (lean condition) blown coupler (lean condition) No fuel filter needle full of trash (lean condition) Fuel filter stopped up acting as a primary needle (lean condition) pipe too long makes the engine sound rich by ear causing the boater to turn the fuel pratically off to get a clean needle by ear (lean condition) Over Cooling (READ AGAIN) OVER COOLING the engine (operating it under 100 degrees) causes the boater to turn the fuel off on the needle to make Engine Heat (lean condition) These engines Must Have Fuel Pressure to Make Power. I make sure the engine is correct and flow the needle I know what to expect as soon as I throw it in the water. meaning I know the approx window of the needle. it is going to be real close If it is not something is wrong with the boat not the engine......... the fuel system starts at the pipe pressure fitting and stops at the spary bar. Just flowing a needle is not the entire system. all of this info is considering steve or someone you can trust has Originally set you engine up and it was correct? The stk 101 head button Does Not have a Enough Volume for high nitro use. IT MUST be Opened Up. If this One Adjustment was made it would run out of the box....... Steve I have ran the couple of sets of RS101 engines you have done for me and they Performed FLAWLESS & Won Many Races. If you need more work? Let me know I will have Stu send you some more engines. Many times the engine problem is the result of something being wrong with the boat itself......... these big ass engines are hard on header orings,fuel tubing, They flow twice as much fuel as a normal engine there for they stop up quicker. I back flow my fuel filters after every heat race to make sure I do not starve the 101 engines for fuel. we are relying on pipe pressure to maintain the fuel pressure it is not consistant. Are we at the point of needing a fuel pump onboard? I say YES..... My twins eats 52 oz of fuel in about 11 laps. YOU MUST have larger pipe pressure fittings and large fuel lines 5/32 tubing in all locations of tank. and Move the needle away from the carb venturi so you have plenty of fuel on the low pressure side of the fuel valve needle and seat. If I have a engine problem I dont just throw another engine in untill I find out what happened?? It will Repeat the problem if you dont find out what just happened.....p.s. the brass head buttons help tremendously to help the engine make heat and you can run fast on a Richer needle setting I like this.....cause it takes fuel to make power........But your fuel system must be able to feed the engine fuel Under Load and at High Piston Speeds.
 
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Great post Steve!

After reading the above posts, it sounds like it confirms your thoughts.... and expounds on them. I think what has been discussed here has merit for all sizes of motors... if people are listening. Thanks for the well worded post, and also to the folks that responded to the thread with great input.

DJ
 
Fuel,

I did 10 pistons including billetpistons until I found out run the engine much hotter and richer.
 
At 80% efficiency a 1.01 needs 12 CFM to run at 26000 rpm.

Charles how much did you say that zoom .560 carb flowed 6 CFM?

You need a minimum of a .650 carb to feed this eng.

Heck a MAC .84 has a .550 on it.

So a .550 will feed a 1.01?

maybe on %20 nitro it will and we are trying to put what %60 thew it.

More nitro needs more "AIR" not the same amount as %20 to burn. So we go lean.

This eng was not made to burn high nitro. It was made to European racing specks.

Make it as hot as you want and the bowl as big as you want it will still burn up when pushed to the limits.

Hopefully the new eng will address these concerns.

As for now just run it rich and hot and keep your finger off the needle. If it dose not look like a steam eng out the ex it Will go by by.

When the smoke disappears so will the piston.

David
 
David,

What size is the spray bar ID on your mega carbs??

For heat racing, has anyone seen any advantage in running 60% in the RS .91/1.01's?
 
i have 80 zoom carbs on my Twin 101RS and there .550 bore i don't have a problem feeding fuel to the motors. i run 60% i have run 50% and there is not difference really by the time we add Klotz lubricant to our fuel the of nitro drops. the problem is making heat and not leaning on the needle people are trying to Mod the hell out of the engine that's the problem too. i take away and add water as needed depending on the weather and i hardly have to needle down my engine

to me with what we do to our engines im pretty happy at the moment. people are trying to mod the engines like there 21's thats the problem 100MPH heat race boat is not needed to win the race.

Julian
 
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i have 80 zoom carbs on my Twin 101RS and there .550 bore i don't have a problem feeding fuel to the motors. i run 60% i have run 50% and there is not difference really by the time we add Klotz lubricant to our fuel the of nitro drops. the problem is making heat and not leaning on the needle people are trying to Mod the hell out of the engine that's the problem too. i take away and add water as needed depending on the weather and i hardly have to needle down my engine

to me with what we do to our engines im pretty happy at the moment. people are trying to mod the engines like there 21's thats the problem 100MPH heat race boat is not needed to win the race
If you don't see an advantage in running 60% over 50% then why do it?

What kind of engine modifications are you refering to Julian?
 
Well, I have the very oppsite of what Jul said. And he was there when it happened..........."Oh, he was busy" B) ;)

Very noticeable difference.............but you have to Burn the nitro,if not you do not see the difference.
 
Well, I have the very oppsite of what Jul said. And he was there when it happened..........."Oh, he was busy" B) ;)

Very noticeable difference.............but you have to Burn the nitro,if not you do not see the difference.
Chuck,

WHAT kind of difference?? What kind of advantage??
 
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