Moparts

MSD distributor shaft broke

Posted By: noplanb

MSD distributor shaft broke - 11/05/11 01:06 AM

The shaft on my MSD 8387 distributor broke today. Nice clean snap.

The oil pump and cam didn't seize, the intermediate shaft gear isn't galled, the timing chain didn't break. The @*&! thing just snapped.

The shaft tang fits all the way into the slot on the intermediate, but it does wobble slightly. Would this, combined with Offshore Quality Materials, account for the break? Just wondering if I should be looking at a new intermediate as well as the distributor shaft. The shaft was from Mancini, and looks fine.

FWIW, the engine's a 493, oil pump's a Melling M63HV. Everything turns freely and the oil pump makes pressure with a priming shaft.

Attached picture 6903959-2011-11-0417.09.45.jpg
Posted By: RapidRobert

Re: MSD distributor shaft broke - 11/05/11 01:14 AM

Quote:

The shaft tang fits all the way into the slot on the intermediate, but it does wobble slightly. Would this, combined with Offshore Quality Materials, account for the break? Just wondering if I should be looking at a new intermediate as well as the distributor shaft.

Is it an eccentric wobble (rare) which could do it or rotational play between the tang/inter slot felt by twisting the rotor back/forth which is common but has never done it that I've heard of. yes offshore stuff can be junk. Keep the inter gear/shaft/get a new inner dist shaft replacement
Posted By: 82ramIndy493

Re: MSD distributor shaft broke - 11/05/11 01:22 AM

Also check to be sure your distributor shaft bushing is not worn and shaft does not have movement in the bushing. If replacing the shaft gear assy. I would have someone who has proper tools to replace the bushing as well.
Posted By: noplanb

Re: MSD distributor shaft broke - 11/05/11 01:24 AM

By wobble I mean that the tang fits all the way into the shaft but doesn't securely bottom out, it wiggles slightly back and forth in the slot.

I tried the intermediate shaft on an old Mopar dizzy, it fit about the same.

I wasn't running the car hard, just slowing down for a stop sign when it bucked and died.
Posted By: noplanb

Re: MSD distributor shaft broke - 11/05/11 01:27 AM

Quote:

Also check to be sure your distributor shaft bushing is not worn and shaft does not have movement in the bushing. If replacing the shaft gear assy. I would have someone who has proper tools to replace the bushing as well.



I just got the car back on the road, it has less than 100 miles on it. I ran the engine for tuning and moving the car around the garage, but the dizzy is basically brand new.
Posted By: RapidRobert

Re: MSD distributor shaft broke - 11/05/11 01:37 AM

Quote:

it wiggles slightly back and forth in the slot.

Rotational slop. I'd bet on defective shaft as all dizzys have that slop from excessive play as the tang is not as wide as the intergear slot and never seen one fracture. The cure is to appropriately pound each side of the dist tang end to expand it and or adding the 1/2" ID collar (McMaster/Carr & others) with the set screw onto the end of the shaft (snug then mock it up to set the exact distance on the shaft) then carefully pull it up/out & tighten the set screw fully then put it back in & this is done to stop spark scatter (timing jumping around) rather than preventing stressing a shaft so I'd say a new shaft will take care of it whether you eliminate the slop or not EDIT when you go together with the new dist shaft add some 1/2" ID flat washers above the collar with the roll pin till the axial play in the dist shaft to dist housing itself is .005"
Posted By: noplanb

Re: MSD distributor shaft broke - 11/05/11 03:56 PM

Thanks Robert.

I'm going to talk with MSD tech support Monday about the axial free play, but I'm also going to check the overall length of the shaft compared to the Mopar dizzy. Have to accept the materials situation, but I don't want to just replace the shaft and hope for the best. I was lucky with the circumstances of where it broke this time, don't want to press my luck.
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