the biggest i have raced is 0.030 over, i have one crank here i hurt racing and was told i could get a 0.040 over bearing, so i don`t think it will lead to a premature failure problems, i will have to see if i ever use that crank
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| Max crank regrind? https://slantsix.org/forum/viewtopic.php?t=26288 |
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| Author: | sandy in BC [ Tue Dec 18, 2007 9:38 am ] |
| Post subject: | Max crank regrind? |
Turns out the mains are OK but one rod bearing moved enough to pile up a rod journal ( already 10 under) The crank has less than 40,000 miles on it .......originally from a 1 1/2 ton dump truck.....it matches my block......rotates in the mains like a dream. Whats my maximum oversize? |
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| Author: | terrylittlejohn [ Tue Dec 18, 2007 11:43 am ] |
| Post subject: | oversize |
the biggest i have raced is 0.030 over, i have one crank here i hurt racing and was told i could get a 0.040 over bearing, so i don`t think it will lead to a premature failure problems, i will have to see if i ever use that crank
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| Author: | Joshie225 [ Tue Dec 18, 2007 12:02 pm ] |
| Post subject: | |
I'd say the smallest rod journal you can safely run is the smallest bearing you can find. |
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| Author: | Doctor Dodge [ Tue Dec 18, 2007 12:44 pm ] |
| Post subject: | |
I have see .040 u/s in the past... I am not sure if they are available these days. Welding-up the journal is also an option. DD |
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| Author: | Dart270 [ Tue Dec 18, 2007 1:55 pm ] |
| Post subject: | |
I believe I have seen 0.060"-under bearings listed at some point, and Cameron Tilley says this is what he uses on his race motors. Apparently you can get 0.060" down undah. This gets rid of the factory undercut so you have a properlay radiused journal flowing into the crank throw/bob. I have only run 0.010"-under, but I would have no problem going as small as.... Lou |
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| Author: | CARS [ Tue Dec 18, 2007 3:04 pm ] |
| Post subject: | |
Wouldn't this be a good time to off-set grind the crank to get the piston to the top of the block? |
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| Author: | Joshie225 [ Tue Dec 18, 2007 3:27 pm ] |
| Post subject: | |
Quote: Wouldn't this be a good time to off-set grind the crank to get the piston to the top of the block?
Can't do it with a 225. You have to weld the crank to get that much stroke increase.
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| Author: | ceej [ Tue Dec 18, 2007 4:43 pm ] |
| Post subject: | |
Depending on what you wish to accomplish, this would be a good time to grind for a different rod big end thickness. Sixty under can put you in seven inch Ford Flathead rods.... For less drag, the narrower rod journal with smaller diameter is a way to go.. Check Eagle rods for the flatheads. CJ |
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| Author: | Dusty Desks [ Tue Dec 18, 2007 9:05 pm ] |
| Post subject: | |
If you regrind the rod journal not over .010, there is still a slight drop off near the edge of the machined & polished part, and the radius of the fillet is not affected; Chrysler recommends not regrinding more than .012 inch. Why is that? Is there some possible problem with regrinding a new radius fillet at the edge with greater undersizes, possibly cutting through some surface metal treatment (nitriding or shot peening?), and in case you do have to regrind to a larger undersize to save from scrapping a crankshaft are you supposed to machine a slight drop off at the edge of the part of the journal which touches the bearing to duplicate the original contour? Also, I noticed that original Mopar brand replacement rod bearing shells for the forged crankshaft are 1 1/16 inch wide while all the aftermarket brands I have seen have 15/16 inch wide bearings, and I think the OEM factory-installed bearings are also 15/16 inch wide; why is that? |
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| Author: | Charrlie_S [ Wed Dec 19, 2007 4:30 am ] |
| Post subject: | |
The crankshaft journals are "tufftrited", but I was under the impression the tufftriding was much less then .010. Something in the order of .001-.002 deep. The bearing specs in the 1966 FSM is 1.015 wide for the rod bearing. I miked two differend brand rod bearings I have on the shelf and got .990 and .995 wide. I do not have any Mopar factory rod bearings to check. It might be that the aftermarket makes the bearing just slightly narrower so there is no chance of the new bearing riding on an unworn section of the journal, if the bearing are just replaced, without the crank being serviced. When I say unworn, I am talking about tenths of thousands, and this is just a guess. |
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| Author: | slantzilla [ Wed Dec 19, 2007 6:05 am ] |
| Post subject: | |
Sandy, it wouldn't scare me a bit to just grind one journal. I know you can get at least a .030" under bearing. 
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| Author: | Charrlie_S [ Wed Dec 19, 2007 6:12 am ] |
| Post subject: | |
Quote: Sandy, it wouldn't scare me a bit to just grind one journal. I know you can get at least a .030" under bearing.
I aggree
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| Author: | sandy in BC [ Wed Dec 19, 2007 6:41 am ] |
| Post subject: | |
I actually have 3 scuffed journals...1 of which is not so nice. It goes to the sheen shop today for an acurrate? analysis.... |
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| Author: | AnotherSix [ Thu Dec 20, 2007 1:58 pm ] |
| Post subject: | |
I would do what I had to and not worry about it. It is not that much of a decrease in area for that to be a problem. I have read that too thick a bearing shell can run hot, but it is the oil that cools it and I have never seen any evidence of heat problems on a journal that was not toast for some other reason. The radius on the crank can be an issue, and I suspect this is why many bearings are narrower, to avoid contact in this area. It is not usually reground with a new radius, I have seen many cranks with a step in that area. I had to chamfer a set of bearings on a chevy that had a larger raduis on the crank than normal. Since then I normally take a quick look on assembly to make sure this is not a problem. I would give the rods a real good check and maybe resize them while they are out. It might be that part of the bad rep on undersizes has to do with a problem with the rods or block. If they are not straight and round, the new undersize bearing has trouble and gets blamed. |
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| Author: | sandy in BC [ Fri Dec 21, 2007 7:12 am ] |
| Post subject: | |
I took the crank to the machine shop. (they were impressed by the way I had it bagged) They seemed interested in turning the rod bearings down 60 and reradiusing. I asked them to figure how much the bad journal needs to be done.\ Rock Auto has Sealed Power bearings up to 40 thou in singles $8 and unplated 60 thou sets for under $50.... |
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