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8N crankshaft opinions welcome.

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Greg in Kansas

04-12-2001 05:00:34




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Hi everyone. I have 49 8N that has been due for overhaul for some time. I had a couple of cylinders down to about 50 psi. compression and an oil pressure problem. The pump seemed to have a problem picking up a prime at times. Sometimes it would pick up pressure immediately. About 30 psi. cold. At times it would take several minutes. I wouldn't wait on it if it would have been a fresh motor. Last Sat. I decided it was time. Now everything has been through the solvent tank and the block is on the engine stand. The crank had .030 under bearings on the mains and .040 under on the rods. The main journals mic right on the money, and look pretty good. The rod journals mic about .002 under and don't look as good as the mains, but still not bad. I really don't want to spend the money on a new crank, or have the rods built up and turned back down. I haven't been able to locate an acceptable used one in this area. I am inclined to take the crocus cloth to the rod journals, put new bearings in of the appropriate undersize and if the plastigage says the rod clearance is under .0035, drive on happily. Would any of you guys go this route yourself? If I am going the wrong direction please steer me right. Thank you.

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Greg in Kansas

04-12-2001 09:47:17




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 Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 05:00:34  
I want to thank all you guys for the help. I spent a lot of time on the phone this morning and found one at a tractor salvage :$175 and no gaurantees. I finally did find a local machinist who was familiar with these tractors. He will weld mine up and turn it and staighten it for $200. I think this is the route I am going to take since I am rebuilding it completely. He also said he has access to the .060 under bearings but they are copper and he does not like to recomend them. As for the oil pump issue, I am going to rebuild it of course, but I can't really find anything wrong with it. That bothers me.

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Jim

04-12-2001 10:42:01




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 Re: Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 09:47:17  
Greg, On the oil pump, look for wear on the housing(Frt bearing cap), on the gears themselves, and more than likely the bolt-on end plate/pickup tube has worn circles on it. A rebuild kit will take care of gears, resurfacing may take care of the end plate, housing is available but expensive. Check the end clearance (side to side)on the gears with some plastigage on the end plate when torque closed. The pickup tube have been known to come loose from the end plate, so check this very carefully. If it is cracked or has a hole at the joint, this would explain the loss of oil pressure on startup (sucking air)

Jim

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Greg in Kansas

04-12-2001 15:41:19




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 Re: Re: Re: 8N crankshaft opinions welcome. in reply to Jim, 04-12-2001 10:42:01  
Thanks Jim. It's been about 20 yrs. since I've been through an engine. There is some wear on the cover plate, maybe .008 or so deep. After I put it all back together in the vise I found a few problems. The driveshaft is way sloppy in it's bushing and shaft surface is pretty rough. And the gear backlash of .003 to .004 is closer to .030 to .040. I can see now why it had problems. I don't think I need the main cap and housing, but everything else will be new. Thanks again for making me look closer.

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Jim

04-12-2001 06:31:41




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 Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 05:00:34  
Greg
If I remember right I have seen .060 undersize rod bearings in the parts book from Walts Tractor. That would be my first option.

Jim



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bj/8N/mt

04-12-2001 07:19:29




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 Re: Re: 8N crankshaft opinions welcome. in reply to Jim, 04-12-2001 06:31:41  
there are .060 under bearings listed in Stevens catalogue

my first answer is still my opinion which is what you asked for

your mileage may vary



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Duner Wi

04-12-2001 06:29:30




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 Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 05:00:34  
It should work fine. If it was mine I would get the clearance down to less than .002 via shimming the bearing that fits in the cap. .0035 may work but as long as you are fixing why not get it to .002 or less. Tapered shim and flat shim stock is available. I would probably use the flat shim if shimming .002 or more. A light swipe with a file off the end of the bearing shell should take care of buckleing of the bearing due to the shim .
This takes time and may not be cost effective but for your own machine it works fine.
DO FIGURE OUT THE OIL PUMP PRIMMING PROBLEM.

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bj/8N/mt----d/b/a Rod Bearing

04-12-2001 06:05:05




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 Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 05:00:34  
If you had decent compression I could see an argument for putting some shim stock in there and slapping it back together. With 50 psi of compression you aren't that far from rings and valves and putting it back together with that crank is just putting off the inevitable. Unless of course the thing is seriously for sale.

your mileage may vary



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Babbitt Rod

04-12-2001 05:21:29




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 Re: 8N crankshaft opinions welcome. in reply to Greg in Kansas, 04-12-2001 05:00:34  
Greg, if you are going to put all new parts in the engine, pistons, sleeves, new valves, and all the other stuff, I (on my own engine) would find a better crank. my 2 cents worth.



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