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‘74 250 - timing chain - how much slack is acceptable?

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‘74 250 - timing chain - how much slack is acceptable?

Post #1 by 62Ranchero200 » Sun Mar 22, 2020 10:08 am

My 250 has about 10,000 miles on it. Pulled the old cam out last night, and timing chain can be deflected about 1/2”. There are no wear marks and everything otherwise looks good. Gearset with chain were new when engine was built six years ago.

Is this ok?

62 Ranchero, 252 cid, 300 rods, RaceTek pstns, ARP mains bolts & studs, balanced & blueprinted, CI AL head, 1.6 adj rckrs, Smith Bros, 274/274/108 cam, CI int, Holley 500, DSII, CI SS hdrs, PowerMaster strtr and 1wire alt, Optima, V8 rad, T-5z, 10" organic clutch, 5 lug 8" w/3.80 Trac Loc, rear drums, front 5 lug discs, Centerlines. Next: ?.

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timing chain - how much slack is acceptable?

Post #2 by chad » Sun Mar 22, 2020 11:24 am

"... how much slack is acceptable?..."
my eye & fingers say 'none'. Sorry don't
have a 'deflection measurment' ona dial
indicator. If I could move it a 1/2 inch I'd
start over...look at other 'looseness'.
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
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Re: ‘74 250 - timing chain - how much slack is acceptable?

Post #3 by wsa111 » Sun Mar 22, 2020 12:15 pm

Since its not a roller chain, replace it. If gears show wear do the same.
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Re: ‘74 250 - timing chain - how much slack is acceptable?

Post #4 by CZLN6 » Sun Mar 22, 2020 4:03 pm

Howdy Bob and All:

Since you have it apart, replacing the chain is cheap insurance. You said the current chain has 1/2" of slack, or deflection, check the new chain for comparison. And let us know. You might also do some testing on how many degrees of cam movement between the two points of slack. Chain slack, due to wear, causes the cam to act like it is being retarded. That is not near as bad as if it is being advanced- for performance. Chain slack, as the engine accelerates and decelerates causes wear to the cam gears.

Also check your rocker arm shaft to make sure that oil is getting to the front rocker arm and draining freely down.

Keep it coming.

Adios, David
co-author of the Falcon Performance Handbook

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