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Old 09-30-2020, 09:35 PM   #1
Carmen Black
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4.3L Vortech - No compression in Cylinder, should I junk it?

I needed a 4L60E transmission for a 1986 S-10 Blazer project I am working on. I did not want to spend all the money for a new transmission, torque convertor and controller. But I was able to find an ad on Craigslist for a 1998 S-10 Blazer that had a recently rebuilt transmission and lots of other stuff I could use, and it was cheap because it needed an engine.

So I meet the guy and the Blazer has a great transmission, but it hardly starts, doesn't idle and if the RPMs get below 1500, it shuts off.

The guy bought the blazer two years ago for his step-son and he obviously did not have a high opinion of this kid. So the kid says the truck started running rough one day, and the guy takes it to his mechanic who tells him that cylinder #5 has no compression and whatever the problem is will be big money. The guy is tired of the Blazer / money pit, so he puts it on craigslist.

The guy wasn't shady, but everything he told me was what the kid told his mom who told him or what his mechanic told him that he didn't understand because he knew nothing about cars. It was like when your wife comes home after getting her oil changed at the dealership and says they had to replace the headlights because the rear tires were not putting out enough voltage. So everything was very squishy, but I didn't care about the engine anyway.

I drove it home about 100 miles, and it ran mostly okay at 50mph which was the fastest I could drive because the "recently rebuilt" front end kept trying to throw me off the road. Just for kicks, I put a compression gauge on cylinder #5 and the gauge wouldn't move. I couldn't get to cylinder #3 because of the steering shaft, but cylinder #1 was about 150psi. I took out the engine, transmission and transfer case as one unit, split them up and put the engine on a stand.

Of course, I couldn't just let it sit there knowing it had a problem so I pulled the valve covers and turned the engine by hand and all the valves were moving freely. I put a leak down gauge on the bad cylinder, shot air into it and the air just freight trained straight out the exhaust port. I pulled the head and immediately saw a witness mark on the piston where the exhaust valve had hit it. I put a flashlight in the exhaust port and I could see the light coming around the face of the valve. The gap was probably big enough to slide a nickel through.

The whole time I am doing this, I am thinking this 4.3L Vortec would fit better in my S-10 project chassis than the small block I was intending to use, it would weigh over a hundred pounds less and probably make about the same power numbers as my high mileage 1970 vintage iron head 350.

So I start trying to figure out the condition of the 4.3L. The blazer had 220,000 miles on the clock, but the valve cover and intake gaskets looked new, there was no sludge in the engine, and even the exhaust manifold bolts turned like butter. I could clearly see cross hatching in two cylinders and some cross hatching in two more. I could just very barely catch the ridge ring with my finger nail. My cheap Chinese digital caliper would not measure deeper than the ridge ring, but I measured the bore every which way I could and came up with 3.992 to 3.998 inches.

I can't believe this could be the original engine with 220,000 miles on it with visible cross hatching, but I would also think a remanufactured / rebuilt engine would be over-bored (if I am measuring it correctly). I guess a previous engine could have been replaced with a brand new GM engine, but that doesn't seem to me like something many people would do.

I don't have any experience with engine internals. So, how do I determine if this could be a good motor by just replacing one valve, or even a cheapy rebuild? And what would have caused the piston to kiss an exhaust valve and how do I keep it from happening again. Or is this engine just not worth the time or money?

Thanks everyone
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Old 10-01-2020, 11:32 AM   #2
truckster
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Re: 4.3L Vortech - No compression in Cylinder, should I junk it?

Your best bet here is going to be a reputable machine shop. Disassemble the engine, take it to them, and pay them for their diagnosis. They'll tell you exactly what needs to be done and what parts you need to replace.
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Old 10-01-2020, 06:03 PM   #3
vince1
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Re: 4.3L Vortech - No compression in Cylinder, should I junk it?

I had an 88 and an 89 Astro van with 4.3's that had a leaking coolant problem into the #5 cylinders. I think they had cracked heads. By 96 they were OK.

I'd pull off the left bank cylinder head and go from there.

My brother in law had a 4.3 in a P/U and it was still running at 490k kms, over 300k miles. Some of that was pulling a loaded horse trailer and according to my brother on one trip doing a pretty good job of keeping up to the diesel P/U.

Last edited by vince1; 10-01-2020 at 08:21 PM.
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