MTFCA Forum

I had Ron's Machine shop pour a set of rods for me about 4 years ago. I abandoned that project and now am looking at the rods to use with my 27 project. I have two crankshafts that were reground in the past. In each case the width of the rod at the big end is anywhere from 20 to 50 thou smaller than the journal it rides in. I see on the MTFCA publication on engine rebuilding the width of the rod journals on the crank should be 1.505" presumably to allow 5 thou clearance. Mine journals are greater than that and the rods themselves vary in thickness about 15 thou. I wonder if crank grinders routinely widen the rod journals perhaps to grind out rust pits etc. I suspect they do. So what does a guy do with my problem? I hate to purchase another set of rods with widths to match a crank I have. What happens when there is too much clearance there? I've certainly seen it in the past. I see there is not enough clearance to cause a problem at the piston end as the wrist pins are recessed quite a bit and no way will the top of the rod hit the piston bosses. Will I hear a banging or rattle while driving down the road from the rods slapping the crank journals back and forth? Should I forget about it and put the engine together? Perplexed in Folsom.

Ford Rod prints state rod width at big end 1.480 -- 1.490 . I do not have the Crankshaft print.

I am surprised. The MTFCA restoration book The Engine says the crank journals are 1.505". It claims the numbers are from the Ford Service Course (Bulletins?)
I'll check and see if any of the Bulletins address it. If so the clearances should be between 15 and 25 thou. That surprises the heck out of me!
Thank you, Dean, I appreciate the input.
Any others?

[quote=rgould1910 post_id=19273 time=1553644114 user_id=1436]
I had Ron's Machine shop pour a set of rods for me about 4 years ago. I abandoned that project and now am looking at the rods to use with my 27 project. I have two crankshafts that were reground in the past. In each case the width of the rod at the big end is anywhere from 20 to 50 thou smaller than the journal it rides in. I see on the MTFCA publication on engine rebuilding the width of the rod journals on the crank should be 1.505" presumably to allow 5 thou clearance. Mine journals are greater than that and the rods themselves vary in thickness about 15 thou. I wonder if crank grinders routinely widen the rod journals perhaps to grind out rust pits etc. I suspect they do. So what does a guy do with my problem? I hate to purchase another set of rods with widths to match a crank I have. What happens when there is too much clearance there? I've certainly seen it in the past. I see there is not enough clearance to cause a problem at the piston end as the wrist pins are recessed quite a bit and no way will the top of the rod hit the piston bosses. Will I hear a banging or rattle while driving down the road from the rods slapping the crank journals back and forth? Should I forget about it and put the engine together? Perplexed in Folsom.
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The only way your rods will make a noise is if they are out of alignment, if everything else is right.

A standard Model T Rod is 1.500 wide.

Herm.

Herm is correct. If the rods are straight and not twisted, as they certainly should be, they will not be working backwards and forwards on the crank journals. I would rather see a wider gap than one below spec, to allow oil to get to the bearings more easily.

Allan from down under.

Have someone with a rod alining fixture check and adjust your new rods for you. In my experience, new rods from the major vendors and major manufacturers do require a check of alignment and adjustment before use if you want good longevity.

If you don’t choose to have them checked and they are out of alignment, you typically may not have any issues until you get to someplace in the 1,500 to 2,500 mile range. The misaligned rods will bounce forward and back on the journals until the babbitt compresses a bit, clearances open up, and the “dancing” rod begins to make noise from slapping fore and aft. The hammering eventually crystallizes the babbitt and pieces start to fall off. Sometimes the entire thrust surface falls off either a little at a time, or all at once. The crystallization goes all the way down to the bond with the steel and has the appearance that the bond failed.

Thanks for the helpful advice. I will test the rods for bend, twist and offset if I will use these rods. I can't help but remember that the engines I had rebuilt by David Daigh came back with close tolerances in the rod journal area. I have inspected all the cranks I have and only one has crank journals that fit my rod with what looks like the right clearance. All were reground at some point. Appears to me grinders grind away at the fillet areas to clean them up. If the one crank could clean up to fit my rods Id have it reground and use it. Still chewing on replacing the rods giving instructions to leave more width, which I can cut down to size.