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1987 225 powerhead

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gradywhiteman

Contributing Member
My mechanic did a compression test on the engine and it has one low cylinder. It has 100,95,95,90,90,60. I can't afford a re-man powerhead job so my question is this, if I were to take the powerhead apart myself can I just replace the rings or piston also if needed on the bad cylinder without machine work just to get through the season?
 
You have a 40 psi difference between the lowest and highest compression reading. The first thing to do is to remove the cylinder heads so that you can inspect the pistons, cylinder walls, underside of the cylinder heads, sealing surfaces of the heads and block, etc. Perhaps you'll be lucky and only have a blown head gasket.

If a worse case senario (blown piston), machine will no doubt be required, otherwise a repeat of this problem will be in the works.
 
Joe thanks for your reply. What is the most common cause for this type of problem? Bad winterization, not being used? I am going to use the boat anyway because we paid for the slip. I thought if it really did'nt run right I could through some new rings in that cylinder and get some better performance from it.
 
Much debate on this. Some say running lean (think fouled carb). Others say carboned rings. I subscribe to the carboned ring theory. I will use seafoam or similar regularly now.
 
Thanks Martino, My mechanic is de-carbing the engine today in hope that it will free up whatever might be stuck in there. If it doesn't work I am trying to get a plan together so I can salvage most of the season. In your opinion do you think that de-carbing can make a difference? Also I have heard of sea foam before but I am not sure what it does?
 
Thanks again Joe. So if that is what happened it would lead to exessive wear in that cylinder. If I were to pull the head off and the cylinder wall was not scored then would ring replacement be okay?
 
I'd prefer that you remove the head so as to inspect everything as per my previous reply. After which we can go from there.
 
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Joe my mechanic de-carbed the motor today and nothing has changed, compression still low in that cylinder. I am going to try and use it keeping the rpms down and if I can get the remainder of the season doing that I will probably not touch it until the fall. If it doesn't work I will be taking it apart much sooner. In your opinion Joe how long would a job like that take for a backyard guy to do?
 
I don't want to jinx things, but the first V6 Johnnyrude I owned came with no lower unit, and was described as a parts engine. I put a lower unit on it, and it seemed to run fine. I used it for a whole season. Then when I checked the specs on the boat, I found that the boat should top out at over 50MPH, not the 30-35 I was getting. I then did a compression check. Four cyl's were in the 100 range, one read 60, one read like 40. I rebuilt at that point. Considering I was running on about 4 cyl's, it really didn't run all that bad. My only concern was the rough idle. I think the danger is that something comes loose or seizes, and then you have big problems. You sound way better off than I was. Mr. Reeves is the pro. His advice is way better than mine.
 
a decarb,w 40 psi diff,is not gonna help...u need to properly,....overhaul this eng,...to have a reliable,..power plant...
 
I plan to do something with it over the winter wether I re-build it or look for another engine. Not sure if putting a lot of money into a 23 year old engine is a wise thing to do.
 
Personally, if it were me, I'd yank that cylinder head to make sure the problem is or is not simply a blown cylinder gasket or O Ring seal, whichever applys.

If a bad seal or gasket, the problem is solved and you don't run the risk of damaging the engine further by running it with the failed gasket/O Ring.

If the gasket or O Ring seal is okay, at lease you klnow what the problem is and all you're out at the moment is the price of the gasket/seal.
 
Joe I lost the internet last night so I couldn't reply until today. If it is a gasket that would be great. The mechanic I brought it to did not mention that at all and he did two compression tests on it one before the de-carb and one after.
 
You would need to tear the engine down, sort the good parts from the bad parts, find the cost of whatever machine work might be needed, then total the cost of all the parts to answer that question.

Second question..... Compare the above cost with the price of a new engine.
 
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