compression changed after new headgasket

[fisheymikey]

I have a 125 1987.

I recently changed the head gasket during the winter months.

I followed the process of torque,

last year I had 141 on all 4 cylinders now im getting 125 on all 4.

can my compression gauge be the reason or a weak battery could do that?

thanks

mike

 

[pnwboat]

Re: compression changed after new headgasket

Why did you replace the gasket?

Either one could be a reason for the discrepancy in the readings. Have you started the motor and ran it at operating temperature then re-torqued the head bolts?

 

[fisheymikey]

Re: compression changed after new headgasket

I replaced it because I think I had a leak in the bottom cylinder.

did not have a chance to run in the water. if I run it a bin at idle for 20 min can I do that? then retorque?

 

[pnwboat]

Re: compression changed after new headgasket

Yes the bin is fine. You want to get it up to operating temp. and then re-torque.

 

[fisheymikey]

Re: compression changed after new headgasket

ok thanks ill do that

 

[Big Fish Billy]

Re: compression changed after new headgasket

Anywhere from 125-141 sounds good........

 

[Jiggz]

Re: compression changed after new headgasket

Follow the re-torquing process as suggested which is actually required with new head gaskets. However, if the compression stays at 125 I wouldn't worry for now until something more drastic is affected like WOT speed or RPM.

 

[MickLovin]

Re: compression changed after new headgasket

141 sounds a little high for an engine that old, 125 sounds more like it...

Mine was 150+ except cylinder 2 which was 148 so why is it high for an old motor? Mine is 1979, it may not have been used much.
Mine was immaculate inside, indicating hardly any use, it wasn't a rebuild, everything on my engine is/was original even down to the metal Chrysler muffs. Also the 100hp Chrysler is speccd at 150 - 165psi, so I wouldn't be surprised if the 125 Force was around the same maybe a little lower. It is unusual but it does happen

 

[jerryjerry05]

Re: compression changed after new headgasket

My motors are 26 and the comp on all 6cyl. is 150#
The compression with a good/reliable gauge should be around 145-150-155.
The 125 reading on all cyl. Just means the gauge isn't the best.
The important thing is all the cylinders are reading the same.
When you put on the new gasket the compression shouldn't be any different after you run it.
If the head and block surfaces were clean and the bolts tourqed right, there shouldn't be any difference after it's re-tourqe'd.
I was taught that if it's installed right you don't need to re-tourqe.(that's gonna start some s%$#)

 

[Big Fish Billy]

Re: compression changed after new headgasket

Sounds good.............

 

[Jiggz]

Re: compression changed after new headgasket

The re-torquing process with new head gaskets or even with used ones, is more of a troubleshooting process than anything else. With the problem presented in the OP, what do you suggest he do first? Get a new and more expensive compression gauge? Remove all head bolts and replaced them? Or would you do a little back tracking and suggest double checking his torque settings? The 125 compression is really not that bad considering there is no large discrepancies between cylinders. As suggested, double check the torque or re-torque and move on unless something drastic change in the engine performance and then investigate further.

 

[MickLovin]

Re: compression changed after new headgasket

They retorque car heads after 1000 Kilometers after a rebuild due to expansion and contraction of the motor after run in, so why would a two stroke motor be any different? This is a question not a statement.

 

[jerryjerry05]

Re: compression changed after new headgasket

The thing I'd do is get a second opinion. Or another gauge.
The important thing is that all 3 cyl are reading the same.
Why would he replace the head bolts?
They have almost no torque. So they probably weren't stretched or weakened.
If they weren't rusted or corroded then they can be used again and again.
If they were the head bolts on say the Mercruiser 170 inline 4 I'd replace the head bolts.
If I remember right the torque is 160#. That would stretch the bolts.

"IF" the head and block surfaces were clean and the bolts torqued right, there shouldn't be any difference after it's re-torqued."