brianrheffron

I don't understand why damage to the block at the thrust bearing
means the scrapping of the engine.
Surely a good machine shop could just build up the damaged area with
weld, heat the block and the giirdle in an oven to relieve the stesses
induced by the welding and then machine the block and girdle back
to the original sizes. This sort of work is done all the time to
salvage damaged castings, sometimes by welding and sometimes
by metal spraying.
If there is some fundamental reason that this cannot be done how about
machining the block and girdle to allow the insertion of shaped packing
pieces to support the new thrust bearings. These could be fixed in place
using LOCTITE Green, or similar, then machined as above.
It would be a tragedy is a shortage of good blocks became the last
nail in the 928s coffin.

Ben

My TBF block had several cracks in it where the bearings had become so hot, so in my case it was scrap.
Paul Anderson in Stroud has apparently restored a TBF block by welding, like you've mentioned above. It can't have been too badly damaged though, else that block would most likely have had cracks too.

I would have thought it more cost effective to just replace the engine/block with a known good one at the moment. Maybe if in several years time the quantity of used engines dries up, then restoring the damaged blocks might be a viable option.

hacker-pschorr

The damage is not always isolated to the thrust bearing location. If bearing material had a chance to circulate the motor, you can end up with scored cylinders too, and who knows what else that you cannot see. Which is why you should do a full tear down for a rod bearing failure, even if the rod / crank are not damaged.

I scrapped a 944 block due to this. The crank area was fine, two of the cylinder walls were too far gone to fix (along with those two pistons).

Adam Geist

I've seen damaged blocks from vintage light-weight alloy type race engines (Coventry Climax) that were welded and then machined back to spec - good or better than new. The one benefit of welding, I believe, is the welded area is now stronger than the surrounding original material.
Adam

IcemanG17

cracks are the main death kneel for TBF blocks....... another reason many other options aren't explored (repair options) is how relatively cheap good blocks are too

jon928se

I have heard of but not seen the area of the main journal that gets machined out by the thrust bearing when it spins being repaired by machining the the damaged area flat then repaired using "a washer cut in half" (easiest description for a piece machined specifically to fit.) fixed in place with countersunk machine screws.

slate blue

When welding is done, the material is not stronger but generally it is harder but more brittle and this is mistaken for being stronger. Also when items are welded distortion is a real issue. So it is a difficult and expensive undertaking with no garantees of success. You may end end up with a spun bearing down the track.

Greg

GregBBRD

I've seen dozens of engines with the thrust bearing damaged. I've been able to save one (1)...all the rest are cracked beyond use. The cracks will migrate all the way to the water jackets and halfway up the cylinders. The upper crankcase section is made from an aluminum alloy with high quantities of silicon...for the cylinder bores. This alloy is very brittle and cracks very, very easily. If the thrust bearing spins more than a few times, it is all over.

The one block I did save needed to be surfaced and then align bored.. The hole where the oil seals sat and the oil pump goes had to be made "round" again...after surfacing. Very expensive to fix.

Imo000

I HAVE!

There is a local S4 owner that bought his fire damaged '87 and it turned out it also had TBF. He took the engine totally part, had the damaged journal machined out, then a spacer was made. He ended up using a'85-'86 32V bearing for the repaired area (apperantly the early bearings had a much larger surface area than the S4s) and S4 for the rest of the mains. This is when I saw the engine, just about ready to re assemble. A few months later, I wisted him again to look at an irregular miss (ignition related) and it ran amazingly (except for the slight miss). A few months later, he managed to hunt down the miss and the engine has been running like nothing ever happen to it ever since. This was 2, maybe 3 years ago. He came to see me when the engine was at 100% and I can assure everyone that the works was top notch.