Identifying the correct crank gear for an aluminum timing gear

m_mman

I previously talked about doing preventive timing gear work on my 1942 eight.  I have only had it about 6 months and while it does run well I dont know what type of cam gear it is currently running, fiber or aluminum. (why pull the cover until you are ready to replace something?) 

It came to me with a box of loose parts in the trunk and I just recently went back and looked through them. Turns out there are 3 fiber gears in there and an aluminum cam gear. <great!> and one crank gear. (all brand new) 

So, I can now remove the covers and if it is a fiber gear I will certainly want to change it to the aluminum version.

HOWEVER, I understand that the crank gear is different for fiber and aluminum. How do you identify if a crank gear is correct for an aluminum or fiber type cam gear?  Are there numbers or other things to look for? 

Geoff

No, the crank gear is the same for both fibre and alloy.   The difference was before 1941 the angle of the teeth was different, so you can't intechange with the earlier versions.   

Old Fogey UK

Is there an easy way for an idiot like myself to measure the teeth angle ?
Or should I take both my gears into an engineering workshop and get them to do it for me ?

allan

The Hudson gears I have, have a part number on them.

Toddh

As a reminder, the front engine support plate needs to be modified to accept the new aluminum gear. The bolt hole directly behind the timing gear needs to be chamfered to allows the use of a flat head machine screw in place of the bolt to provide clearance.  

54coupe

I would think you could fully mesh the teeth of two gears together, and see if the faces of the gears were parallel... if not, the angles are not the same.

Toddh

You could also set the gear on a surface table and use a protractor to determine the angle

Old Fogey UK

My alloy gear is from a batch made for the ROC many years ago (so I don't know if it's the pre or post 1941 type) and the steel gear (which is chipped and therefore needs replacement) doesn't have a part number, so I think it'll be a trip to the engineering shop for me.

Geoff

Mesh the gears and see if they bottom in each other.  if there is a large gap at the bottom they are mismatched.

hasktavern1

Old Fogey, If you need or want it, I can send you a copy of the original instruction sheet which came with the circa 1940s gear change kits.  A fairly simple process...the only difficulty I had was removing the confounded harmonic balancer.

Geoff

You can visually determine the gears too, but  you have to have two different types to note the difference.  The original gears were 14-1/2 deg pitch.   Now to clear confusion, the pitch is not the angle at which the gears are cut in relation the  front face, but pitch is the angle they are cut in the groove, Hence the earlier gears have a wider notch at the bottom of the groove, and thinner peak, if you can visualise this.  The later 20 deg. gears have a narrower groove at the bottom, and thinner peak, hence there is more material at the base, which makes it stronger.   The earlier gears used to break off at the base.   I probably haven't described it  sufficiently, but if you have a pair of gears, they should mesh deeply, with very little light showing between the  tooth and base.  Hope this helps.

35 Terraplane

Here’s a pic of a set I have. Both are marked 20. You can the 20 on the larger cam gear near the crossed out 10 on my desk blotter. 

Geoff

Thank you for the pic, it shows exactly what I described as full depth mesh.  It also shows the thicker metal at the base of the teeth.  

Old Fogey UK

hasktavern1 said:

Old Fogey, If you need or want it, I can send you a copy of the original instruction sheet which came with the circa 1940s gear change kits.  A fairly simple process...the only difficulty I had was removing the confounded harmonic balancer.

Yes please, I'd really appreciate that !

Old Fogey UK

35 Terraplane said:

Here’s a pic of a set I have. Both are marked 20. You can the 20 on the larger cam gear near the crossed out 10 on my desk blotter. 

That's really helpful, thank you - and also to Geoff.
I'll post a pic of my gears later today.

Hans

When I place and early cam fiber gear flat on the bench and the later cam fiber gear next to it, the later gear is thicker.

I Identify them that way.

While I have crank gears for use with the Aluminum cam gear, I have never compared the crank gears for thickness in the same way.

Goeff, perhaps you can provide my missing info.
 
Are the early and late crank gears the same thickness?

This may help to Identify gears more quickly.

Hans

Geoff

Hans, this is a separate issue.  The '32 to '35 models used a thinner gear.  In '36 the gear was 1/8" thicker, but all gears up to  and including 1940 were 14-1/2 deg. pitch. They changed the pitch to 20 in 1941, and  post war they used alloy gears.   

hasktavern1

Old Fogey UK said:

hasktavern1 said:

Old Fogey, If you need or want it, I can send you a copy of the original instruction sheet which came with the circa 1940s gear change kits.  A fairly simple process...the only difficulty I had was removing the confounded harmonic balancer.

Yes please, I'd really appreciate that !

I sent the illustrated instruction sheet to you as an email attachment.  Let me know if you do not receive it.

Hans

Thank You, Geoff, for your info. 

Old Fogey UK

hasktavern1 said:

Old Fogey UK said:

hasktavern1 said:

Old Fogey, If you need or want it, I can send you a copy of the original instruction sheet which came with the circa 1940s gear change kits.  A fairly simple process...the only difficulty I had was removing the confounded harmonic balancer.

Yes please, I'd really appreciate that !

I sent the illustrated instruction sheet to you as an email attachment.  Let me know if you do not receive it.

It hasn't turned up yet, I'm afraid.
Did you send it as a private message or as an ordinary email ?
David.

hasktavern1

I sent it to the email listed for you in this forum, beginning with "del".