Camshaft Gear Backlash

[hambone]

Back in 1843 when I was a gearing industrial designer, I recall how important it was to have a gear and pinion machined as a set, and to adjust the backlash very carefully to ensure strong silent operation. Now granted these are for refrigerator sized gearboxes with insane torque values. But I believe the fundamentals are the same.

I recall reading that camshaft gears used to be stamped with a number to ensure a proper mate. Well it doesn't seem like this is done anymore, so how does one know if their internal gears are happy? Do you just buy new parts, bolt em' in and take your chances?

[Amskeptic]

We must endeavor to save our old gears even as we change out our worn camshafts. Then all we have to do is call out our needs at overhaul time and wait for a fellow forum member to check in. 0 gears are the most common and found on pretty much all of the replacement gears sold by our favorite vendors. + gears in the upper ranges are getting rare +2 and +3 gears are hard to come by, I've been told. All gears in ranges above or below 3 are drying up.

I have personal experience with loose mesh. You do not want loose mesh. It makes your fresh overhaul sound like marbles in a vacuum cleaner at idle. Tight gears are whirrish, and the badly tight ones will peel aluminum or magnesium flakes off that look like chunks of vermiculite in the oil strainer plate.
Colin

[hambone]

So, the pinion is actually on the crankshaft. They probably are falsely referred to as GEARS in this application though. When one is ordering a new "pinion", is there any option as far as sizes go? Or do you get what you get?
More imporant (to me): how do I proceed on a typical new engine build? I'd imagine most people are just ordering what is available and hoping for the best.
I wonder how the factory is addressing this issue these days. Betcha the quality isn't German on those new injuns. Duh......

[Amskeptic]

So, the pinion is actually on the crankshaft. They probably are falsely referred to as GEARS in this application though.

They are gears, they qualify as gears. The definition of pinion we reserve for differential ring and pinions. As Jim mentioned, crank gears are the control variable, the cam gear is the test variable. Theoretically, the crank gear is indeed the pinion in the crank/cam set. I go for no, nada, nyet, slop in the mesh and no walk-out when crank is rotated backwards. To make life more challenging, I am finding some gears are machined slightly off-center, so you can have a gear that is meshed too tight and 180* away it is clicking sloppily. Somebody shoot me, I can't take it anymore.
Colin

[hambone]

Ok then: let's say I went ahead a bought new parts. Upon assembly things don't work out quite perfectly. What to do? Keep going back to the parts store until you get a proper match? Or is this irrelevant 90% of the time?

I was always taught that the pinion drives the gear. Maybe it's just different terminology in an automotive application vs industrial machinery.

[chitwnvw]

I've never heard of a new cam gear that wasn't a 0. So your option is to go and find a used gear. I'd think with type 1 this isn't that big of a deal.

How do you know if you chose wrong? It'll sound like they are hammering your soul away back there 'rat tat tat'. It sounds like gnomish blacksmiths are using their sledgehammers on your engine. It becomes a fixation. But it was a GEX so what do you expect? A good Gex, though, with 100k on it!

[hambone]

Jim I really appreciate taking the time to write all that. Helps me to get my head around "how things are done".
It seems that with a brand new case and everything assembled and machined properly, a 0 gear would probably work out OK. Indeed, that seems to be the current standard.

Can I reuse my old gear from the crankshaft, or am I better off getting a new one? I guess it depends on the wear.

Man I would love it if some engine rebuild guru would drop from the sky and teach me all of these secrets and fill my head with nonsense. Instead I have to harass you fine people. Well at least once I learn it I can pass it on too.

[Hippie]

I was always taught that the pinion drives the gear. Maybe it's just different terminology in an automotive application vs industrial machinery.

Depends. There is also "pinion" in a transmission which drives the drive shaft in a RWD car.
There is some overlap there.

Speaking of lap. I do the way I learned it in How to Rebuild Your Volkswagen Engine. With everything layed into the left half of the case, I slowly rotate the crankshaft backwards. If the camshaft lifts out of its bearing halves at any point, I keep lapping the gears together with course valve grinding compound. I have yet to find a new set of gears that was too loose, but this is in only the three builds I have done with both new crankshaft and camshaft gears. You also want no more than a barely perceptible "click, if any, when you work the two gears back and forth at all points of rotation. There is a spec. for this, but I don't have it handy.

The mechanic at Vee Village in Kansas City told me that excessive tightness is the problem they see, too. He regularly gets back rebuilds at about 1000 miles with a burnt number 4 bearing because the cam gear pushes the crankshaft gear down too hard and squeezes the oil film out of to crankshaft to bearing clearance space.

I also de-burr the crappy new gears with a fine file at the edges, if/as needed.

PM me for pictures if you want.

[hambone]

I'm gettin th Wilson book this week.
Thanks everybody. I'll prob have more questions once I get into the belly of the beast.

[Westy78]

I'm gettin th Wilson book this week.
Thanks everybody. I'll prob have more questions once I get into the belly of the beast.

Hey Bob, I've got the Wilson book. You can use it for as long as you need. I'll bring it this weekend.

[dhoch14]

hey hambone...

I went through this "fun" stuff this summer. Not that I'm too valuable of a resource, but if you want some help....feel free to ask.

I've got an unused engine stand in my garage if you are interested in borrowing.

-dave

[hambone]

Thanks Dave! I may take you up on that.