Timing chain vs. gears
 

What are the plusses and minuses of using a roller timing chain vs. timing gears?

ok, here's my experience with gear drives. This is a very disputed topic on alot of other message boards as well.

Pros of gear drive
Absolutely no chain stretch
more reliable in VERY high HP
It sounds like you have a blown car...

Cons of gear drive
More expensive than a good double roller
up to 7% loss in hp due to frictional loss (dyno proven)
Not really meant for a vehicle that gets driven a fair amount of time
Even the quiet ones get annoying!!!
they can cause a "jitter" in your distributor which throws your spark out of wack
Many times when you use gear drive it wears your cam bearings out faster on the top side (the gears try to spread)
did I mention they get REAL annoying? To the point where if you are driving for a longer amount of time say an hour or more you WILL have a headache!

Alot of people who have had gear drive for any amount of time will tell you to use a double roller or a silent gear drive at a minimum. The noisy sets will just plain drive you insane! Most of the people who stand firm on gear drive as a great product, haven't had it long or use it in a car that is in essence a race only car.

IMHO a double roller timing set is hands down the best option. Why pay $150+ for a gear drive when a double roller can be as low as $32 and that's for a comp cams, not a no name. Without knowing what engine you plan to put this in... This is, IMO, one of the best options http://www.naparts.com/ProductDetail.cfm?ProductId=2052 And still about $50 cheaper than your lowest price gear drive.

Here's a good reference about the matter which came from the reher-morrison engine building manual
http://www.members.cox.net/fastnuf/ChainDrive2.jpg

Josh

WOW, sorry about the big picture!!!! Contact a local engine builder and ask him what his experiences are when tearing down a motor that had gear drive. They almost always say the cam bearings were badly worn.

In the defense of the gear drive wearing on the upper part of the bearing, wouldn't the same hold true to the chain but on the bottom?

Gear drive is pointless for a street car.If you are after every 1/16th of a hp,then maybe.Or you like the sound of a Polish blower.

A Polish blower? I think I dated.........oh, nevermind!:o

Josh basically hit all the right points. The double roller just doesn't have any real competitors for street use.

Just a side thought when Chrysler went Nascar racing with the new Hemi's in 1964 they could have easily used gear drives - cost was not an issue and they were easy to fabricate for guys like the engineers at Chrysler. They used the double row roller! That implementation essentially ushered in the double roller for broad based automotive usage.

No significant improvements for our type of usage yet.

Ed

I had gear drive for a bit in my 351W. Started eating distributor gears, could not figure out why. Put in a double roller, now she is quiet and I have not ate a gear in 5,000 miles. Gear drives sure sound good though.

Timing gear
 

Last timing gear motor I heard was on my 65hp flathead 38' Ford. Not sure if that was the hp at the rear wheels or motor only. My wife has a dog that makes a mean noise but when you see the mutt in action you laugh. :JEKYLHYDE

Looks like a double row roller chain is the way to go. Thanks to you all as always for your expertise!

Josh

My nephew is at Camp Bucca, with the guard guys from Illinois, tell him hello for me

Donald D. West
Cpt,OD
33rd Mp Bn
Camp Bucca



Jerry Clayton

Wow. I never really thought about gear drives, but given the info above, I can't imagine why anyone would go with gear drives.

.

Something else to think about is a belt drive.

http://store.summitracing.com/partde...5&autoview=sku

Tom, Did you see the price?
 

Very expensive for what we are doing? Buy a Roll master billet set and never look back!

http://www.romac.com.au/

The gear drive info presented here is not for the type of gear drives that any top fueler runs---this is the Pete Jackson type gear drive that came out many years ago to replace the old link type chains and plastic/fiber gears--the type of cheap gear drive up to then required a reverse ground cam to work--the Pete Jackson type would work with standard rotatation camshaft

The Donovan, Kieth Black( built for Black by Donovan) and the copy cat Milodon gear drive used a single idler gear that had the gear mesh set and doweled to the block. This type gear drive does not push the cam upwards as the gears mesh on there proper lines and the cam turns in place---the Pete Jackson drive has the gear driven between the crank and cam forcing them apart causing the wear to the top of the cam bearings.
However they are expensive in todays world------

Jerry

I've been looking at a single idler setup that has it's mounting plate fixed to the front of the block. Everything running on either ball bearings or torrington rollers so hopefully power loss should be minimal.

