Line bore

[4sd911]

Update post no. 5

Received the case back from the machine shop after cleaning, fixing some threads and checking the bore. He said that the bore measured round but didn't have anyway of seeing if it was strait. Told me to install new bearings oiled with crank and torqued it down to 25 lbs. and see if the crank turns freely. So i did and it does turn easy with fingers but if left to sit for a minute or two it sticks just a bit to start it turning again, once turning it I don't feel any resistance. Opened the case back up then installed plastigage. Bearing 2 thru 7 all measure 0.002", bearing 1 measures 0.001". See picture below of these measurements also is a picture of the old bearing shell at no. 1, this bearing does show like is been pinching the crank. I assume this case should be line bored? Any opinions of what you see here.

[4sd911]

Here's a better shot of bearing 1.

[Flat6pac]

There is always more wear on #1 because its always taking the beating from the flywheel and clutch. Put it together, if its alittle bit tight when you start it and run it it wont make any difference.
If you cant get it to turn the thing to do is go for 25 ft# but go to 20# first then go up one at a time and check the spin with each torqued bolt.
Bruce

[J P Stein]

A non-pro opinion.

Used mag case main bores are seldom round. I have checked several and all are the same. They tend to collapse across the case spilt....in the same direction of the through bolts. Your #1 bearing shows that via the wear pattern on the bearing.....regradless of what your shop said.

I would take it to someone that can actually check it for roundness & straightness.
Since the crank does semi-turn there is a good chance that a "drag hone" (line hone) is all you need to correct any out of round condition on the bores. I have had this done to a case by a local shop.....not a "Porsche Hero" shop, just a good machine shop that is well versed in air cooled engines, including the 911 motor.

Mine has been flogged on for 9 years.....with a rebuild at 7 years. Nuthin' wrong with a mag case*if you keep it cool*.

[4sd911]

I've rechecked the plastigage this time using it on both sides of the case. Only a few shells are showing at 0.002" the others are between 0.0015" and 0.001" a few expand just a bit beyond 0.001". If I read the spec book right clearance should be between 0.0004" and 0.003" from #1 thru #7, does this sound right?

My biggest concern is the condition of the old bearings as they are pitted badly, the wurst are in the middle. I posted this once before and it was recommended this is caused by bearing flex. Which makes since being there is nothing holding the center of the case. So I think I'll have the center web pinned, any reason I should just pin all the webs? Here is a picture of the old mains. The rod bearings not pictured look good without pitting.