Engine: Cam gear backlash (lack thereof)

[Ian Mackellar]

Have had to line-bore main bearing tunnel on 232 V8 to resize. Machinist tells me that he only moved crank centre line .005" however I now have no cam gear back lash. This could have been a production issue as the reason for the line bore was to rectify the undersize bore on one of the mains that had to be original. Can anybody tell me how to reinstate the cam to crank centerline dimension. Do I have to regrind the cam or crank gear? I have had a similar problem with an earlier 289 but the cam backlash was ok but I had to redial the bell housing due to setting the crank higher into the block.Any tricks or suggestions?

[doofus]

Try a set of used gears? Luck Doofus

[JoeHall]

That just sux. I agree, try a used fiber gear. I have seen fiber gears that had worn to a point they definitely excessive backlash. But not sure about depth of the gears being worn. Still, it sounds like a well worn gear may be your best bet. I would not bother trying to find such a worn crank gear, its the fiber one that wears the most, by far.

With 259/289s, I specifically tell the machine shop, do NOT line bore. But I know, its a little late to mention that now.

Good luck.

[64studeavanti]

Did you put on one of the re-pop crank gears. I had to try several different ones to either A) get them on the crank, B) get any backlash on the cam gear. The backlash problem was with both a new re-pop aluminum cam gear and a good original Avanti cam gear.

[PackardV8]

With 259/289s, I specifically tell the machine shop, do NOT line bore. But I know, its a little late to mention that now.

Joe, rather than re-assemble a known problem in the main bores, first consider a line hone. If that doesn't correct it, line bore, then adjust cam/crank gear mesh with a skim cut on the lathe.

jack

[Dan Timberlake]

Hi Packard V8,

Are you suggesting creating backlash by turning down either gear's Outside Diameter ?

I haven't played with Studebaker gears yet, but generally speaking gear backlash should be controlled by the thickness/width of the gear teeth at the "pitch diameter", well in from the OD.

http://www.hondogarage.com/image_assets/500px-Backlash.svg.png

Increasing backlash would require "thinning" all the teeth on one gear while maintaining the scientific "involute" profile. That would require a fancy gear cutting machine.

[PackardV8]

Hi Packard V8,

Are you suggesting creating backlash by turning down either gear's Outside Diameter ?

I haven't played with Studebaker gears yet, but generally speaking gear backlash should be controlled by the thickness/width of the gear teeth at the "pitch diameter", well in from the OD.

http://www.hondogarage.com/image_assets/500px-Backlash.svg.png

Increasing backlash would require "thinning" all the teeth on one gear while maintaining the scientific "involute" profile. That would require a fancy gear cutting machine.

"Backlash" is not what we're finally concerned about. Many engine designs over the years have gear driven cams and inevitably some of those have to be line bored or line honed. Upon assembly, it's standard procedure to check the clearance between the tooth tips and root. If the line boring/honing has reduced this dimension below the desired clearance, usually the cam gear OD is lightly cut on a lathe. It's done every day.

FWIW, when fitting the aftermarket aluminum cam gears sold for Studes, the clearance has not always been precisely what it needs to be. Even when an engine block has not been line bored, it sometimes has been necessary to reduce the OD of the new cam gear. (The dimensional problem couldn't have been that way from the factory, as we know Studebaker foundry and machine work was always of impeccable quality :>)

jack vines

[Dwain G.]

Originally there were two cam gears available for the 232; Standard Limit, part#532129 and High Limit, part #532130. 532129 was dropped later and 532130 became the only one available. Now if a guy could find an original 532129 (a long shot) it might solve the problem.

[JoeHall]

Joe, rather than re-assemble a known problem in the main bores, first consider a line hone. If that doesn't correct it, line bore, then adjust cam/crank gear mesh with a skim cut on the lathe.

jack

Jack,
To me, careful inspection upon dis-assembly can save a lot of headaches. If the old main bearings were wearing OK, and no atypical wear pattern visible, I see no need to be concerned with line bore/hone. Yes? No?

[PackardV8]

Jack,
To me, careful inspection upon dis-assembly can save a lot of headaches. If the old main bearings were wearing OK, and no atypical wear pattern visible, I see no need to be concerned with line bore/hone. Yes? No?

Agree, if it ain't broke, don't fix it.

jack vines

[Ian Mackellar]

By all accounts it had been tinkered with before. Crank was .010/.010 when stripped down and car had only reasonable milage,under 100k. Also underspec main tunnel was evident with tight bearing. So it was checked and rectified, with line bore. Thanks all you guys for your help.

[jerezstude]

Jack
Have had backlash cam gear problems on several of my engine rebuilds, especially when using AL gears. Always checked pitch dia. to try to find gears that would work with limited success. Never though of reducing dia. to solve the problem. Thanks for the tip. Jerry Kurtz