Cheers

Mike

If thats for the LS type engine, its going to be a little cramped under the timing cover

I'm looking at putting the new dry sump pump on mine with the zo6 front cover and balancer--

One of the really neat things about the Donovan type gear drive is that you can just remove the front plate to change your cam timing or even change camshafts

Jerry

It's an Aussie built unit made by a company called Diecrest engineering. They make a lot of the belt drive setups and export them to the US. I think they may be under someone elses name over there. They are just up the road from me and seem like nice people on the phone.

Here's a couple of pics of the setup:

http://www.clubcobra.com/photopost/d...ar_drive_1.jpg

http://www.clubcobra.com/photopost/d...ar_drive_2.jpg

It looks dead easy to change cam timing with the offset dowels. With a 2 piece cover or a cover with a removable window it would be easy to change without pulling the balancer. I'm thinking about machining up the stock front cover to have a removable panel.

This should work fine with the Z06 dry sump setup as it sits behind the oil pump in the standard timing chain position.

Price is not to bad either @ around $400 Aussie compared to $180 Aussie for a Rollmaster timing set.

Cheers

That looks good Mike--keep me advised how it works out for you and what there company name is up here.
The ZO6 timing cover is larger to fit over the double oil pump and takes a different Harmonic balancer then to clear the cover.
Definitely make a cover with a window for cam timing changes as it is not very easy to get the lower pulley off and on and aligning the front cover is critical

Jerry

You are correct Jerry, that info was for the typical run of the mill, "I want to put a gear drive in my car," gear drive. The single idler's are much better than the double idlers but IMHO, are not going to outperform a billet double roller on the street. On the track, I'd agree, but not for a car that gets 95% of it's time on the street.

Just a side note, many, many, many, many, many, engine builders in my area will not put a gear drive in an engine that they built. If the customer requests the gear drive, he supplies them with a roller and tells them they will have to install the gears themselves. I guess they don't want the liability or the people talking about how poorly the engine was built etc etc if it failed due to gears. A poor reputation as an engine builder isn't going to get you very far!

Just to clarify, I am not a gear hater! Although after reading my previous posts, it would seem that way. I have in the past and have friends who run them. Most of which rebuild their engine annually or have less than 1000 miles put on their vahicles per year. I drive the wheels off my cars, that's what their for! It's just my opinion that for the majority of people with a cobra, a double roller is just money better spent!

Thanks for clarifying the single idler Jerry, I think my first post may have made the gear drive look like it is simply a waste of metal! haha

Josh

BTW Jerry, I passed your hello on to your nephew. Small world huh?

Double roller gears
 

OK; was confidnet going with a belt drive, then changed to Milodon gear drive and now I'll stick with a double roller.

Will use a setup with timing changed on the crank (9(?) different position at 2 degree increments).

Think the ones with adjustable cam gear won't offer any positive as long as I don't have a removable front cover for easy adjustments and also because it makes the gear a little heavier!%/

Anyway; here's a thought of double rollers.... The slack in the chain after some years of use & wear are caused by both by worn teeth on the gears, the chain stretching and rollers being ground down.

Will a billet/billet gear have any positive effect on wear (as oppsed to a billet/ forged or forged/ forged gears, given the chain is identical?

Or is it just another gimmick of sales?

I saw a thread with photos on one of the Mustang forums a year or two ago about a gear drive that had failed. The idler gears had come free of their bracket. Very spectacular carnage.

Z.