babbit tolerance? .000?

[BRENT in 10-uh-C]

Originally Posted by Railcarmover

That's my point,time wasn't spent with the knife If a crank didn't spin easy,it was assembled and burnished by spinning on the 'break in stand'.They didn't use shim packs much either,as you say there was one spec, and machines were calibrated regularly.

You mentioned burnished on a break in stand. Do you have evidence of a break-in stand? If you are calling what I have pictured below as a break-in stand, I don't believe that is what this unit was.


Burnishing is accomplished by multiple heat cycles of spinning the crankshaft until the babbitt becomes slightly 'fluid-like' or 'plastic' then allowed to cool. The unit pictured below never spun for long due to there not any engine oil or trans lube in the assembly.


Your comment about them not using shim packs much kinda needs some clarification. First, the shims were specified to be 0.002 - 0.0025 in thickness. Ford did not line-bore the blocks and caps together. The babbitt in the blocks was specified to be bored to 1.623" - 1.624". The caps were specified to be bored to 1.618" - 1.620". The crankshaft main journals were to be ground to 1.622" - 1.624". When the three components were assembled, it effectively had 0.000" tolerances when you do the math, so 'one can assume there was indeed 0.000" clearance requiring burnishing however I have never seen pictures that show this process. To clarify my statement about what Damon said in the video, it is true that at one point in the original machining process where the babbitt did have 0.000" clearance however it did not leave the factory with that clearance. That would be like saying the engine cylinder cases (blocks) were bored to 3.8735" in size. While that is accurate statement, that was not the finished bore size after honing.

[mike657894]

interesting. So assembled with .001-.002 tight on the block mains and .005 tight on the main caps and 3-4 or so shims to give a .001-.002 tolerance on crank from factory?

[Railcarmover]

Originally Posted by BRENT in 10-uh-C

You mentioned burnished on a break in stand. Do you have evidence of a break-in stand? If you are calling what I have pictured below as a break-in stand, I don't believe that is what this unit was.


Burnishing is accomplished by multiple heat cycles of spinning the crankshaft until the babbitt becomes slightly 'fluid-like' or 'plastic' then allowed to cool. The unit pictured below never spun for long due to there not any engine oil or trans lube in the assembly.


Your comment about them not using shim packs much kinda needs some clarification. First, the shims were specified to be 0.002 - 0.0025 in thickness. Ford did not line-bore the blocks and caps together. The babbitt in the blocks was specified to be bored to 1.623" - 1.624". The caps were specified to be bored to 1.618" - 1.620". The crankshaft main journals were to be ground to 1.622" - 1.624". When the three components were assembled, it effectively had 0.000" tolerances when you do the math, so 'one can assume there was indeed 0.000" clearance requiring burnishing however I have never seen pictures that show this process. To clarify my statement about what Damon said in the video, it is true that at one point in the original machining process where the babbitt did have 0.000" clearance however it did not leave the factory with that clearance. That would be like saying the engine cylinder cases (blocks) were bored to 3.8735" in size. While that is accurate statement, that was not the finished bore size after honing.

it appears those model T engines were set in a stand and spun by an electric motor,that large meter behind them I'm sure read amperage,the load on the motor told them if it was spinning at their prescribed load for acceptable resistance of an assembly,in essence a 'break in' stand,in fact Ford did not fire the engines till the car was completed at assembly,so that stand was all the break in the engine got.The same technique was used with the model a engine. I don't know if Ford line bored or not,it would stand to reason that they did,its the only true way to set the main bearings in alignment,just cutting bores on caps to a .005 difference than the bore on the block makes no sense.
Burnishing is the act of polishing metal with metal,ie spinning a crankshaft in a babbit bearing can help set the bearing through polishing..a process that does work with minimal lubrication,which would slow the desired effect.would be interesting to know how ford approached that.