Full Groove Bearing Wear (pic)

[82Waggy]

There has been some discussion lately about using full groove bearings.

Below is a pic of a full groove main cap bearing. These were in my used 401 when I tore it down for rebuild. Also shown is the number 7 rod bearing that had spun, the stock nylon timing gear, and a blown out lifter.



Note the chipped nylon teeth at the lower right corner of the timing gear - many more teeth were chewed up than those shown in the pic. IMO this is the number one cause of oil system failure. This stuff gets ground up and distributed throughout the system and clogs up oiling passages. In this case I found nylon stuck in the pan pickup strainer and elsewhere - I suspect it had everything to do with the failed lifter and spun #7 bearing. Engine was full of dino oil sludge as well. Sorry guys, but a valley bypass line is not going to fix what caused this bearing failure.

All main cap bearings looked like the one shown and all other rod bearings looked normal for wear, no signs of scoring on any crank journals including number 7 rod. Crank cleaned up 10/10 under.

In contrast, my 390 had been run on Mobile 1 most of its life (115k miles), looked clean as a whistle, and bearings looked good for another 100k miles. The 390 also had full groove main bearings (looked new).

I'm really torn about using full groove bearings. I know they provide half the oil film strength of non-grooved cap bearings but these seem to have held up well under the circumstances, and I like the idea of oiling the rod journals through a full 360 degrees of crank rotation that full groove bearings provide.

I already have a set of new Clevite half groove bearings for the rebuild - but.....

PS: You can see an oily gritty paste stuck to the spokes of the timing gear, the top of the left lifter, and down in the groove of the main bearing. This is the kind of stuff that was cloggin things up.

[Blown7]

I think full groove bearings would work satisfactory in your build, your not going to have high bearing load pressures. Or another option would be to cross drill the crankshaft that'll give you the same 360 degree crank main and throw oiling.

Who manufacturered of the old bearings?


Jeff

[jeepsr4ever]

The only real place the nylon can go is the pickup if the oil filter bypass isnt open. I think you can use the no groove bearings for your build. Sad to see spun bearings indeed...oh and I hate those nylon timing gears.. .what were they thinking?

[82Waggy]

I think full groove bearings would work satisfactory in your build, your not going to have high bearing load pressures. Or another option would be to cross drill the crankshaft that'll give you the same 360 degree crank main and throw oiling.

Who manufacturered of the old bearings?


Jeff

Wish I could answer that for you Jeff. Unfortunately I have since discarded them and don't recall that I discovered any markings.

My crank has already been prepped, so I won't be crossdrilling at this point. At the time, I discussed cross-drilling with my machinest and he talked me out of it. He also does not think full groove bearings are necessary these days - does not use them on anything he builds (which is a lot) - but what does he know LOL!

[82Waggy]

...oh and I hate those nylon timing gears.. .what were they thinking?

No kidding. Though not shown in the pic there are also several teeth completely missing and lots of radial cracks. Pure garbage and nuthin but a frap waiting to happen.

[Blown7]

Wish I could answer that for you Jeff. Unfortunately I have since discarded them and don't recall that I discovered any markings.


I find as with all the engines I do whether aircraft or automotive I never throw anything away until the build is done and running old parts are great for reference.

My crank has already been prepped, so I won't be crossdrilling at this point. At the time, I discussed cross-drilling with my machinest and he talked me out of it. He also does not think full groove bearings are necessary these days - does not use them on anything he builds (which is a lot) - but what does he know LOL!

What was the crank balanced to in IPS?
Full groove bearings aren't really needed , actually I can't think of a reason for using them unless your running heavy weight oil. I agree with him, I want more bearing load capacity myself..

[82Waggy]

What was the crank balanced to in IPS?
Full groove bearings aren't really needed , actually I can't think of a reason for using them unless your running heavy weight oil. I agree with him, I want more bearing load capacity myself..

Hell I don't know. I placed my trust in them for the balance job.

You know engineers, they love to change things. Guess I'll stick with the Clevites.

[Blown7]

Just looking at the balance holes on the crank, was the crank balanced with the vibration dampner and flexplate your going to use?

Jeff

[82Waggy]

Just looking at the balance holes on the crank, was the crank balanced with the vibration dampner and flexplate your going to use?

Jeff

Yes. Bearings and file fit rings were included as well.