compression on 98 Johnson 115 SPL

[fredzahed]

I am about to buy a boat with a 98 Johnson 115 SPL motor. The compression is 120 on one bank and 100 on the other. Is this normal? or is it capable of being run? any ideas as to how to fix it? it jut had new pistons put in, and maybe they rings havent had a chance to get broken in yet? please help!!!

 

[rodbolt]

Re: compression on 98 Johnson 115 SPL

do a leak down test. it is much more accurate than just compression. also was the motor rebuilt or patched ?<br /> IE if only one piston was replaced it is possible to have a fresh rebuilt worn out motor. the piston to wall clearence is usually less than .003. anyway I have seen many omc motors with 10 to 15 pounds difference bank to bank. my 120 is one and I put pistons in it in 1995.<br /> good luck and keep posting

 

[rickdb1boat]

Re: compression on 98 Johnson 115 SPL

One "Bank" had 100 and the other "Bank" had 120? Makes me wonder if they only did one side. Huumm!! do as rodbolt suggests before you purchase.

 

[The Marine Doctor]

Re: compression on 98 Johnson 115 SPL

I am not too impressed with those numbers either.<br /><br />TMD

 

[fredzahed]

Re: compression on 98 Johnson 115 SPL

thanks for the advice, I will have them do a leak down test tomorrow

 

[clanton]

Re: compression on 98 Johnson 115 SPL

It may run, but the compression was a lot closer when new. Some of these engines had problems with pressure relief valve sticking and would run hot. If you think the compression numbers are correct, I would pass on this engine and keep looking, unless you are prepared for a rebuild.

 

[Dhadley]

Re: compression on 98 Johnson 115 SPL

Are the heads a matching set? Are both head gaskets the same?

 

[TimW]

Re: compression on 98 Johnson 115 SPL

The edges of the original factory head gaskets will usually be painted over in the engine color.

 

[Dhadley]

Re: compression on 98 Johnson 115 SPL

The thickness of each gasket can still be seen. If the heads are a matching set then you can look at the head gaskets to make sure they are both standard or "fat" gaskets. <br /><br />Good luck!

 

[TimW]

Re: compression on 98 Johnson 115 SPL

Oh right. I just meant that you can usually tell if someone has replaced the head gaskets by looking for the paint.