Compression question: 3-Cyl '88 90HP

[MattinTally]

3-Cyl '88 90HP ELPTO. Checked compression this evening with cheapo tester from Harbor Freight. Got 90-90-92 from a cold motor with all plugs removed. Although very even numbers, these values just "seem low". Was expecting something in the 105 - 120 range from reading other posts. Does anyone know what the factory spec is on this model motor, and if 90psi is within range?

I see older posts that may indicate that 90 (or even 70) was somewhat normal / acceptable PSI for these:
http://forums.iboats.com/showthread.php?t=205044
http://forums.iboats.com/showthread.php?t=113374

I cannot warm the motor due to a blown lower unit. Motor ran fine before foot blew and never really have any issues with it in the SHORT time I have owned it. Was on a 24' pontoon boat with no tach / no speedo, so I'm not really sure what the RPMs or speed was before the lower unit went.

 

[crem1]

Re: Compression question: 3-Cyl '88 90HP

That would have been my suggestion, warming it up. Good even readout on the pistons a very good sign.

 

[Texasmark]

Re: Compression question: 3-Cyl '88 90HP

If you are worried about rings, take a reading and yes on a warm engine and then take a squirt can of oil and shoot the cylinders good, especially around where the rings ride and retake your data. I'd say a 20 point or so jump would indicate worn rings.

My engine service manual for the later versions of that engine specifies 120 as the min acceptable value before you suspect heavy engine wear. 150 is considered max and all should be within 15% of each other, per the manual.

HTH (well, maybe not, sorry)

Mark

 

[MattinTally]

Re: Compression question: 3-Cyl '88 90HP

OK, So after putting the lower unit back on and running a can of seafoam thru it, it smoked like crazy and after letting it run for a while I rechecked the compression. Even 105ish on each cylinder.

Is this thing worth fooling with, or is it likely on its last leg. I can get a complete parts motor with a good lower unit for only $400.

Should I go ahead and fix it? or just scrap it?

 

[crem1]

Re: Compression question: 3-Cyl '88 90HP

If you are handy mechanically, putting in new rings improves the compression immensely.

 

[Texasmark]

Re: Compression question: 3-Cyl '88 90HP

If you are handy mechanically, putting in new rings improves the compression immensely.

I had to laugh at this. Hopefully it won't come to that.

Mark

 

[Faztbullet]

Re: Compression question: 3-Cyl '88 90HP

The biggest problem with motors on pontoons is that people overprop them to try and increase speed which in turn lugs the engine big time. Carbon build up increases and so does wear. If it was mine I would :
A) Install a tach to see if engine is in rpm range and reprop if needed
B) Give it a good tune-up and decarbon
C) Run several tanks of fuel thru it with decarbon additive
D) Recheck compression after (C) with 2 guages as all testers do not read the same

 

[MattinTally]

Re: Compression question: 3-Cyl '88 90HP

Everything is finally back together and back on the pontoon. Took out to the lake about 10 days ago and it ran like a champ. Fired off with barely a touch of the key, ran WOT with strong, good sound. Still looking for a tach that will work to check RPMs. After a few more thanks of fuel+sea form, I'll recheck the compression to see if its jumped any. I checked prop and its a 13 pitch, which seems to be what's recommended for a pontoon. Thanks again for everyone's input.

 

[JB]

Re: Compression question: 3-Cyl '88 90HP

Don't get hung up on psi, MT. Differences in guages, conditions and technique can make as much as a 50psi difference in the readings.

What is important is the span, and your span is ideal. It ain't broke, so don't fix it.