Did it look  like the powerhead had been apart before?  Perhaps someone has been inside, attempted to bore, or perhaps over honed that cylinder in an effort to get rid of scuffs and scores.  It is usually pretty easy to tell if someone has had the powerhead apart, paint off the crankcase screws, unpainted sealer oozing out between crankcase halves.   I would carefully measure the cylinder bores, piston skirts, and check ring end gaps using the old rings.

You mention that the pistons were not scuffed, and the cylinder walls were clean with no aluminum transfer of scoring.   You said that you surfaced the head, but it has a slight wobble, that is no good.  You must make sure that the cylinder head is perfectly flat.  Perhaps the block is not true/flat as well, but it is much harder to try to true up that surface because you have the steel cylinder sleeve to deal with.  Excessive sanding on the block will just grind away the aluminum leaving the steel sleeves relatively untouched.

I suppose it is possible that the aluminum in the head is cracked or damaged somehow allowing the compression to leak out, but not real likely.  What did the head gasket look like, you can usually see burn thru marks if it has failed.  Did it look like the head gasket had been replaced before??

I know I have mentioned alot of things, but you really need to find the cause of compression loss before just putting the engine back together.  I just don’t want you to spend alot of money on rings/gaskets, and then still have low compression after reassembly.

I guess I should have led with questioning the compression gage.  That lower plug hole is buried down inside the pan on those engines, making it a little more difficult to thread the compression gage in there properly.  Are the plug threads OK in the cylinder head?  Perhaps the gage wasn’t threading completely/properly into the plug hole.

Now that you have it apart did you check the end gap of the rings?   Take the rings off the pistons then slide the rings back in the boar, push them down about half way of there travel.   Use the piston to make sure the rings are square with the bore.  If they are worn you will have a big gap.  Somebody on our site here will know the proper spacing.   These motors rarely need rings but if that space is wide you will have an idea about wear.

dale

OK, so it seems like the powerhead has never been apart, so it seems unlikely that someone has tried to bore/hone the cylinders in the past.  Nonetheless, I would measure the piston skirts/cylinders.   Try to check the ring end gaps on the old rings, and definitely check all ring end gaps on new rings, especially if using aftermarket rings.  Clean those piston ring grooves thoroughly using one of the old rings, then check the side clearance of the new rings to make sure new rings fit properly and don’t get stuck easily.

OK, the engine surely had cooling issues, guess it was used in salt water.  But, it seems like you have gotten it all apart without breaking bolts/stripping threads.  I would go ahead and clean all the threads with a tap, and check them all carefully.  The last thing you want is to have a thread strip out while torquing the head bolts.  Be sure to check the plug threads also, look for a decent used head if plug threads are badly worn/stripped, I don’t recommend trying to repair plug threads with helicoils etc.

I feel pretty confident that the stuck rings were the cause of your low compression readings.  The engine didn’t get proper maintenance, wasn’t cooling properly, probably was using crappy oil.  You mention that the impeller did not look like the right one, would love to see some pictures.  There are two different water pump kits for this engine, the old style with the aluminum housing, and the newer style with the plastic housing and smaller impeller.  None of the parts are interchangeable.  Was the gear oil in decent shape?  No sense reinstalling the gearcase if the lube was milky or had water in it.

Sounds like this engine is in decent cosmetic condition, and is worth resurrecting.  Feel free to ask more questions and post pictures.  I have seen those OEM rings for sale on ebay, don’t know if they will ship overseas though.

William MacNeill wrote:

The gear oil was more like sludge than oil. I don’t think it was ever changed or if it was not often. I do believe it has been resealed at one time as there was very little trace of water in the oil. It was black and not milky at all. I appreciate all of the input. It’s good to have other’s insight as to what might be going on. This is not the first motor I have tore down nor will it be the last I’m sure. I always seek out the obvious first when starting to work on a motor. Compression, spark and fuel. From there as we all know without the 3 working nothing else will either. I would of bought this motor even if I had checked the compression on it first because of it’s appearance. It will end up staying in my personal collection as I will never get out of it in sale for what I have into it.

OK, so the lube was black with minor traces of raw water?  It is a good idea to pressure test in order to check for actual leakage issues.  This gearcase uses a crazy spring loaded shock absorber in the lower driveshaft just below the gearcase upper seal/housing.  This feature has a tendency to fail in a way that extends the lower driveshaft forcing it upwards so it rubs/grinds on the bottom of the upper seal housing.  This condition can result in binding, or damaging/breaking the gearcase seal housing allowing water to enter the gearcase.

In your case, I am fairly confident that the stuck rings probably are the cause of the low compression.   But, I will always bring up simple issues that might also be to blame.  It sure sounds like your cylinder head is not true/flat, so that needs to be checked.  I mentioned the plug threads because this could be an issue as well.  I just want to help you avoid doing all the work of replacing the rings and reassembling, on to still have low compression on that cylinder.

And again, I would love to see pictures of your water pump pieces parts to understand what you are referring to when you say that the impeller is not the correct fit/part.

• This reply was modified 1 year, 4 months ago by fleetwin. Reason: addition