4.7 valve timing and damage assesment - Jeep Garage - Jeep Forum

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Old 09-26-2014, 08:57 AM
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4.7 valve timing and damage assesment

99 Grand Cherokee Limited threw the timing chain completely off the right cam sprocket. I think it jumped teeth on the left side as well as I cannot read any compression in the #1 cylinder when TDC mark passes (turning by hand). Failure occurred at low speed and started with a miss then stall and no start. Engine turns easily by hand.
Questions are: How do I reset correct time for both cams? Without pulling heads, is there a way to determine if I have valve damage? How much chance do I have of having escaped doing major damage by attempting starts (cranking) with the right cam disconnected?
Really could use some feedback from others that have seen this problem!

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Old 09-26-2014, 01:10 PM
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Re: 4.7 valve timing and damage assesment

I don' t think that using the startermotor did anything, most probably damage already occured when the chain got of of the cam sprocket and the engine spooled down completely. If it was only at idle for example, then it was still making 650 rpm, and after loosing the cam drive, the cam most probably stopped quite abrupt, but the crankshaft, with its bigger mass, for sure continued several revolutions still, bending the valve(s) which where full open. With luck its maybe only one valve.
The valve cover is of i believe you said, so you can now see which valves are open by looking at the cams. The ones completely open now have a good change to be bend.
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Old 09-27-2014, 07:10 PM
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Re: 4.7 valve timing and damage assesment

Starter motor will do damage, ask me how i know.
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Old 09-27-2014, 08:02 PM
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Quote:
Originally Posted by Doug4230 View Post
99 Grand Cherokee Limited threw the timing chain completely off the right cam sprocket. I think it jumped teeth on the left side as well as I cannot read any compression in the #1 cylinder when TDC mark passes (turning by hand). Failure occurred at low speed and started with a miss then stall and no start. Engine turns easily by hand.
Questions are: How do I reset correct time for both cams? Without pulling heads, is there a way to determine if I have valve damage? How much chance do I have of having escaped doing major damage by attempting starts (cranking) with the right cam disconnected?
Really could use some feedback from others that have seen this problem!
To set correct time there is a dot on the crank sprocket that should be at 6 o'clock, mark on idler sprocket should be at 12 o'clock, and the "v8" on each cam sprocket should be at 12 o'clock. After you set timing, do your compression test. If you have a cylinder leakage tester you could use that. Also, if you have an air compressor, you can can hook up air pressure to the same adapter you would use to do the compression test but make sure you set each cylinder to tdc as you test them (you will need to take the valve out of the adapter for this though). With air hooked up there should be no air escaping the cylinder so if you hear/feel air from the intake or exhaust you know that cylinder has a bent valve(s).
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Old 09-28-2014, 09:06 AM
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Re: 4.7 valve timing and damage assesment

Ordered a borescope online yesterday. Going to try and visualize pistons and valves when it comes in. Guess if I see damage I will send the timing chain kit back and part out the Jeep. I can't afford the expense of pulling heads and doing a valve job.
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Old 09-28-2014, 09:27 PM
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Re: 4.7 valve timing and damage assesment

Cost me $500 for heads to be redone and few hundo for gaskets ect......
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