How common is stud pulling on a mag case?
 

I have a high compression 2.4 E motor I rebuilt 15 months ago. I think the studs are pulling out of the 7R Mag case on one side. Is this somewhat common?

Symptions are that the head bolts are all lose for the second time on the same side.

Chris

73 911 E

Usually the stud pulling problem is rare on 2.0, 2.2 & 2.4 engines (common on 2.7s), but if you drive in a spirited fashion, do DEs or time trials, or if the engine is modified, then case savers are a must for all mag case engines.

On 2.7's would the studs pull or break? I thought they were prone to break?

Chris

Due to the weakness of the mag case any rebuild should include shuffle pinning and case savers, otherwise you'll be doing its again soon. Just as you must now.

2.7s, except for 1977 models, used steel studs, which rarely break. But they did pull the threads out of the engine case! '77s used Dilavar lower studs, and those could, and do, break.

Add on smog controls like the Thermal Reactors add excess heat....hence pullling studs.

Stupid engineering paractices like dis-similar studs from top and bottom lend to snapped studs.

Still need to confirm they are pulling but I strongly suspect they are. My research has found that if I am going to replace the studs to use the 996 or modern dilavar studs. Coated so no corrosion / breakage and similar thermal expansion to the engine.

If you can turn them w/o pulling out or dropping into your hand....they are pulling. If you find nuts that are rattling around in the valve covers....

If you just think they are loose, pulling or broken, the sound of a playing card in bike spokes on accel is a clue.

Before I tightened them about a month ago the engine was louder than usual and did not idle smoothly when cold (did not like the cold). As soon as I tightened them all on the right side a 1/4 turn the engine was much quieter, smoother when cold at idle and perfect in all regards. The symptoms have returned but have not pulled a cover off yet to confirm.

Usually OK forever on a stock 2.4. Higher compression puts added pressure on the studs......Sad, but it sounds like they are pulling out of the case....

Only use dilivar studs if you have aluminum cylinders. If you have the stock biral cylinders you need to stick with steel studs. Just get the timeserts or case savers installed.

-Andy

I have Nickacell (sp?) cylinders and JE pistons

Chris

Once you get the headstud situation sorted out, you'd be well served to upgrade to a front mount cooler. For a 2.4 you'd be fine with just later model (SC/Carrera) oil lines and a trombone. Heat + mag case = sig decreased lifespan. Keep that motor cool and it will live a long, happy life. The pulled headstuds on the 2.7's could be easily attributed to cooling issues that were most exacerbated by the thermal reactors, which I surmise is why you don't see pulled studs on the earlier cars.

Yep, they are definitely pulled. Doing the open engine surgery myself by the end of the month. Sending all machine work out to professionals. Is it a bad idea to use the same studs (pulled not broken) with case savers? Or are new studs a must?

Thanks,

Chris
73 911 E 2.4, 7 R mag case, high compression(9.5 ish), Carrera cooler in fender.

why take a risk use the ARP studs. I certainly wouldn't use Dilavars.

apart from the case savers, did you have your case shuffle pinned?

+1, the problem is more related to high oil temperature and corresponding very weakened mag case than other factors.
Get a nose cooler and keep the oil temps low once you get that new motor installed.