I've had an odd thing happen with my damper lately. It's done it twice, the first time I thought I was seeing things so I dismissed it, but I noticed it again today and I'm sure something odd is going on.

I have a new (rebuilt) 460 engine that I have yet to start. I'm hoping to do the break-in sometime next week. In preparation, I've been turning the crank by hand to make this and that adjustment. This last time I was trying to set the distributor timing so it would be right where I wanted it, which just so happens to be about 15* BTDC.

So I turned the crank (by hand with a breaker bar) until I felt air coming out the #1 cylinder, stopped when the timing mark got to 15*, and set my distributor. Ok, great.

That was a couple days ago. I go back to look at it today, and now the timing mark is showing 10*!

Unless someone is sneaking into the garage and turning my engine over, I'm at a loss for how the damper and/or crank is turning on its own.

I'm hoping to God it's not a bad damper. It's a brand new Ford Racing damper (M-6316-A460) so theoretically it should be perfectly fine.

All my spark plugs are in - could the pressure in the cylinders somehow slowly cause the crank to keep turning a few degrees over the course of several days?

Could the damper somehow be lagging behind when I turn the crank, and slowly "catch up"? I guess if that is the case, that is pretty much the same as a bad damper.

I'd sure love to hear this is some kind of common thing, but I have a sinking feeling in my stomach that my damper might be bad...

 

I can't imagine that the damper is doing that. They are bonded with a rubber-type material and shouldn't move at all, much less over a period of time when all motion is long gone.

So I'm leaning to pressure in the engine. Did you have only the #1 plug out when you turned it or all of them? If just the #1 then I'll bet it is cylinder pressure.

 

Maybe the pressure in some cylinders is leaking down faster than in others. Then the ones that keep the pressure longer cause a little crank rotation.

 

I'm blaming the designer hallucinogens.

 

Right, the #1 cylinder was the only one with the plug out, all the others were in.

The more I think about it, I can't imagine it's the damper slipping. For a while I was thinking maybe the crank pulley was putting drag on the damper while I turned the crank - but now I'm pretty sure the crank pulley is bolted to the center of the damper, not the outer ring. So there shouldn't be any pressure on the ring. Even if the damper had slipped, it should theoretically show the same wrong timing all the time, not vary overnight.

I thought of a way I can test it - I'll turn the engine over a few times again, mark the location of the distributor rotor with a piece of tape, and check it again the next day. If the rotor has moved, I'll know for sure it was the crank turning on its own.

 

In case anyone wondered - I did my test, and yes in fact, the entire crank rotated, not just the damper.

A bit unexpected to me anyway, but I guess it makes sense that it could.

Carry on!

 

So... What?

"My Damper Ain'tSlippin'.... But Somebody' Been Yanking My Crank? "



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Glad to hear you aren't crazy. Or, maybe I should rephrase that - your balancer hasn't slipped. Because being into old trucks this far sure looks crazy to me.