Leave head studs alone or replace?

[blue72s]

Hi all,

I'm planning to do a top-end rebuild of my '72 2.4S including new P+C's. As I'm going to leave the bottom-end totally alone (60,000 documented miles), I'm wondering whether I should leave the head studs alone without removing it from the case, or replace them and install case savers?

Thoughts?

thanks

[john walker's workshop]

you shouldn't have any problems leaving them. 2.4s had way less tendency than a 2.7 to pull studs, and they're already all steel.

[HarryD]

I just had my 2.4 L top end done at 118,000 miles and we had no problems witht he studs. Also, is there a reason you are changing the P's and C's? Mine were fine (also still had some hatch marks on all cylinders) and we left them alone.

[Wayne 962]

I sortof disagree with JW on this one. If you're taking the engine apart, you should put case savers on the case. However, in your case, with low miles, it's a toss-up...

Cylinders and pistons must be in spec with respect to ovality, and ring grooves.

-Wayne

[dtw]

I was planning on bringing my 2.4 case back from the shop without the inserts. Unfortunately, I could not bring myself to do it, in light of the extra assurance that the $175 'sert job bought me. I'd recommend getting the inserts as one of the top "while you're in there" upgrades/mods, along with oil bypass/updated oil pump, chain tensioner upgrade etc.

I'm not sure you could do the inserts without splitting your case. Not sure how other machine shops do it, but mine has a precision jig they use to locate each stud bore for the insert. This jig requires a naked case half. Then again, if it was me tearing down the top end of a 31 year old engine, I would go all the way to the crank, regardless of mileage.

[blue72s]

There are 2 reasons why I want to change Ps+Cs:
a) I want Nikasil liners, not Biral.
b) Compression ratio of stock pistons is too low (8.5:1). Will go for 2.2E or 2.2S pistons, but most likely the former. I know 2.2E pistons are cast, not forged, but perhaps Mahle could make 2.2E forged pistons on special order?


However, I have a fear of splitting my case because Wayne’s book says that:

“As the magnesium case is exposed to thermal cycles and combustion forces, it will deform in many different directions, bending, stretching and twisting across many axes and planes. The case-bearing saddles will become egg-shaped and the entire case itself will twist. In addition, the magnesium case will relax and deform farther after it has been disassembled. The stresses placed upon the material have a tendency to create hidden stresses on the case that are not apparent until the case is split. When the case is bolted together, the two halves support each other and help to keep the proper structure of the case.
You can sometimes observe this when you separate your case halves. Before you split the case, make sure that the crankshaft can turn freely in its bearings. Split the case and let it sit overnight. Then retorque the case halves together with the crankshaft and bearings installed. It is not uncommon for the crank to become stuck and offer resistance to being rotated. The is because the case halves – no longer supporting each other- have relaxed into their natural, deformed orientations.”


So, if I split the case, I would have to resize the case by reboring the center bearing bores (gasp!), which is something I could do without.


Wayne,
Not sure what you mean by that P+C must be in spec with respect to ovality....
If all P+Cs are brand new, it won't matter, will it?

[dtw]

-With respect to center bores: I have just had my 2nd 2.4 case center bored, and both have been returned to spec without having to go to non-standard bearings. As noted in Wayne's book, should you not wish to center bore, or if your case required more extreme surgery, you can have the case mating surfaces shaved and the center bore re-rounded. CE does this. Note that splitting the case simply helps the forces that were already at work, manifest themselves. IMO, the benefits obtained from splitting the case and performing the necessary & recommended tasks outweigh your perceived disadvantages.

-Ovality not an issue w/new P&C's

-Getting Mahle to produce a custom set of pistons is doubtful and would probably cost cubic $. No need to do this when JE will forge you up a set of custom pistons to your specs for less than $1k.

[Wayne 962]

dtw, right-o. The stresses in the case are there, and become more apparent, particularly when the engine is hot. It's not exactly like a big spring, where you unmate the case, and all of a sudden it springs out.

Doing a top end rebuild on a mag case has a tendency to disturb the studs. If this were a 2.7 engine, and you did only a top end, you would probably have about a 95% chance of the studs pulling out. As it is, you've already disturbed the case by removing the heads and cam towers. I would say that leaving the mag case and lower end alone is not the *correct* way of doing things. Who knows, when you bolt the thing back together, you may have disturbed it enough to create a bunch of oil leaks. If you don't care about leaks, then okay, but if you do, then I would redo the bottom end while it's out.

Or, go wild and upgrade to a 2.7RS spec. You would only need a few things:

- Recal the pump (the stacks are the same as the 2.4S, I think the throttle boddies are the same too).
- RS pistons and cylinders
- Bore out the case, and increase the mounting area for the cylinder heads (the heads are virtually the same). Or, if you're wanting not to molest your original case, then just buy my 2.7 case - already done and ready to go.

That's it - everything else is basically the same (same cams). For that you get better driveability, more HP, and better low-end response.

I like to think that if you're spending $6-$8K on an engine, you might as well get more performance out of it, as long as it doesn't cost you too much more. Actually, I think that the 2.7RS set is about 1/2 the cost of the regular 2.4 set right now!

