head studs

[gtihop]

while dropping the engine from a 83 911sc to repair transmission troubles, I took off valve covers and have 2 broken studs The engine has 74000 miles and the compression and oil pressure is good. (checked it before removing engine, no oil burning). Should I just dissassemble to replace the studs or should I go and do rings, bearings, etc. Don't really want to break the bank yet !!
Is there any easy way to replace the lower studs, and what type do you guys recommend?

[johnsjmc]

With low miles you can get away with just replacing the broken studs. I would replace all of the lower dilivar with steel like the uppers already are. The steel seldom if ever break. I had a 1980 3.0 with similar situation and replaced only the lowers at 95000.Still runs strong and uses no oil 10 years later.

[Henry Schmidt]

The truth is that you can just keep driving the engine.
Chances are that the 2 broken studs are not effecting the performance of the engine at all.

I would hope that the two studs are not adjacent to each other. One on each bank would be optimum.

There is very little damage that will be caused by running the engine for a few thousand more miles. 25k-50K ? Who knows ?
I have seen good running engine with 6 broken studs and no real indication of this condition.
If you have the time and the money and you just want it right, then by all means replace all the Delivar studs.
A little self promotion: use Supertec studs.
But if you just want to drive your car and enjoy it on the street (no track events) you have my blessing.

One more point: It would make sense to check the lower head stud every so often (10K or so) to verify that no more studs are breaking.

[gtihop]

thanks guys. I'm looking to drive it once a week for pleasure, no racing. I bought it as a toy to play with (mid life toy) and don't really want to get into a rebuild. Just did that on the Golf Gti that the engine blew up on the way to get this porsche. The studs are the lower, on cyl 4 and 6.

[Jim Sims]

If the engine is dropped and you can get the broken studs out of the case (without heat) this task can be done with a minimum investment of funds and effort. There is always the risk of not being able to get the studs out without separating the case (or other problems with the heads) and this must be weighed against the risk of continuing to run with broken studs. A broken stud transfers additional load to the remaining sound studs which may cause them to then fail sooner than usual. One leaves the cam tower and heads together and removes them as a unit and the case doesn't have to be split. I have assisted a friend with this very job (replaced the lower studs on the passenger side only - '82SC) with the engine sitting on wood blocks on a garage floor - transmission was already separated. Special tools required: cam nut wrenches, Z blocks and dial indicator gages, "camming" type stud remover (Sears sells), Snap-On stud tool with collet, wrap type ring compressor (one that can be installed and removed in place) and thread chasing tap (not a cutting tap) for the case stud holes. Basic parts required: studs, cylinder gaskets, cam end gasket and o-ring, chain case cover gasket, o-rings for the oil return tubes and valve cover gaskets.

[Henry Schmidt]

Originally posted by Jim Sims
If the engine is dropped and you can get the broken studs out of the case (without heat) this task can be done with a minimum investment of funds and effort. There is always the risk of not being able to get the studs out without separating the case (or other problems with the heads) and this must be weighed against the risk of continuing to run with broken studs. ..........................

Big "ifs"
Continuing to run the engine offers very few risks.
If you take it apart and you find it should be rebuilt, then you're stuck.
If you continue to drive the car, with the understanding that it will need to come apart (some day), then you can save for the possibility that it will need a complete. If at that time it doesn't need a complete all you've done is started saving for something else. Who knows ?

[Jim Sims]

"Continuing to run the engine offers very few risks."

Unless more studs break on the cylinders with the failed studs. What is the minimum number of exhaust studs on a side to avoid undue head, cylinder and case damage?

[Henry Schmidt]

I have seen 4 broken studs on one bank with no, let say that again "no" damage to anything but the studs. No cylinder damage, no head damage. At that point there was a pretty substantial oil leak but no damage to other parts.
If the engine had been driven unusually hard it iwas possible to damage a cylinder or two.

Jim, I wonder why you think I would recommend something that would be unnecessarily detrimental to the engine?

I have recommended running engines with broken studs to people who asked me for engine quote and to this date none of them have suggested it was a bad idea later.

It allows a person to plan a solution not react to a problem.

[Jim Sims]

Were they four exhaust studs on one bank? (just a question - I want to get an idea of where the limits are)

No, I do not think you would give out advice that you knew to be detrimental to an engine.

One person's reaction can be equivalent to another's planning ahead - people have different needs and philosophies. The engine is apparently out and the transmission separated for repairs. The original question (quoted below) was if there was an easy way to replace the lower studs:

"Should I just dissassemble to replace the studs or should I go and do rings, bearings, etc. Don't really want to break the bank yet !!Is there any easy way to replace the lower studs, and what type do you guys recommend?"

