Those mysterious main bearings

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Those mysterious main bearings

Post by AdminJeff » Fri Sep 20, 2019 5:41 pm

I just pulled apart my 3rd 26/27 motor inside of a week. The last one looked great, except for the rear main. ALL of these motors had issues with that bearing. I thought it would be educational to show pics of these so folks understand how important it is to have clean oil running thru these motors. Seeing is believing. There is just no protection for these bearings if there's crap in the motor.

The last 2 shots were of motors that showed no signs of any damage. in fact, the rods were almost perfect as was each of the transmissions. My motor on the other hand, well, lets just say that I had a "steep" learning curve going up my hill. Lots of rod babbit was floating around in there.

This is my motor:
These last 2 I just pulled apart. Obviously, I don't know the history on these motors but it is interesting nonetheless. The last one looks the best but has an interesting crack in it.

Obviously none of these are optimal, but the middle one looks like it could be serviceable for a while. Thoughts on this? All the caps also looked pretty good except mine (of course).
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Norman Kling
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Re: Those mysterious main bearings

Post by Norman Kling » Fri Sep 20, 2019 7:59 pm

Main bearings should show more wear on the cap than in the block. This is because of both the weight of the crankshaft and also the downward push of the power stroke. The rear main also supports the weight of the flywheel and transmission.

Art Wilson
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Re: Those mysterious main bearings

Post by Art Wilson » Sat Sep 21, 2019 12:10 am

I found on a couple of 1925 1926 blocks I disassembled that the rear main bearings had a considerable amount of contaminants embedded in them. On earlier engines that was not the case.
I believe this is because the later blocks have oil supply holes for the rear main drilled on both the front side and rear side of the rear web. The earlier engines only have the oil supply hole on the front side of the web. The rear side of the web has a lot of oil and crud splashed up on it from the flywheel, whereas the front-side oil supply hole is in a cleaner environment so to speak.
My observations are limited to only a few engines so I would not put a whole lot of weight on my findings, but the amount of crud on the later bearings was substantially more than the earlier ones.

Wayne Sheldon
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Re: Those mysterious main bearings

Post by Wayne Sheldon » Sat Sep 21, 2019 1:56 am

All that gouging trails after the hole where tiny bits of everything from cotter keys to road dirt finds its way in and splashes into the oil hole. A well cleaned engine, with reasonable oil changes should not have that problem. One of the block mains you show should be fine for tens of thousands of miles with little more than a good cleaning and checking the crankshaft for proper fit. The one with the crack should not be run except as a near emergency and for a VERY SHORT time! Basically, re-Babbitt or bust!
The other one you show (with the most gouging!) also has a suspicious maybe beginnings of a crack. It would need to be very carefully examined, and may also be re-Babbitt only. IF (my big "IF" again) what I see can basically be determined to not be a failing Babbitt pour (the usual cause of such cracks), the gouging, while a bit much, is not enough to seriously reduce the life expectancy of the main. As Norman K points out, it is the cap that takes the most weight and force, so a relatively minor loss of bearing surface in the block will not reduce the bearing's life substantially. Some gouging actually can aid in oil distribution within the bearing.

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Re: Those mysterious main bearings

Post by It's Bill » Sat Sep 21, 2019 7:05 am

I am no expert in T engines, but the cracks look like they are propagating from the ends of the oil slots, which appear to be cut to full depth right out to the ends. Can these slots be tapered to zero depth as they approach the end of the cut? In other words, cut them to resemble a rounded keyway?

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Re: Those mysterious main bearings

Post by Kerry » Sat Sep 21, 2019 7:53 am

Yes Bill, it is a problem, many a bearing end up as pieces.
I cut the block deeper so the oil slots are still babbitt.
Robbie's T block 007.JPG

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