ford 850 rebuild

looking for info on my ford 850 build, doing a complete rebuild on 1955 850 with 172 gas engine. ordered new crank, 4.0 overbore pistons and sleeves, when installing crank, main bearings (std) have right at .002 clearance which seems perfect but the rod bearings (std) are between .001 and .0015 when torqued to 45 ft pounds picture included. looking for what others think about this clearance. I talked to yesterdays tractor parts where all parts were purchased and they confirmed the correct crankshaft sent. opinions on the rod bearing clearance please.
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Can you turn the crank when the bearing is installed ? If you can after every bearing is installed. I would run with it.

It takes a lot to turn it not sure it would turn with all caps on and torqued with the starter. my shop manual calls for the measurement on the rod journal to be 2.2988-2.2978 this one measures 2.3125 on all journals I just don't trust that this is really the correct crank. I actually think it may be a diesel crank.

went back to book and diesel crank journals are the same size, so this is really a head scratcher. would hate to sieze a new motor because of it. comments appreciated

If all are in that category, I would schmeeeere Lubriplate Engine Building Grease on them and run it. Jim

They will surely exchange it. If not it should polish out. At a crank regrinder shop.

I have a Motors brand manual from the early 70s for heavy duty trucks in the back. In the back I t has these farm tractor spec pages as you can see in the picture it shows a varying allows clearance of 0.0004 - 0.002 in. so what you are showing us should be well within that spec. It does not show a 850 but the line above my fingers shows an 801, 901 which has the same 172 engine as is shown by the 3.90 inch bore shown in the first column. The old mechanic that showed me how to overhaul engines told me to use this little trick as a final check. When you get the rod torqued take a small hammer and tap on it on the outside of where the bolt goes through, kind of at an angle. Small taps like youre trying to smash grains of salt on a steel plate. While youre doing this, hold the rod between your thumb and forefinger and feel for movement sideways and watch as well. Tap it from both directions, should move back and forth by the amount of side clearance it has. If you get this sideways movement the rod is loose enough to run just fine.
Editing to add: If the hammer test does not show movement then there should be concern and measures taken to investigate the problem before the final assembly is complete and ready to move on with installation of the pan etc.


This post was edited by used red MN on 08/04/2023 at 10:06 pm.

There is 172 gas engines out there diesel cranks in them. I have seen a 61 or 62 801 gas with diesel crank from factory and I have put diesel crank in gas power unit, worked fine.

With that oil clearance I would put it together and run it.Size of the crank pin is really unimportant if you have the correct oil clearance on both the rods and mains. I would hate to see the oil clearance on the smaller pin size as it would almost be loose enough to knock or pound out from use. I would worry more about it being to loose than it being to tight. Sounds like it is just about right to me.

Have you checked the mike's calibration against a known standard? That would be my first suspicion vs a crank being oversied.

Photo dropped off when I did the edit, cannot get it to load again. Hopefully it will post here.

dreid52 welcome to YT! I was taking a break from house painting when I replied yesterday so I did not notice you were new here. The crank pin numbers you gave us cannot be right. Your numbers 0.0137 in. difference. That just cannot be right. If it was off that much that plastigauge would have been squeezed into particles and the crank would definitely not turn. I agree about checking your mic to the standard. I certainly hope you oiled the rings and cylinders when you slid them in and you are using oil or assembly lube on the bearings for final assembly. Maybe you have moved on, hope it turns out okay for you.