Straight Cut Cam Gear Failure

[FJCamper]

Recently at Road Atlanta, in a LeMons endurance race, The EMPI straight cut cam gear failed in a way apparently different from the usual.

Typically, the large gear bolted to the cam breaks. In this case (and our first straight cut cam gearset failure ever) it was the smaller gear that slips over the crank and is held in position by the large Woodruff key. The gear weakened, and was about to split at its weakest point, the Woodruff key notch.

As the gear expanded toward separation, the gear began to rock and hammer the Woodruff key, actually deforming it. The cam, in turn, began to twist out of time, and the exhaust lobe for cylinders 1 and 3 struck the crank's counterweight and broke off part of the lobe.

Here's how our driver, the genteel Dr. Johan by day and the infamous (use your own judgement) Mr. Speed on certain weekends described it to the press. https://www.youtube.com/watch?v=-ofkMdVaUgg

There's no more to the story than this cautionary tale. Make of it what you will.

FJC (RetroRacing)

[terryly]

Awsome discrption

[woodsbuggy1]

Sorry to hear of your problems and thanks for sharing.
I was recently having a conservation with a 75yr old engine builder that commented how much more difficult straight cut gears are to remove from the crank compared to German gears. I have not had the chance to compare id measurements between straight cut and German gears but am now curious if the id is smaller on straight cut gears and possibly caused your failure.
Kenric

[Ol'fogasaurus]

https://carfromjapan.com/article/car-ma ... explained/

Or

http://automotivethinker.com/transmissi ... s-helical/

This might give you some ideas of the advantages of strait cut gears and the dis-advantages of them too when comparing about helical cut gears.

Lee

[Max Welton]

Here's how our driver, the genteel Dr. Johan by day and the infamous (use your own judgement) Mr. Speed on certain weekends described it to the press. https://www.youtube.com/watch?v=-ofkMdVaUgg

He is hilarious!

Max

[Clatter]

FWIW, I've seen some affermarket woodruff keys that were dimensionally wrong.
They ended up being too big and made a tight spot on the gear.

Maybe that had something to do with it?

[Ol'fogasaurus]

FWIW, I've seen some affermarket woodruff keys that were dimensionally wrong.
They ended up being too big and made a tight spot on the gear.

Maybe that had something to do with it?

https://www.mechanicaleducation.com/202 ... tages.html

Woodruff key failure with straight cut gears is an old problem, the fit between the materials (tight or loose fit e.g., shock loading especially if the fit is off) and add to that the aging of the materials causing brittleness is, again, a very old problem. Straight cut gears can also be a problem with shock loading, if I remember again correctly, is an old problem.

Lee