Moderator Curtis Jacobson Portland Oregon (4577 posts) Registered: 10/12/2007 02:16AM Main British Car: 71 MGBGT, Buick 215 |
composite vs. iron vs. steel timing gears
This morning I was reading a very old book about Model A Fords, and it cited that in 1929 69% of all American cars produced were fitted with "fabric" (canvas and phenolic resin composite) timing gears because they run quieter and with superior wear characteristics compared to iron gears to ensure accurate camshaft timing over many miles of service.
I've seen various kinds of "plastic" timing gears on American V8s, but never really paid attention to which engines had which gears. I'm pretty well certain that GM, Ford and Chrysler have all used gears with nylon teeth around steel hubs on their V8 engines at least from time to time. I think I remember removing a fully plastic (composite) gear from a mid-seventies Olds 350 and replacing it with an iron gear. The Des Hammill book on Rover V8 recommends steel replacements over iron ones for better durability, but makes no mention of plastic or composite alternatives. The timing gears on my 1962 Buick engine are undoubtedly aftermarket parts, and as I recall they're iron. Questions: 1) Did Buick originally use composite or iron gears on 215? 2) Are any of you using plastic or composite gears? 3) Are plastic or composite gears even available for BOPR? 4) What differences - if any - have you noted? |
mstemp Mike Stemp Calgary, Canada (223 posts) Registered: 11/25/2009 07:18AM Main British Car: 1980 MGB Rover 4.6L |
Re: composite vs. iron vs. steel timing gears
Curtis,
3) Most of the Rover V8 used the plastic gear on teh cam, at least the SD1 did. RPI and Rimmer Brothers should have them but are not recommended due to wear issues and timming changes. |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: composite vs. iron vs. steel timing gears
The nylon teeth on the cam sprocket, had some advantages, from a design standpoint. Problem is, the real world doesn't always work that way. Nylon is quieter and has less friction, and for a "while", works better on a stock motor. It doesn't like high mileage, heat, hot/cold cycles or hotter cams, with more valvetrain stresses. Mopar engines used to shed their nylon teeth, in higher mileage motors. I suspect similar problems with other motors. IMHO, not suitable for a hi performance engine. Iron will retain slighty more oil, over steel, is less expensive, and should be suitable for most BOR. engines. Good Luck, roverman.
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MGB-FV8 Jacques Mathieu Alexandria, VA (299 posts) Registered: 09/11/2009 08:55PM Main British Car: 1977 MGB Small Block Ford, 331 Stroker |
Re: composite vs. iron vs. steel timing gears
I tend to agree with Art; high pressure valve springs and quick revving engines are a killer on composite gears. Also after awhile they fluctuate too much. A premium double full roller timing set is the only way to go........
Cheers |
WernerVC Werner Van Clapdurp Lynchburg, Va (108 posts) Registered: 09/06/2009 12:56PM Main British Car: MGB 1977 Rover 3.5 |
Re: composite vs. iron vs. steel timing gears
I drove a Ford Vedette (French built) V8 wich had composite timing gears. They didn't hold up very well and had to be replaced after about 10K miles.
That was in the early 60ties and the engine was build in early 50ties so not good composite quality available. Werner |
Moderator Curtis Jacobson Portland Oregon (4577 posts) Registered: 10/12/2007 02:16AM Main British Car: 71 MGBGT, Buick 215 |
Re: composite vs. iron vs. steel timing gears
I thought you guys might be curious to know more about Model A timing gears...
The following is all from a remarkable little book called "Know The Ford" by Murray Fahnestock, circa 1930. The book explains nearly every design feature of the Model A and compares/contrasts the Ford design with competitive cars. Some features of the Model A were incredibly clever - often decades ahead of its time. On the other hand, the book gives me the distinct impression that dual carburetors had not yet been conceived. Ford (and Fahnestock) took for granted that a driver must be able to frequently and manually adjust fuel mixture to meet changing conditions right from the driver's seat. The book aggressively bashes Chevrolet cars for having overhead valves, as though that were a terribly backward design. Did you know that Ford welded the spokes of Model A wheels at both the hub and the rim after initial assembly and balancing? No tire punctures caused by loose spokes! (I wonder if any racers were still using that trick in the fifties... It would obviously make for a much stiffer and stronger wheel.) Here's the section about composite "fabric" gears: Quote: |
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DiDueColpi Fred Key West coast - Canada (1366 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: composite vs. iron vs. steel timing gears
Volvo also used the fabric gears for years.
All of their pushrod motors used them right up to 1975. These gears routinely last 400 to 500 thousand kilometers. I even use them in race engines that won't see more than 7000 rpm. Above that speed the teeth start to fret. I don't think that it is a gear failure as much as a harmonic problem. Even the steel and aluminum gears have problems at the higher rpms. Anyway, these are a different animal from the traditional cast aluminum/nylon coated chain gear that most are familiar with. Cheers Fred |