I feel i am a pretty competent small engine mechanic. Ive rebuilt TONS of 2 and 4 strokes but im out of my realm in terms of the X30 engine and am looking for some insight.
I kart on a club level budget and yeah maybe the rotax would have been a slightly more logical choice but frankly the simplicity of the x30 made me grab hold and not let go. I play with carbs all day at work, last thing i want to do is play with carbs racing.
Im closing in on 8hrs on my top end and feel i can tackle this myself over the winter and save myself a lot of money. 2021 id send it out for a top/bottom build though.
My main questions are in terms of the cylinder. For dirt bikes, atvs, mowers, blowers, etc (as long as they dont grenade) id just measure the piston size, buy the next size up piston and have a respectful shop bore and hone cylinder and id assemble it. I dont think thats the case how it works with these engines??
Ive found the manual with clearance specs but it doesn’t say anything about the factory specs of new parts so im a bit dumb founded as to how to know what size piston i have/would need as to who to have the cylinder bore and honed as well.
Have you ever tested the main bearings? My procedure is to put a dial indicator on the crank and try to move it, by hand, up and down. No movement at all indicates good bearings, more than .001" or .002" indicates to me that the engine is in need of new bearings. At the same time, using a .0001" indicator, check the crank run out. More than .0002" is bad. None is best!! No engine of mine ever went more than one race without checking these things. Probably not totally necessary, but I never wanted to leave anything to chance.
If I recall correctly there are two “color of dot” of pistons with respective clearances and those pistons display the BORE size on them, vs the actual piston size.
If you are running an out of the box engine and are happy with it’s performance, it’s a pretty easy job if you have the right tools. To replicate a factory build:
1). have the cylinder honed (on a real honing machine, not a drill hone)
2.) measure the finished bore and fit a piston that is .11mm/.12mm smaller
3.) replace the stock .40mm base gasket
The above specs will not maximize performance, but will provide an easy to tune, long-lived (relatively speaking) motor that will never fail tech. If you want maximum performance, you will need to have the engine “built” or, at the very least, play around with different piston clearances and base gaskets. You can send your cylinder the Comet Kart Sales and they will hone it and fit a piston for you (I do not provide this service). I suspect they will provide a factory spec piston size, not what they would use on a fully built engine.
No, you don’t need to replace the head (it lasts a very long time), you just need to have the head honed, then replace the piston, piston pin, top cage bearing, base gaskets, and o-rings.
Yes, the cylinder. I thought he was referring to the cylinder jug itself as the head. Most Rotax folks always seem to refer to the cylinder as the “head”
Dom, There seems to be a terminology problem with your question. The head sits on top of the cylinder and normally lasts the life of the engine.
I’m not sure what you mean by the piston head, never heard that term before. The piston goes up and down in the cylinder and gets replaced on a top end rebuild. It’s the cylinder that gets honed,
Thanks. That answers the question. I was under impression the piston in it’s entirety was replaced in a top end. I got confused because it sounded like it wasn’t.
Best piece of advice I can give is to find a local builder and ask them to do the machine work for you. I think you will be surprised with how willing they are to do this for you.
Send them the jug, buy piston kit from them, have them fit the piston then you do all the assembly work. I bet you pay no more than $75 to have them Bore/ set wall clearance for the new piston so that it’s a headache you don’t have to worry about.
The rest of the work is cake if you are used to wrenching. I send my cranks off when I need them split for a new rod because I don’t have the proper tools to split them and true them correctly. Also surprisingly inexpensive if you do all the labor.
IAME assembly and tech Docs are all out there on the internet to get you all the torque specs.
Long time no update! So this is something i still consider doing some day but finding out how cheap it actually was to have a semi local and professional x30 rebuilder do the work for me i gladly handed over the engine. Some day i will do the work though! (besides the bore/hone)
