Worn Dizzy gear
 
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Worn Dizzy gear


Dale Bowman
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Had the car to John Sleath for a full rolling road set-up. Initials finding were strange ignition timing so he took the distributor out and founf the counter weights weren't returning properly (very easy fix with some electrical lube and a bit of finger work). What we did find was the bronze gear was well worn (3500miles). John said it looked like it would need replacing in the next 1000 miles or so.

After some research and a few emails I find that I have a billet steel cam which are only to be used with bronze or composite gears. MSD (my ignition) do not have a composite so looks like I'm stuck with Bronze and replacing every couple of years.

I've been onto Lyle at Southern Automotive and he's been informed by the cam supplier (Demos) that their cams can be used with iron gears (even though they're billet). Lyle has a build in a few weeks with a hydraulic lifter so he's going to try out an iron gear and see if it destroys itself and report back to me before I go ahead.

Anyone clever got any thoughts on the subject?

Ta D

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David Beck
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Crikey, good job you did not come on the road trip you would have needed a couple of spares 😀 

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Paul Blore
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I have an iron dizzy gear and it hasn’t been changed from new. I now have 40,000+ miles on it and it shows no obvious signs of wear.

I think the original camshaft was iron, but this one could be steel.

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Paul

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Barry Jones
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I know of a lot of problems with bronze dizzy gears, they don't usually last more than 2000 miles, I avoid them at all costs even if it means down grading the cam spec. I have herd that they are for forged cams. The composite gears don't last as long, we was replacing one every race on a big block Corvette. That's a 1 hour race. Fitted an iron drive against general wisdom and that done a season before the car was sold.


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Dale Bowman
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https://www.enginebuildermag.com/2009/07/properly-matching-your-camshaft-and-distributor-gear/

 

I'd prefer to change to a cast iron gear for longevity but will wait to see if Lyle has any problems when he fits one to a steel cam. Last thing I want is for the dizzy gear to wear the cam gear.

This post was modified 2 years ago by Dale Bowman

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Roger King
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@dale-b

The standard I have always worked to is the old US engine-builder’s dictum of a cast-iron gear for a cast-iron cam and a steel gear for a steel cam. It’s never failed me in 35 years of building pushrod V8s, some of which have now covered fairly serious mileages. 

Like Barry, I wouldn’t be happy with a bronze gear, and I wouldn’t touch a composite one. For every aftermarket distributor and cam combination I’ve ever used I’ve found the appropriate gear at Summit and changed it if necessary. Flat tappets all used to be iron, rollers steel, but that may have changed with ‘progress’. 

John Sleath is a great guy - the Mustang’s been to see him 3 or 4 times now and he really knows what he’s doing. Please give him my regards next time you see him. 

R

edit:  Dale, just did a quick google and it seems MSD still sell loads of steel dizzy  gears. That’s what I’d fit. 

Edit2:  The Mustang has a Lunati steel roller cam with a steel dizzy gear, 15 years and 45,000 miles, no problems. I built my Tiger’s 260 with a cast iron cam and an iron gear in ‘84 and it’s still going strong in Oz. 

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Dale Bowman
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Hi Roger, I found the steel gears, it's not so much the finding, as being compatible with a billet steel cam. I've sent a message to MSD asking the question.

Lyle at SA has been in touch with Demos (cam maker) who replied to him mentioning Iron gears being ok with their cam but no mention of steel.

I'll see what MSD say and wait for Lyle to do his 'test' with an iron gear on a Demos billet steel Hyd roller cam. He said it will be a few weeks for that engine to reach that stage of build as there are a few flat tappet engines he's building first.

This post was modified 2 years ago by Dale Bowman

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Roger King
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Posted by: @dale-b

Hi Roger, I found the steel gears, it's not so much the finding, as being compatible with a billet steel cam. I've sent a message to MSD asking the question.

Lyle at SA has been in touch with Demos (cam maker) who replied to him mentioning Iron gears being ok with their cam but no mention of steel.

I'll see what MSD say and wait for Lyle to do his 'test' with an iron gear on a Demos billet steel Hyd roller cam. He said it will be a few weeks for that engine to reach that stage of build as there are a few flat tappet engines he's building first.

A steel gear works with a steel cam...

I would be wary of using a cast iron gear with a steel cam.  You might get away with it, but I have always understood that the softer cast iron will wear more quickly.  It's not so much the gear wearing out, more the metal contamination throughout the lubrication system that would concern me.

It may be that technology has moved on - I don't know.  I'd make sure MSD's response doesn't relate to race parts for engines that get torn down every few months and replaced routinely. 

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