Line Bore Diameter - Spec Needed
 

Anyone out there have the specification for hard to find line bore diameter and tolerance?? Machinist can't find for my rebuild - 1984, 944 na. I suggest taking measurements off main bearing and crankshaft + clearance, but we're being cautious here and don't want to guess at this point.
Thanks much,
Scott K.

Even for racing or ultra-high power or had a failure, line boring is not normally necessary and I've never seen it done on a 944 block. To line bore that type of engine with the crankcase-girdle type of construction is not like a Chevrolet or similar.
Once the crank is measured and confirmed as straight there should be no problems. If the crank was bent or had a "problem" like bearing failure, the case can be checked, but again not really likely to need line-boring.
You can temporarily assembly the case with the bearings and measure the bearing bores..dimensions are in the workshop manual or tech spec book.

Definitely not common.

If it were to be done they normally check for straightness and no warpage on the bottom rails.

You can then skim the girdle and line bore the hole you need.

This keeps the deck height the same. That is the distance between crank center and deck.

This way you re-use standard bearings. No need to oversize.

But as brit mentioned not common. I have only heard of ONE car that this was done to.

Thanks Brit.., I was waiting to hear from you in particular. The original crank had significant thrust bearing failure so I abondoned the crank for another that was in good condition. The bore is straight, but measures+0.002 inch lateral (like an egg) so each bore is somewhat non-concentric. There are no apparent signs of failure. I figured there would be some concentricity brought in by adding the loctite sealant, but not 0.002 inch. I'm working with an excellent machinist with limited Porsche or aluminum block experience and so he is excersizing precaution here. Any other comments appreciated.
Thanks,
Scott

As a side thread, how have others faired with extensive engine rebuilds, experience in performance, longivity, etc. In other words, if done right, will a good rebuild go for another 200k !!??

I would clean the case, torque the lower case onto the block and then get a good machinist to measure it.
To be honest, dealing with a machinist with limited experience of both aluminum and Porsches, no matter how good he is, wouldn't be my choice.
With the amount of time and money it takes to do these engines, you don't want to be wrong.

By the way, Tom at Carquip in CO has a ready to go short block for a reasonable price.

why not just PM him? :D