Hi guys. I'm here because you guys have a wealth of experience in Zenoah and Zen clone engines & I'm hoping that you'll help me.
I'd like to use one of these in a gasser RC helicopter conversion that I'm custom building. I bought this 2 bolt Rovan 29cc which I think is a Zen clone ;

www.aliexpress.com/snapshot/100945138.html

I've test bench run it & it's vibrations are more nasty than a rattler's tail.
I'm about to fit this stuffed stroker 30.5cc crank/cylinder/piston kit to see if there's any improvement.

www.aliexpress.com/snapshot/101096004.html

Part of my reasoning in chosing this upgrade is that 'there's no substitution for cubic centimeters' although I'm aware that the smoothest running Zenoah & clone was probably the 23cc. Maybe because of the lighter piston weight ?

Please insert your opinions here.

Anyway, I'd like more power & torque than a 23cc offers but without the tempermentality that porting & high RPM modifications might incur.
I'm thinking of rubber mounting the engine for vibration minimization & driving through the clutch & clutch bell housing that's attached to the engine. I'll couple to my pinion via a rubber (urethane?) vibration absorbing 'flexible spider' coupling. This isn't usually done in gasser or other RC helicopters. They usually have the clutch bolted to the cooling fan & the clutch bell fixed to the pinion. All vibrations from the engine & any clutch run-out are transferred to the airframe. Gyros, other electronic & also the mechanical components aren't too happy with any subsequent vibration.

Here's my questions ;
1 - Can I replace the front & rear crankcase oil seals with plastic shielded bearings so that the engine becomes a 4 bearing mod to stabilize engine vibrations a bit ? Any particular seal type ?
2 - Can I dremel/burr out the inside of my piston with the intention of reducing it's weight & reducing vibration ? How much weight should I attempt to remove. Current 26mm diameter piston weight is 31 grams. I see that this is done as a performance mod by Jeroentune & maybe it will have the benefit of vibration reduction in my application ?

Yes, yes, I know I should have bought a $450 Zenoah but I'm happy to tinker and would like to see what I can achieve with this type of engine.

I also test bench-ran this other cheap 4 bolt engine which might be of interest to you & it ran as smooth as silk.

www.sdshobby.net/huasheng-26cc...ing-p-3517.html

- Yep, only $82 plus approx $30 postage !
I replaced the water cooled cylinder head with one that Hobby King in Hong Kong sells for $15 that has cooling fins.

www.hobbyking.com/hobbyking/st...?idproduct=7859

(If someone wants the water cooled head then you can have it - free of charge. Just pay for the postage & give me good advice here and be someone who's advice is based on many years of Zen clone engineering. lol)
Problem with this engine is the configuration though. The clutch is at the 'wrong' end for convenient fitment in my heli project. And it's 26cc. I prefer the idea of extra 4 1/2cc of the modified Rovan.

I hope you can help me reduce this 'Rovan' engine vibration with advice other than 'Buy more expensive stuff'. Thanks.

I have the Miniture Aircraft's 26cc heli. And at idle it is pretty radical with the vibration. Once I come up on rpms it smooths out. The rubber mount idea I'm not sure about... I think the abilty to "wobble" on the mounts would mess up your clutch alignment. I scratchbuilt a large Chinook that had a Homelite 30cc on it. Vibration was an issue with that one until I came up off of idle. I say hard mount it and try it to see what happens. Personally, I would really like to see some pics. Good Luck!

Thanks for your input.
There won't be a clutch alignment problem because the clutch bell is in the bellhousing & bolted to the motor wth a top bearing after the clutch (like many of the marine Zenoah clones. Check out the link in my initial posting of the $80 boat motor for that image). I made a bottom bearing block for the pinion which, of course is attached to the heli frame. The pinion has a shaft through it that protrudes out of the bottom of this bearing. Between the output shaft of the motor (after the clutch) the is a vibration absorbing spider coupling that couples to the pinion shaft.
The down side is that the motor is mounted 30mm (the length of the coupling) lower in the heli frame than yours is.
The vibration absorbing rubber mounts for the engine should be tight enough to not allow 'wobble' but will absorb some of that nasty vibe.
I have a mill & rotary table & I'm going to mill out a spare piston that I have to lighten it like this ;

Lightening A Piston - Modelgasboats.com - RC Boats Magazine

Maybe that will reduce some vibes.

If I post some photos it should be in a Helicopter Forum. I came here because these guys know these motors intimately.
Send a private message with your email & I'll take some photos & email them direct. I don't think that ModelGasBoats Forum will be happy with Helicopter images. lol

Check crankshaft run out, then balance flywheel ... if no better after that ? getting engine smoother running adding a lighter piston is not going to do much ?

Frankly spending half what you paid on engine for a mod piston is along the lines of some other bad investments we can all relate too made in our life times.

JMO ...

Thanks Scott. Is there something I can do if I discover crank run out ? Link please if there's a cure.

Thanks again Scott. Also I've heard of 4 crank-bearing engines. Can I remove the crankcase oil seals & replace them with sealed bearings ?

"IF" ... crank case design is clone Zonoah like ... The outboard BIG seal on pto side can be removed and replaced with a double sealed bearing ( 6001-C3 2RS type ) making bottom end a 3 bearing. Mag side is different and at least in zonoahs not able to have a bearing where seal is.
This does add stablity and may or may not smooth engine out further if crank is indeed flexing down it's length ?

Crankshaft run out was less than 2 thou. Flywheel needed less than 1 gram removed from one side. It still vibrates severely.
If it's true that vibes in single cylinder motor design is inherrently a result of the piston mass changing direction then a significant piston weight reduction might reduce some vibration ? No ?
I just wonder why the 26cc marine engine to which I fitted a cooling fin head and why reports of the 23cc Zen don't vibrate anywhere near as much ?

It is true a single engine Can Not Be balanced like a multi can, but will be/ can be quite smooth at some rpm.

Without seeing internal pictures we are only guessing on what engine is built like etc ...

If handy with a die grinder, go after the piston on inside areas and see what you can do removing some metal ... test and see if smoother ? if it is at least you know your going in the right dirrection.

Here some reference for doing some lightening: www.modelgasboats.com/Lightening_a_Piston/

Well, I milled 6 grams out of the piston exactly like the article you mentioned by Julius de Roo.
I knew that the rotary table would come in handy one day. lol (It's had plenty of use actually)
WOW ! By estimation I'd say that the vibrations are less than half of what they were before - probably only 20%. I have no way of measuring vibration to quantify the improvement but the result is fantastic.
Thanks Julius.
Thanks Scott.