-Wayne

[Graem Elliott]

I removed the studs from my 73 2.4. All of them came our fine and the case was ok too. None of the studs had pulled out and stripped the mag threads out. Assuming I get inserts in the case, can't I reuse the studs?

[Wayne 962]

Yes, these should be the early studs, which are magnetic, and are okay to reuse.

-Wayne

[Britwrench]

If you are thinking of up-grading the engine, I think you should split the cases and do the job properly.

[Bobboloo]

If I had a 72'S with a healthy motor I think I would leave it alone and take some DE's to learn how to make use of an already great motor.

Then if I was still itchin to do motor work I would find a decent 2.7 or 3.0 core motor to build into a 2.8 or 3.0RS motor.

[blue72s]

Originally posted by Bobboloo
take some DE's to learn how to make use of an already great motor.

What is DE?


My motor is healthy but the valve guides have gone (smokes under deceleration) so it definitely needs a top-end rebuild.

[Wayne 962]

DE = Driver's Ed. I hate abbreviations...

-Wayne

[blau911]

After you get the top end off, the case only takes a few more hours to split. Take advantage of the chance to open it up and see how things look. Best case you change the bearings and chains and put it back together knowing its fine for another 100k + miles. Worst case, you find problems and deal with them before spending all the money upstairs and having the engine fail and destroying all your time and effort. Go the extra mile so you sleep well at night. If it's a matching number S engine 911, the case is irreplacable.

[blue72s]

Thanks all, much obliged.


However, I still don't understand:
"Take some driver's Ed to learn how to make use of an already great motor"

[blau911]

Some people, much like the scarecrow from the Wizard of Oz, seem to think that you need to get a diploma in order to feel smart. Then there a few who seem to have the instinct, reflexes and feel for 911's to drive them well. Then there are the mojority who falkl in the middle.
Some people need to be formally taught. I taught myself by looking at my manuals and seeing the max hp per gear at various rpm levels, and then going out on an empty road and accelerating thru some sharp corners where there were no trees and and no ditches. Eventually, you will figure out what your car can do and what it can't do. If you can't figure it out by then, its time to buy a 1999 C4 with idiot proof computer controlled stabilizers built in.

[HarryD]

Originally posted by blue72s
Thanks all, much obliged.


However, I still don't understand:
"Take some driver's Ed to learn how to make use of an already great motor"

Drivers Ed First:

Drivers Ed is an opportunity to drive your car at a place (race track) where the the risk to you an others is less if you lose control. This is due to the fact there are wide places to run off and the other drivers will not be doing stupid things in from of you.

If you are uncomforatable with driving fast on a track, another avenue to consider is Autocross where you will learn car control at relatively low speeds. The only things to hit are orange cones and your ego.

"Already a Great Motor":

I think what he is telling you is that if you start using the car on places like the track, you will begin to see what the current engine can do. On the highway you are limited due to other drivers and speed limits. The track or Autocross offers the chance to use the engine in ways not possible in ordinary driving.

Does this help?

[blue72s]

Thanks Harry for the clarification. I only asked what is Drivers Ed because it's a phrase that we never use in the UK.
I can't believe Bobby brought it up, because this is an Engine Rebuilding Forum. If I wanted to talk about racing, I'd have gone to an appropriate forum. I came to this forum because my engine genuinely needs a rebuild. PERIOD.

[HarryD]

Originally posted by blue72s
Thanks Harry for the clarification. I only asked what is Drivers Ed because it's a phrase that we never use in the UK.
I can't believe Bobby brought it up, because this is an Engine Rebuilding Forum. If I wanted to talk about racing, I'd have gone to an appropriate forum. I came to this forum because my engine genuinely needs a rebuild. PERIOD.

I think you fellows there have a more interesting term than us yanks.

You may want to do a few things before you fully commit to a total rebuild:

-When they pull the heads, you can check the Ps and Cs to see if they need replacement (roundness and ring lands).

-With one P&C removed, you can check it's rod and rod bearings to see if they are worn.

This may give you enough info to proceed with a full rebuild or limit your work to the top end.

I faced a similar issue when I brought my 2.4L in for a rebuild. I knew the valve guides were shot but had no idea about the rest of the engine. I decided that I would go for a top end only but if I needed new Ps and Cs or bottom end work, I would do a 3.0 conversion. When the heads were pulled my wrench inspected the P&C's and told me that from all the evidence he saw and his experience I would be ok to go with heads only. I pressed him a bit to be sure he was not trying to "save" me money and he stood firm.

As far as the racing bits. While off topic, I offer this food for thought... AutoCross is a way to simulate panic driving situations you may experience on the highway in a place where an error will bruise only your pride. Hopefully you will gain some skills that may save you, your car, or another person unintentioned harm. If you have not tried it, I think you owe it to your self to do so (it will be the most intense 60 seconds of driving you may ever experience). Of course I am biased since I think AutoCross is fun and try to get out and do it whenever I can.

Good luck!