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GM 4.3 "how much stupid can them valves handle?"
04-23-2017, 07:25 PM
Post: #1
GM 4.3 "how much stupid can them valves handle?"
OK. This a 4.3 carbed (I'll get the year when I can) GM V6 in a freakin boat! I don't do boats! But here it is in my yard... this poor feller... he's generally a reasonable fart smeller uh, smart feller... but replaced the heads on this engine and was under the impression that when you put the rockers on, you just tighten them down all the way and your all set. He finished the job by cranking over a fair amount but it didn't start so it sat all winter. Now it seems to me that at some point GM did make some heads for some engines that the rockers were not adjustable. That's another thread to find out what engines those were. But it was rare, and not this engine. So I got all the rockers off but three are stuck because the dished washer thingy (what is that called?) won't slide up the treads, so there just turned sideways. 3 push rods are so bent it's hard to believe they came out! 5 that are quite bent, much more bent than my... and 4 that might be bent some but look straight at a glance.
Here's the question: Is it even possible this thing didn't bend any valves?? Like maybe the rockers just can't move that far, or springs bottom out, but valves survive??
Owner only wanted me to adjust the valves LOL. Now he wants me to throw new push rods in and adjust valves. I can see that, yes it is a lot of work to pull the heads back off because it's in a boat. Also, I don't know exactly what's directly behind the motor regarding any pump(s) or how it connects to the drive (inboard/outboard setup) that can make breathing noises... But with now rockers on valves, they all "appear" to be fully closed. When I turn the crank by hand I keep hearing air bleed off... I can't tell (yet) if it's bleeding off into the exhaust (cause it's a freaking boat) or if it's into the crank case but it sounds like the latter. I don't hear it coming up the carburetor.
Guess I'm looking for how to prove that replacing push rods is definitely NOT going to work so I can tell him to bring it somewhere and do it up right $$$. OTOH, if I can slip new rods down her and set it up... i get paid for that regardless of the result. But I don't want to do that if I can determine there's no chance it can work. Holy crap. It's a freaking boat! I don't DO boats! : )
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04-24-2017, 01:01 AM
Post: #2
RE: GM 4.3 "how much stupid can them valves handle?"
I don't do boats either but I have a fleet of 4.3 engines so I'll throw you a few bones and see where that goes.....

First I will presume the engine is early enough that it's got adjustable rockers, which puts the automotive equivalent somewhere in the 80s. (the later engines have no adjustment) That said, an engine is an engine so if nothing in the valve system is bent you can double check using compressed air through a plug adaptor at bottom dead center with valves closed. If it holds air enough to push the pistons all the way down (maybe add a squirt of oil to the cylinders because it's been sitting) then you know the valves are not bent. From there you can replace what seems to be "FUBAR" and do a base line valve adjustment. (zero lash plus a half turn?) If it will run then you can get the lifters pumped up enough to do a real adjustment, which will be somewhere between zero and a half or full turn more.

BTW, with the rockers off (completely off) you can place a straight edge across all of the valve stems to see if they are fully seated. Any variation that's obvious to the eye will tell you the valve is not all the way "up" so means there's a bent valve, fallen seat, etc.

Hint: if the air pressure won't push the piston down then the air is leaking somewhere.... bent valve, hole in a piston, etc. Between these two last tests you should be able to cut to the chase fairly quickly or proceed with repairs as necessary.

