Repair of 911 Magnesium 3R engine case

Chemboy · 08-13-2008, 05:51 AM

Hi all, got a respected engineer looking into the repair of my 1971 911 2.4 S cases. These are magnesium and have suffered damage to one of the crankshaft bearing carrying saddles.
The damage cant be cured by line boring as it is too far out, it needs material to be built up first by welding, but there are issues of this causing case distortion? Metal spraying has also been mentioned. Has anyone else had this type of repair done.

Fast Corners · 08-13-2008, 06:01 AM

I have no experience with metal spraying. The mag case can be welded but it takes a quailified welder.

Is the car of collector quality? If yes, than having the engine case reworked may be a good choice. Other than that I would store the original case and buy a used 3R or better yet 7R to use for the re-build.

YTNUKLR · YTNUKLR's Garage

Ollie's to the rescue...

They are moving to Arizona...but look 'em up

if the serial numbers are not critical, i would use a 7R like Fast Corners recommends...'73.5 911T CIS engine, 7R 2.4L case (not 2.7L unless you want to build a 2.5 or 2.7)

Chemboy · 08-13-2008, 07:10 AM

The cases are from my 2.4 911S late 71. I really want the original repaired. The serial numbered side of the case is the least damaged, but still needs a repair. The other half needs more work so i may consider changing that half then getting a line bore. If anyone has a cheap 3R half case fitted with case squirters let me know!

Fast Corners · 08-13-2008, 07:23 AM

Chemboy,

What happened to the case anyway? Spun bearing? Rod detonation?

The mag welding shouldn't distort the case if it is done properly. The bearing webs are pretty stout pieces so they should be even more resistant to warping.

Chemboy · 08-13-2008, 07:54 AM

Yes a spun bearing, damaged just the one set of saddles.

YTNUKLR · YTNUKLR's Garage

even if you find a good other side, it will need to be surfaced and line-bored back to standard..

i would recommend finding a competent mag welder and having the original case half repaired...welded up, then all studs are removed, the case halves are milled back to flat, and then the bearing bore is rebored back to standard specs. (straight, which compensates for any possible warpage caused by the welding, etc.) also the original halves are matched at the factory...down the road the next builder will think it is funky that the cases do not have matching "match numbers" which you should find on the top of the case, i think one stud back from where the alternator ground strap attaches

Ollie's can do this repair, only question is $. Should still be reasonable given it is your original 911S case. you might ask around, there may be other guys that can do it, of course

my 2c

good luck,
scott

Shoepop · 08-13-2008, 08:24 AM

+1 Ollie's, I have same problem on 69S case. I phoned, described and W/O hesitation was told "not a problem to repair" MAX $800. Mark S

Chemboy · 08-13-2008, 10:51 AM

A few people were suprised that my motor was on 3R cases, and only one is marked 3R the other is blank but they have matched number stampings on the top to show they are a matched pair. As i said it is a late 71 2.4S, were these 3R cases from the last of the 2.2 engines?

YTNUKLR · YTNUKLR's Garage

Not uncommon for Porsche to use up some of its "last year" parts to make the "new year" cars...there aren't any noticable (if any) differences between a 3R/4R/5R that I can point to off the top of my head. The 7R was a major improvement, though