While I'm in there ... 2.7

Porsche_monkey · 09-10-2003, 04:37 AM

Well after five years of rebuilding my 74 911 I got my car on the road. Within a week my throttle stuck and the engine over-revved when I depressed the clutch.

The damage is not that bad, I have pulled the top end apart and found three bent exhaust valves. But, now that I'm this far:

should I put in timecerts (11R case)?
should I use dilivar head studs?
should I split and re-seal the case (I don't think it leaks)?
should I just do the top end (I'm leaning this way)

The engine ran strong with no issues (other than oil leaks) before the 'incident' and the pistons/barrels are like new.

Suggestions?

ChrisBennet · ChrisBennet's Garage

This is just my opinion:
If the bottom end is not leaking I'd leave it alone but if you want to put in case savers or Timeserts you'll need to split the case for that.
Don't use Dilivar studs.
Check rockers for cracks.
I'd replace the valve spring keepers and check or replace the retainers. (I normally replace these when I do a rebuild. Cheap insurance.)
Consider using a higher pressure valve springs and a rev limiting distributor or equivelent.

BTW: I've pnly worked on one 1974 2.7 but I thought it had a 7R (not 11R) case. '74's are great 'cause they were pre-thermal reactors so they didn't get as heat stressed as later ones.
-Chris

Porsche_monkey · 09-10-2003, 05:59 AM

So I should use new Porsche studs, not re-use mine?

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by PBH
So I should use new Porsche studs, not re-use mine?

I would use new Porsche studs on the bottom.
If you live in a cool climate and don't track the car I would be tempted to leave the studs alone. If you want to replace the studs you really should have Timesert's or Case Savers put in. Heat is what what stresses these cases. Up here in New England, 2.7's don't have as many problems with pulling studs.
Any time you disturb the studs on a 2.7 like (when you do a top end job) it awakens their mischievous nature they are likely to pull soon after. At least it seems that way to me.
-Chris

Porsche_monkey · 09-10-2003, 06:27 AM

I live in a reasonably cool climate, when it's hot I do not drive this car. I drive it hard for short periods of time occasionally. It will never see a track.

So based on this you think I would be safe re-using all my studs?

I should also mention I do not know the history of this engine, it might have been time-certed earlier. I think I need to pull a pot off to check this don't I?

john walker's workshop · 09-11-2003, 11:56 AM

2.7s are a can of worms. if you open one up, you should go thru it thoroughly. the cases always need a lot of machine work, the valve guides are shot, the cylinders are usually worn out, etc, etc.

Porsche_monkey · 09-11-2003, 11:59 AM

I came to that conclusion last night. I've split the case and I'm going to do a full inspection and rebuild.

JW: do you use dilivar or not? time-cert or case-savers?

john walker's workshop · 03:21 PM

case savers are what most guys use these days. timeserts would probably be safe , but they are narrower, and in rare instances, pull threads from the case just like the studs did.
the 2.7 mag case, being softer and weaker than aluminum, is the only one that i would consider using diliver on, bottom row only, as opposed to steel studs. they are designed to match the expansion rate of the cylinders, and therefore will stress the threads in the case less than if you used steel studs. be sure they are new, and are the black powder painted ones.