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Installing the rear main cap cover correctly:

jlaird

Great Pumpkin
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Installing the rear main cap cover correctly:
When overhauling an engine, it is not absolutely necessary to disturb the positioning of the rear main cap cover. I chose to remove mine due to concerns about destroying the cover-to-block gasket material during hot-tanking of the block. I left this cover off while checking bearing clearances with plastiguage. I then removed the crank and installed the rear cover/cover-to-block gasket in the following manner. After coating the gasket on both sides with Permatex Aviation Form-a-Gasket #3H I positioned the cover and tightened the three bolts firmly to squeeze out excess sealer before loosening them up a little so the cover could be moved around as much as the bolt holes would allow. I placed the crankshaft on the lubricated bearings and pushed the rear cover tightly against the crankshaft sealing surface before tightening the rear cover bolts to approximately 1/2 final torque. This exactly centers the rear cover, but leaves the rear cover too deep against the crank. (When the main cap is installed, the rear cover will be pushed away from the crankshaft sealing surface the proper distance). I then installed the rear main cap (with lubricated bearing) and torqued it to specifications before tightening the rear cover bolts to final torque. The crankshaft should spin freely without any rubbing on the rear cover. If not, the adjustment sequence will have to be repeated. After removing the rear main cap again and cleaning the cap mating surfaces with carburetor cleaner on a rag, <span style="color: #FF0000">I coated part of the rear main surface on the block from the "oil sealing surface" on the crank out to the edge of where the rear main cap would fit with Form-a-Gasket #3H, being careful not to use too much.</span> All main caps were then installed and torqued to specifications.

I bet I have read this 50 times. What is he saying where I have highlighted?
 

JerryB

Jedi Warrior
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What is he saying where I have highlighted?

I think he's trying to say that sealant is necessary between the rear of the main cap where it contacts on the adjustable scroll cap. There might be a small air gap between the main cap and the 2 top surfaces of the scroll cap.

What you want to do is clean the spiral groves on the crank of any old caked on oil etc. Then use non hardening Permatex or Indian head Sealer on the gasket both sides and screw the scroll cap on barely snug so it still can be moved for adjustment. Then take a straight edge (a good Starret or comparable) and lay the edge down the main saddles (with the main bearing shells removed). Adjust the scroll cap up down and sideways as necessary for ZERO clearance to the straight edge. (Shine a strong light). You want to check at 3 or 4 places....bottom, at 45* and at 90*. When your satified, tighten the three bolts and recheck...readjust if necessary. Take your time as your working toward a very small dimension. That done, then when you lay the crank and the rear main cap, you want to use non hardening P'tex on the mating faces of the REAR of the cap where it contacts the scroll cap. Do NOT use on the cap to case (block) horizontal face.

Mo bettah??
 

Glen_B

Jedi Trainee
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All good but the last. As the instructions suggest, the best, closest clearance is gotten by having the crescent too close and allowing the torquing of the rear main cap to push it (down/up)as its torqued. This will result in the absolute minimun clearance.
If it leaks after this, re-check positive crankcase ventilation(gulp valve), re-do your sorry-old leaky rings, and/or re-establish the tight origianl clearance of the rear scroll seal. This is done by building up the scroll area of both the rear main cap and the crescent. The explanation is long, but the instructions with Paul Asgeirsson's kit are clear.
Jeesh, I pimped Paul twice in one day. NFI, he just happenss to know his stuff.

Glen Byrns
 
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jlaird

jlaird

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Cool, that's just what I did.
 
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