Timing Chain Jump? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-15-2005, 12:19 PM
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Timing Chain Jump?

I have recently purchased an 88 YJ with a 4.2L that has had issues reagrding the intake for the engine. Instead of creating vacuum in the intake and taking the fuel to the cylinders, it blows air out of the top of the carburator. Has anyone dealt with such an issue on a 4.2L? This engine has 150K on it and I am unsure if the timing set has been replaced. Does this sound like a possible jump timing issue? Does the 88 4.2L have steel or nylon gears?
Thanks for any help.....getting frustrated.
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post #2 of (permalink) Old 12-15-2005, 02:49 PM
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Re: Timing Chain Jump?

Possible jumped chain or misadjusted/leaking intake valve(s), called blowback.

If it cranked/spun sounding easier/faster than normal, suspect chain. If it spun at normal speed but seemed to have an "easy spot" suspect valves.
Just remember how it sounded. But try not to contunue cranking it. If you haven't already bent a valve, you still could by playing with it. Turn it by hand now.

Try aligning the timing marks at about 10 degrees BTC. The rotor should be pointing pretty close to #1 on the cap. If not, suspect chain.

Try rotating the engine in one direction by hand until it shows TDC. Turn it backwards while watching the rotor, if you can turn it backwards more than about 15 degrees before the rotor moves, suspect it jumped from being loose.

Often it jumps a tooth or two, but the distributor still turns. If the distributor no longer turns - it jumped for sure.
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post #3 of (permalink) Old 12-15-2005, 03:17 PM
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Re: Timing Chain Jump?

Thanks...I'll try looking into that. Was hoping to not have to tear the front off, but it keeps looking more and more like I'll have to.
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