Itinerant Air-Cooled

What would have caused this, and how do I prevent it in the future? (1978 2.0L Type IV GD Case)





Saddle:

vwlover77 wrote: ↑

Sun Oct 27, 2019 11:27 am

What would have caused this, and how do I prevent it in the future? (1978 2.0L Type IV GD Case)

A) Do you have evidence of shear on the thrust surface? It looks like something happened there. That could twist the shoulder of the bearing and cause a torsional crack.

B) Seems unlikely to me, but excessive crush might cause the same sort of global crack across the bearing. That would be an oversize bearing in the case dimension getting squished due to a standard case taking an .020 oversized bearing or a .020" case taking a .040" oversized bearing.
Do you have any bearing size stamped on the bearing shell?

Sheesh, Don.

Amskeptic wrote: ↑

Sun Oct 27, 2019 10:17 pm

A) Do you have evidence of shear on the thrust surface?

Are you referring to the thrust surface of the engine case? You can see from the photos of the pock marks in the bearing faces that something was going on there.

Amskeptic wrote: ↑

Sun Oct 27, 2019 10:17 pm

B) Do you have any bearing size stamped on the bearing shell?

There are no stamped markings left on the bearing shell. The machining marks are also gone. The bearing OD surface and the case seat surfaces seem to show fretting. Could it have been the opposite situation of an undersized bearing in the case dimension getting beaten around in there due to too much clearance?

I'm planning to borrow some good calipers from work to get measurements of the case, bearings, and crank.

Also related, is there excessive wear and/or heat damage evident on the flywheel shims?

vwlover77 wrote: ↑

Mon Oct 28, 2019 5:08 am

Are you referring to the thrust surface of the engine case? You can see from the photos of the pock marks in the bearing faces that something was going on there.

There are no stamped markings left on the bearing shell.

Yes, the actual rotation interface on the bearing itself looks damaged. I saw the shiny fretty stationary surface looked problematic as well. You're on this ...

Yes, measurement is required, and that is going to include a cleaned and torqued case with no bearings installed.
Then, measure your current bearings' ODs.
Colin

Amskeptic wrote: ↑

Mon Oct 28, 2019 8:36 am

I saw the shiny fretty stationary surface looked problematic as well.

Note the abrupt change in the fretting at what I assume are the case half boundaries. Are the seats not aligned properly? This engine started life as a GEX. Could the case halves be mismatched?

Amskeptic wrote: ↑

Mon Oct 28, 2019 8:36 am

Yes, measurement is required

Unfortunately, I don't have the required gauges to measure case bearing seat bores with the case halves assembled. However, I did use digital calipers to measure the seat diameters at the unassembled case half mating surfaces, and a micrometer to measure the bearing ODs.I also measured the crankshaft main bearing journal diameters with the micrometer and the bearing bores with the calipers (except #3, which is still captive to the crankshaft).

Long story short, it appears that the engine case has never been align-bored, as all my measurements of the case bearing seat diameters are less than 0.1mm larger than the original specifications in the Bentley.

The crankshaft has apparently been reground to a minus 0.25mm size as all of my measurements are 0.24mm less than the max limit of the original specs.

The bearing bores all measured around 0.1mm larger than the corresponding journal diameters.

Specifically for the cracked #1 bearing, I measured the following
- Bearing OD in 3 locations: 70.03mm, 70.12mm, 70.17mm
- Case seat bore: 70.06mm on both halves
- Bearing bore: 59.85mm
- Crank journal OD: 59.75mm

Regarding the case halves.....maybe they match. One case half is clearly stamped "072". On the other half, the first digit is illegible, but the the last two are definitely "72". Does it look like a leading zero to you?

Amskeptic wrote: ↑

Mon Oct 28, 2019 8:36 am

You're on this ...

New discovery: The #1 bearing seat on the right case half has a bulge in it right at the mating surface. I can see it and feel it with my finger. Would this have caused the bearing to crack, or is it a result of the cracked bearing?

Is this case junk?

vwlover77 wrote: ↑

Tue Oct 29, 2019 7:42 pm

The #1 bearing seat on the right case half has a bulge in it right at the mating surface.
Is this case junk?

Get a brand new flat razor blade. Rake the vicinity of the mating surface at the bulge.
Is there evidence of a raised area on the *flat surface* at the bulge? Take it down until the razor blade shows up as raking the whole surrounding area smoothly, like you are screeding the new pour on your concrete driveway.

Get the case align-bored if it checks out in all other ways.
Colin