How tight is too tight a press fit?

[SLK001]

I would disregard the 0.006" size differences and shoot for 0.002" MAX differences. Even the 0.002" size differences is at the MAX size for a FN5 class fit. With 0.002" difference, there is no way your pin is going to spin.

 

[JRaut]

Well, I really appreciate all the good advice on this one.

But it appears I got all hot and bothered over nothing. I did a test run tonight to see how it might work out with just a press and nothing else (no heat, no cold, no lube).

I drilled / reamed a hole (3 holes, actually) in the same material that the crankshaft is made from (4140 prehard), and the same thickness (0.355"). Used the same exact reamer, and a dowel pin from the same batch I intend to use for the crankshaft.

The reamer was 0.3105" and the dowel pin was 0.3125", so 0.002" of interference. That equates to 6.4 thou per inch of bore, for what it's worth.

I lined it up in my 3-ton Japanese made no-name arbor press, and PRESTO! And while it certainly was a tight squeeze, I didn't max out my arbor press. So figure 2 tons of force or so to drive it home.

Anyway, that'll be my route forward with pressing the crank pin into the crankshaft web. Unless someone convinces me otherwise...

 

[jmkasunich]

Well, I really appreciate all the good advice on this one.

But it appears I got all hot and bothered over nothing. I did a test run tonight to see how it might work out with just a press and nothing else (no heat, no cold, no lube).

I drilled / reamed a hole (3 holes, actually) in the same material that the crankshaft is made from (4140 prehard), and the same thickness (0.355"). Used the same exact reamer, and a dowel pin from the same batch I intend to use for the crankshaft.

The reamer was 0.3105" and the dowel pin was 0.3125", so 0.002" of interference. That equates to 6.4 thou per inch of bore, for what it's worth.

I lined it up in my 3-ton Japanese made no-name arbor press, and PRESTO! And while it certainly was a tight squeeze, I didn't max out my arbor press. So figure 2 tons of force or so to drive it home.

Anyway, that'll be my route forward with pressing the crank pin into the crankshaft web. Unless someone convinces me otherwise...

Just goes to prove the old saying that an ounce of actual experimenting is worth more than a ton of theory. Thanks for sharing the results with us!