Crank Regrind of big ends?

[timbigden@icloud.com]

I’ve got a 1935 engine that’s been laying unused for years. On stripping it I’ve found the big ends to have rust staining (no desernable pits) they measure an average of 0.002” under the 1 5/16. Is it possible to have big end pins re ground? Rods would need re babetting anyway!

TIA

[Robert Leigh]

It is certainly possible to have the crankpins ground, but more important than undersize is the ovality. If the pins are circular (measure in two planes at right angles) any slight rust traces can probably be removed with a strip of fine emery cloth pulled back and forth all round the pin concerned. If the journals are circular and clean after doing that I suggest that you measure the metalling in the rods to check whether it matches the journals or whether remetalling is needed. I recommend John Kirkby in Croydon, S London for the metalling, and he would do grinding as well if it is needed. By entrusting the work to a vintage specialist such as John Kirkby it will be done right (I have used him over many years) and there has never been a problem. He would probably take only 5 thou off the journals if you ask him, rather than the 10 thou any one else would grind. This leaves more metal on the shaft for maximum strength and potential for future grinds if you get to needing another after much happy motoring!

[timbigden@icloud.com]

Thanks for your comprehensive reply, I will certainly call John Kirkby on Tuesday morning.
What would you suggest is max ovality, my worst pin is 0.004” which I suspect is too much?

Tim

[Robert Leigh]

I think 4 thou is too much, and at that you are probaly in for getting the regrind 10 thou under the original. In olden days it was not unusual to find crank pins 40 thou undersize after 4 regrinds. It sounds as though your crank has not had a great deal of use compared with many. Some of us take the view that a new crankshaft is a 'single premium insurance' against breakage. I have done this on both my engines. Having said that a lightly used original crank is unlikely to be a problem in ordinary light use.