PSA: Check Your Distributor Clamp

[HaKs319]

PUblic Service Announcement!
Check your dizzy for any play. If you can easily spin it, tighten up that bolt. Distributor still spins? Check your distributor clamp!

Truck completely died on me while driving down the road one day. Backfired and shut off. Tried restarting and nothing. Towed it home and did all the regular diagnostics. All ignition pieces had been replaced 14k miles ago. Ignition coil, coolant temp sensor and ignition module tested good. Fuel at injectors and spark at plugs. Figured timing was off so went to remove the distributor. The hold down bolt was tightened down but dizzy was still able to spin! Removed the dizzy found TDC and back in she goes. Fired right up! Used a washer on the clamp down bolt while a new clamp came in. Dizzy still spun but required some force.

Figured the dizzy must have spun just enough to throw the timing off causing engine to misfire and die on me. All because of a $3 to $7 part!

AC Delco/GM Distributor Hold Down Clamp 10096197


Old vs new clamp.

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[1ton-o-fun]

Hmmm. I wonder if this might be the cause of my dad's Tahoe's "death"? I'm going to have to check it out.
He (81 years old) said it made a loud noise and quit running. Wouldn't start again. He has a number of "spare" vehicles, so it has sat ever since.

 

[HaKs319]

Easy enough to take a look at. if that dizzy is easy to spin, timing is more than likely off.
Took me five minutes searching through Google to figure out the clamps flatten out over time.
New AC Delco Part number is 10096197

 

[Schurkey]

Why buy new?

Do you own a hammer? Pound the curve back into it, don't over-tighten the hold-down bolt.

 

[BOOT]

Never liked the stock ones if it's gonna be removed/set to often, once bent they just bend again easy, prob got a dozen floating around my garage. I liked an aftermarket chrome type with a full curve and paws but looks like some have cheaped out and are hollow on the underside, so I wouldn't trust that to not bend permanently easy either. MSD clamp is nice n beefy but pricey(two sizes one for MSD and one for HEI shaft). Never used one of the alum ones that looks kinda like the MSD steel clamp but got one of those floating around in a bin someplace.

 

[Erik the Awful]

Could be worse. Cadillac used a flimsy stamped steel hold-down on the 472/500s at one point. I have one of those somewhere. I've never had a problem with the ones pictures above. Just don't crank down on it. Once your distributor doesn't move, you're done. I've even left it just a hair loose before so I could make timing changes on the fly with a firm hand.

 

[thinger2]

A common yet often overlooked problem.
For a bunch of reasons.
The clamp gets installed upside down and "back bends" when you reef on it
Flip it over and it is now deformed and may crack when you try to reef on it again.
Failure to push the clamp all of the way onto the collar of the distributor.
The oval slot in the clamp is there as a tolerence slop to compensate for casting differences between the dist body and the manifold.
Wrong gasket. The dist gasket does a couple of things. It is part of setting the depth of the dist to cam gear engagement.
It also seals the oil.
And, it keeps the dist from spinning while running.
It is a "friction gasket"
In other words, the clamp is only used to hold the dist to the manifold so that friction gasket can do its job.
Dist. gaskets come in different thicknesses.
The cheap aftermarket ones are paper thin garbage.
They allow the dist to spin and the steel clamp will dig a huge burr into the dist collar and when you reset your timing because it spun, you can land that clamp onto the burr on the aluminum housing and crank it down and stuff the dist too far into the cam.
And now you have chipped or warn gears.
Treat your distributor with the same care and caution as you would with backlash on your diff