The top chain ramp here appears brown. This would be the incorrect location if I recall correctly as it should be only on the 4-6 side of the engine on top.

What intermediate shaft number is on there? What case #? Looks like the intermediate shaft may not be original to the case. Edit: looks like you have a 64-68 intermediate shaft installed. What crank is installed?

Think you would need intermediate shaft from the later engine here. one similar to this:

0510 PROJ964 03 Z Photo 3

I believe you have to run the old style IS in a 65 case? Early aluminum cases have no IS bearings and the shaft runs in the plain bore. So the IS has to be sized to run in the plain bore, or else the bores are enlarged for bearings and you use the later shaft?


There's a picture of an early aluminum case in Bruce Anderson's book with a caption that says "Inside the sand-cast-aluminum crankcase, the layshaft runs in the crankcase w/out insert bearings. This particular layshaft was only used in these early crankcases"

My book is the 2nd edition and the picture is top left on page 53

Sounds like this special engine build allowed the previous owner to run in a particular racing class. The shop will have no liability. Sorry to hear about your trouble, but thanks for sharing as it is very interesting. Good luck in your new build!

Yes, I believe its the right parts. But why are the gears so unaligned when the shaft cover is on and should the IS wear such groves in the cover?

Haven't checked the year of the case, but it is a rare early 65-68 sand cast alu case.

As a side note it has MFI reconfigured to 3 liter and S-cams. It had a lot of torque and a really good throttle response, a bit chocked an the top above 5500 with SSI. The heads are 2.4S (Y-alloy) or possibly 2.7 carrera , slightly ported I think.

The sand cast cases did not use bearings for their intermediate shaft. Don't really need them, in fact. So that's the IS shaft in this motor.

End play is set with gasket thickness under the IS end cover (that plate you show with wear) and there is a spec for that. The end plate for these motors is cast iron, not mag or aluminum. I suppose it is cast iron because Porsche thought that the shaft end and the plate might occasionally come into contact?

On my sand cast motors I found I could use the softer metal end plate without wear issues. Pressurized oil is in that area, and I have supposed that it helps push the IS shaft toward the flywheel end of the motor a bit, offsetting what the diagonal cut of the gear teeth want to do by way of shoving it this way or that depending on whether you are accelerating or decelerating.

The IS gear on the IS shaft is different for these early shafts/cases. If you put on the gear from a later engine, it will be offset like this one is. I ran into that when I talked a guy into having some straight cut gears made for this application (stripping the teeth off an aluminum gear was an incentive here to have something stouter, though not everyone has such problems with aluminum). I gave him dimensions from later IS shafts, and when it came time to put the ones I bought into my motor I found I had an offset. I was able to change something (turn the gear around?) to minimize the offset, and (perhaps because both are steel) have had no issues at all with that setup.

You can't just put the later IS shaft into a sand cast case. You can machine the case to accept one of the bearings for the later cases (I think the non-thrust end, but may have that backward), but not the other. The bearing seating surface of the case is too large for the later bearing. So you either have to weld up the case and rebore, or make some kind of trick insert to fill the gap between case and bearing.

Since this case has no bearings, it is running the early IS shaft.

But it makes sense that having the chain for the left bank (isn't that the one?) only on one row of teeth at the IS shaft was pressing the shaft toward the crank pulley end of the motor, thus causing the scoring of the cover plate. And maybe exaggerating any gear mesh offset there might be.

Having the chain off like this is one of the things Bruce Anderson's book cautions against! Along with installing the cylinders wrong side up. Hard to fathom this, and the angularity should have made noises which could not have been adjusted out with the cam shims. Even with no shims you still would have had noise which shouldn't be there. And removing shims would have thrown measured gear parallelism way off, since it is based on the gears (which probably were in OK parallelism) and not the chain angle, so a mechanic would probably not have gone there.

It isn't all that hard, when reassembling a motor, to get a chain off like this. But it also isn't hard to notice this, and to correct it on the engine stand: stand the engine on its side, drop the chain down so it is loose, and move it over so when you pull it back up it is where it belongs. You can see this before you put the chain boxes on, and you can use a mirror to see if all is right after they are on (or, nowadays, a borescope too).

Well, no. Just a wacky build...

Good information Walt!!
Wrong IS gear, I'll give it a good look to verify that.
I also think it would have rattled like crazy, but I have no experience with such an error.

Reviewing the pictures, no question that this is the early IS shaft. Note that there is a large flange on the crank pulley side of the shaft, but no corresponding flange on the side toward the right side chain gear.

http://forums.pelicanparts.com/uploa...1380490740.jpg


This is one reason you can't use the double flanged bushing (thrust bearing each direction) with these early IS shafts.

So the IS flange holds the shaft in position in one direction, and the cover plate in the other. The setting spec for the cover plate provides the right clearance for the thrust surfaces in each direction, with the pressurized oil coming out of the bearing surfaces of the shaft at that end providing the oil cushion end to end.

