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Rear Main Oil Seal Conversion - Bearing Cap debris


Senior Member

With so many that have done the Moss conversion kit for the rear main oil seal, I was hoping someone can comment on the metal debris as a result of drilling and tapping.

In my case the main bearing cap and the rear of the engine block were perfectly aligned, not requiring me to remove the oil sump and undo the rear main bearing cap nuts to adjust.

I am happy about that, but in the instructions, there was made mention the the cavities of the rear main bearing cap would have to have metal debris removed as a result of the drilling. I cannot feel any cavities as a result of the drilling to the depth of 10 - 12 mm that I have done.

Am I missing something, or would I be wise to drain and remove the sump for an inspection anyway. Any comments would be appreciated.

- Andrew -

Dave Russell

Yoda - R.I.P
If you are ABSOLUTELY sure that there are NO microscopic chips remaining, where they can get into the internals, It might be OK. I would be nervous about it.

Ed Kaler

Jedi Warrior
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] I would be nervous about it. [/QUOTE]

I would be <span style="color: #990000"><span style="font-weight: bold"><span style="font-style: italic"><span style="font-size: 17pt">WORSE</span></span></span> </span> than "nervous", gents!!

I'd be scared silly!!!!! :pukeface:



Country flag
Re: Rear Main Oil Seal Conversion - Bearing Cap de

Am not sure what folks are worried about here. One drills into the block, but not through into the inside. Any chips either fall outside or remain in the screw holes.

As I recall the instructions called for drilling to a certain depth only. That's how I did mine and it wasn't difficult.

The Moss kit I bought had metric screws and I replaced them with stainless 10-32s, as I had a 10-32 tap and didn't believe in putting metric threads at odd places on a Healey.

Dave Russell

Yoda - R.I.P
Re: Rear Main Oil Seal Conversion - Bearing Cap de

It's true that you are drilling blind holes that don't go through into the inside. But, do any of the chips fall down on the exposed crankshaft or the rear main bearing joint. ANY grit here will cause major problems.

See if this helps:

Where Moss suggests replacing the felt plugs with silicone sealer, I've found that silicone sealer will never set when it is injected into a deep closed hole. It requires exposure to moisture in the air to set.

I had much better luck injecting a fast set two part compound called "Duramix" into the felt plug holes. Duramix is used by body shops to repair flexible "rubber" bumpers.

Also be very careful to seal the main cap bottom to the sump flange. If the main cap surface is the slightest bit below the surrounding sump rail surface it will leak. The sump gasket kits often supply a thin cork strip "extra gasket" to fill this space.

I would also use a thin coat of sealer on the -main cap to block- horizontal parting surfaces.

I can tell from experience that this is NOT a job that you want to do twice!

Bob Hughes

Luke Skywalker
Country flag
Re: Rear Main Oil Seal Conversion - Bearing Cap de

A bit late for Andrew, but I used a foul smelling heavy cutting grease that kept the drill swarf on the bit itself so that there was little or no spillage and the holes were clear. This was checked out when I cleaned the grease from the holes as I used loctite on the screw threads.

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