Bad smoking

[PaulW_NJ]

I recently had the head from my 240U rebuilt by a reputable machine shop. New valves, seats, guides, springs. I bought the tractor last year, and while it hardly smoked at all,it ran very rough. I discovered it had a frozen intake valve, which had caused several bent valve push rods.

Here are the compression tests before the head rebuild. The first column is dry, the second after oil injected:

1 130 160
2 0 0
3 125 160
4 145 170

Just started it after the rebuild. The engine now smokes like a locomotive. Cars going past slow down to see where the fire is. Runs very smooth, but spraying unburned oil out of the stack. Everything is covered with droplets of unburned oil. Doesn"t smoke for first 30 seconds, but then smokes like crazy, idle and load. Plugs are wet, black,and very oily. Have only run engine for less that 15 minutes.

New compression tests:

1 115 130
2 120 130
3 135 145
4 138 145

Blow down test:

1 15%
2 15%
3 4%
4 10%

Why should it go from no smoke, to a serious smoking problem? Before I go back to the machinist, could the head gasket have somehow broken during installation? Anything else I should check? Looking for answers.

 

[PaulW_NJ]

sorry . . . that's supposed to be cylinder leakage test, not blowdown est

 

[Gary from Va]

I worked in a machine shop with my father a few years ago. We would rebuild a set of car heads for a customer, and they would return a few days later with the same problem. Turns out, when you put a new set of tight heads on a worn-out bottom end, you run a good chance of blowing the rings. Not sure if this happened to you, but I've seen it happen to two chevrolet engines.

 

[CNKS]

That is my opinion too, and there is WAY too much difference in compression between 1,2 and 3,4.

 

[old]

LOL classic problem. Rebuild the top and you will stand about a 95% chance of blowing out the bottm or the other way around. Simple fact is you now have for the most part a new head but running old bottom end so yes it will smoke bad, you just got unlucky that it didn't last a few months. Sounds like its time for a complete rebuild on that engine because the lower end rings etc are bad. If you keep running it that way you stand a 50/50 chance of blowing the rod.main bearing out also
Hobby farm

 

[charles todd]

My old college truck, now "Farm Truck" is a 1979 Chevrolet C20 Bonanza, 350 cid 4bbl. It has 150,000 miles and bout 30 years of grinding around at 3000+ RPM (4.10 ratio, no OD). I KNOW the heads are shot.

I called a machine shop to quote a head job and they told me to save my money and drive it until it quits or starts knocking. He explained that the tight heads will basicly blow out the the bottom end. That was 7 years ago and I am still driving it on the factory engine, never even has had a timing chain change (can probably touch the chain together between gears).

Good luck on your bottom end rebuild! Gotta do it now...

Charles

 

[MN Scott]

You started the rebuild job now you need to finish it. Shortcuts always cost more in the long run.

 

[Janicholson]

If the engine has only 15 minutes on it, it needs 2 hours to get all the residual oil out of the intake track, and system. Run it hard for a while before condeming it. If it did not smoke it is probably going to be OK. If not, the others are right. Still a cheap test. JimN

 

[Anonymous-0]

Yeah, I agree. I can't argue the new head on an old motor problems, but he really only gained compression on the stuck valve cylinder, the others did not change a lot. If the thing sat long enough to stick the valve hard it could have a stuck ring too. But if everything else looks cool, I would run it for a while to see if it clears up, if it was soaked good they can really smoke for a while, it won't hurt it.