Crank shaft backlash
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Senior User
Joined: Apr 2018
Posts: 153
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From: Des Moines, IA
Crank shaft backlash
Today I was reading several posts trying to figure out why my engine is unreliable. One page I stumbled into mentioned timing chain issues and that one way to check was to turn the crank back and forth by hand and see how much it moved before the vavle train started to move.
I put the engine at the dampers TDC marked and watched the roator on the distributer for movement. There appears to be 7 degrees of backlash between my crank and distributer. Now since there will be a bit of backlash between the cam and distributer gear I took the vavle cover off and checked the rocker arms. Same result.
Is this a normal amount of backlash or an I going to be pulling the front end off of my engine ... Again?
I put the engine at the dampers TDC marked and watched the roator on the distributer for movement. There appears to be 7 degrees of backlash between my crank and distributer. Now since there will be a bit of backlash between the cam and distributer gear I took the vavle cover off and checked the rocker arms. Same result.
Is this a normal amount of backlash or an I going to be pulling the front end off of my engine ... Again?
Lead Driver
Joined: Aug 2006
Posts: 8,093
Likes: 652
From: Brentwood, TN
Interesting troubleshooting technique for what seems to be a broad malady..."unreliable".
As for checking valve train movement, I am not sure that the distributor is a good indicator of "valve train movement". I think that if you looked at the actual valve train, ie. pushrods, rockers, etc. you may find that your 7 degree measurement may drop. How do you define "unreliable"? I have never personally used this technique or have ever related slop in the timing chain/gears to an unreliable condition. I hope you find some concrete resolution to what you are seeing.
As for checking valve train movement, I am not sure that the distributor is a good indicator of "valve train movement". I think that if you looked at the actual valve train, ie. pushrods, rockers, etc. you may find that your 7 degree measurement may drop. How do you define "unreliable"? I have never personally used this technique or have ever related slop in the timing chain/gears to an unreliable condition. I hope you find some concrete resolution to what you are seeing.
More Turbo
Joined: Feb 2010
Posts: 661
Likes: 6
From: parma
You didn't mention why it is unreliable. What does it do? The only purpose I know of to check rotating that back and forth is if your checking your cam to make sure it's degreed in correctly. I don't know how sloppy a chain can be, but, 7 degress isn't much play as far as I'm concerned. And if the distributor is sloppy you're getting even a worse reading. You need to give us the basics of the problem
Fleet Owner
Joined: Jul 2004
Posts: 27,294
Likes: 1,055
From: NM
When timing chains wear, it retards the cam timing and also the ignition. The ignition timing can be compensated for by resetting it, cam timing can't. But I agree, it wouldn't make your engine unreliable, just not as peppy at low speeds. Might also make some noise if it's really worn. What engine are we talking about?
I have heard stories about aftermarket chains being garbage, but mostly in the context of OHC engines with long chains. Otherwise they should last 100k miles at least.
I have heard stories about aftermarket chains being garbage, but mostly in the context of OHC engines with long chains. Otherwise they should last 100k miles at least.
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Senior User
Joined: Apr 2018
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From: Des Moines, IA
Your right "unreliable" is a bad way to describe my problems. My engine is a 223 I6, there is no exhaust on the manifold yet. I can get the engine to idle fine but when I try to rev the engine it stumbles and tries to stall out. I can get it to rev higher but I have to slowly apply the gas to do that. After a period of "high" RPM's, when I let off the gas the manifold shoots flame. I say "high" because I can't go WOT without the engine trying to stall out. I will try and get a video of the engine running tomorrow and see if that helps.
Cargo Master
Joined: May 2008
Posts: 2,486
Likes: 336
From: Bakersfield, CA
Is the carb rebuilt? What kind of distributor does it have, the original Load-O-matic? Is the vacuum line hooked to the carb? What is your distributor timing set at?
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Hotshot
Joined: Oct 2009
Posts: 16,173
Likes: 4,780
From: Burbank, WA
You need an exhaust manifold on it. Having an oxygen source that close to the combustion chamber will mess with your tuning, and it's really hard on the exhaust valves to be exposed to cold air like that. You can warp them.
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