BBC gear drive

[prairiehotrodder]

I've been doing lots of reading mainly on blown alcohol engines in a book by Paul Chirayath. He says that any blown alcohol engine should have a high quality 3 gear drive. So i've wondered if this would also be a worthwhile upgrade for my BBC race engine. I was looking at the milodon setup and it looks pretty decent. Seems to me when big cams come into play with fairly tight PTV clearance a gear drive might be worthwhile. Plus i think the spark timing should be more consistent and maybe even make more hp. Are they difficult to install ?

[lefty o]

having run, and owned a few gear drives over the years, imo they introduce a whole nother set of harmonics into the valvetrain. if offered a gear drive, or a belt drive, id take the belt every single time.

[ClassAct]

Having run gear drives since 1988 I don’t use anything else. As long as it has a fixed idler gear it will be as accurate the day you install it as it is 30 years later. I run them in street/strip stuff and on my drag race stuff.

I have yet to see a single paper of note that shows a FIXED IDLER gear drive causes more harmonics than a chain. Not even here has anyone produced such a thing.

If it IS a big factor then surely there should be an SAE paper or similar to discuss the topic. I haven’t seen one yet.

I’ve run my P/V as close as my piston to head clearance on the intake valve and never had one hit. That was .055 with aluminum rods.

[af2]

RCD makes good quality drives.

http://rcdengineering.com/product/big-b ... ear-drives

They made this for our small block raised cam over the winter so we could run a chain drive and run the fuel pump.

[rustbucket79]

If you’re running a fuel pump off the cam it’s a good idea.

If you’re just building a decent solid roller engine, stick with a quality billet timing chain set. I despise gear drives on the engines I dyno, you can’t easily differentiate between the god awful gear drive noise and the valvetrain noise. (3 gear isn’t as bad as the dog bone style)

[af2]

If you’re running a fuel pump off the cam it’s a good idea.

If you’re just building a decent solid roller engine, stick with a quality billet timing chain set. I despise gear drives on the engines I dyno, you can’t easily differentiate between the god awful gear drive noise and the valvetrain noise. (3 gear isn’t as bad as the dog bone style)

I wanted to run the pump off the chain drive..
I know the gear drive is what it is BUT >>>> RCD did a one off because there have been others that want to go the same raised cam deal..

Sorry to hyjack but RCD does have the best gear drives made. And they are quiet!!!

[prairiehotrodder]

so far i've looked at milodon, RCD and Donovan gear drives. They all look good. One thing i think is at least with the milodon it looks like you have to modify your block in a way that there is no going back. Thats not good.

[ClassAct]

If you’re running a fuel pump off the cam it’s a good idea.

If you’re just building a decent solid roller engine, stick with a quality billet timing chain set. I despise gear drives on the engines I dyno, you can’t easily differentiate between the god awful gear drive noise and the valvetrain noise. (3 gear isn’t as bad as the dog bone style)

If you have a fixed idler gear drive and it makes noise it’s either installed incorrectly or it’s worn out (never seen the latter). If you have an engine that can take what some call a “cheater” gear drive like the Milodon for the SBM, Ford, Pontiac...whatever...you won’t know it’s in there because they don’t make noise.

[swampbuggy]

The ultimate camshaft gear drive set up is simply ( 2 gears only ) with a reverse rotation engineered camshaft. I am sure this will get some kick back, but it is arguably the simplest most dependable set up possible. Comments welcome, Mark H.

[ClassAct]

so far i've looked at milodon, RCD and Donovan gear drives. They all look good. One thing i think is at least with the milodon it looks like you have to modify your block in a way that there is no going back. Thats not good.

I have to go look it up but I don’t recall modifying a BBC permanently for a Milodon GD.


Edit: yes, you do have to modify the timing cover dowel pin holes (I forgot about that) because the cover has the idler gear in it. So yes, you will always have 5/16 dowel pins in the block.

I suppose if you ever wanted to put a stock timing cover back on the engine you could ream the holes in the cover to size (I don’t like that idea too much) or you can machine a set of stepped dowel pins.

[prairiehotrodder]

looks like you have to pull the dowels out and drill the holes bigger ?

[dannobee]

The ultimate camshaft gear drive set up is simply ( 2 gears only ) with a reverse rotation engineered camshaft. I am sure this will get some kick back, but it is arguably the simplest most dependable set up possible. Comments welcome, Mark H.

Possibly, but with caveats.

The old Chevy inline 6 cylinders and the Pontiac "Iron Duke" engines ran gear to gear. Both of them had noisy timing gears (at least noisy to the end consumer) and would occasionally strip the cam gear teeth. The "updated" cam gear had fiber teeth to combat the noise, but even those would sound like a skeleton jerkin' off when they'd go bad. The noise was obnoxiously loud when the gears were worn.

At race level engine speeds, the harmonics get transferred up through the timing gears. Chains mitigate that problem.

[6.50camaro]

looks like you have to pull the dowels out and drill the holes bigger ?

Or if they are centered you could use a bushing to go from std size dowel I.D. to 5/16 O.D.

[cv67]

Hate to start a thread to ask one question nor hijack

Class act what GD do you recommend for a st/strip sbc?
How long to jesel belts last for street use?

[ProPower engines]

so far i've looked at milodon, RCD and Donovan gear drives. They all look good. One thing i think is at least with the milodon it looks like you have to modify your block in a way that there is no going back. Thats not good.

I have seen that issue where guys want to go back to std. timing cover but the solution is machine 2 pins to fit the larger holes in the block and locate the std. type cover..
The other thing is the seal has enough compression onto the balancer that you can just loosely install the cover then put the balancer on then tighten the cover.
I see this issue often with marine stuff and never a leak issue afterwards