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Old 03-20-2017, 10:36 AM
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72 Monte Carlo engine

sbc 350 put engine together adjusted valves tried to start and timing chain broke. turned by hand OK to adjust valves. It popped 1 time throught carb and just cranked. found dizzy not turning pulled vlv covers and rockers not moving either. found broken chain push rods are not bent and vlv springs all same height. anyone have any suggestion or causes. Put 268h cam and ported and polished 186 heads on.

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Old 03-20-2017, 12:16 PM
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Quote:
Originally Posted by murph0828 View Post
sbc 350 put engine together adjusted valves tried to start and timing chain broke. turned by hand OK to adjust valves. It popped 1 time throught carb and just cranked. found dizzy not turning pulled vlv covers and rockers not moving either. found broken chain push rods are not bent and vlv springs all same height. anyone have any suggestion or causes. Put 268h cam and ported and polished 186 heads on.
I'd be thinking that maybe I dropped a bolt or nut between the chain and sprocket and didn't see it. Keep looking, you'll find the culprit.
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Old 03-20-2017, 04:04 PM
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Was this an old chain? Made in Asia chain? Maybe valve lash adjusted WAY too tight... Good chance a valve or two got bent... need compression tester...

Seen lots of chains so loose they slipped... stripped the gears, etc... never heard of one breaking on a SBC in my 65 years of engines...
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Old 03-21-2017, 06:55 AM
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Hey Hcompton, It was a Cloyes double Roller and it turned pretty smooth by hand to adjust the valves. I used the 1/4 turn method according to firing order. I can't find the balancer key, but the slot is dead bottom so it could have bounced away when I was pulling the balancer.
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Old 03-21-2017, 08:13 AM
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Is this your first time adjusting valves? It's very easy to overtighten the rocker arms nuts when there's no oil (i.e. little to no resistance) in the lifters. It's kind of an "acquired touch" in knowing when you're at zero lash.

Also, when #1 piston is at TDC compression stroke, where are the dots on the timing gears?
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Old 03-21-2017, 09:05 AM
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no I have been doing it for 50 yrs. was just explaining that engine was turning smoothly by hand so I was stumped as why the chain would break when stated for the first time.
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Old 03-21-2017, 09:32 AM
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Originally Posted by murph0828 View Post
no I have been doing it for 50 yrs. was just explaining that engine was turning smoothly by hand so I was stumped as why the chain would break when stated for the first time.
OK, got it. Sorry for implying you are a newbie.

Can't begin to imagine how a timing chain could break, especially a Cloyes double roller. Were the distributor and oil pump shaft installed when you turned the engine over by hand? Does the distributor gear look OK? Can you turn the oil pump driveshaft using a large flat blade screwdriver?

Please let us know the autopsy results.
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Old 03-21-2017, 10:07 AM
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Have you actually SEEN a 'broken chain'? Or just assuming it's broken because the distributor isn't turning?

Or did the crank sprocket slip because the key fell out of the keyway?

If the chain really did break, please put a picture on here, 150,000+ people here want to see what a broken one looks like...

In any event, as I mentioned, need to check for bent valves... any time crank turns and cam doesn't on most engines...
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Old 03-21-2017, 10:55 AM
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Techinspecter is the only one who has this correct. All this talk about lifter adjustment is a waste of time. And you don't need to be any kind of mechanic to figure this out. If in fact you were able to turn the engine over two three times by hand and then when it starts it breaks the chain no matter how old or how defective, something fell into to the works and stopped the cam gear from turning. Very frankly I'm kind of surprised you're actually asking others for an Analysis. take the damn thing apart which you're going to have to do anyway and let us know what you found
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Old 03-21-2017, 11:35 AM
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Old 03-21-2017, 12:27 PM
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Yep... it's broken... first one I've seen in 65 years of wrenching on engines... and those things are usually quite strong... does it say USA or China on it? Does it have 4 link bars and 4 link bars? Or is it 3 links and 4 links? I can't quite tell in the picture...

I'm also considering toward something falling into the chain... problems with valve adjustments usually just bend the pushrods... unless it's a weak chain...
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Old 03-21-2017, 12:32 PM
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Nice response
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Old 03-21-2017, 12:57 PM
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Any signs that a foreign object got caught between chain and sprocket?

Is the inner crank snout key still in place?
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Old 03-21-2017, 01:12 PM
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inner key is still in place but I can not find the balancer key. to answer the link question it 4 and 4 link ! outside 2 inside 2 middle 2 then 1. I am thinking maybe the balancer pushed the key out o the slot and back into the chain area because you can not see it once the balancer is started on. No bent push rods so gonna put back together and pray. Hey ford nothing personal. Just every body needs a little help sometimes.
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Old 03-21-2017, 03:37 PM
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hcompton that makes a lot of sense. thank you very much. should I pull the pan and heads or just the pan. I have not looked at that aspect yet but when it turned by hand so easily that did not enter my mind. thank you I will investigate that first thing tomorrow and let you know with picture what I find. Thanks man

Last edited by murph0828; 03-21-2017 at 03:39 PM. Reason: spelling
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