Recommendation: Hours on top end before change for a 125 and a 250 2 stroke?

[EdLennon]

Hi all,

I wanted to get a recommendation: at how many hours should I change the top end in my son's RM125 and in my RM250?

I am running a Wiseco piston kit in both, am anal about cleaning the air filter and intake tract and use Klotz 2 SuperTechniplate 2 stroke oil in the engine.

Thank you for your advice,
Ed

 

[2-Strokes 4-ever]

Our RM250 has seen extensive porting work (perhaps shortening top end life) and is woods ridden... not seeing high RPMs too often.
We get 80-90 hrs out of a piston, but ring it at 40-50.

RM125 also woods ridden, but that motor is worked hard.
Piston about 70-80 hours and again, re-ringed half way through (This old 98 RM125 is really easy on top ends... but hard on breaking power valves :| )

 

[julien_d]

A good method to go by is the compression. Check it when you do the top end, that's your base line. When it starts to drop, time for a top end. Many people will replace rings once, then piston and rings the second time. For me, if I'm tearing into it, I'm probably going to go ahead and replace the piston.

 

[EdLennon]

We talked with a Wiseco rep at the Steel City National last year. He said that we could go like 50 hours or so. My son's bike had 30.3 hours on it and the piston shattered. So I am thinking like 50% of that time I guess? IDK, that's why I'm asking.

Everything was fresh, freshly plated cylinder, bottom end bearings, crank, etc. 100% rebuild. Just trying to avoid all that yet again.

Thanks,
Ed

 

[2strokerfun]

Was it a Wiseco forged piston? Does your son race it? 30.3 hours on a piston used for racing is Big Hours. Even bigger on a 125. Jetting, premix and tolerances at last rebuild will also certaintly play into this. But people don't recommend 10 hour (or less) piston replacement for racing engines just because they enjoy spending money and changing slugs.

 

[whenfoxforks-ruled]

Was it a Wiseco forged piston? Does your son race it? 30.3 hours on a piston used for racing is Big Hours. Even bigger on a 125. Jetting, premix and tolerances at last rebuild will also certaintly play into this. But people don't recommend 10 hour (or less) piston replacement for racing engines just because they enjoy spending money and changing slugs.

Thank you. Racing engine and how the rider is using it. The rider gets fast enough, those seemingly "crazy" short hour intervals in the manual, are wayyyyy too long. The 5~7 hour top end on the 125 could be 1 hour, hopefully. Vintage Bob

 

[EdLennon]

Thank you for the replies!

Wiseco Forged piston: YES
Race: YES like 2 times per month

So is 10 hours like the "norm" or a good benchmark?

Thanks,
Ed

 

[whenfoxforks-ruled]

Probably on a good, true bore. But if it gets rode like it got stole, 5 hours would be better. Double the hours on the 250. It will cost you a set of rings, and top end gaskets to get an idea of how long you can go. The looser it gets, even after re-rings, the quicker it will go away. I sure hope you have a dial bore gauge, or access? Plated bore top ends last longer than sleeved bores.