timing gear backlash

Tom Endy

Tom Endy

Well-known member
Can some knowledgeable person advise what the backlash min and max should be between the cam gear and the crank gear. Also what is the allowable difference at various points on the circumference.

Tom Endy
 
I think it should be in the .003-.005" range and if they get near .010" you'll hear about it.

Regarding what I think you're really asking, the difference, I can't say. I've just checked them in one place and made the decision what to do. Guess I'll start checking in a couple places and see what happens.
 
I set mine at .004 on all motors I build no matter what gear it has. The lash should be the same at all teeth around the gear. If there is a difference, something is wrong.
 
James Rogers said:
I set mine at .004 on all motors I build no matter what gear it has. The lash should be the same at all teeth around the gear. If there is a difference, something is wrong.
Click to expand...

Thanks to all who replied. Could someone explain to me how I would go about setting the timing gear backlash?

Tom Endy
 
undersize/oversize timing gear iz all I know

if you are having a lot of trouble i suspect the crank gear is a cheapo china job
 
Tom Endy said:
Thanks to all who replied. Could someone explain to me how I would go about setting the timing gear backlash?

Tom Endy
Click to expand...
You dont really "set" it. You check it, and if its not in an acceptable range, you have to change one or both gears. It is possible that the same two gears would check differently in another block, if the cam and crank centerlines were different.
Good Luck!:)
 
Ref The Model A Service Bulletins, Page 574 'CLEARANCES AND LIMITS USED IN ASSEMBLY OF MODEL "A" ENGINES'. Time gear backlash .004".
 
James Rogers said:
I set mine at .004 on all motors I build no matter what gear it has. The lash should be the same at all teeth around the gear. If there is a difference, something is wrong.
Click to expand...

Tom
That kind of threw me too.:eek: I thought geez my A is missing something because there is no way to set the lash on mine other than changing gears.
Joe
 
I can set it because I do it when I bore the mains. Once the mains are bored, if it is incorrect you can only adjust it with the gears and that is inconsistent at best.
 
I never have quite got the issuance of oversize cam gears. Since I would understand that if a proper align bore operation would set the crank, and cam gear center lines to a proper amount, any shim removal might bring the crank center line up a bit. I was told that running newspaper between the gear teeth and turning over by hand, if paper becomes cut backlash is insufficient. Removing a shim from mains is really only taking up wear that took place in the main cap, and not the block. I would think a proper set up for align boring can't be overemphasized.
 
I wonder if I know how to check backlash, as I detected zero on my gear(brass), when I had the cover off, this was at about 25,000 miles.
 
KR500 said:
I never have quite got the issuance of oversize cam gears. Since I would understand that if a proper align bore operation would set the crank, and cam gear center lines to a proper amount, any shim removal might bring the crank center line up a bit. I was told that running newspaper between the gear teeth and turning over by hand, if paper becomes cut backlash is insufficient. Removing a shim from mains is really only taking up wear that took place in the main cap, and not the block. I would think a proper set up for align boring can't be overemphasized.
Click to expand...

Oversize gears are to over come poor align boring of the main bearing tunnel something which should not happen with a jig in good condition and well set up
also to over come camshaft and camshaft tunnel wear something not addressed by many
Most of the camshaft tunnels I have seen have enough wear to need rebushing ( bored out and new bearings installed )
While the camshaft bearing journals normally have very little wear most regrinders will take a few thou off to clean up the surface
 
While on the subject of cam and crankshaft centerlines being off, sometimes an undersize gear will save an engine that would otherwise have to be redone. Dan McEachern can furnish undersize as well as oversize timing gears. Most other suppliers only offer standard and oversize gears.
 
Dan just made me a couple of gears to take care of that very problem. It was a fresh babbitt job that had not been done correctly. Saved the motor. But to answer the question .003 to .005 seems to be the number to hit + or - .001
And measure in four places around the cam gear.
 
Hi Tom,

I had my crank counterweighted by Mr. Ron Kelly in TX, whereby he always replaces the crank gear with a new one made by Mr. Dan McEachern.

I next installed the same fiber gear with a metal center because it met clearance specs & was not at all loose. Sounded great initially, but after maybe 50 miles, ticking started & it got worse.

I called Mr. Dan McEachern who knew Mr. Kelley used his crank gear & Mr. Dan recommended his aluminum gear. He thought my new Stipe IB increase cam lift "may" have loosened the metal/fiber gear.

I changed the timing gear out to aluminum, & the engine immediately stopped ticking & was totally noiseless.

On my next engine I will get a Mr. Dan McEachern crank gear with his perfectly "matching" aluminum timing gear. This gentleman is truly a perfectionists.

Furthermore, looks like every time a Model A fiber timing gear breaks a few teeth, it happens like on a Christmas Eve morning, 792 miles away from home, in the middle of a Christmas Parade, with two (2) dogs, a wife, & two (2) grandkids in the car with everyone having to go the bathroom; plus it is raining so hard, the "Rain-X" washed away .

I'll never use a Model A fiber gear again -- one fiber gear failure is enough. LOL
 
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