Dhadley Piston question review

[Jons69chevy]

About a year ago I was just getting started with rebuilding a 1989 200hp evindrude motor that the compression was very low on. You (dhadley I beleive) told me about using some Wiesco pistons from a 1993 and newer 200 hp because they were lighter and it would idle better. I just got the engine back together and was having a few issues with it and wanted to verify the part number for the piston. The piston part numbers that I put is were 3143. Is this the piston that you suggested? My mechanic is concerned that the pistons are causing the problems that we have had and He is going to call wiesco tomorrow and check with them. Just wanted to verify the information with you. I know someone will ask so here is the problem. the motor did not want to idle so the mechanic did a link/sync on it and it didnt help. He tried to get it to idle better but with no luck. He did a compression test on it and the compression was about 75 on each on one bank and 75,65,50 on the other bank. The motor only has 3 hours on it. His thoughts are that the compression issue might be causing the idle issue. The cylinders still look very good. We are running it on premix with the vro disconnected (power and oil lines) Any help is appreciated

 

[dsinger]

Re: Dhadley Piston question review

That does not make any sense to me. New rebuild with a PROPER BREAK IN should not give a compression reading that low. What was the reason for the rebuild and what did you do to the cylinders. Whoever told you about the pistons was correst and it is not the pistons your mechanic should of known that anyway. Is the lose in the cylinder or a gasket or has he tested it that way.

 

[Dhadley]

Re: Dhadley Piston question review

Yes, the number is 3143. For .020 over it'll be 3143P2 and 3143S2, .030 over it'll be 3143P3 and 3143S3 etc.

Before you run the motor any more you need to find out why the compression is that low. Verify the piston is the correct size for what it was bored to. Numbers that low somwtimes indicate a .020 piston in a .030 cylinder. And it will idle poorly as you describe.

The next thing is to verify the pistons are in correctly. Don't rely totally on the stamping on the dome, look at the ring end gap position. Your mechanic will already know that as it's up to the installer to verify ring location. Also ask him what the ring gap was. Each new ring should have been checked as it went in each cylinder. If the gap is correct, we know the ring is correct as well as the bore.

 

[Jons69chevy]

Re: Dhadley Piston question review

The motor was bored on all cylinders 5@.020 and 1 at .040. The compression before the rebuild was down on all cylinders but only 1 cylinder was scored up. During the rebuild we replaced rod bolts, pistons, rings, rod bearings, wrist pin bearings, main bearing except 1 (cant remember if it was upper or lower. the carbs were rebuilt-we tried to do things right. As for the exact cause of the original low compresion we dont really know. I was using the vro at that time but the compression just got lower and lower over a couple of years. We pretty much just chalked it up to getting worn out.

I thought that I would be safe premixing with the vro disconnected. One thing that is the prime suspect is that we used some generic wal mart outboard oil at first (about 2 hours) and noticed that the pistons and plugs were coated with a black coat of something-almost like they were powder coated. It got to where is didnt want to idle-that is how we found the problem with the oil/gas. So i took it in for the mechanic to do a decarb on it and that is how this part of my mess started. Do you think that the rings might just be slow in breaking in? or that the decarb might have washed the cylinders down and that the compression might come back? I will make sure that he checked the head gaskets for any signs of being blown.

I am going to check about the ring gaps and see what we can remember. My dad and I put the motor together (he is a retired auto dealer mechanic) but we are by far not marine mechanics. We were using the oem manual for the rebuild process.

 

[Jons69chevy]

Re: Dhadley Piston question review

If the cylinders are bored .020 what should the bore size be at the top of the cylinder. What we are finding is 3.707-08 at the top. Is this too much if the piston is .020 wouldnt that be 3.685, .002-3 clearance seems like alot to me but I really dont know what the norm is.

 

[Jons69chevy]

Re: Dhadley Piston question review

bump

 

[Dhadley]

Re: Dhadley Piston question review

3.707 - 3.708 is within spec but a little large for a fresh bored motor. Wear tolerance is .004" so 3.708 is within spec. 3.7055 tp 3.706 is what I look for on mine. I wouldn't worry too much about the top but rather the middle and the bottom.