Question for someone more knowledgeable then me on the good old slant six. I believe i have a mid/late year 76 225 block with the forged crankshaft (see pic) that has been machined or forged to cast crankshaft specs (connecting rod/main bearing cap). It does have the knurled surface for rope seal too. I measured the main bearing width to be .873" and the connecting rod bearing to roughly be .7105" (give or take some).
My question is should i order new bearings and such for the rebuild im doing to the later cast crank specs and if that's the case would i be able to use the cast crank connecting rods/crank shaft if i really wanted? This seems like a weird mid year motor that just happened to be in my truck from the previous owner (86 d100). Also the numbers on the crankshaft are 3698966-8 1186 unless I'm reading it wrong. The connecting rod has 3751142 number on it.

My final question is what luck has someone had using the new 2 piece rubber rear main seal with the knurled surface. Should it be polished completely smooth or just to remove the rough edges. If i polish it i dont want to undersize it in that spot creating a leak. Any help would be greatly appreciated.

I didn't know that you could "machine a forged crank to cast crank specs"

Lol me either but either way matches that of the cast crank spec unless im doing something wrong.

A forged crank had wider bearing journals than a cast one. Seeing that "AAWJ" on your pic tells me it probably is really a cast crank, I've seen that designation on other castings like 318 cranks.

The early slant six cast cranks had large counter weights like the forged slant six cranks.
It was in the early 80's that the cast crank counterweights lost weight.
The slant cast crank in the 83 D150 had smaller counter weights than the cast crank slants.

I think what the OP has is an early cast crank, and would need cast crank rods and bearings.

When I looked at the knurled surface with a lip seal in the rear seal carrier it looked to me that the lip ran to the outside of the knurled surface.
I believe that I used a lip seal when I rebuilt the OE motor in the 68 Barracuda, it originally had a rope seal. But this was 10 years ago.
I do know that motor never had a rear seal leak.

Try it, take a look at where the lip seal runs and see what you think.

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Hmm true it probably is if all my measurements are coming out to cast crank spec. I'm just used to seeing the late cast crank with the small weights. Thanks I'll give that a look to.

Yep, looks like you just have an early (pre-80s) cast cranker, which will use simple cast crank bearings. I have used the 2 piece main seal on all manner of surfaces with only occasional (likely assembly-related) problems. You could smooth out the knurled surface with strips of crocus cloth, or ask a machine shop to polish it (but it's not necessary to remove all knurling).

All the best,
Lou

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i have a cast crank with the larger counter weights and larger bearings! not sure which year engine it is from!

Dang i think you got me beat then lol.

I thought all cast cranks were narrow bearings?

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maybe that the finish looks to fine for a forged crank??