Compression Test

[ncnmra]

I have read conflicting reports on how to run a compression test. Should the engine be warm or not? All spark plugs out?

The service manual seems to suggest that the engine should be warmed up, and seems to give different specs for the MR1 HO engine vs some info I've read here (ie: manual states 164psi, here I've read 157psi).

Can anyone clarify?

 

[Cambo]

164 to 157 is a marginal difference you would see more sway than that depending on when the test is done cold motor vs warm or hot .Most gauges are not super accurate you want to look for large variations between cylinders high compression variation could be carbon build up . Low could be numerous things warn rings, worn valves , gasket leak . Post your results and was the engine cold warm or hot

 

[Gym]

I have read conflicting reports on how to run a compression test. Should the engine be warm or not? All spark plugs out?

The service manual seems to suggest that the engine should be warmed up, and seems to give different specs for the MR1 HO engine vs some info I've read here (ie: manual states 164psi, here I've read 157psi).

Can anyone clarify?

Yes, engine should be warmed up so the piston rings have expanded against the cylinder wall. For convenience pull all spark plugs. Also pull the lanyard switch to prevent damage to the ignition.

 

[AZDANSX230HO]

I decided to change my spark plugs last night and do a compression test, I did not want to change my plugs with a warmed up engine so I did the compression test cold. I was right around 130 Psi cold, but I live at 5500 Ft Altitude, so the correction factor at this altitude is 0.853 which puts my 130 Psi right around 155 with the altitude adjustment. My boat has under 80 Hours on it, so everything seems to be doing fine.

 

[ncnmra]

Thanks guys. I'm waiting for my gauge to come in. @AZDANSX230HO : what gauge did you use?

 

[AZDANSX230HO]

Thanks guys. I'm waiting for my gauge to come in. @AZDANSX230HO : what gauge did you use?

I have a set from Craftsman, it has fitting for every size spark plug:

http://www.sears.com/craftsman-comp...orcycle/p-00947089000P?intcmp=ken-pdp-buy-cta

 

[ncnmra]

Strange, the link doesn't work. I ordered this one, hoping the 10mm thread works:
http://www.innova.com/en-US/Product/Detail/3614

 

[AZDANSX230HO]

Strange, the link doesn't work. I ordered this one, hoping the 10mm thread works:
http://www.innova.com/en-US/Product/Detail/3614

That will work just fine, here is what my kit looks like:

 

[ncnmra]

Thanks! One more question: did you hold the throttles wide open while doing the compression test? I presume you need to depress the button on the side of the throttle to allow the engine to turn over, otherwise it won't crank if the throttle is open, right? Or is there a better accepted method?

 

[AZDANSX230HO]

Thanks! One more question: did you hold the throttles wide open while doing the compression test? I presume you need to depress the button on the side of the throttle to allow the engine to turn over, otherwise it won't crank if the throttle is open, right? Or is there a better accepted method?

It's best to hold open the throttle on compression tests, I forgot about the button, I had my Wife put the throttle forward and it would not start, so we did it with the throttles closed. When I buy jet ski's to flip for a profit I always compression test them, it's the only way to know if the motor still has some good life left in it before a rebuild.

 

[ncnmra]

I know it won't turn over with the throttles forward, but I read that the button will allow you to bypass that. Otherwise I suppose you could pull the throttle cable manually at the engine because I have a feeling that the override switch is at the throttle lever itself.

 

[AZDANSX230HO]

I know it won't turn over with the throttles forward, but I read that the button will allow you to bypass that. Otherwise I suppose you could pull the throttle cable manually at the engine because I have a feeling that the override switch is at the throttle lever itself.

It's not crucial, but it does give a more precise reading. With mine closed it still pulled very close to what it needed to be at.

 

[Scottintexas]

I don't understand, how does having the throttles forward give a more precise reading? is it injecting fuel and that is increasing the pressure?

 

[AZDANSX230HO]

I don't understand, how does having the throttles forward give a more precise reading? is it injecting fuel and that is increasing the pressure?

It opens the throttle bodies to allow air into the cylinders.

 

[ncnmra]

Per the service manual:

 

[MSans]

Hi to everyone.....I have a 2006 Yamaha SX230 with two MR1 4-stroke. Can anybody tell me witch are the Compression numbers for the engines?.... 150-160-180-190 I really dont know. If there a standard or something in the internet to find it. Thanks for your help.

 

[Scottintexas]

Hi to everyone.....I have a 2006 Yamaha SX230 with two MR1 4-stroke. Can anybody tell me witch are the Compression numbers for the engines?.... 150-160-180-190 I really dont know. If there a standard or something in the internet to find it. Thanks for your help.

The picture from post #15 just above says compression should be 164psi

 

[Gym]

164 per the spec but more importantly all cylinders should be relatively close in compression.

 

[ADJR]

I’ve got a motor not starting on my 2018 Yamaha 240 to limited S. The other seems to be functioning properly. Ran a compression test today on both motors. Motor that isn’t functioning read 40, 40, 40, zero. Motor functioning read 170, 155, 115, 170. I’ve come to terms that I’m screwed for the non functioning but do I really have the other motor going bad as well?!