1989 OMC 3.0 runs ok but dies after a few minutes

[offshore79]

Hi all, It's my first post.
I've been reading alot of posts of similar issues and then some and I still dont have a solution to my problem.

What I have and what I've done.
I bought a fixer upper 19 baja with a bad OMC 3.0 engine. The head was cracked and the cylinders were rusted. The inside of the engine was like new.
I had it bored .030 to clean up the pitting and deck surfaced to clean up a divet(I think the previous owner dropped the head on it). New pistons and rings. Pistons were snug but at the bottom of the tolerance. Ring gap right on the money.
Used but very good replacement 3.0 (correct one) head.
Everything torqued to spec.
New gaskets and seals all around
Valve lash adjusted.
New coil, points, condenser, wires. Point gap.019, fire order 1342, timing 1 deg btdc.
Thermostat - tested - functional.
Rebuilt carb. Adjusted choke.
Plenty of fuel (new) and new fuel filter.

It starts, idles well, comes up to 175 deg, with oil pressure at about 35. I let it run for about 2 minutes at idle, picked it up to about 1500rpm, runs for awhile 3-5 minutes and then starts to stumble and then drops off. I backed off on the throttle and it died.

I thought timing, carberator, valve adjustment. Checked and rechecked everything.
Resitor wire seems fine also.
The only things I notice is that it runs slightly less then perfect...when just started.

I am so out of ideas. Thoughts?

Thanks
Offshore79

 

[offshore79]

Re: 1989 OMC 3.0 runs ok but dies after a few minutes

After some further thought I checked the fuel pick up tube in the fuel tank. Maybe starving for gas at a higher RPM.
Nope, the pick up tube was clean and clear.
My thought is going to the pistons and rings. When I gapped the rings they were all good however when I assembled the oil ring I did notice that when the top and bottom rings were put on the expander this prevented the rings from closing to the gap. This ring was very, very snug on all four cylinders.
I'm starting to think the engine shop or ring manufacturer gave me the wrong thing.
When newly installed I thought the engine turned hard by hand but being new rings I thought that was more than likely normal. I'm thinking now that when the engine warms that the oil ring is expanding and causing too much friction.
Again, when checking the gap on the individual rings they were fine but on the expander they are really tight. The profile of the expander doesnt seem to let the assebled set expand and contract. Being new-ish to engine building I figured it was as it should be.
When the head was removed and it was only crank, pistons and rings, I had to use a 12 inch bar or so for leverage and there was quite a bit of resistance.
Without the pistons I could spin the crank with a few fingers. How hard should it have been to spin the crank with the pistons in?
Any other thoughts before I pull my engine back out of the boat and tear it down again?

thanks
Offshore79

 

[offshore79]

Re: 1989 OMC 3.0 runs ok but dies after a few minutes

Ok, if anyone is interested, I pulled the engine out ant tore it down yesterday. I first was pleasently supprised to find no real damage to the pistons or cylinders but it also didnt apear to be oil grove becuase I would expect to see wear only where the oil ring rides.
Keep in mind I only have about 20 - 30 minutes of run time on the engine after basically a fresh rebuild.
What I found was that the cylinders were very shiny with almost no scoreing left from the hone. The pistons look good but when I got to piston # 4 I saw just a few scratches like something had gotten between the cylinder wall and the piston. I took a closer look at the walls and noticed that on all four cylinders I could see where the piston skirt had rubbed on the walls. I only have calipers to measure with right now but I measured the pistons and the cylinder again.
I'm getting about 4.026 on the cylinder and about 4.024 on the pistons. Eureka....I think. Even if I put a fudge factor of .002 because Im using a caliper instead of a bore guage and a mic, I still think this is the problem. I figure if the cylinders were correct I should at least have 4.028 or 4.029 with a caliper.
When I had the engine bored they also ordered the pistons and rings so I would think they would do and order correctly. They are the pro's right?
I called the machine shop and told them what I thought and of coarse they said that was impossible but if the oil ring was too thick then shame on me for not checking theyre work. Bitting my lip because they need to fix this yet.......

I've been doing my research and cylinders dont usually look this worn out at 150,000 miles. How many hours is that? And mine only has 20 or so minutes on it.

This is an engine after 75,000 miles (I've seen many like this after even 150,000 miles)
Until next time.
Offshore79

 

[offshore79]

Re: 1989 OMC 3.0 runs ok but dies after a few minutes

So I said "self!" because that's what I call myself when I'm talking to myself. I'm keeping a thread going by myself.....go figure!
It's time to take the block in....agian.
This morning I was finding .0279 - .0299 over the standard 4" bore (correct gauge). The pistons came in at 4.0275 +/- .0002. Hmmm, a little close and probably the issue.
After work tonight I took it in and although he didnt think it was a problem he did say it was a bit tight and said he can hone it some more. And honed it he did. All cylinders are now 4.0301-4.0308 I checked this with a new and calibrated dial bore gauge.

 

[offshore79]

Re: 1989 OMC 3.0 runs ok but dies after a few minutes

Just a quick comment.
I think I managed to find the worst engine shop there is. I went to go pick up my gaskets and main bearings. They were both wrong but of coarse the shop said, it's the wright ones. Intake/Exhaust ports were all wrong on the gaskets and I saw a exhaust ring seal in the package. He got to keep them. The main bearings have two holes and a slot where my old ones had one hole and no slot. After some research I found I could still go ahead and use them as long as one of the two holes lines up. Neither did. When I called the shop he said I must be doing it wrong.
1..2..3....4.....5......6........7..........8...........9...........10. Ok I'm better now.
More delays.