Cheers, Jim

[gtihop]

at this point I'm just going to replace all lower studs. I may replace valve seals and lap valves in, just because it's apart. Not going to get into lower end at this time, maybe in a few years. I won't be driving it everyday in the summer, just on weekends. (too many cars now!).
The compression was ok, both wet and dry, no oil burning, just lots of leaks that I'll be doing as well. (range from 170- 181 dry), (200-205 wet). It would seem that the engine has already been apart before, was missing bolts, etc)

[Henry Schmidt]

Good luck with your project.
Remember to use this forum when in dought.
Cheers

[gtihop]

got the engine torn apart. all lower studs came out thanks to snap on stud tool!. Question about spring tensioners; Should there be any movement with the piston by finger pressure? There is 1/8" on the left side tensioner if you push it by your finger.

[Jim Sims]

Original design or oil pressure fed tensioners?

[gtihop]

original design.

[Jim Sims]

The shop test spec. for the tensioner is: mounted vertically (plunger up) in a vise and 12 lbs resting on the plunger, the plunger shouldn't drop more than 10 mm (~.394") in a 5 to 10 minute interval. Back sure the tensioner is filled with engine oil and bleed of air before doing the test. The factory shop manuals and several after market shop manuals cover the bleeding (and rebuilding) procedures. If the tensioner fails the test, it can sometimes be rebuilt; the kits (PN91110590101) are about $22.50 each from Pelican. Some engine gasket kits may also contain some of the rebuild parts: rubber o-rings and "intermediate piece". Below is a description of rebuilding by John Walker. This would also be an opportunity to install the pressure fed Carrera style tensioners and associated fittings which are considered an upgrade by many (but at significantly more expense than just rebuilding the original units). Cheers. Jim

"the kits can be had from the dealer for sure. doesn't pelican have them? 911 105 901 01. i liked the o rings better in the dealer kits, rather than the Worldpac ones. used to do them all the time. no big deal. bleeding them of air is the most important thing. actually, a more important thing is never look directly down at the spring loaded piston when removing or installing the snap ring that secures it into the tensioner body. it can pop out and get you in the eye.

clamp unit in a vise by the lower mounting. remove top snap ring and collar under it. remove bolt in the side of the body. grab the inner raised collar of the aluminum disc with small pliers and pull up and out. swab out oil under it so you can see the top of the piston and the snap ring that holds it in. the piston is depressed a tad so the ring can be removed. it's stiff and must be rotated so one end is in the notch, so a awl or pocket screwdriver can be inserted in the notch to pry the ring out used. be patient, and keep your eyes away. when the ring is off, turn the unit upside down and remove the piston. usually the check ball, seat and springs come out with it. pay attention to their order. fish the very last piece out of the bottom of the bore. clean everything well. inspect piston and bore for excessive scoring. assemble the misc. pieces onto the main spring, lower the piston over the stack, turn the stack upside down and lower the tensioner body onto the stack. hold with thumb and put it back in the vise. start the inner snap ring into the groove on one side with a small screwdriver and hold it there. with another small screwdriver, press the other side down until it seats. (may take some cursing to get it in). don't let go of the piston while you do this. keep your eyes away. tilt the body so the side bolt hole is angled up a bit. install bolt into the side of the body loosely. fill the reservoir with bubble-free oil. insert a key tag wire into one of the holes in the top of the piston body to move the check ball off it's seat. slowly pump the piston to bleed out the air. the idea is to go slow so you don't aerate the oil. refill if needed. when it has no squishy play you're done. put new o rings inside and outside the aluminum disc. open the side bleeder bolt until you see the bleed hole in the threads. push the disc down into the oil reservoir and let the air go out the bleeder. tighten bleeder. install small spring, cap and snap ring and you're done."

[gtihop]

thanks. I'll check it this week. I'd like to upgrade to carrera`tensioners but at the moment we're into a semi major rebuild. A little more than I intended to do but at least I'll know what I have when it's done. That's why they invented MasterCard!!!

[Jeff Alton]

In the mean time you can install tensioner gaurds for piece of mind. They are cheap and I have used them on a couple of rebuilds for folks who did not have the extra money to spend when a surprise rebuild appeard in the future. Then, when funds permit, go and put the carrera tensioners in.

Cheers

[sammyg2]

I had one broken stud on my engine at the #5 cylinder when I bought it (yes i knew about it and the price was adjusted accoprdingly).

I drove it for a year, then added a turbocharger and ran it for another year.
I eventually took it apart to replace the lower studs and found no damage, no wear, nada. It had 100,000 miles on it and the insides looked like new.

[Jeff Alton]

Some will win some will loose. I have only taken apart one motor that had broken studs. It was driven about 10k with the broken studs. We took about 10 thou off the heads to clean them up. Otherwise it was no big deal. But, you are taking your chances on causing more damage. There are plenty of stories on both sides of the debate about damage vs no damage.

Cheers

[Henry Schmidt]

We have taken apart hundreds of air cooled 911 engines.
The anecdotal evidence is that with a 3.0-3.2 and one or two broken studs the damage does not justify a half a**ed repair.
What's that means, if your budget can not handle a proper repair then it's better to drive it or park it until the budget warrants the complete repair.
That does not complete overhaul, it means complete repairs as necessary.