Help: 911 Crank locks during rebuild process

[mic034]

I am rebuilding a stock 1969 2.0l 911t engine. I haven't had any issue with the rebuild at all, until I started tightening things up. More specifically, the "through bolts'. and m8 nuts surrounding the case.

Here is the situation:

When the two cases are joined snugly against each other, the crank rotates freely. Only, when I finish the Torque process on the through bolts, my crank no longer freely 'spins'.

I am using Wayne Dempsey's "How To Rebuild and Modify Porsche 911 Engines", and there is no information on what happens when the crank locks once the bolts are torqued.

I have replaced the case/rod bearings... could this be the issue? I am at a loss here.

This rebuild is an huge learning process.
Thank you,

[Jase77]

I am a few weeks behind where you are and I agree that this is a huge learning curve, but an enjoyable one. (So far)

There are some very experienced people on this forum that could no doubt give you some pointers. From my limited 911 engine rebuild experience I would first of all ask if you had the engine cases line bored before you started the rebuild? The cases can warp when they are split apart and the mating surfaces will need to be skimmed flat and then the Crankshaft bore will need to be re-bored too.

If you didn't have the machining done, but replaced the case/rod bearings then it's probably too tight after you have torqued everything down. Maybe try torqing down the through bolts but checking the rotation of the crankshaft after each one. This may help you to diagnose where it is binding in the case.

Good luck and keep us informed please.
Cheers,
Jason.

[Dpmulvan]

Case machined? If yes measure main bearings. You could get some plasti gauge.

[JJK78-951]

I remember a few years ago a guy did some very precise measuring on the main bearings and found the Glyco bearings that were coming out of like South Africa? were not nearly as precise as they should be, causing the same issues you are having. He measured them all out with a micrometer and found a relatively huge discrepancy in tolerances. Then he bought a set of bearing from Porsche AG which had gone through the control qualitat process or whatever and found them to be very much so within spec.
Installed the Porsche bearing and viola - problem solved.

Either way it definitely sounds like a bearing or main bore issue - what was the cause for the rebuild?
Good luck
J

[safe]

Originally Posted by mic034

When the two cases are joined snugly against each other, the crank rotates freely. Only, when I finish the Torque process on the through bolts, my crank no longer freely 'spins'.

Thank you,

Your case is probably warped, very common on mag cases. Do a search here and you will find plenty of information.

[mic034]

Thank you for all the responses. I have not yet bored the case lines, and I would not be surprised if the case warped upon dis-assemnly. I will have the case taken to my machine ship. I guess this sort of thing is important when replacing the main bearings against the main bore!

[mic034]

They are indeed Glyco bearings... I will have this checked as well. Very interesting stuff. Thank you for helping me out with my rebuild!

[safe]

I had a 2.0 mag case and I could see the warpage when I put a simple ruler on the bearing saddles. Nothing spectacular had happened to this engine, it had just been taken apart...

[tharbert]

Originally Posted by mic034

Thank you for all the responses. I have not yet bored the case lines, and I would not be surprised if the case warped upon dis-assemnly. I will have the case taken to my machine ship. I guess this sort of thing is important when replacing the main bearings against the main bore!

I'd be more surprised if you had posted that the assembly went fine despite not having the machine work done. There are some other common procedures suggested for 2.0 cases: add pistons squirters and perform oil bypass mod. And, upgrade to a 4 rib oil pump. These are factory mods found in newer cases.

Have head studs been time serted? There is also a stud in the case web that should also be time serted as well. This is a must-do for mag cases.

[mic034]

Time Serted studs.. I will research that! thank you

I found an interesting post on case warpage:
warped mag case & line boring

[DRACO A5OG]

+1, get your case checked, I just had my 3.2 case check and she is straight, will be plasti gauging with new bearings shortly.

[Walt Fricke]

Quiz your machinist about this. The preferred procedure these days is to "deck" the case parting lines - take a little off of each, so that the widest part of the likely oval main bearing bores is at its standard dimension. That way the boring bar will return the bores to standard, and you can use standard bearings. You do not want to have the case overbored, which requires using bearings with an oversized OD. These are hugely expensive, if you can even find them. Plus you want to reuse your #8 nose bearing - these don't wear in normal use, and are also extremely expensive, even more so if you want one with an oversized OD.

The shop, after doing this work, ought also to check the deck height - the distance from the crank centerline to the base for the cylinders. Those all need to be the same height so that the tops of all the cylinders will be at the same height, and when the heads are installed and the cam carrier bolted on everything lines up. If one head is a bit high or low, you can bend the cam carrier, causing the cam to bind.

If the shaving of the case parting lines causes the piston to head clearance to be reduced below factory spec, you can get thicker cylinder base spacers to move things back out. This also helps keep the cam lined up where it goes through the hole in the chain box.

If all this seems unfamiliar to your machinist, you might consider looking around for a shop which does this kind of thing regularly - they will have all this worked out.

Same with the Time Certs or case savers or whatever - it was the 2.7s which showed the greatest inclination for the head studs to pull out of the mag cases, and the steel cylindered early motors like your T didn't face the differential expansion problem between steel studs and aluminum cylinders. Still, at this point it has to be worth while to take this extra step.

[BartdeBruijn]

Hi,

Well I did the engine rebuild of 1969 2.0T (as yours) myself and did run into the same issue!
These magnesium cases are relative unstable. After all these many temperature changes during their lifetime all kind off stresses do build up. So when you split the case and wait over night the relaxation of the stresses start ending in warped case halves. There is not a lot to do beside machining the case. To solve this you have to line bore then I would advice the ' oil mod' and case savers/ timeserting the case.
I even did shuffle pinning but that is normally done on race engines.

Hope this helps!
cheers,
Bart

[ChrisBennet]

I agree with Walter; you don't want to simply line bore the case. You want to "resize" the case.
This will set the internals back to factory dimensions and make the case seal up well.

While the machinist has it, have them lightly deck the spigots (so the cylinders all sit the same height and are square to the crank) and bevel the through bolt holes on the side of the case that didn't come that way from the factory.

Note: You may need to use thicker cylinder base gaskets after all this.

[Alex115]

Hi all,
I too have disassembled a 1969 2.0T. The previous owner rebuilt it (poorly) but never had it installed because it leaked so badly. I assume the case is warped too.
Anyone knows of a shop in Central Europe, preferably in or around Belgium, that has a good reputation of working with mag cases?
Many thanks,
Alex

[kwikt 911]

I'm getting my mag cases back from Ollies in a few days and was to told mains were still fine from last align bore. Woohoo