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100 Main Bearing Caps--removal in situ

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Looking at the exploded view of the bottom end of the 100 engine on page D/224 of the service manual I see that there are two horizontal bolts that fasten the front main cap into the block that are, I assume, accessible via the timing cvhanin cover.

I do not see such hole(s) for the rear main cap. Are there any horizontal bolts going through the rear plate into the rear main cap that would require the removal of the engine or transmission for access to them?

Judging by the condition of the oil pump gears and end plate I do believe that a lot of the lost oil pressure will be cured by replacing the pump. I have not yet removed the front main cap but the center main shell and crank journal were in pretty good shape with no discoloration, scoring, etc.

I'm certainly willing to replace the rod bearings and mains that I can access with the engine/transmission in place but do not want to pull it or the transmission if possible. I know that best practice would be to replace all mains but if there are such bolts and I choose not to pull the engine or transmission to access them I am making a big mistake by replacing only the front and center mains?


Jedi Knight
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You might want to consider an easy quick check with some plastigage to see what the bearing clearance really is before you bolt in a new pump. Do this especially if you are putting the same shells back in. If You are going with new shells you would probably do this any way. Forgive me if You've done this or were planning to.
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I've selectively replaced a main bearing shell insert before, so I see nothing inherently wrong by doing it.

I'm not familiar enough with the 100 block to know for sure if you can pull the rear main cap in situ, but given that there's only three (3), I'd want you to!

By letting the crank hang in the two (2) remaining caps, you can push the upper shell out and a new one back in for the main you're working on. You wouldn't want to leave it hanging there overnight, but during the shell swaps, shouldn't put any undo strain on the xmsn input shaft.

Can't argue about checking them with Plasti-gauge__it takes nothing for granted!

But you've probably already done this a time or two ;)


Jedi Trainee
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Michael, the front main cap should come out with the removal of the 2 lower timing cover bolts plus the 2 main stud nuts. There are no bolts INSIDE the cover.
The rear main may be more problematic. Part of the cap extends rearward past the motor plate about 1/2 inch. There may also be one or two rear plate bolts threaded into the cap. If I get a chance, I will take a closer look at my spare block tomorrow evening.


Jedi Trainee
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The rear main is not coming out without pulling the trans, flywheel and rear engine plate. The two bolts shown go into the main cap. You can see the hole with the end of the bolt visible behind the main stud.
Even if you could get the two engine plate bolts out, there is the "scroll seal" extension that will run into the plate.

20171002_203510.jpg 20171002_203551.jpg



Jedi Trainee
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At the front, you also have two bolts going through engine plate and into the front main cap. Once removed, the cap will come off. One potential problem (and it applies to the rear cap as well) is the gasket between block and plate.


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Michael Oritt
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Though I have had input from another 100 owner telling me that there are no bolts running through the rear plate into the rear cap I am abandoning the attempt to remove the cap as even if it comes out there is, as you point out, every likelihood that I would damage the gasket or seal and nevertheless be forced to pull the engine. So, at least for now. the present mains will just have to live a longer life.

Given the amount of wear on the present oil pump's gears and plate I believe that replacing the pump will to a large degree resurrect my oil pressure, and though the rod bearing and journals looked pretty good I am putting in a set of new rod bearings. I'm also putting in a new oil release valve assembly as even though the present one looks okay it was hung up on something (see the other recent string I posted about that issue) and a new spring and plunger seems in order.

Thanks to everyone for the great input and patience with my many questions and without meaning to be critical of anyone I must say that the members of this forum have been way way more responsive than the folks who read the autox list which at one time seemed to be a better source of information.


Jedi Trainee
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As you can see from the pics, the stock 100 definitely has through bolts into the rear main cap. However, on the DWR site, you can find a pic of steel main caps that do not include those holes, nor do his alloy rear plates. Perhaps that's what the other 100 owner is thinking of? It may also be possible that the rear main seal conversion covers or eliminates the use of those 2 bolts.

If your center main looks good, you are probably safe in assuming the others are the same.

When you get the new pump, make sure your machinist pulls the end plate and checks/adjusts the gear-to-housing end clearance.

As to the stuck plunger, that was likely caused by a bit of aluminum from the pump or a bit of that tensioner debris. Take a close look at the oil pickup screen assembly for any gaps between the screen and top/bottom plates.
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