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Checking for rod bend on a lathe

Posted: Sat Aug 03, 2019 8:08 pm
by rgould1910
Pretty simple. Made sure the cross slide was exactly perpendicular to the bed and the crank was centered. Used a 2 thou shim to hold the rod tight to the crank and swung the crank so the piston laid flat. Running a feeler guage along the skirt revealed any rod bend.
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Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 8:23 am
by Allan
Richard, that's a different take on rod alignment. I would be wanting some kind of check on the methodology. If you undid the rod and rotated it 180 degrees on the crankshaft, any discrepancy should see the difference in any clearance shifted from top to bottom or vice versa.

Allan from down under.

Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 9:58 am
by rgould1910
Allan, a check on things is accomplished by moving the carriage to where the piston rests against the other side of the cross slide. Since the cross slide is perpendicular to the bed and both sides are parallel, placing the piston on the other side confirms the reading you got initially. I prefer to keep the rod in the same position it will run in the car as opposed to reversing the rod on the crank. The methodology is no different than using a fixture with a stub ito mount the rod and a vertical plate against which the piston is checked.

Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 2:42 pm
by Jerry VanOoteghem
... but, you still need to check for twist.

Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 6:00 pm
by Philip
A false crank pin and a wrist pin in v blocks on a surface plate will show you
What is bent. And most are bent and I suspect they get that way soon after
They Re installed. Philip

Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 6:50 pm
by Kohnke Rebabbitting
Jerry VanOoteghem wrote:
Sun Aug 04, 2019 2:42 pm
... but, you still need to check for twist.

And the off set. Best to check the rod, only for, twist, bend, and off set. Far to many maybes with piston added.

Herm.

Re: Checking for rod bend on a lathe

Posted: Sun Aug 04, 2019 6:56 pm
by rgould1910
Absolutely must check for twist. That's the next step. I just now finished straightening bends. Three of the four had slight bends. The fourth was out quite a bit out. All are now within 2 thou deviation at the top land area measured one side against the other. By that I mean the max difference between the edge of the cross slide and the ring land area on one side vs the other was 2 thou measured by a feeler guage. The block has been accurately bored and honed to give 4 thou clearance. A max 2 thou deviation in bend will work well.