cylinder wear

[Rancherlee]

I just got my 88' 88spl last week and the previous owner had it overhauled 2 years ago (1 new piston/sleeve and 3 hone/rering) and he showed me the reciepts. It has about 100 hours on the overhaul and the compression looked good on his gauge (110-120 on all 4). So I bought it and brought it home and installed it on my boat and took it for a spin and it seemed to move my boat pretty good but I was expecting a bit more out of power wise as my old 55hp pushed my boat 31mph and I only got 38mph out of it with this 88spl but the motor seemed to run smooth with a slighly rough idle and I put it back on the trailer and went home to raise it up one more hole. I decided to change the plugs and notice a decent amount of carbon on the pistons/plugs so I checked the compression with my own Mac tools digital compression tester before runing seafoam thru it and the the right bank pistons are down on compression.
#1-97
#2-117
#3-92
#4-119
And after seafoaming
#1-99
#2-117
#3-92
#4-118

SO a borrowed a bore scope from work and I noticed the #1 and #3 (lower compression one) cylinders look very smooth with no scratches or anything and the #2-#4 (good compression ones) I can still see light crosshatching and no scratches. Assuming that all 4 where honed the same what would cause the glazing / accerated wear on the 1-3 cylinders or it is possible that these two cylinders never seated the rings or weren't honed enough? Also this guy lugged the motor pretty good as he got 31-32mph out of it on a 18' cuddy and with the 17 pitch props he gave me with it that only comes out to 4600rpm @ WOT. Is it possible that putting it on my lighter 16' boat and running 5200rpm caused any damage since it was used to running 4600rpm and got carboned up?

 

[AlanR]

Re: cylinder wear

Your compression isnt all that bad.. Its a little low in Number 3 but i dont think better compression will increase your speed much more than what your hitting right now.

 

[G DANE]

Re: cylinder wear

Well things like that happen now and then, I seen that too. They probably decided those two cylinders were fine and let them alone. They were only honed on the bill !! Ive seen a rebuild I bought, have one old and one new piston in it, even two different styles, both standard size. The old one was visibly worn, but compression was even somehow, on that motor. I had it apart, as I could hear piston rattle from the one cylinder. I think you are good to go, compression can wary on banks. Yours wary to the edge though.

 

[emdsapmgr]

Re: cylinder wear

Did you take the compression with all the spark plugs in or out of the block? If you hone properly, you should get a nice cross-hatch design. This promotes ring seating. If you just put the hone in the cyl and don't move it up and down, it just creates circles (instead of X's) of honing, which may tend to disappear (wear) more quickly and the rings may not seat as well.

 

[Dhadley]

Re: cylinder wear

If it was only running at 4600 on the other boat you can bet the rings are coked up severly. Especially on the starboard side (as your compression test shows). You may have to do the decarb 2 or 3 times. You've seen a slight improvement so that indicates you're going the right direction.

 

[Rancherlee]

Re: cylinder wear

well the first decarb seemed to work decently I checked the cold compression this morning after it sat all night and they are up to 105 and 94 on 1/3 from 99 and 89 cold yesterday. Time for another can of seafoam.

 

[Rancherlee]

Re: cylinder wear

Problem found, Head gasket was gone on the #1 cylinder and the #3 has ALOT of wear (probibly take most of a .020 over to clean up). Is it normal for a cylinder to wear severly on the bottom and still have some cross hatching on the top (I'm going to assume yes by the way these engines sit) I contacted the previous owner and he is willing to refund me 600$ if I want to keep it or give me the full 1200$ if I want to return it since it was sold to me as a recently overhauled engine with "good compression" and come to find out his gauge was B.O. I think I'm going to keep it and spend the 600$ on overhauling the powerhead since the rest of the engine is very clean, shifts smooth, and it has a fresh leg on it.

Which pistons should I look into, OMC , Wiesco, or others? I figure 600$ should get me most of the way through an overhaul doing all the work myself (expect punching it .020) and I've never tackled an outboard before (rebuild many, MANY car engines and a few snowmobile engines also)