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neilca's Avatar
 
Join Date: Oct 1999
Location: Marietta, GA
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Grooving Main Bearings

I received a new set of main bearings from our host and was already set up on the lathe to groove them.

Here is a set of bearings already done with a another ready to go to the lathe. I did open up the case and the bearing holes to 3/16.




Here we are cutting on the lathe.




I grooved and opened the holes on all of the bearings. I will also be cross drilling all but the number 7 main in the crankshaft.

Old 10-17-2010, 09:01 AM
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Are you doing the cross drilling of the crank?
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Old 10-18-2010, 11:06 AM
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Looks great. i should send you a set to do for me
Old 10-18-2010, 07:48 PM
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My plan has been to drill the crank myself. I have an old dead crank I have been using for set up. I start with a carbide spotting drill to get through the case hardening, Then switch to a cobalt bit. I use cobalt here because when you break through the oil passage the cutting surface becomes very irregular and could break a carbide bit. My problem now is how to finish the holes. I need a radius on the hole. I just bought an inside radius tool, but I am not sure it will work. I don't like the idea of hitting it with a die grinder, for fear of it bouncing on the bearing surface.

I have worked out drilling out the passage plugs and threading them with an 8MX1.25 plug from Home Depot. Again I use a cobalt bit to open the passage to the size for tapping and then use a twisted cobalt TiN coated tap I bought from Grainger.

Sorry 0396, I barely have time to do my own stuff. I post it on this board so others can use the info to do their own. I know I have learned a lot from these boards.
Old 10-19-2010, 03:14 AM
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Great information Neil, Thanks.
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Old 10-19-2010, 07:47 AM
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Neil

Were you able to tap all the holes with that one tap?

The more I see of this, the more sense it makes to me to go whole hog and have the grooves cut in the crank instead of in the bearing. Should speed up and simplify the 40 or 100 hour rebuilds - just slap in new bearings out of the box.

But if I had a lathe maybe I'd see this route as less expensive overall.

I've always wondered if that weakened the crank, but Henry's super cranks are done that way so I suppose it doesn't.

Walt
Old 10-19-2010, 05:32 PM
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Walt,

I don't know yet if the tap will last for all the holes yet. I have tried it on my scrap crank with one hole. You do have to be careful not to over torque the tap. I can tell you a standard tap will not get you very far.

I tried grooving the crank, on my scrap crank. It worked well but it kind of freaks me out to take a cutter to a main journal. An old gunsmithing saying is you "rework the cheapest part". That is why I went with the bearings. If I were going to pay someone to cross drill and groove, Like Marine that does it all day long, I would groove the crank. They would do it without creating stress risers.
Old 10-20-2010, 03:22 AM
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Looks familiar



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Old 10-20-2010, 07:03 AM
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You are correct Tim. I used your earlier post to make my jig. I told you I learn a lot from this board.

Thanks,

neilca

Old 10-20-2010, 07:07 AM
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