Itinerant Air-Cooled

Are the number of teeth on the camshaft gear and on the camshaft drive gear prime?

whc03grady wrote: ↑

Tue Oct 29, 2019 12:04 am

Are the number of teeth on the camshaft gear and on the camshaft drive gear prime?

Well, the camshaft gear can't be, because it has to have exactly twice the number of teeth as the drive gear.

Thanks SlowLane. I had a long reply typed up on my phone and fell asleep on it... That saved me a lot of math and editing :)

Mitch, why do you ask? :)
Robbie

whc03grady wrote: ↑

Tue Oct 29, 2019 12:04 am

Are the number of teeth on the camshaft gear and on the camshaft drive gear prime?

52 Cam 26 Crank. I counted them when I had to file each and every one of them on Chloe's engine ...
Colin

SlowLane wrote: ↑

Tue Oct 29, 2019 7:53 am

Well, the camshaft gear can't be, because it has to have exactly twice the number of teeth as the drive gear.

Right. <slaps forehead>

asiab3 wrote: ↑

Tue Oct 29, 2019 11:18 am

Mitch, why do you ask? :)
Robbie

Because if they are prime (or even relatively prime), a given tooth on one won't regularly contact a given tooth on the other, thereby potentially reducing wear.

Amskeptic wrote: ↑

Sun Nov 03, 2019 8:39 am

52 Cam 26 Crank. I counted them when I had to file each and every one of them on Chloe's engine ...
Colin

I wish the crank teeth were lettered A-Z.

whc03grady wrote: ↑

Mon Nov 04, 2019 7:19 pm

Because if they are prime, a given tooth on one won't regularly contact a given tooth on the other, thereby potentially reducing wear.

VW floats a number of components to reduce wear.
a) distributor drive gear has a spring (YOU KNOW THIS) that allows the brass gear and pinion to vary their contact.
b) valves and lifters are designed to rotate in operation to spread the wear

c) piston rings are invited to rotate slowly with honing patterns that have just a tad of "english"

d) a generous .016" float between the rods and the crank journals and full-floating wrist pins

Colin

whc03grady wrote: ↑

Mon Nov 04, 2019 7:19 pm

Because if they are prime (or even relatively prime), a given tooth on one won't regularly contact a given tooth on the other, thereby potentially reducing wear.

Again, because the cam:crank rotational ratio must be 1:2, there is no choice but for the same teeth to meet every revolution. As to the actual number of teeth used, I suspect things like strength of materials and tooling constraints ( ie. if the cam/ crank gear teeth are the same size as the teeth on other gears elsewhere, that may help with production efficiencies) to be predominant.

I suspect the tooth size was a function of how many teeth were needed to mesh with such consistency that:

A) The camshaft would never have too much backlash
B) Increments could be made (economically) to the gear pitch to allow for crank/cam interface tolerance (+7 to -7 cam gears, 15 in all, for T1's. How many for T4's?)
C) The expansion rate of the dissimilar metals was compatible.

Or something like that.
Robbie

asiab3 wrote: ↑

Fri Nov 08, 2019 12:20 am

I suspect the tooth size was a function of how many teeth were needed to mesh with such consistency that:

A) The camshaft would never have too much backlash
B) Increments could be made (economically) to the gear pitch to allow for crank/cam interface tolerance (+7 to -7 cam gears, 15 in all, for T1's. How many for T4's?)
C) The expansion rate of the dissimilar metals was compatible.

Or something like that.
Robbie

Oh my ...
Packaging constraints on the one side, shear strength of magnesium/aluminum on the other. Helical cut at best achievable angle for quiet without drilling the camshaft through the ends of the engine, all of these considerations.
It is interesting to consider if any considerations were given to gear design size to control the range of mesh clearance through temperature range, but I am pretty sure they just said "f**ket, this thing is so damn noisy anyway, we just need a quiet mesh at warm idle." And that is exactly how it works out at "0" clearance cold.
Colin

Amskeptic wrote: ↑

Fri Nov 08, 2019 7:06 am

I am pretty sure they just said "f**ket, this thing is so damn noisy anyway, we just need a quiet mesh at warm idle." And that is exactly how it works out at "0" clearance cold.

I would love to believe that. 71whitewesty's SnoCat 1600 single port reminded me how quiet you can really get these things with a long enough exhaust! Like a late bus…

I was just thinking that Buddy's engine was sounding rather magnificent, until I pulled up to a friend's house with a fresh hydraulic lifter Type 4, full of perfectly sealed NOS exhaust parts Even our smog tech commented on the note… (Which is a brief dopamine rush until one realizes what it says about the state of our hobby community…)

asiab3 wrote: ↑

Fri Nov 08, 2019 7:30 pm

Amskeptic wrote: ↑

Fri Nov 08, 2019 7:06 am

I am pretty sure they just said "f**ket, this thing is so damn noisy anyway, we just need a quiet mesh at warm idle." And that is exactly how it works out at "0" clearance cold.

I would love to believe that. 71whitewesty's SnoCat 1600 single port reminded me how quiet you can really get these things with a long enough exhaust! Like a late bus…

I was just thinking that Buddy's engine was sounding rather magnificent, until I pulled up to a friend's house with a fresh hydraulic lifter Type 4, full of perfectly sealed NOS exhaust parts Even our smog tech commented on the note… (Which is a brief dopamine rush until one realizes what it says about the state of our hobby community…)

I like the clattery valve train noise of solid lifter VW engines. And my solid lifter 2.0 sounds better than my hydraulic lifter 2.0 in the cabin.
Colin