Compression

[TRAIL]

My bike is getting easier to start and its not "hard" anymore. When i ride the bike the power still feels there,most of the time. I am going to do a compression test on it but i dont know what is considered still good? I heave herd 150-160 is good?Is this right? and anything below means it needs a topend?
thanks

 

[darringer]

If its a newer bike, (within the last 5-6 years), it should be at least in the 190-200 psi range. For example, my 99 cr250 has 210 psi with recent top end. ;)

 

[TRAIL]

The highest I have heard of is 180 being good. I am getting a wide range from people here in town. I am not calling you a liar but do you have thin gaskets (raising compression)?Would i benifit from thin gaskets when i do a rebuild?

 

[TRAIL]

I have a 2001 CR 250. my sig wont work???????

 

[darringer]

My bike is stock except for FMF Fatty pipe and pro series reeds. Before I did the top end the compression was around 195. Having just bought the bike I decided to tear it down and inspect. Piston skirt was worn slightly so I decided to do the top end since it was already apart. I cleaned the power valve, removed all carbon from the head, and then used a Wiseco piston kit. After several rides compression is still at 210. I block the throttle wide open when I do the test. I don't know if you should use thinner base gaskets. I believe using thinner gaskets will boost low end power. I tend to judge how a bike performs and not worry about the numbers as long as everything is in good working order. :thumb:

 

[TRAIL]

Thanks. I guess i am buying a compression tester tomorrow!
How much do they run?

 

[darringer]

They aren't very expensive. All auto parts stores and I believe even Kmart and Walmart sell'em. Probably under $40. I've had mine for 20 years so I don't recall what they cost. By the way. After I checked my compression with my ancient one, I borrowed a buddy's new one and got almost the identical results. Good Luck, Darringer :thumb:

 

[TRAIL]

I went out and bought a compression tester it was 20 bucks. and it read 160. And i did find on eric gorrs site it says they should be about 170-200. So i am in need of a rebuild.

 

[marcusgunby]

Dont put too much faith in the comp readings-my 125 was reading 140psi and the engine had lost power-a new piston gave 150psi and the engine gained over 2hp.If i had gone on just the comp reading i would not have rebuilt it.It sounds like yours was overdue as it was very low.

 

[steve125]

Heck Marcus if i had an engine that only had 140 psi i would think there's a serious problem with it. :confused: Your air must be really thin over there :debil: pip pip and a cherio :yeehaw:

 

[marcusgunby]

Steve we need to send each other our guages for verification-you 1st;)
I think mine reads a bit low and yours a bit high??

 

[steve125]

Marcus maybe your not kicking hard enough! :moon:

 

[darringer]

Hey Marcus, even my worn out 99 rm125 had about 175 psi before I did the top end!

 

[marcusgunby]

OK i know;) my guage reads a bit low-however a friend just did his stock 03KX125 and only got 165psi and with a new piston and VHM head it had 175psi.Lets have a survey on average comp readings for 125s;)

 

[steve125]

Pssssssssst darringer! Marcus has a bog in his kicking foot. :eek:

 

[Studboy]

My KX250 has 190 PSI (Cold) and 200 PSI (Warm) with 15-20 hours on the top end. I don't know what it was when the top-end was new because I didn't test it until I read this.

 

[darringer]

Steve, maybe he's kicking on the wrong side of the bike!

 

[darringer]

Steve, maybe Marcus is kicking on the wrong side of the bike!!!

 

[yzrider_69]

i heard that for a 125 145-160 is good

 

[bigred455]

235lbs on my 00 kx 250 after break in.I was getting 230lbs after 45 hrs,I still did the top end after 50 - 55.

 

[Studboy]

235 PSI, is that on a stock 250? That seems to maybe be a bit high.

 

[TechKid]

I have a 2000 RM125 and when I bought it used the comp. reading was at 105PSI and I thought "OH S&*$ thats way low". I did a complete toipe end w/ new piston and rings and it only read 110 PSI. It runs great. :think

 

[Glitch]

TechKid, are you kicking the bike over many times and holding the throttle at wide open? Were you testing it cold or warm? That seems real low.

 

[125 rider]

Originally posted by TechKid
I did a complete toipe end w/ new piston and rings and it only read 110 PSI.

I can tell you for a fact that either your gauge is (highly) inaccurate, your testing procedure isnt perfect, or a combination of both. The only time i've had a 125 blow near a 110, is on my old yz which the top end was about 20 hours past service limit, even then it was at 120 lbs.