Rebuild of rotax

Purchased a used Rotax Evo end of last season and the previous owner said it has fairly low hours 15 or so but wasn’t sure. It seems to run good and seems competitive as I am mid pack due to weight and skill.
I thought about getting the piston and ring changed as I don’t know the actual hours. Would it make any difference at all to put a new piston or do Rotax run the same if they are 1 hour old vs 40? What roughly is the cost for this and is it something I could do?

Thank you

Contact a local engine builder and inquired about costs for a top end, and for a full rebuild. Also ask about a maintenance schedule. You could go beyond 40 hours. Depends on how you race the engine. But the longer you go, the closer you get to a failure. Failures are expensive.
Pull the head and check the cylinder walls. If there is still cross hatching, button it back up. Focus on keeping the carb clean, the power valve clean & functioning and replacing the packing in the exhaust pipe. If there is any water leaking near the lower part of the engine, it’s likely the water pump. Fix it before you go out again. Good luck.

15-20hrs is the general guideline for a top end rebuild, although the engine will continue to run fine beyond this once you’re using good quality 2 stroke oil.

40-50hrs is the general guideline for a full rebuild. Again engines may run beyond this but as tony mentioned you do risk catastrophic failure the longer you push it.

My current senior is approaching 25hrs and runs fine still, the cylinder still has crosshatch but I can see some where on the piston and blowby past the ring.

Be careful. Check the regs in UK - here if you break the seal you’ll never race that engine again. Only authorized Rotax centres can break it. Break it yourself and they cannot re seal it. If it’s not sealed you can’t race it.

If I pull the head off, should I just change the piston and ring while at it or is there some technique to it?

https://www.rotax-kart.com/upload/files/4729.pdf#page47

Follow that to get correct piston size, replace the head seals, piston and ring, pin and small end bearing.

What regulations are you specifically referring to there?

Hi mate. Rotax Max Challenge UAE

The regs don’t explicitly state that. There’s caveats for broken seals and re-sealing.

“Engines with a broken/invalid seal may not be used. In the unlikely event of a broken seal
it must remain attached to the engine for inspection to be made by Al Ain Raceway.”

and

"If an engine seal has been broken (for whatever reason), the engine must be checked completely for compliance according to the Technical Specification. Re-sealing may only then be
carried out at the discretion of Al Ain Raceway. "

This rule is in both tech and sporting regulation documents but don’t actually line up properly. One mentions that broken seal must remain on engine (how they define that I don’t know) and the other doesn’t.

What they do state is in reference to what you say is

“IF AL AIN RACEWAY SUSPECTS THAT AN ENGINE HAS BEEN TAMPERED WITH, THAT
ENGINE WILL BE EXCLUDED FROM COMPETITION AND WILL NOT BE RE-SEALED UNDER
ANY CIRCUMSTANCES.”

They don’t state what they mean by tampered with and this rule may also include ‘sealed’ engines. The regulations are pretty poorly written and it probably means they’ll blacklist any engine without a seal that can’t be explained properly as you say, but it’s not a black and white regulation. It obviously means any ‘broken’ they deem as a deliberate act would be considered as ‘tampered’ with, but like i said they don’t explicitly state it.

it’s just poorly written regs, nothing unusual there ha

It should be noted I’ve not found anything like that in UK regulations for Rotax.

P.S i hate sealed engine racing because of this nonsense. Why own the engine if you can’t even look inside. May as well do lottery engines and arrive and drive and be done with it.

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Lol yeah you’re quite correct. But it’s applied quite draconianly - you break the seal it’s done. They won’t re-seal it.

I broke mine quite innocently, they wouldn’t entertain doing an overhaul and re-seal it. I stuck my fingers up at that and traded it in for a shiny new X30, 33% discounted for the trade in. Best thing I ever did lol

[quote=“Alan_Dove, post:9, topic:6352”]
P.S i hate sealed engine racing because of this nonsense. Why own the engine if you can’t even look inside. May as well do lottery engines and arrive and drive and be done with it.
[/quote] 20 characters

100% true.

As long as I get the correct piston size, I should be good to fit it myself? Read somewhere that fitting the piston in takes some skill.

Nah. Piston is a piece of cake bud. It’s the bottom end that requires a bit more depth of knowledge.

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Thank you for all the help. Much appreciated