George 911-V8

Big dave I know of a new supercharger motor ready to drop in, it was built with a new block. I think it can be bought for a great price.

George

Big Dave

Thanks for the info George. It's reasonable to assume that Rob doesn't want to supercharge. He's using a mechanic because they're giving him a 2 year warranty when the work is done. I doubt anyone would offer that if there's a supercharger involved.

Lagavulin

What are the specs on the engine, and what's the price?

Jim bailey - 928 International

Who built it ? where did they find a new block ? what pistons ? what compression ratio ? which camshafts ? any crank modifications ? Why is it being offered for sale "at a great price" ; has it been started and tested ?

bcdavis

Is it a Chevy? Hahahaha!

George 911-V8

The reason he wants to sell, I think he wants to make the car a drag race application. He spent big coin on this motor and he never fired it off yet, its sitting on a stand ready to drop in. I know the block is brand new not used and the supercharger is polished. The complete set up looks great. I will put him in touch with anyone thats intrested. No its not a chevy


George

Erik - Denmark

Jim,
Exactly, that's also my point
The 'twisting' theory also confirm the 'Loctite-Fix' theory (Even I do not want to use the Loctite if I can avoid it)

Then 2 comments:
1. I do not understand that it should be so difficult to repair the block after trust bearing damage - I mean if a professional block renovating shop (or a good machinery shop) get the block, that it must be possible to machine the damaged area and install a distance ring to the original measure

2. It is not 100% correct that the Trans shaft cannot move in the rear spline connection due the slot for the bolt - I have seen mine was moved 2-3 mm forwards, and I pushed it back – BTDT
Regards from Erik in Denmark

jon928se

I'm convinced that the "Jim Bailey" theory is the correct one.

I saw the TT front clamp being undone on a friends car that had TBF - the clamp moved aft by about 7mm (1/4")

His block was repaired by welding new metal onto the aft face of the centre main bearing journal and then grinding it back to the correct size - remember that the block/crank ladder only holds the centre main/thrust bearing in position it is not the bearing itself.

I also have seen a different repair where the block/ladder face that gets worn away when the bearing shell spins is machined flat and then the thickness is made up with 2 semicircular shims fixed to the block with countresunk bolts.

Sitting in my garden is the block of a TBF engine - the only damage to the block that needs to be repaired is the aft face of the centre main/thrust bearing. It seems that there is sufficient tolerance in the piston pins to allow the rods to move forwards without loading the pistons. Crank needs a regrind though!

Cheers

Jon
Black SE
now with slipping clutch.

Earl Gillstrom

John,

If I counted correctly, you know of 3 TBFs. What was the cause of these failures?

If we knew, maybe we could prevent the failure.

OrionKhan

Sorry to hear the news on the TBF. I went through the same problem a year and a half ago. Have him make sure the mechanic doing the install knows what he's doing. The cheapest mechanic ain't always the best deal. I have personal experience to back that up...

jon928se

Earl

For definite two of the three TBF's that I "know of " were a result of the front clamp having never been released, which would have allowed the front clamp to slide back to it's "at rest" position. As I said earlier I am convinced that is purely caused by the shaft shortening under load, which results in the end of the shaft being pulled out of the clamp. When the load is released (foot of gas pedal !) the shaft returns to its normal untwisted state and length but the clamp is now slightly further forwards on the shaft - hence the overall length of shaft and clamp is longer thus putting a permanent load on the crank and thrust bearing.

This ratcheting kind of action is quite a common cause of failure in cyclical load situations, but it tends to occur more in buildings than it does in mechanical engineering scenarios.

I believe that Porsche kind of acknowledged this problem and released a service bulletin advising that the clamp bolts be tightened 10% tighter than the original spec. Or am I dreaming and it is the condensed advice of the experienced hands of the various 928 boards around the world ?

Cheers

Jon
Black SE

Earl Gillstrom

Jon,

Your theory of the shaft shortning under load makes the most sense. The "Loctite Fix" that I developed seems to solve the problem of the migrating hub. It has been used for over 4 years and I have not heard of a TBF on any car that it was done on. The only problem that I have heard of is that it works too good. It is almost impossible to disassemble if necessary.
One thing that bothers me is, I have seen many high mileage cars ( before Loctite) with the hub jammed against the flywheel, yet normal crankshaft end play. Why do only some cars have TBF?

SharkSkin

Earl,

Not sure if this helps any, since I'm unfamiliar with the nether regions of my 928(so far)... But Loctite Red & Blue turn to powder at about 400ºF and let go. I've used loctite red to hold a pillow block bearing inner race on a shaft, then when the bearing needed to be replaced I just heated it up and then removed the bearing as usual. I doubt there is enough room down there to apply that kind of heat without damaging something. But for small assemblies you can throw in a 400º oven, it's the "hot" tip...

S

Earl Gillstrom

Dave A,

I have been told that it takes a lot of torch heat to loosen the Loctite on the shaft, and then a lot of prying and beating. luckily we both have 5 speeds.

Big Dave

Another update:

The mechanic is saying it looks like the block will need to be replace (no surprise there). Unfortunately, it looks to me that this saga is not going to end up well. Rob told me that the mechanic doesn't even have the 928 workshop manuals. He doesn't even have access to the engine specs to see what the recommended torque settings are.

I don't like the direction this is going for Rob at all.