Rod Bearings without splitting 2.7 case
 

Hi all,

I'm in the midst of a top-end rebuild on my 2.7 1977 911S which I've had just over a year. It's been rebuilt once before at 120k miles complete with inserts for all the head studs, upgraded tensioners, 11 blade fan etc. It's been loved. I'm at 190k miles now and I found some leakage in the heads, so I commenced a top end rebuild.

https://castledb.me/images/2024/02/17/IMG_4043.md.jpg

heads are out for work, cylinders are being replated in nikasil so I can re-ring them (though apparently one is damaged, so it will be replaced.

here's the larger thread about the rebuild: https://forums.pelicanparts.com/porsche-911-technical-forum/1151942-ben-s-77-911-winter-rebuild-seeking-advice-guidance.html

This seems like a good time to do the rod bearings while I have things apart - Is this possible without splitting the case? it certainly appears so, but hoping to verify before I take things apart.

thanks!

Rod bolts saved and torqued up checking for permanent stretch using the orig torque from porsche spec book. No permanent stretch, re-use. Other than that, I thought it was easy... new bearings, measured all around at torque spec, same as orig and in spec. Back together with bolt tang already in final lock condition before even torque up.
My biggest difficulty was new rod bolts being fat and bearings that weren't square.

I'm assuming the rod bolts are stout like on the 3.0 SC and have a tang to pre-locate.

Done with case together, 911 sc.

Phil

Roll the cap around to the back of the journal and stick a long screwdriver thru the other side to hold it in place while you mate the rod to it. Before torquing, look thru the space on the other side with a flashlight to be sure the bolt head tangs are seated and not hung up on an angle.

Thanks all!

Be aure to have the bearing lock tabs on rod and cap mated together on the same side.

I have never been a fan of this procedure.
Too many thing can go wrong. First is the fact the the rod journals are no longer round. Second is the likelihood of case and # 8 main bearing leaks after jostling the engine around. Given the 90K mileage and the relatively low cost to split the case, why risk it. Save a few bucks? How much do you save when you do it twice.
There is a pretty good chance that the crank was not ground the first time around. The journals now have 190K on them. Guaranteed, they are oval. By bolting the rods onto the crank in the case you won't be able to feel how they spin. Believe me, we have installed many a rod on a crank where both measured within specs and still didn't rotate the way wanted. We've scene tight spots and side to side trust differences.
A lot of the talent in building these engines involves finesse, a mechanics feel.

I’d tear it down check the mains, measure/ polish the crank, new wrist pin bushings et. These motors aren’t $3000 anymore.

I had the same plan while doing my 3.3 (replacing the rod bearings and rod bolts with the case closed), when I attempted the 1st one I knew I made the wrong decision, so I decided to just split the case and do it the correct and safe way, and I'm so glad I did!

Ugh, I’ve been trying hard to keep this as simple as possible.
Thanks for the insight though. I may well just do that.

I did pull the rods yesterday and everything LOOKS really good, but that’s not the same as measuring out to spec. So far, everything on this engine has looked better than I expected. The cams look great, the rod bearings have a little wear, but nothing nuts.

That said, I’m already 90% of the way there, may just crack it open. I’ve just read so many horror stories about the magnesium cases and cracking them open as a last resort

You got that right.

Word has it you should assume it'll need a bunch of machining as it'll probably warp once it is disassembled. Thousands of $$.

Right about which part - opening it as a last resort - or that I should crack it open as long as Im this close?

Last resort.

Since when is doing it right the "last resort"?
My experience has generally been, where you stop is the point of the next issue.
I get what you're saying about a can of warms, but I would never improve the top end then hope the bottom will cooperate.
If the owner is confident about the engine condition, why bother with rod bearings?
In the overall scheme of things, aren't 2.7 rod bearing pretty bullet-proof?

I am swapping out the rod bearings because they're right there and easily accessible.
The plan is to plastigauge them and make sure the new STD set works. the old ones are also STD and some have a bit of copper showing as a line right down the middle, but really in pretty good shape overall.

This car has run pretty well but was a leaky mess with known melted spots on the harness. Also a really bad transmission leak from the gear selector shaft. As much as anything I was pulling the engine to really get everything clean and to get my eyes on everything.

I found some clear leakage at the valves during a leakdown when the engine was out, so the top end is getting a workover.

I don't mess with mag case rebuilds unless I'm presented with a case that has had all the proper machine work done. Can-o- worms otherwise. Binding cranks, pulled head studs, pulled perimeter studs, worn cylinders bases, etc. Even doing just a top end can end up with pulled head studs on reassembly. Do it all or don't get involved. The guy asked how to do rod bearings without splitting the case and I told him how. That's all.

I checked out your thread, all that time and money you’re putting into it. Seems ridiculous to leave a 200,000 mile unknown bottom end in the car to save a few bucks. Just my opinion. Also looks like one of your galley plugs is leaking oil from the pics in your other thread.

Grillage: I've been watching this thread but not commenting because the other guys here haver much more experience with magnesium cases than I do. Mag cases are not robust like the 3.0 and later aluminum cases. Take their recommendations.

There is no good reason to swap the rod bearings just because they are accessible. Measure or plastigage the middle rods. if they are in spec, bolt them back together with the old bearings and new bolts (unless the last rebuild used ARP bolts), and leave the rest alone. if they are out of spec, you can pretty well bet that the case needs work too. At that point, it becomes a full rebuild with case reconditioning.

But, it's your money, so decide what you want. I would just put it back together, reseal the top end, and motor on until it's burning oil or down on compression or something like that.