Technical 4-banger insert rod bearing question

Hello, fellas... helping Dad put a 32-33 model B together, and when we torque mains down, crank turns over with ease using breaker bar.. but when he torques rod caps down, we can’t turn motor even with the breaker bar...

Did some mic’ing and also did plasti-gage, and looks like he has .0006-.0008 tenths of clearance, which is way tight looking at spec sheet for original build (Babbitt bearings)...

My question is, what are your thoughts about putting caps on rods w inserts, torquing nuts, and taking them to machine shop, where someone with Summen hone can take one thousandth’s out, and keep em round?


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What sort of rods and bearings? Thanks

 

The outer coating on the ID of the bearing probably isn't thick enough to hone .001" out of. You will be better off honing the rods housing bores to get most of it and maybe polish the crank to get the rest of it to achieve your clearance.

 

I'm not real clear here. Do you have inserts in the Rods or are they still Babbet?

 

How do your inserts look compared to the radius of the jurnol ends? Some inserts are made to clear on one end only for V8 use. Might not work as is depending on how your rod jurnols are ground.

 

Kiwi 4d,

I’m not sure what type rods and bearings are... just stopped by Dad’s, and he was struggling to turn engine manually, after torquing rod caps


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The rods have insert bearings.. I will get a pic next time I’m there.


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Rich Fox,
I haven’t inspected them closely... I will take a close look, and get some pics on here for some feedback.

Thanks to all you guys who posted with some helpful tips and direction.


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Thanks Cnc-dude... that does sound like a better option than hitting the bearings


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Rod inserts have a specific Rod journal to size to for proper fit once torqued to spec. I wouldn't open that up if it's sized correct. Some cranks get a larger radi at the counter balance end of rod throw. Wrong style inserts have been known to cause issues (so I've been told). Proper bearing fit is generally done by sizing the crank throw to the insert I.D. at torque spec.

 

Did you check how it turned one rod at a time?You might only have one out of spec doing it.If it starts turning hard with one,and gets worse then you know its all out of spec.Have a machinist measure the inside of the bearing/rod end with a mike,and then the crank journals.If you don't have the clearance you need you will have to either replace the rod/bearing,or if its close consider polishing the crank journals to get the correct clearance .