I have been looking for a 74-77 911, and have looked at and driven a few with top end rebuilds. They have been done by reputable shops.

My question is with over 100,000 miles on these cars with the top end rebuild, how long would you expect this engine to last ?

After reading Wayne Dempsey's book on rebuilding these engines, I am not sure all the bottom end wouldn't be out of tolerances, and I will be looking at a total rebuild sooner than hoped for.

I would like to find a car I can drive for 5-6 years on weekends only and then after I retire, I plan on re-doing the entire car.

Jonny A

BMW 635 csi, Highly modified.
looking for a 911.

 

Jonny: There are potential problems with a 2.7 liter car that's had a "top end." First, we have to define "top end." Normally, that term covers a valve job, removal/replacement of the pistons and cylinders, and possibly replacement of the rod bearings without splitting the case. A proper top end job would also include conversion to pressure fed Carrera timing chain tensioners. That said, merely doing a top end on a 2.7 liter 911 opens up a very big can of worms - one that can be costly and carry with it reliability issues. That one issue is the cylinder head stud/magnesium case inability to survive a single cylinder head removal/reinstallation. The threaded holes in the crankcase are under tremendous stress, and when the heads are removed the studs relax in those holes. When the heads are reinstalled and torqued, those studs once again stretch, and so do the threads in the case, which harms the threads that hold the head studs. Sooner than later, usually in less than 15K miles, the studs start to "pull" from the case, as the threads can no longer hold them secure. The cure to fix the head stud issue is to (1) disassemble the entire engine, remove the head studs, put each case half in a vertical mill, drill out the threaded holes and install steel sleeves called case savers. (More often than not, when the case is split, it will be discovered to require a main bearing line bore, a specialty machine shop operation.) Then you can put the lower end together and do the top end. Or, (2) you can do a top end job and do it all again a few thousand miles later! If this explanation is insufficient my book (my avatar) covers this issue thoroughly.
Pete

 

Peter:

No, your answer is exactly what I though after reading waynes book.

Both of the last two cars I looked at have just recently had the top end, valve guides, chain tensioners addressed, but nothing else.

I am sure glad to be able to ask for knowledgable help with this forum.

Thank you.

I will keep looking.

Jonny A.

 

Hey Pete

Is the rod bearing the one that fstens the rod to the crank or am I all mixed up naver taken an engine apart to that extent. The reason I am asking is because I am trying to figure out how you could possibly change these without splitting the case . ?

 

Ice: Yes, you've got the right bearings. They are half shells, one half fits inside the rod, the other half in the rod cap. The rod is slipped over the rod journal on the crank, then the rod cap is put into place. Each rod has two bolts, which will stay in place in the rod cap's bolt holes, and two nuts which are put on and torqued. Fortunately the hole in the case where the cylinder fits, commonly called a spigot, is large enough to allow the operation. An extra point to make is that rod bolts and nuts are a use once and discard part, if they've been torqued, and then loosened, replace them.
Pete

 

My 2 cents worth - would endorse Pete's comments but I would add that the camshafts and rocker gear can get pretty worn on these engines (had to replace the lot on my '76 after 104,000 miles as part of total restoration). I found that all the big bucks were spent on the top half - the case was split, shuffle pinned, crank reground, new bottom end shells, oil mod etc - but in addition to the cam gear I finished up with new pistons and barrels so the top end was definitely expensive. Moral of the story is that their are top ends and then there are top ends!

PJC