'74 911 bummers...head stud pulling

[paulhagedorn]

Well, it looks as if my brother gets to take out the engine in the 911 for a rebuild. The mind-boggling thing of the matter is, the engine only has 10,000 miles on it since being rebuilt by my father back in the 80's. He rebuilt it then, due to one head stud pulling...and it seems as if it is happening again. The engine was sent off to some place in Florida way back when, and they put in heli-coils, I believe. The sound coming from the engine is like an exhaust leak. It is cyclic and is like a fwooph. It can be heard better while above the engine, as opposed to underneath. Only one stud seems to have started pulling. It was completely loose, but could be put back in and torqued down, although this was also the case when my father rebuilt the engine. All studs were torqued down, and everything put back together...but the sound still persists. The exhaust bolts were checked before the head studs were torqued down, and were fine.

More things will be checked before pulling the engine, but it seems as if we already know the answer.

The question is, what should be done while engine is out? New oil return tube seals, and possibly the tubes themselves, update to carrera chain tensioners, check for leaks and fix them...

The engine already has solex cams, euro pistons, and webber's, so the performance is pretty much where we want it without getting wild into spending all sorts of money.

Any suggestions on what to do, what to check, and then, what to replace, look at if engine comes out?

Thanks guys,
Paul

[Adam]

Paul,

Heli-coils won't do the same job as Timecerts. They're basically what's required when working on Mg Crankcase engines. My 911, in the PO's experience only lasted 2,000kms between rebuilds (twice!!).

Just make sure that whoever does the job this time uses timecerts (sp?).

Good Luck!

[john walker's workshop]

maybe there's a burn path between a head and cylinder. the main reason that heads get loose soon after a rebuild is that the mating surfaces at the case and head are not on the same plane. most mag cases need to be align bored or honed, the cylinder bases on the case trimmed to the same plane as the crank centerline, case inserted, the cylinders trimmed at the top a couple of thou, if they're being reused, and the heads flycut. given that, the heads stay tight.

[paulhagedorn]

I realize that Timecerts are the way to go...but I am not sure if they had them back when the case was sent off to be fixed. Most likely, the engine will come out, and will be looked at closely.
Thanks for the suggestions, especially about the cylinders and being trimmed.

They will definitely be checked. They were new, 10,000 miles ago, so I hope they don't need replacing.

Paul