Mag Case Split?
 

After reading Wayne's book and searching this forum I have become reluctant to rebuild my bottom end. It seems that if the case is split it will warp. Is this always true? I have A 76 2.7 S R7 case before disassembly it had good oil pressure but 3 pulled studs and the associated puddles. No inserts on any stud hole. Four of the Cylinders were also passing some oil through the exhaust.

I have checked as far as the CR bearings and they have an even gay color with no copper with clearance in the mid range, could have been changed some time in the past.. It is probably a stretch to assume that the mains are the same, 200,000 miles but I have read where 250,000 is the average lifespan.

I have measured the spigots and they are within .004 Inch of round and are all even.
I was thinking of pulling a center through bolt and checking if the hole was round. If it was check another and so on. And if all O.K. finish the split.

Any input from the sages ?

You have to split it in order to set up for the drilling and tapping of the stud holes. If the center bore needs a line bore, between that and the stud work you need to spend the money on a 3.0.
The stud work needs to be done, the through bolts are not keeping the case from twisting.
Bruce

Crap, I did not know that I had to split the case to install the case savers. What do I do about the 7 I already have in?

Wayne's book mentions the case will relax to its warped state after removing the through bolts and tell tale sign like out of round spigots and oval through bolt holes.

My question was should I look for signs like that and if I don't find any might I not have a 50/50 shot at getting away with a case split?

Anyone with hands on experience want to comment?

We did not have any problems with our 2.7 but it was from a cooler climate, upper Michigan and had the fan upgrade. heat is what distorts these cases. Where is the engine from?

When I split my mag case I had no problems with warping or distortion, but it's a 2.2T, so the stress on the engine has been about as low as it gets for a 911 engine.

I only know that it spent some time in Georga,and has the fan upgrade. It looks as though the studs pulled after some valve work. The engine looks good down to the crank so I might try it.

Thanks for your response and the 2.2 guy.
Regards,

Shops that build engines will not build a mag case without align boring it because they don't want to take the chance on it. And probably they are right about most of them being warped. Since you are doing the work yourself it's up to you if you want to try to get away without the align bore. It's really up to you if you want to try the build without splitting the case. You can see why very few people try to rebuild a mag case engine.

-Andy

I found this video on the Peter Morgan 911 channel:
YouTube - petermorgan911's Channel

There the engine builder Nick Fulljames talks about the mag crankcases.

He says most of the times a line hone back to standard is required and machining the spigot surface is always required. This is in England, which is not known for its hot climate ;)

Watched Video Informative
 

Thanks for this information. I will bookmark and watch again.
Regards, Ed

I watched the video a couple of times. The guy says that the main bearings tend to spread at the case split and contract along the center of the case. This is exactly what the main bearings in the center showed. Wear on the centers from about 20degrees before the bottom too about 40 degrees after and little wear at the case split. Anyway on reassembly it turns smoothly so I may have got away with it.

Ed

To be sure the case is good, make sure your crank is Std size on the main journals and make sure the bearings are not worn. Better yet...Use new bearings for the crank rotation check.

My mechanic, who has done a lot of 2.7's, convinced me that the line bore was smart given the 2.7 case's well known characteristics. THese things cost a lot of money. You don't want to do it twice. IMHO.