Baja Junkie

G'day all, I'm in the process of purchasing a new engine (Zenoah G290RC) but I'm ultra confused about the whole 3rd bearing vs Zero Drag Seal vs Std Seal thing.
Can someone please explain what the 3rd bearing is there for, if it needs to be replaced anyway?
I will be running the standard Zenoah clutch at this stage, I haven't driven it sand yet, mostly I drive it in grassy or dusty paddocks or BMX tracks.
I know this will probably make my head ache even more, but, which way do I go, and why?
I'm after as many opinions and reasons and as much info as I can get from you, the guys that run and build these things.
Thanks heaps, these forum's are awesome, so much great info.
Cheers, Lee.

ShoestringRacer

What Zenoah motor are you talking about? Do you mean the G270 which has the 4-bolt head? That is a 34mm head engine which is 25.4cc on the stock 28mm G270 crank. Or are you referring to a company that replaces the stock head with a Zen 36mm head which yields 28.5cc with the stock 28mm crank and they sell that, but is is not like that from the Zen factory.

For the 3rd bearing in the Zenoah G270, the engine has 2 bearings on the clutch side. A lot of people say this 3rd outer bearing should be removed and replaced with an oil seal due to the risk of worn clutch shoe residue entering the engine through that bearing and causing damage. Supposedly the extra support of the 3rd bearing here isn't needed for RC use and the 3rd bearing is there for the engine's use in other applications.

I have a Zen G270 which I installed a 36mm head for a 28.5cc engine. But I guess I am a rebel and live dangerously because I didn't replace that 3rd bearing with a seal. Guess I'll see how the engine does and I hopefully wont have to learn any lessons the hard way.

If you want to replace that 3rd bearing with a seal use the larger oil seal from these two oil seals. Hope this helps:

http://www.davesmotors.com/s.nl/c.88...t.A/id.1278/.f

Baja Junkie

Thanks Shoestring, there are a couple of shops over here (Australia) that sell the 270 with the 28.5cc upgrade and they call it G290RC, fairly sure I will get the third bearing replaced with an oil seal. How long have you had your engine up and running for? How does it perform? Thanks again, Lee.

ShoestringRacer

Ok got you on the G290RC. I've been running mine the last few months probably a little under 2 gallons or so. It performs very well - definately a solid improvement over a 25.4cc. I don't know what you have been running but I think you'll be happy with it - even moreso if you've been running a 23cc.

Actually the stock G270 and the upgrade 36mm/28.5cc head have a lot of versatility because Zenoah designed a large squish (distance between the piston top and cylinder head inside) into them. The 36mm head can be used with a +1mm (29mm) "stroker" crankshaft with the stock base gasket which yields 29.5cc to get even more power from it. Or, if you want a 30.5cc, you can use a +2mm (30mm) "stroker" crank and a 1mm copper base gasket and for even more power. (I have that 30.5 on my bench patiently waiting for its chance to run so I can't comment on it performance wise.)

So, you have some power options with only a crank and base gasket change if you ever want to increase the displacement down the road.

What will you be running the new 28.5cc in? Did you get it yet?

Baja Junkie

Hey Shoestring, I have the KIng Motor, KM 2.0,(5B clone)all alloy, 2.4 ghz radio, 29cc engine. The thing was seriously fast, straight out of the box!!!
Ended up cracking the head, hence the Zenoah going in, the KM 29cc motor was awesome, heaps of torque and really revved hard, which was thereason I liked the sound of the 28.5cc Zenoah,
I figured with same bore and stroke with Zenoah quality, it should perform as good or better, but with reliability.
Haven't ordered it yet, still talking options.
What is your 28.5cc in? Lee.