Mike Simard

I noticed that there seemed to be only 1 dowel on my crankcase halves even though there are 2 counterbored studs, one at the front and one at the back. The manual shows 2 dowels in photos but mentions installing the oil pump during crankcase assembly for alignment purposes. Did Porsche change the crankcase alignment method at some point to just use the rear dowel and front oil pump instead of 2 dowels? I've been concerned about crankcase rigidity and have been contemplating more dowels. So far what I've done is machine some dowels out of some unobtanium lying around with a zero clearance fit the the 2 existing crankcase halve counterbores. When I mock assembled the halves the front was out by .0037"/.094mm. To correct that I moved the counterbore and fitted a sleeve, it's now perfectly aligned using the 2 dowels but I'm still concerned about crankcase rigidity and whether I should take more steps. Any comments appreciated. Here's a pic of the modified front dowel counterbore:

Vilhuer

I believe front dovel was delete as unnecessary when #1 main bearing was changed to one piece. Of top of my head this was in '82 '83 period.

Mike Simard

That makes sense but it's odd that they kept on drilling the counterbore into 87, it's even a nicely finished feature on my block.

Jim bailey - 928 International

Looks like 1981 was the change to only one dowel pin which does coincide with the switch to the one piece front bearing.

Jim bailey - 928 International

Old 911 race engines is it is SOP to "shuffle pin" dowel each and every main bearing cradle on both sides !

6.0-928S

Whenever I build a motor (for my personal use) from the ground up I always build the short block like I was building an all out race motor so if I decide to modify it more later on I don't have to tear it completely down to start from scratch. That's how I'm building my stroker. I had additional dowels put in it, had the block 'halves' surfaced, align bored, & remachined the oil pump recess, just in case I decided to supercharge it later. I didn't want the skirt trying to walk around on me. Here's a pic,
Hammer

PS. Yer right Jim. (as usual my friend) that's where I got the idea. I used to work in a Porsche race shop.

BC

Todd has mentioned that the head, through all the wear and tear it goes through under boost - doesn't move much. What he did find moving was the two halves. This is a good idea, though I have not yet "heard" of many problems. With the higher HP we are and will be seeing, this is all very good effort. My blocks are still apart - is alot involved? A machined dowel, and the recess machined in the maching area?

I think someone mentioned having bigger studs or stronger studs for what we see above? Does anyone remember that?

ZEUS+

Hammer, very impressive. It pays to have old school knowledge and the ability to incorporate this with a shark. Looking good.

atb

I put the extra one in up front on the Rear Mount Turbo motor I built. Couldn't hurt.

6.0-928S

It's been a few years but, I bought my head studs from Raceware & at the time they didn't offer main studs for a 928. I was told that they had tested them & felt there wasn't much room for improvement so I stuck with the factory stuff.
Hammer

BC

Sounds good to me. The GTS went to bolts for the bottom half IIRC. Maybe for ease of use, but it probably had more dowels if it only had bolts.

6.0-928S

Your right Sterling. All of this was discussed when I had the work done. I shipped the block cross country to have it all done by the machine shop referred to me by Devek when I bought the stroker kit. I have to trust that they knew what they were doing. They did all the block machining, boring, honing, etc. I haven't found any flaws so far. Everything fits as it should & has the proper clearances by my measuring with my Starrett equipment. That's all I can do.
Hammer

Mike Simard

Jim, that's interesting that it's SOP for 911's. Those engines are right out of crankshaft heaven with individual main bearings and counterweights for each cylinder and an opposed layout, you would think that's the last engine that needed additional stuff. The 928 on the other hand has force from the power stroke pushing at a 45 degree angle and harsher rotational imbalances.
I wonder if Devore's crankshaft failures had anything to do with things moving around?
Hammer, it looks like you have the right idea. It's not obvious how to go about doweling a 928 block because of the oil channel. Here are 2 methods I've thought of:
1-milling keyway channels on each side. This requires careful machining to pick up the position of each journal and mill slots exactly a certain distance from center, The keys themselves would also need a retention method.
2-Bolting the halves together and reaming dowel holes. On the side without the oil channel it's straitforward and I've even pictured not using the stud hole but the recessed area in between the big and small studs. The center journal has areas outside of the block where a bolt goes on each side, that may be beneficial to dowel, it's inline with that center journal.
So how did the line boring work Hammer? I have fears of it going wrong and being oversize or having areas that didn't clean up.

6.0-928S

"So how did the line boring work Hammer? I have fears of it going wrong and being oversize or having areas that didn't clean up.[/QUOTE]

Hi Mike,
As I said in my last post, I have to trust the machinist. I haven't started the engine yet but, you can see where there was a small amount of metal removed from each crank seal mounting surface on the skirt of the block to compensate for the align bore. The seals fit snugly into the bores.
Sterling, I'm aware of all the pitfalls if not done correctly but as I said, I have to trust the machinist. I'm not going to allow a fear of failure to stop my projects. I assess as many angles of my modifications as possible before I do them & just do my best. It hasn't let me down so far. Even if I had a problem I wouldn't regret the attempt, I would correct it.
Mike, as you said the oil passages made it impractical to put dowels on that side of the block. However I feel that dowels on one side cuts the 'walkable' surface area in half & should be sufficent unless I go to a blower & nitro! At any rate it significantly stabilizes the block over the factory standard. that was my goal. The only way to positively eliminate the movement would be to weld the halves together, I passed on that option.
Regards, Hammer

Mike Simard

Hammer, do you have a Mopar 440 crank and main bearing set lying around? I've always wondered if they could be modified for a 928, they have the same bore spacing and the main bearing size is within a few thou'. The 440 stroke is the same as many stroker cranks used although the rod journal is huge. Wouldn't it be nice if Mopar main bearings had a slightly larger OD so that you could align bore a 928 block to fit them? I wonder what the width of the thrust bearing is hmm...