Piston and ring size for 29cc KM?

[turbohvn]

My understanding is tht the KM engines are clones of CY, which are clones of Zenoah.
I need a new piston ring for my 29cc T1000 truck. I can remove cylinder and measure, but would like to order new ring, have in hand and do the replacement job all at the same time.
My question is,is does the 29cc KM motor use 35mm or 36mm piston and ring?

 

[Lan-Ed-Tul]

go on ebay, look for Dans ebay store, king motors, and shoot him a PM, he may know the size.

 

[turbohvn]

Dan does not have them. again, anyone know the size? It's either 35 or 36 mm

 

[jackobyte]

It should be the 36mm, 34mm is for the 26cc, 35mm is for the 27.5cc

 

[turbohvn]

Thank you.

What a great forum this is!!!

 

[funbob]

It's 36mm

And here's a handy little chart...

32mm bore + 28mm stroke = 22.5cc
32mm bore + 29mm stroke = 23.3cc
32mm bore + 30mm stroke = 24.1cc
34mm bore + 28mm stroke = 25.4cc
34mm bore + 29mm stroke = 26.3cc
34mm bore + 30mm stroke = 27.2cc
35mm bore + 28mm stroke = 26.9cc
35mm bore + 29mm stroke = 27.9cc
35mm bore + 30mm stroke = 28.9cc
36mm bore + 28mm stroke = 28.5cc
36mm bore + 29mm stroke = 29.5cc
36mm bore + 30mm stroke = 30.5cc

 

[airflow]

99% sure it is the 36mm. the 29cc is actually a 28.5cc

 

[turbohvn]

All the zenoah and/or CY 36mm pistons I have located have smooth domes. Looking into the exhaust port of my King Motor 29cc, I can see the piston has a distinct "dish" in the center.
Dan does not stock these pistons. Has anyone replaced their piston and ring in their original King Motor cylinder" m
are the dished and non dished pistons interchangeable?

 

[quentrm250]

I have the Rovan 27.5cc. Would that be the 34mm x 30mm then? The spark plug has bad threads (basically new motor) so if I am correct I already have the +2mm crank. To upgrade the motor to the 30.5cc all I would need is the piston and cylinder correct?

 

[rovanmadlunatic]

I don't think its actually a dish. Just a small flat where they maching out the little hole in top of some pistons from the machining process.Any replacement piston of the correct dia will work.

 

[rovanmadlunatic]

I have the Rovan 27.5cc. Would that be the 34mm x 30mm then? The spark plug has bad threads (basically new motor) so if I am correct I already have the +2mm crank. To upgrade the motor to the 30.5cc all I would need is the piston and cylinder correct?

You would need to make sure you get something that will work with a 2mm stroker.Not all cylinders will. You may find yourself needing a thicker base gasket.

 

[quentrm250]

I was wondering about that. Just be sure and get one for the 30.5 not just one that is 36mm. For instance the cylinder for a cy29 (28.5cc) probably is too short and won't work. That sound correct?

Only been an owner for a few weeks. New to the 1/5th completely but have engine experience with auto's. Going to have a lot of questions.

Thanks for the help!!

 

[rovanmadlunatic]

I was wondering about that. Just be sure and get one for the 30.5 not just one that is 36mm. For instance the cylinder for a cy29 (28.5cc) probably is too short and won't work. That sound correct?

Only been an owner for a few weeks. New to the 1/5th completely but have engine experience with auto's. Going to have a lot of questions.

Thanks for the help!!

If it were a 1mm stroker than most cylinders would work with a slightly thicker gasket. I am not aware of any 30.5 that are compatible with 2mm strokers. It doesn't mean there arent any, i personally haven't looked into it. If you are not set on 30.5 you can get the top end for a cy f270. Large scale rc has the complete top ends on for 24.00. They seem to be really good motors (i bought two of these kits myself) and from what i have read on various forums they make really good power. Otherwise if you go 30.5 its quite possible you will have to replace the crank as well.