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MG MGB Technical - Keyway slop in crankshaft/damper

When I move my fan on my 72 BGT, there is motion translated from the fan/alternator/damper through the belt, but the crank bolt is not moving. Just slight motion in the damper, maybe 1-2 degrees.
Is this an issue and will it cause any harm. I don't know how long this has been this way. I just installed a new belt and noticed the motion when I moved the flan blade back and forth.
DAM Montabana

I'd say there has to be some play between the pulley and the crank even with the key fitted, as otherwise it would have to be drifted on. Is the bolt tight? You will probably need to fold back the locking tab to check.

Or is the pulley delaminating at the damper, and the outer part is moving but not the inner?
Paul Hunt

This is a rubber-damped pulley? Sounds like the rubber has given up. Can't imagine the keyway not fitting tight.
If the rim is moving but the bolt isn't, that will tell you!
Art Pearse

I put a mirror down where I could see the nut and it and it stays still, but the inner damper moves, so it's not separated.
I'll get someone to check the tightness of the nut. That's beyond my skill set.
DAM Montabana

The bolt will be loose and the key/keyway worn - there should be NO play in the key, it is a drive fit into the crank and the pulley needs to be tapped into place.
Chris at Octarine Services

Even if the nut is loose the pulley should still be locked on the keyway. Take it all apart and look!
Art Pearse

This was a common problem with Suzuki Samuari engines. When the timing belt was replaced, mechanics removed the entire crankshaft drive assembly when only the pulley needed to be removed. Consequently, the crankshaft bolt wasn't tightened to the proper torque when it was re-installed and the belt drive was left to rock back and forth on the drive key inside the crankshaft. This would lead to an enlargement of the keyway in the crankshaft itself. A proper fix required the replacement of the crankshaft, but I found that if you welded up the drive key and filed it down, you could eventually get it to fill the entire void left by the rocking crank gear. I've been successful in doing this on several engines, including the one in my own vehicle, which has since covered over 50,000 miles. Sure beats replacing the crankshaft. RAY
rjm RAY

This thread was discussed between 18/08/2013 and 19/08/2013

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