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Old 02-15-2018, 06:47 PM   #1
JFC10
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Help with small block timing gear carnage

Hi all,

I recently pulled the 350 out of my 69 C10. I was informed it had low compression, skipped timing chain, and various other issues (fully trashed) by the local small town shop. I have paperwork from a rebuild from 1987, although I realize that means nothing at this point. Since i would have it rebuilt or build it myself, I figure I'd inspect for damage; it had to come out regardless, right? Out comes the hoist and engine stand, followed by a record 2 hours of thrashing.

During damage control I found bits of the infamous nylon timing gear teeth scattered around in the lifter valley. I pulled the timing cover to reveal the broken teeth and a chain I could remove by hand. The thing is fairly crusty inside, valve stem seals and intake show signs of leakage. Despite my best efforts I cannot find a definite answer about wether or not a stock 350 chevy circa 1969 is an interference motor. It would sure be nice if it wasn't; I'd slap a timing set on it and throw er back in...

So I decided to test for bent valves, which would normally be accomplished by pulling the heads. Instead I like to do things the hard way and removed the check valve from my compression tester, screwed it in each spark plug hole, and hooked it up to a hose from the air compressor. Theoretically, air will leak past any bent valves and out the exhaust/intake. It was also entertaining to turn the engine over with compressed air, hear the air hissing past the rings, and tap the valve stems to produce a puff of air.

Well, it does leak, in EVERY one of them... Some more than others, intake and exhaust. Although my test probably isn't very scientific, I thought it would still be obvious which valves bent. Examining the valves, I see they are very crusty, and I would assume that because air is very thin, it would still leak past the smallest seam created from crud on the valves/head; which would otherwise let the valves operate without issue while running. My question is, (if you made it this far, whew) how much air should be leaking past the valves? Either every valve in my engine is bent, or a small amount of air will leak past in everything but a newly-lapped valve. Again, they all leak somewhat, a few more than others, but it's impossible to tell the difference.

I know what the right way to do this is, but I am just trying to get it running good enough to sell, as money is very, very tight. I'm not looking for suggestions on what to do with the project; and I'm sure every one of them is more expensive than a timing set and some gaskets, although I will listen to most with interest. A $500 craigslist engine was the previous plan after all. My level of caring is pretty low for this engine already, as it has been sitting for 4 winters. Assume I know nothing, and that my knowledge on engine building is little to nothing. Just looking for an old, wise gearhead's opinion on what a bent valve really sounds like when you shoot air in the cylinder.

Last edited by JFC10; 02-16-2018 at 12:30 AM.
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Old 02-15-2018, 07:19 PM   #2
LONGHORN1962
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Re: Help with small block timing gear carnage

350 is not an interference engine. If the valves are thin and crusty, that could be the problem. Weak valve springs can cause the problem.
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Old 02-15-2018, 07:33 PM   #3
AussieinNC
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Re: Help with small block timing gear carnage

Just my ten cents worth here...

Save up and buy a new GM engine like a 350 Fast Burn...search "350 GM Fast Burn on google...

Something like

http://www.jegs.com/i/Chevrolet-Perf...SABEgLefPD_BwE

Great daily driver street engines...try and stay away from rebuilds...

or sell it as is with the bad engine...


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Old 02-15-2018, 08:22 PM   #4
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Re: Help with small block timing gear carnage

When I got this current '69 from the estate of the original owner after he died, after a couple years in heavy commercial use the timing chain skipped and the result was 8 bent pushrods. I just hammered them straight, put a new timing set on and drove it another couple years. My research showed that these were NON-INTERFERANCE engines, so maybe the original owner put a cam in there at some point. But the valves were not bent, just the pushrods.

Of course you will have low compression if the timing chain has slipped.

You could put a timing set on there and do a compression check. I would look for the cheapest way to get it going, but then that is how I always think.
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Old 02-15-2018, 08:25 PM   #5
Mike C
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Re: Help with small block timing gear carnage

My experience with SBC is if the chain breaks and the motor is turning it WILL hit the valves and bend them.

If it were me, I'd be looking for a lower mileage Vortec 5.7 to swap in. Only drawbacks are hooking up the temp gauge and having to run electric fuel pump. But this way you get Vortec heads and hydraulic roller cam which would both be fairly expensive upgrades to your rebuild (but worth it IMO!).
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Old 02-15-2018, 08:57 PM   #6
clay68c10
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Re: Help with small block timing gear carnage

Loosen all the rocker arms to shut the valves and re-do your test. If the valves are bent, you will hear lots of air coming out thru the intake or exhaust.

