25hp johnson 1988

[Jeremy1986]

Hello, I have a 1988 johnson 25hp that had 120 psi in both cylinders. I went to change the spark plugs and I over tighten causing it to strip out. I bought another head cylinder and had it shaved down and new gaskets. Now I'm only getting 75 psi in both cylinders. I torqued the head to 240 in pounds. I haven't started the motor. What can be causing the low compression? Thanks for the help. Jeremy

 

[tphoyt]

Did you torque the bolts in the proper sequence and pattern? Or use a sealer on the gasket? No sealer required it can cause blow by. Just looking for clues.

 

[Jeremy1986]

I did the torque sequence and pattern which I did it two times. First time at 120 then went back around at 240 in pounds. I didn't use any sealer on the gasket.

 

[Faztbullet]

Correct head?

 

[Jeremy1986]

Correct head?

I bought it off a guy that parts out alot motors. I told him I had this 25hp and he said yes I have a couple of them and sent me this one. How can I tell if it is wrong?

 

[Crosbyman]

did you not compare the nw (use) part with the stripped one.

you could always try to retap the plug hole and install a new sleeve

Amazon.ca

 

[tphoyt]

Yea sounds like you need to pull the head.
check to be sure it is the same internal lay out not just the bolt holes. Put a straight edge on it and be sure it really is flat.
check the block for any areas of erosion on the edges. If all else fails next best thing is to install a helix coil for for the plug.
Best of luck

 

[tphoyt]

I’m just wondering what caused you to check the compression before you changed the plugs in the first place?
Were you having some trouble?

 

[Jeremy1986]

I’m just wondering what caused you to check the compression before you changed the plugs in the first place?
Were you having some trouble?

I just recently bought the motor two months ago and I went to check the compression. When I installed the spark plugs, I over tighten them causing it to strip out on the buttom cylinder. Thank you, I will inspect both heads to see if there is a difference.

 

[Faztbullet]

Should be a casting number in the aluminum

 

[Jeremy1986]

Hello everyone. I wanted to inform you that I found the solution. It was a faulty compression gauge that I ordered off of Amazon which says made in China. I was able to borrow my brother's snap on gauge and I got these results. The top cylinder three pulls was 100, 115, 125 and the bottom three pulls was 115, 125, 125. Thank you again for all the help. Jeremy.