Crankshaft grinding...

Reply Subscribe

Thread Tools

Search this Thread

Apr 9, 2014 | 01:02 PM

TMI

Thread Starter

Laughing Gas

Joined: Nov 2002

Posts: 1,198

Likes: 9

From: Fairmont

Crankshaft grinding...

After grinding so many crankshafts, I have seen a consistency in the 400 Ford crank. I set the machine up on the #2 journal, then I do not change the stroke.

I have found that as I go to #1, #3 then #4 journal, that #1 is always off. In fact it is off so far that sometimes I can't get it to clean up at a .010" undersize.

#3 & #4 are very close to #2. This video shows that without changing the stroke, how different they are.

Enjoy...

Apr 9, 2014 | 04:06 PM

BuzzLOL

Laughing Gas

Joined: Dec 2012

Posts: 801

Likes: 7

From: Toledo, Ohio

. Are you saying stock we're getting more or less than 4" stroke on #1... or the crank is twisted?

Apr 9, 2014 | 10:12 PM

TMI

Thread Starter

Laughing Gas

Joined: Nov 2002

Posts: 1,198

Likes: 9

From: Fairmont

On the average, there is extra stroke.
Maybe .005"-.010" extra stroke.

Apr 10, 2014 | 08:40 AM

hollenjoe

Posting Guru

Joined: Jul 2007

Posts: 1,355

Likes: 1

Thats why you prefer to send your reground cranks already .010 over right? Quality control on 70s stuff was meh, were close enough was good enough...

Apr 10, 2014 | 10:17 AM

BuzzLOL

Laughing Gas

Joined: Dec 2012

Posts: 801

Likes: 7

From: Toledo, Ohio

Quote:

Originally Posted by hollenjoe

Thats why you prefer to send your reground cranks already .010 over right? Quality control on 70s stuff was meh, were close enough was good enough...

. Actually, the terminology is .010" UNDER... unless you're talking about raw casting cranks needing their first final grind...

. So, do you adjust specially for #1 compared to 2 - 4? Or just grind more than .010" off to make all throws the same stroke? i.e. .020" or more undersize...

. On a stock crank engine, this means the quench for #1 throw should be measured/figured separately from 2 - 4... if rebuilding with a stock non-reground crank, maybe a box of pistons' compression heights should be measured precisely, and the two pistons with lowest height used on the #1 crank throw... to balance out quench and compression ratio among all 8 cylinders...

. Wonder if this is over the whole run of years of 400 cranks, or just one season or production crank grinding machine... usually production precision grinders are tested at least hourly, shiftly, or daily... and measurements to the .0001" are used... but if an inspector's test fixture is incorrect, the problem could last a long time...

Apr 10, 2014 | 10:38 AM

hollenjoe

Posting Guru

Joined: Jul 2007

Posts: 1,355

Likes: 1

yes i meant 0.010 under, my bad

Apr 10, 2014 | 10:50 AM

BuzzLOL

Laughing Gas

Joined: Dec 2012

Posts: 801

Likes: 7

From: Toledo, Ohio

. Yes, a common mistake, especially when talking about the bearings, because the 'undersize' bearings are actually thicker than the stock ones... and most of us deal more with the bearings than with the crank throws... so we get to thinking in terms of something 'bigger' ('oversize') needed... instead of the 'undersize' on the crank... and bearings are sold via crank size terminology...