using a gear drive on a sohc

[hbstang]

has any one used a milodon gear drive for the primary drive on a sohc?any long term effects on the secondary chain.just have one that i may use.crank was made with a bbc snout and it came with the gear drive to fit.

[pumpbldr]

Herre is a picture of Milodon gear drive on a sohc. Not my build, but I know its possible.
   
Doug aka Pumpbldr
Precision Oil Pumps

[pbf777]

          Boy . . . . I gotta say as cool as all that gear-drive is (who's?  ), it would seem like with all of that inertia of turning gears coupled with the hammering effect, that perhaps with a few good "throttle-snaps", or some brutal gear changes (with a tight clutch), and the camshaft gear retaining fastener & key would just maybe surrender?   

          Looks like a good application for a "splined" juncture between the drive gear(s) and the nose of the camshaft stub.   

          Scott.

[Barry_R]

An expensive and complicated (but pretty) solution - looking to fix a nonexistent problem.

[jayb]

An expensive and complicated (but pretty) solution - looking to fix a nonexistent problem.

+1 on that.  In fact, on all but one of the SOHCs that I have tested, the chain stretch will retard both cams a few degrees at high RPM (one engine saw the left cam advance a couple degrees while the right cam retarded, but that's another story).  So around 4000 RPM you can get the benefits of advanced cam timing, but by 7000 RPM the cam timing retards a few degrees, which is what the engine wants to make a little more power.  It's like variable cam timing on a modern engine, but just using the stock SOHC configuration.  It is an advantage over a gear drive.

Back in the 1960s Sneaky Pete Robinson ran a gear drive on his SOHC dragster, but the way he did it turned the two cams in opposite directions.  This solved the problem of the differences in geometry between the valve train action between the left and right cams, so he could run aftermarket grinds (which were the same lobe on both cams) without any loss of power due to different valve train geometries on the left and right side.  Nowadays, thanks to work that Barry and I did with Billy Godbold at Comp Cams, you can get cam grinds that have slightly different lobes on the left and right sides to compensate for the left to right geometry issues, just like Ford did with their original SOHC cams.  As a result, from my perspective anyway there is no reason to use a gear drive to run the cams on the SOHC.

[hbstang]

of course i was only asking about the primary drive from crank to stub cam.you have to be on another planet with unlimited time and budget to do that one pictured.lol.
also the crank in this engine uses a bbc snout and i would have to find a crank gear for the primary that would fit.

[Quisp21]

Isn't the main problem not having arched guides?

[jayb]

Arched guides per se are not really the issue; as I understand it they are used on modern engines because the guides have tensioners attached to them to keep the tension on the chain constant.  A straight guide can't be used if the guide is going to be moving around from a tensioner pressure.  So really the main issue with the SOHC secondary chain drive is the fact that chain tension can vary with temperature, RPM, load, etc.

Having said that, as a guy who has been running these engines for 20+ years, the chain drive as-is is not really a problem, as long as you tension the chain correctly, go easy on the engine until it is warmed up, check the chain tension periodically, etc.  But it sure would be nice to have an automatic chain tensioning system on the SOHC.  I know someone who is working on that...

[e philpott]

Who made the Belt Drive for the Cammer ? Seems there used to be a belt drive set up on ebay

[jayb]

I think that was Jim Green.  But in order to make it work you had to hack off the front of the SOHC valve covers, weld on a plate with a hole and a seal for a shaft to go through, and then bolt on the belt drive parts.  Same issue with the front cover.  Cool idea, but hard to make it work in practice, and again, with proper attention to the chain drive, wouldn't really be necessary.

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