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Tractor Talk Discussion Forum

fluctuating timing marks

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charles nash

01-01-2006 15:02:50




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Why would I get a fluctuating timing mark read when checking the timing on my 1956 Case tractor ? It runs rough, has low compression in #2 cylinder, and badly needs a valve job.

Would this cause the strobe light to "dance" back and forth across the TDC mark on the flywheel ? Maybe this normal for the old girl The head is in the machine shop for a full rebuild.

I'm new to messin' around with antique tractors. Thanks for any advice.
Charlie

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bradk

01-01-2006 16:41:23




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 Re: fluctuating timing marks in reply to charles nash, 01-01-2006 15:02:50  
Charles,timing gears/chain generally causes fluctuating timing mark.Also,if the engine has alot of hours,the added compression from the valve-job can cause the bottom-end to go! May not be bad idea to freshen bottom (rod & main brgs.)Been there , done that. ~brad



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charles nash

01-01-2006 17:16:07




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 Re: fluctuating timing marks in reply to bradk, 01-01-2006 16:41:23  
BradK, "Freshen the bottom" ? I'll have to freshen my bank account first ! I'm keeping my fingers crossed. Only #2 cylinder had low pressure, 50 lbs. Other 3 had 95-105 lbs. Its unknown how many hours on the machine. Thanks,
Charlie
CT



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bradk

01-01-2006 20:42:51




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 Re: fluctuating timing marks in reply to charles nash, 01-01-2006 17:16:07  
Inserts are alot cheaper than a reground or welded crankshaft.You might be surprised how cheap!Now's the time to consider w/ head off? At very least check one of each,only drain your checking account the price of an oil pan gasket.Peace of mind if tractor is working hard.~brad



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Bob

01-01-2006 15:12:36




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 Re: fluctuating timing marks in reply to charles nash, 01-01-2006 15:02:50  
Most commonly, a badly worn upper distributor bushing, allowing the shaft to flop around, which causes the point gap, dwell, and ignition timing to move around.

Possibly, also, a worn out centrifugal advance mechanism, in addition to all the other poster has mentioned.



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Gene Davis (Ga.)

01-01-2006 18:13:44




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 Re: fluctuating timing marks in reply to Bob, 01-01-2006 15:12:36  
A sure sign of worn distributor bushings is to put a dwell meter on it and look for bouncing around of the dwell angle.



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charles nash

01-01-2006 16:50:14




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 Re: fluctuating timing marks in reply to Bob, 01-01-2006 15:12:36  
Thanks for all the tips. I'll begin with the distributor( Autolite) and check bushings, springs, etc. Last week I put in new points, condenser, and static timed the engine but still got the fluctuating marks with the gun. I'm still hoping to avoid a worn cam/crankshaft gear issue. My rebuilt head should be finished and torqued down next week.

Meanwhile, the machine shop guys were impressed it ran at all with the burnt valves, almost non-existent seats, and slop-city in all guides ! Thanks again.

Charlie
CT

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PunkinDillon

01-01-2006 15:08:57




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 Re: fluctuating timing marks in reply to charles nash, 01-01-2006 15:02:50  
Worn distributor, timing gears, or chain (if applicable), or even eccesive cam end play can effect timing mark stability if helically driven off side of cam.



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RayP(MI)

01-01-2006 15:24:30




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 Re: fluctuating timing marks in reply to PunkinDillon, 01-01-2006 15:08:57  
Or is your timing light really picking up the spark signal properly? If your ignition is weak, timing light may not be getting a strong enough signal to be accurate.



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