Cylinder compression

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pyromaniac

Member

Jun 25, 2000

377

0

• Oct 11, 2002

• #1

Hey

I took a compression test on my new bike(yes the bike was warm, throttle wide open, repeted kicks..). It works great and everything i just did it for fun. Isnt 110psi way low for almost brand new bike? I read somewhere that stock pistons have a little bigger gap than for example a wiseco, is that right? The guy who had the bike ran 2% TTS oil which in my oppinion is too little. Yet i dont think it should wear out the piston so soon. What should the psi be in a 00 rm125?

 

marcusgunby

LIFETIME SPONSOR

Jan 9, 2000

6,450

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• Oct 11, 2002

• #2

you want at least 150psi-do you trust your guage?

 

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pyromaniac

Member

Jun 25, 2000

377

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• Oct 11, 2002

• Thread starter
• #3

I have been thinking about that, it only showed 150 on my 250 but it does have many many hours on the piston. I think it could be the cauge between the different sizes of threads(i cant figure out a better way to explain) on the tool. It did come loose when i screwed it in and i just tighened it by hand, probably the cause. Thanks for making me remember :think:

 

marcusgunby

LIFETIME SPONSOR

Jan 9, 2000

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• Oct 11, 2002

• #4

Yep those type are very hard to get a good reading.

 

P

pyromaniac

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Jun 25, 2000

377

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• Oct 18, 2002

• Thread starter
• #5

I did a new compression test the other day. Tighened both sealings real hard but got only 120psi! Either the tool is wrong or... :scream: What could be causing this with a almost brand new bike thats never been apart and works great?

 

W

whyzee

Never enough time !

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Dec 24, 2001

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• Oct 18, 2002

• #6

Pyro, I replaced the top-end on my 125 at 160psi after new rings, piston, bore, and porting I was reading 190. I would have to say 110 to 120 is very low.

 

P

pyromaniac

Member

Jun 25, 2000

377

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• Oct 18, 2002

• Thread starter
• #7

Yes i know 110 is very low. But yet i cant understand why. The same tool showed 150 on my 250. Sure it have many many hours on the piston but when you kick it you feel its way harder. Maybe the tool is showing too little. I can feel on the 125 it builds up pressure if i push the kick with my hands.

Gotta be the tool since a bike under 100psi shouldnt even start and mine works great with 120psi.

 

M

Moto Squid

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Jul 22, 2002

853

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• Oct 18, 2002

• #8

borrow another tester

190 psi!!! holy crap, after a new top end I only got 155

 

1

125 rider

Sponsoring Member

Oct 1, 2000

408

1

• Oct 19, 2002

• #9

If the bike realy does have 110-120 psi it should be a pig to start and you would be able to pull the kick starter down with 2 fingers. Also, it would have the bottom end power of a 60 :scream:

 

Jaybird

Apprentice Goon

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Mar 16, 2001

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Charlestown, IN

• Oct 19, 2002

• #10

I found the same as Squid with my 125sx. 160psi max with fresh rebuild and after several heat/cool cycles. Proper ring end gap and all.
The amount of oil in your pre-mix will effect a static reading somewhat as well.