250girl

Mod Ban
Dec 19, 2007
320
0
Did a compression test on the 2000 rm250, taken while engine was cold (not sure if that makes a difference). It was 190..... is that good?? Dad said he looked in the manual and it didn't say what it should be.... but maybe he didn't look close enough.

What should my compression be?
 

Brandon H.

Member
Mar 26, 2009
199
0
Thought it was hard to tell by doing compression test because 2 smokes use oil in the gas, which seals rings for better compression.

Either way, doesn't tell if the piston is worn too much anyways, last thing u want is a broken piston skirt just because u thought it was good because u had good compression.

Though your compression seems good.

Im sorta a noobie though, so more will chime in.
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
Brandon is right, the piston can be ready to explode and still provide good compression.

Seeing as how you already know it is overdue for a top and I would just do it.
 

RM_guy

Moderator
Damn Yankees
LIFETIME SPONSOR
Nov 21, 2000
7,045
208
North East USA
I'll chime in and say the same thing. Compression sounds good but if you are using an OEM piston (or a cast aftermarket--or if you just don't know) and it's been in for more than 40-50 hours then you have a ticking time bomb and need to replace it. Put a forged Wiseco piston in and you can get a lot more time on it in the future--60-80 hours and more if you never wind the piss out of it.
 

250girl

Mod Ban
Dec 19, 2007
320
0
It "supposedly" has a Wiseco in it, but I have yet to look and see if it is true. That's another thing I was wondering.. should I just ge ta Suzuki piston.. or is the Wiseco actually worth all the extra money?
 

Matt90GT

Member
May 3, 2002
1,517
1
If you are going to replace the piston, you need to measure the bore first. Make sure the bore is clean and round. If not, you need to fix the cylinder first thing.

once you get a good cylinder and bore size, you can order up the correct size piston for the motor.
 

2-Strokes 4-ever

~SPONSOR~
Feb 9, 2005
1,842
4
Missouri
Every bike will wear differently. I've learned from experience that our '03 RM250 needs a new piston at about the 80-90 hr mark, and that's with a ring change at aprox 40 hrs. These bikes are truly high performance and need careful maintainance.
 

Matt90GT

Member
May 3, 2002
1,517
1
usually more than the piston wearing, it is the power valves needing to be cleaned with the modern 2 strokes. I always tore down a top end yearly
 

RM_guy

Moderator
Damn Yankees
LIFETIME SPONSOR
Nov 21, 2000
7,045
208
North East USA
250girl said:
... is the Wiseco actually worth all the extra money?
Yes. They are forged instead of cast and will last much longer than the stock cast piston. They will both wear the same amount since they are both made out of aluminium but the difference is in when and how they fail.

The cast piston will develop cracks that you can not see and after a time the skirts will suddenly blow apart. The forged piston is much tougher due to the forging process that elongates the grain structure. These elongated grains will hold it together a lot longer and when it does fail it's not as catastrophic.

Be aware that with a forged piston you have to be more careful when breaking it in. You have to go through several heating and cooling cycles to relieve the internal stresses. If you don't it will seize up but once it's properly broke in it is no different than a cast piston.
 

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