Crank ground size vs new insert rod size

[MikeK]

Mike, Standard Model A Rod Pins are 1.498, to 1.499.
1.499 is to tight, you are going to smear some babbitt, so we always grind from 1.448 to 1.448-50.
The Standard Ford Rod Hole was cut to 1.500.
Thanks, Herm.

Herm, gogrannygo said he would be using new insert rods. I gave him size tolerances that are consistent with inserts. Yes, exactly what is "std" for a 1 1/2" journal is different between babbitt and inserts. Yet another Model A can of worms that others found out about the hard way!

 

[Kohnke Rebabbitting]

Mike, the way we would do it is get the rods first, then grind the shaft to fit for .001-50 thousandths clearance.

Herm.

 

[CarlG]

gogrannygo: You keep mentioning re-boring the head. Do you possibly mean re-boring the block?

 

[Chris in CT]

Two things/thoughts here.



2nd), Chris with regard to what you are saying about crankshafts being turned on centers vs. chucks, I am not sure I am following your logic or wisdom. Most machine I have been looking at have interchangeable chucks and centers on the heads. Correct me if I am wrong but the chucks are non-adjustable as far as run-out ( -as is centers ) however the heads on each end are adjustable in 4 directions to compensate for this. Therefore if this is fact, then a machinist who has the proper indicator for the machine that can measure 10 thousandths should surely have 100% capability to set-up the crank to those tolerances using centers. What am I missing?

.

Nothing, Brent, you are right on. Fact of the matter is that there are many cranks out there that are eff'd up with enormous run out at either the flywheel or timing gear. Many of these were set-up in the grinder on dead centers. Some were set-up by trying to find the average round of a main bearing(!!!). My statement was an uncomplicated way of saying that whatever else you did when grinding the crank, the flywheel flange and the timing gear surface must run true.

 

[Richard/Ca]

Mark your block or any parts you send out for work in a way you can indentafy it. I took my diamond block to a will known model a shop trusted them because they wrote my name on it. Went back about a month latter to check to see how things were going. Man said what Diamond black right then I new it was gone. He said that trere is no blocks in the shop with my name on it. Silly me for trusting some people. Richard/Ca.