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Old 05-15-2018, 11:23 PM   #1
apbright
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Default Strange Engine Knock -> Crank Pulley

Hey folks,

I have experienced - on two separate engines now - a worrisome engine knock; it appeared only for a narrow range of rpm's (I'm guessing 1500-1700), and only under load (i.e. knock audible under acceleration or cruise; not audible with throttle closed / descending hill for same engine rpm). I first suspected loose main bearings - fearing long hours underneath engine with oil dripping in face - not happy.

However, each time (on each engine) I finally noticed that the crank pulley was a bit loose. The first engine on which I noticed this I have since pulled from the car. The second one, however, was on a brand-new rebuild, recently installed in the car. On that one, tightening the crankshaft ratchet nut solved the problem, temporarily. After a few 10's of miles, the nut and thus also the pulley came loose again, and the knock returned. I tried adding a 5/8-inch washer (between the nut and the pulley) and tightening the unholy heck out of it. That worked... for about 100 miles, and then the knock returned again. I tried re-tightening, and repeated this limp-home procedure for.... ooh... 450 miles for a long Sunday home. (Also refilling a leaky radiator every 60 miles, but I digress...)

Post-mortem shows a deeply cracked crank pulley (see pictures, crack highlighted by red oval). I consider these scrap, and have ordered replacements along with a new ratchet nut.

Question: Anybody seen this, and have tricks to prevent recurrence?

Safe driving,
Andrew
Attached Images
File Type: jpg CrankPulleyCrack.jpg (41.6 KB, 152 views)
File Type: jpg CrankPulleyCrack2.jpg (36.7 KB, 140 views)
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Old 05-16-2018, 05:44 AM   #2
Jacksonlll
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Default Re: Strange Engine Knock -> Crank Pulley

They do break. It does not help to try to turn the engine over pushing on the fan blade. That puts too much load on the pulley. It was designed to drive the fan etc, not the engine.
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Old 05-16-2018, 06:56 AM   #3
rocket1
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Default Re: Strange Engine Knock -> Crank Pulley

you might want to try a two piece pulley I have been running one for decades.
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Old 05-16-2018, 07:26 AM   #4
chap52
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Default Re: Strange Engine Knock -> Crank Pulley

Thanks for sharing your discovery. Gives us all another option to consider when a similar situation arises, and it will. Chap
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Old 05-16-2018, 07:56 AM   #5
katy
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Default Re: Strange Engine Knock -> Crank Pulley

Quote:
Originally Posted by chap52 View Post
Thanks for sharing your discovery. Gives us all another option to consider when a similar situation arises, and it will. Chap
Ditto
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Old 05-16-2018, 10:06 AM   #6
John Stone
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Default Re: Strange Engine Knock -> Crank Pulley

You have to make sure the slot in the pulley isn't too small to accept the key. Also make sure the slot is deep enough. If it has to be forced over the key it will probably crack the pulley.
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Old 05-16-2018, 11:24 AM   #7
Purdy Swoft
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Default Re: Strange Engine Knock -> Crank Pulley

I've had that problem and posted here about it, you will have to go back a long ways to find the thread . The problem was ill made parts . Remove the pulley and take a close look at the back side of the pulley . There should be a mark on the pulley or the front motor mount yoke where the pulley was striking the yoke . My fix was to grind just enough material off
the pulley or yoke to solve the problem. Usually not much material will need to be removed . A little bit of spray can black paint will hide the fix . This worked for me every time . A lot of the reproduction parts need a little bit of fitting , one way or another .
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Old 05-16-2018, 11:46 AM   #8
denniskliesen
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Default Re: Strange Engine Knock -> Crank Pulley

I had a 2 piece that always leaked. The last time I had it off I noticed it had a rub mark where it made contact with the front cover. I tossed it and bought a new one piece. It doesn't leak...yet.
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