Overhauling Farmall SMD Dumb Newbie Question

I am overhauling this SMD Farmall I just got and have new sleeves and pistons the bearings don't look real bad with minor scratches?? in them should I Just reuse Old rod and mains or can I just install new ones and not turn crank

To know that you have to measure the crank or have someone do it to see if it meets specs. The worst thing you can do is to put new bearings on an old crank without knowing if they fit or not.

I would NOT use old rod bearings with new pistons and rings. You would have a tight cylinder assembly and loose rod bearings. That can be a recipe for disaster!

You might be able to use the old mains but before you do, get some Plasi-Gauge at you local parts store (not expensive) and follow the instructions that come with it. It will tell you what the gap is between your crank main journals and main bearings. Your Tractor Repair Manual gives that gap spec. If that spec is larger than specified, then you run the risk of having low oil pressure. A thing you really don't want with new rings and rod bearings.

Another tip is to measure your rod bearing journals with a micrometer. You will probably find that they are a few thousandths undersize (again, you repair manual gives you the measurement for your rod journal diameter). They sell .002 over rod bearings on this site and other parts sites. That way you don't have to have your crank turned at a machine shop to .010 over if your rod journals are only out of spec by just a few thousandths.

The only visual inspection that is reliable is, if you can see copper showing on ANY of the bearings then they are most likely no good. All of them.

I don't have a manual for your tractor or I would have included the specs you need. If you don't have a manual I suggest you pick one up. It will be useful as long as you own your tractor and repair it yourself. There are LOTS of helpful guys on this site and if you don't want to invest in a manual, I'm sure someone will post them for you if you ask.

HTH
Dave

(quoted from post at 18:26:09 09/17/11) I am overhauling this SMD Farmall I just got and have new sleeves and pistons the bearings don't look real bad with minor scratches?? in them should I Just reuse Old rod and mains or can I just install new ones and not turn crank

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Like others have said, you need to use a micrometer and measure the main and rod bearing journals to determine if they are worn. Here are the specs:

Connecting rod journal diameter: 3.2475-3.2485
main bearing journal diameter 3.7475-3.7485

Maximum permissible main bearing clearance before reconditioning: .009"

maximum permissible journal out-of-roundness before reconditioning .004"

Main bearing running clearance: .0018-.0048
Connecting rod bearing running clearance: .0017-.0047

Maximum permissible connecting rod bearing clearance before reconditioning: .007"

Have the machine shop measure the crank and they can tell you. If you spent the money to get new pistons and sleeves, I would make certain the bottom is good. If something comes apart, you are going to have a disaster. I rebuilt my SMD a few years back. Very expensive to work on, but they are the neatest tractor around.

Also look on the back side of the bearing shell and it should be stamped standard or maybe .020 or .010 which means the crank has already been turned down, not a bad thing, you would just need undersized bearings.

i would if they look good ,if their was something wrong the bearings would show it,if you cant see copper run them it is not like you will put 10000 hours on this engine our will you?i reused the bearings in my b450 and a 320 waukesha sometimes you have no other choice if they are not available