Bryan

Ok, this is only for the hardcore engine junkies.

At some point, on the 8-valve blocks, Porsche changed the number of bolts that hold on the balance shaft covers. Specifically, two slightly larger bolts were added right above and right below the rear balance shaft bearings. My '88 block, M44/09, has these extra bolts (and revised torque specs for all the balance cover bolts).

Was '88 the first year for this, or did it start earlier - '87 maybe?

Basically, my M44/09 has heavily damaged bores - a ring broke on #3 and gouged the hell out of the bore. I found an '87 block (M44/07 I think) for sale locally that's in great shape. But I don't know if there are differences between the '87 and '88 blocks (M44/07 and M44/09).

Does anyone know about the balance shaft covers or any other differences between '87 and '88?

Thanks,

Bryan

Perry 951

They changed in late '86.

The bolt pattern is the same, but the earlier cars had a seperate bearing bridge. The later has the bridge as part of the cover.

Here is my '86 block. (converted to '87 style tensioner)

<img src="http://members.rennlist.com/perry951/images/motorbuild/Rebuild047sm.jpg" alt=" - " />

Covers cannot be changed, as they are milled with the block. If you get another block, be sure to get the covers for that specific block.

Bryan

Cool. So I assume the front of the balance shaft cover is milled flush with the block so the front balance shaft bearing holder fits flush?

Is there any advantage to the later style cover with the built-in bridge, or is it just a cost-cutting measure? I'm going to have a top machinist building up this engine, so he could make my '88 covers work on the '87 block if there's a good reason to do so.

Bryan

Perry 951

The '86 are a little stronger, but the shafts do not need a ton of support. I hope the front covers are not matched to the block, as I am running the ones from my '87 on the '86. There were no machine codes, so they should be fine.

I would not swap covers. They may not seal right, or put even torque on the bearing bridge. If you machine them, you will need different bearings.

Bryan

Ok, I just learned about the balance shaft covers. The curved parts that hold the bearings have to make a perfectly round shape when the cover is bolted to the block. So what happens is that Porsche bolts the covers onto the block then line bores the holes for the balance shafts. This is what "matches" the covers to the block.

So if you want to replace the covers, you would have a thousandth machined off the cover, bolt it up, then re-line-bore it perfectly round again. Any good machinist could do it. It's just like line boring the crank carrier.

But it doesn't seem like there's a compelling reason to use the '88 covers on an '87 block. The '87 covers seem like they would be fine.

Bryan