Top End Rebuild

[gremmen]

Well my boys made it through the race season and I plan on attempting Top End Rebuilds on a YZ85 & (2) RM125's. I am new to dirt bikes as well, so don't know much about doing this. I will have to buy a Service Manual for the YZ85, and already have one for the RM125's. What I'd like to find out is, Which Brand of Pistons to buy? I heard Vertex was the best.

Also I was thinking of looking at the chutches. Whats the best brand for chutch parts? Is there any racing clutches I should look at.

I do have guys that can help me if I can't figure something out, but from what I seen in the RM Manual, I shouldn't have much trouble. Thanks for any opinions offered.

 

[julien_d]

If they're racing, IMO wiseco is the best choice. You have to remember when using a forged piston to warm the bike up properly before wringing on it though, and clearance is important so check the fit. Remember, when going aftermarket with the piston it's usually better to go with the piston manufacturers clearance rather than the OEM specification.

A cast piston can also work just fine and cost a bit less, but there too it's important that the clearance is within spec. Too much slop with a cast piston and you risk shattering a piston skirt, which can cause a great big expensive mess. If you have a shop manual, changing the top end will be no sweat. You'll be surprised how quick and easy it is.

Barnett, EBC, and Hinson all make quality clutch kits. There are also cheaper options that may or may not get your kids through a season, depending on how they ride.

Best of luck!!

 

[2-Strokes 4-ever]

Clutch plates... always had the best luck with OEM.

 

[julien_d]

^ true that. No problem with OEM friction plates.

 

[gremmen]

Thank you guys. I did want to use forged pistons, it's just what I like since I use all forged stuff in my Drag Car. Hopefully all goes smooth.

Oh, what's a good warm up proceedure.

 

[2-Strokes 4-ever]

1- We start em, blip the throttle for five minutes or so (easy), shut off for cool down.

2- Start, let warm up, ride easy (no high revs or lugging) for 10 mins, cool down.

3- As above but ride for 20 mins, cool down.

4- Rip!

(Wiseco's been good to us.)

 

[julien_d]

^^ that's a break in procedure. I think he's asking about warm up?

I just crank the bike up and let it idle while i put my gear on. Then I ride it sort of easy for the first few minutes until it's obviously running cleanly. After that, it's give it hell :).

 

[whenfoxforks-ruled]

I dearly miss Eric Gorr popping in, but do understand, now! Keep at it Julien!

 

[FruDaddy]

I have installed both Wiseco and Vertex into matching KTM 85s. I cannot state with any certainty that you will see a performance advantage with either. Both bikes ran great and my son move on to bigger bikes before I had to replace them again. Wiseco chamfers the wristpin openings making it a little easier to install the circlips.

 

[RM_guy]

Performance advantage--no, reliability advantage--yes. You will get a lot longer life from a forged (Weisco) piston than cast. And when it does fail the forged piston won't cause as much damage as a cast one.

 

[gremmen]

Ok, one more question. Should I Mic the cylinders before ordering Pistons. I know the Yamaha YZ85 was new when I bought it, so it should be standard bore, I think 47.5. The older RM 125's we bought used, one is a 2004, other is 2006, not sure if the pistons were ever replaced on these.

 

[julien_d]

If the piston is oversize, you should see a number etched into the top of the old piston.

 

[Dirtjunkie85]

I've had really good look with Wiseco Pistons and as far as the clutch go Pro X is a great brand to go with but for the money it's probably worth spending a little bit more and getting an OEM Clutch.

 

[2strokerfun]

Yes you should mic the cylinder. Check it for size, round and taper. No point putting a new piston in an oval, overworn cylinder.

 

[julien_d]

^^

Eh, can't tell much with a mic anyway. If you're worried about that, you need a bore gauge. Not a bad idea just to be sure you're getting the right piston, but a standard mic isn't gonna tell you much of anything about the condition of the cylinder.