1984 J90 compression test results

[Steve2603]

Just ran a compression test on my 1984 J90, cylinders 2,3 & 4 all test at 110 - 115psi. Cylinder 1 tested at 95psi.

read the manual on Selec and it's a little confused at the spec, stating most recent updated recomendation from Johnson at 20% max variance between cylinders.. does this look right?

Just wanted to check before I go any further.

Thanks..

 

[iwombat]

Re: 1984 J90 compression test results

yeah, something is up with cylinder #1. Time to take a peek before it goes any further.

 

[junior1113]

Re: 1984 J90 compression test results

i wouldnt be too scared of those #'s try doing the compression test again after motor is warmed up if it was under 90 i would be concerned

 

[kenmyfam]

Re: 1984 J90 compression test results

yeah, something is up with cylinder #1. Time to take a peek before it goes any further.

Steve, read this post. Only sensible choice in my opinion.
One other thing, does the low cylinder have a helicoil in it ?? sometimes they leak a little with a compression tester. Seldom but sometimes.

 

[Steve2603]

Re: 1984 J90 compression test results

OK, thanks guys. No helicoil in there as far as I can see.. I plan to remove the head and take a look inside..

was just a bit confused by the 20% number stated on Selec's online manual..

Cheers, steve

 

[emdsapmgr]

Re: 1984 J90 compression test results

Try a can of Engine Tuner on the engine before you pull the head. It will loosen up any carbon around the rings and may help. If it does not improve the compression any, then pull the head.

 

[kenmyfam]

Re: 1984 J90 compression test results

OK, thanks guys. No helicoil in there as far as I can see.. I plan to remove the head and take a look inside..

was just a bit confused by the 20% number stated on Selec's online manual..

Cheers, steve

Seloc manuals kind of suck in my opinion. 10% is a good guideline.
Have you given it a decarb at all. Won't do any harm only good. Then check compression again. Check "Top Secret Files" for details.

 

[Steve2603]

Re: 1984 J90 compression test results

I'll do a de-carb before I remove the head, just in case that's the issue.

Thanks for all the advice.

 

[iwombat]

Re: 1984 J90 compression test results

See, there I go assuming people are on top of the decarb maintenance. Decarb first is exactly right, especially since this is cylinder #1. Cyl #1 tends to get a little hotter due to air pockets in the cooling jackets and cokes up first.

 

[Steve2603]

Re: 1984 J90 compression test results

Ran some decarb through Cyl # 1 and after re-test it came up to 105psi. Plan to soak the cylinder in decarb solution for a while and then run decarb through the carb again to see if I can bring it up further.

 

[iwombat]

Re: 1984 J90 compression test results

Good news, did everything else come up a little too?

 

[Steve2603]

Re: 1984 J90 compression test results

Only had 1/4 of a can of decarb on hand so decided to use it on cyl #1. Will run it through the rest tomorrow when I get new supply. i did decarb them all about 30hrs ago but guess #1 has more build up.

 

[hoeser]

Re: 1984 J90 compression test results

If you can get all above 110psi you're good on that engine (all within 10% as well).

 

[JB]

Re: 1984 J90 compression test results

Don't get psi hysteria. You want a <10% spread.

No reason to expect Seloc to provide accurate or useful info.

 

[kenmyfam]

Re: 1984 J90 compression test results

Don't get psi hysteria. You want a <10% spread.

No reason to expect Seloc to provide accurate or useful info.

100% agree. Nice comment on the Seloc thing !!! LOL

 

[Steve2603]

Re: 1984 J90 compression test results

OK, Thanks for all the help guys. After a 1 hour soak in cyl 1 with decarb solution and then a full decarb run... now have cyl # up to 125 psi and less than 5 psi spread between all 4. Good tip on cyl # 1 having more carbon build up, something to remember for next time around.

 

[iwombat]

Re: 1984 J90 compression test results

Have you re-run your tell-tale line up and over the block as per the service bulletin in the tell-tale faq? That'll help with the air-pockets in cylinder #1.

 

[Steve2603]

Re: 1984 J90 compression test results

Have you re-run your tell-tale line up and over the block as per the service bulletin in the tell-tale faq? That'll help with the air-pockets in cylinder #1.

No I have not seen this, do you have a link to it?

thanks, Steve

 

[iwombat]

Re: 1984 J90 compression test results

http://forums.iboats.com/showthread.php?t=222677

Post #3 under "Advisable Modifications . . ."

 

[Steve2603]

Re: 1984 J90 compression test results

http://forums.iboats.com/showthread.php?t=222677

Post #3 under "Advisable Modifications . . ."

Thanks.. I'll check it out.