'Nuther hint: Since this engine has been sitting you may want to spray a generous coating of oil on the valve stems just to make sure they move freely as you move forward. I would hate to see someone pull heads again because something was gummed up from lack of use and only needed a bit of lube.
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04-24-2017, 09:13 AM
Post: #3
RE: GM 4.3 "how much stupid can them valves handle?"
Thanks Rupe! Valves look good via straight edge... either the intakes or the exhausts stand slightly taller, as they also do on the old heads he took off. I do think one may be slightly lower, I need a better straight edge and try to measure accurately... even trying to do this is a real pain. The exhaust manifolds (contraptions?) rise up to carb height, with accessories that bolt to them. I had to remove a bunch of this stuff to get the valve covers to barely fit off. There's barely enough room for my long skinny arms to reach any of the spark plugs. It's all the freakin "boat factor"!
These were brand new heads this guy put on. They are bone dry. Rockers and push rods all bone dry. I had one push rod that had oil on the lifter end to wipe off. All else bone dry.
Question: Leak down? I never done that test before. But I understand the concept. I believe this engine was running less then 12 months ago. It had an overheating problem. LOL. He didn't find a definite head gasket failure either, so this may all be for nothing. I suspect it may all be related to however it sucks pond water for cooling... But anyway, assuming the cylinder walls are well drained off but not bone dry... how quickly would one expect compression to bleed off past the rings? Because it sounds like every time I move the crank like 1/8th turn, I hear either compression bleed off or vacuum bleed off (on? in? ; ) ) for about 1 second.
My other concern are the balls (between rocker and nut) that won't slide off the studs. They or the studs must be slightly munched in some manner, so I'm wondering how straight the studs are? Or, how straight do the studs need to be?
Lastly, I'm gonna attempt to pull more plugs and get my bore scope into some cylinders. Owner is convinced valves didn't get hit because he didn't hear anything. I'm thinking a piston could come up and make contact and do damage without hearing it over the starter cranking. If I can find one thing that says for sure it needs to be taken apart further, I can just send it away cause I'm not taking it apart. I was only in for the adjustment. I do have procedure for that printed from the "boat book". It's zero lash plus 1 full turn, at assembly, no further adjusting required. Book shows roller lifters. I'd have to guess his initial setting was zero lash plus somewhere between 10 and 20 full turns? As in crank em all down until all the valve are open all the way, or the nut runs out of thread or until his arms were tired and they felt tight enough to not loosen up??? OMG! Wondering what that could do to a lifter? I'll try to post pics later.
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04-24-2017, 11:37 AM
Post: #4
RE: GM 4.3 "how much stupid can them valves handle?"
On the lifters, you won't know till later. The rollers are fairly sturdy but if they fail (later) you will find small needle bearings on the magnetic drain plug.

On the valves hitting the pistons, it's not something you'd see under normal conditions, but I have no clue as to how far you can crank the adjustment before having a problem.

On the leak-down, we're not looking to do a real leak-down test at the moment. I doubt you'd get an accurate result or even a good compression test on an engine that's been hanging around and cold / not run recently. I was suggesting a squirt of oil mostly because it's been sitting. What I was concerned with was the valves being tight enough (lack of bending) so any compression would move the piston. IOW, if it doesn't leak past the valves then at least that part is good and you can go to the next step.

BTW, on a boat there can be many different situations causing an overheat issue considering the various hoses and raw water pumps, heat exchangers, etc. IOW, not always a head gasket. Heck, it could even be just a bum thermostat.
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04-29-2017, 08:53 PM
Post: #5
RE: GM 4.3 "how much stupid can them valves handle?"
Something that just came to mind...

The automotive version of the 4.3 commonly has issues with coolant leaks at the crossover sections of the intake manifold. (aluminum / plastic intake) Sometimes it's on the outside and sometimes internally. (into the oil) If antifreeze got into the crankcase it's possible to do damage that wont show up till much later. Sometimes it's the crank bearings and other times it's those roller lifters. (just had that problem with an old Astro van) Take a gander at the dipstick to be sure.

You didn't mention if this had a split cooling system or all "raw water" type system so thought I'd also mention checking for proper flow through the heat exchanger (split system) or the intake on the raw water side, which can be an issue with either system. Don't forget the raw water has it's own pump and very often the impellers wear to a point where they don't flow enough.
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05-28-2017, 08:43 PM
Post: #6
RE: GM 4.3 "how much stupid can them valves handle?"
How are you making out with this project?
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