If you have a broken piston you will hear air in the crank case.

If the valves are bent or anything else is wrong then drop in a $500 Craigslist 350 and unload it. Probably the cheapest way to go.
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Old 02-16-2018, 12:22 AM   #7
JFC10
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Re: Help with small block timing gear carnage

1.wow this is a great forum, thanks everyone
2. Using a borrowed boriscope, I couldn't find any signs of piston/valve contact, the coating of carbon isnt scratched or disturbed, and I can't tell if the valves are bent either...

My $500 Craigslist special plan is still probably the cheapest, safest option it sounds like.
As for the Goodwrench engines, I would definitely consider one, I've swapped one into a suburban with no issues in the past... But if I have $1500 bucks to drop on an engine, you better believe it's going towards discount speed parts to build a screamer.
I'm about to pull the heads, the suspense is killing me.
I've always had aspirations of porting some junkyard vortec heads and using them on something I rebuilt. Im under the impression aftermarket heads will make more power per dollar depending on what you get... Now I'm just rambling...
It pains my GM purist soul to sell this turd without it's matching numbers block, but the world will go on.

One last burning question,
What are some opinions (and facts) about slapping on new head gaskets without any machine work? I realize they will never last in the long term, at least on a iron V8, but has anyone tried it with success? Mabye in your foolish younger years? Inquiring minds want to know. I have a feeling it happens more than most would like to admit...
Considering the condition of what I usually find myself working on, this is important information.

Thanks again to those who responded, I'd rather have many other facts and opinions than be left with only my own.
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Old 02-16-2018, 01:19 AM   #8
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Re: Help with small block timing gear carnage

Why pull the heads? If the only problem was the timing gear, and you want to spend as little as possible, I'd put a timing set in it and be done with it.
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Old 02-16-2018, 10:06 AM   #9
clay68c10
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Re: Help with small block timing gear carnage

If you didn’t see anything with the scope, put a timing set in and run it.

New head gaskets on an old block and heads will be just fine as long as nothing is warped from overheating. But why pull the heads on something you’re just selling anyway?
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Old 02-16-2018, 10:54 AM   #10
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Re: Help with small block timing gear carnage

Buy a timing set, It is a 10 minute job and a $20.00 purchase. put the gears and chain on and then do a compression test and if it is not all over the place buckle it up and go. Too much discussion and not enough "Git er done"
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Old 02-17-2018, 08:58 PM   #11
mike16
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Re: Help with small block timing gear carnage

if the valves are bent, when you remove the rockers or push rods all the valves will be at different heights
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Old 02-19-2018, 08:53 AM   #12
panhead59
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Re: Help with small block timing gear carnage

Heck, I've got a 350 u could have for free!||!|! To bad u r so far away. It's an 81 that had just started to smoke a little on start up. Probably valve seals but I'm sure the rest is worn out also.
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Old 02-19-2018, 01:24 PM   #13
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Re: Help with small block timing gear carnage

You will need to drop the oil pan also & clean it out. All those plastic teeth will plug up the oil pickup screen before you get it sold.
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Old 02-19-2018, 05:53 PM   #14
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Re: Help with small block timing gear carnage

If the motor is out, I would go through it-at least a little. By a cheapie rebuild kit from Northern Auto Parts. Pull it all the way down. Get a little bigger cam. Clean it all up and get all the gunk out. Check clearances on the rods and mains. Hone it and put it back together. New rings and bearings. Might even splurge and have the block tanked and put the new cam bearings. That will buy you a couple years maybe.

Or buy a used 96-99 Vortec motor and get the intake for it and run that awhile as somebody else suggested. Probably cheaper, quicker, and give you more power than what you have.
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Old 02-19-2018, 09:10 PM   #15
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Re: Help with small block timing gear carnage

I don't suppose your local small town shop told you that your low compression can be caused by the timing chain having jumped time? It should be a safe bet that the engine was running when the chain jumped time so a new chain and gears properly timed may have that engine once again running as good as it was the day the chain failed. Am I the only one that read "money is very, very tight"
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