You can see from this picture:

http://forums.pelicanparts.com/uploa...1380490929.jpg

why you can't adjust out the offset between the crank and the IS gears. Way too much movement to deal with using a couple of shims. Worse, you'd put chain wheel parallelism way way out of where it should be, and way too much to compensate for with camshaft shims. And you might put a special strain on the splined coupling tube connecting the oil pump to the IS shaft. I don't think there is a spec for this, but if you had only a short length of splines matching on the two, that would be weaker than the normal, longer spline engagement.

So my vote is wrong aluminum IS gear for that part of the issues. Though that offset might be acceptable. You can take a look at the aluminum gear faces to see if they look especially worn where they contact compared to the side where they do not. And try flipping it, or its replacement. Early sand cast IS gears (and didn't the "no separate bearing" system continue on into the earliest mag cases? So those use the same IS gear) may be hard to find new.

One thing you might consider for the rebuild is the steel large IS gear from a 964 (I think from that, if not then a 993 - I'd have to look up what I purchased). If flipping it gives you no more offset than you have (or improves that), it will bolt right in and you won't have to worry about offset there.

Don't know what to think about the crank bearing wear. Worth having the crank checked for straightness, and the case bearing saddles for the same. Those of us running the sand cast cases take it as an article of faith that they never go out of bearing alignment, and never need line boring. But, as with most things, there can be exceptions.

To be clear, you have the right IS shaft for this case. But may well have the wrong IS gear.

I have re-read Waynes book on this part, so I have a grasp om adjusting the early IS end play now.

This engine doesn't have the original 66mm crank, but a 70.4 to take the capacity up to 3.0 liter.
Is it just the IS gear that has a different offset, or is the crank gear different to?


We will probably have to check the crank for straightness. The engine was really hard to turn. I don't think it was that before.
That said, the case might be tweaked, a lot of welding has been done to it before. It has probably been in some accident and/or thrown a rod.

More pieces of the pussle that we missed until we lifted the crank....

http://forums.pelicanparts.com/uploa...1380562742.jpg

Never seen a broken crank before. Might explain the wear on the bearings. Hard to tell but the case looks tweaked, will be sending it out to be measured.

Not sure if this is related to the chains, can't imagine how.

Can't believe the chains caused that! Wow, takes a lot of force to break a crank. Typically you will destroy rods, pistons, the case, etc. before breaking a crank. The chains jamming would likely just break them and the gear/is shaft at most. That crank must have been messed with somehow to weaken it.

wow.. thats depressing. sorry you're going through all this.
probably not what you want to hear but at this point i would just look for another motor.

I don't believe it was, must have been damaged to begin with or the warped case did it.

Instantaneous shock loadings can work nasty miracles inside of an engine!
I have seen cranks in small block chevys do this same thing.
They broke on the center main just like in your picture.
I believe it happens when the hardened crank is subjected to seizure on one end and the point of the break is at the weakest part.
Bob

Yes indeed Bob. I've seen the same with valve springs binding and shattering a camshaft. The crank jamming at one end would be the same. In this case it appears to be the intermediate shaft locked and transmitted the load through the gear to the crank. The inertia of the flywheel likely did the work shearing the crank.

It's hard to tell from the picture but if you look at the surface of the brakage you would see that the edges (counter weight parts) are glossy, smooth and "hammered". The center part is raw and dull.
I would guess that the crank was flawed when it went into the engine and the rest broke along with the chain.

Probably ran for a few revolutions after the break. That'll hammer things down a bit. Usually when you find this kind of carnage it's with a rod that had windowed the case/block making it real hard to tell what happened. I think the relatively high number of webs/bearings in the 911 engine kept the crank revolving in two separate pieces through contact on the shatter joint. Not all are so fortunate.

The 70.4 crank is not, I think, quite as stout as the 66. A friend had the crank break on his '74 911S some years back. They track the car, but there was nothing special one could point to as the cause. I think they, and those of us kibitzing, thought a chain tensioner had failed, so suggested they take it easy driving home from a track. They got home all right, broken crank and all.

I once drove a VW with a broken crank for three hundred or so miles. After the first appearance of some problem I saw that the crank pulley was broken. A welding shop along the way fixed that. A couple of hundred miles later it broke again and it was time to stop.

I'd be inclined to blame the chain failing due to improper installation for this, though you can probably tell from the fracture surfaces whether a crack had developed and was getting bigger, or whether it all cracked at once. The older surfaces would be a bit smoother (unlikely to be rusted or discolored given that they live in an oil bath), and would have a semi circular tree ring like pattern as the crack grew larger. That all ends with the final fracture, which is of a more uniform appearance.

Cranks breaking aren't all that common, but that is not unheard of either.