Stripped cam gear

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John Brooks
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Re: Stripped cam gear

#31 Post by John Brooks »

I think the cam is broken...... Rotates until the closes lobe has pressure on it the it slips and binds, the realigns when rotated backwards, it broke the gear when the cam bound, crank kept turning from the flywheel momemtem. I had one like this in the late 60's broke right at the flange behind behind the gear.
John Brooks

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Mark Schumacher
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Re: Stripped cam gear

#32 Post by Mark Schumacher »

Thanks John
Will know soon enough and will post a photo
Bummer. Dema Elgin modified it for my engine

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mario musto
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Re: Stripped cam gear

#33 Post by mario musto »

Looks like the cam breaking boss in last photo in post #27 is cracked, and if so could be caused by broken cam.

Mark Schumacher
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Re: Stripped cam gear

#34 Post by Mark Schumacher »

Finished tear down. Cam hitting described above was operator error. Since cam gear was off, cam was interfering with crank.
Looks like cause was weak split cam gear, high spring pressure and probably high rpm excursion.
I will thoroughly clean and reassemble, using non-split cam gear. May also re-spring the valves.
I appreciate the comments from the members.
Thank you!
Mark

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Harlan Halsey
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Re: Stripped cam gear

#35 Post by Harlan Halsey »

I would check with Dema Elgin regarding valve springs since it is his cam.

Mark Schumacher
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Re: Stripped cam gear

#36 Post by Mark Schumacher »

I am assembling parts for the engine re-build. Cam was a tiny bit pitted on one lobe, so I had Dema Elgin fix it up and re-grind the lifters.
Walt convinced me the double springs are not adding too much pressure and are more for control of harmonics.

Thinking about a straight cut steel cam gear set. On a thread from a few years ago, the input was they are not too noisy.
Are the 356/912 gears same as VW Type 1? Therefore widely available. Any set better than others?
Looks like a VW cam gear set is about 20% of the price of just a Porsche replacement gear (of course)
Thanks
Mark

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Martin Benade
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Re: Stripped cam gear

#37 Post by Martin Benade »

The post 1961? Vw gears would have to be used as a pair as the gear angle was changed. The cam gear wouldn’t have dowel pin holes, and originally would have been riveted to the cam.
Does anybody know if the straight cut gears make a pleasant whine, somewhat 911 ish, or do they just make plain old noise?
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Ron LaDow
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Re: Stripped cam gear

#38 Post by Ron LaDow »

Martin Benade wrote: Wed Dec 18, 2019 10:38 pm [...]
Does anybody know if the straight cut gears make a pleasant whine, somewhat 911 ish, or do they just make plain old noise?
Dunno about the noise level, but the wear is probably 3X what the helical gear sees, with the resultant errors in cam timing.
Helical gears have the disadvantage of imparting an axial load on the driven shaft (cam, here); the vector of the helix angle. But they engage some number of teeth greater than one, so the load is spread and wear is reduced by (that guess above).
The 616 engine seems to ignore the axial load on the cam, and I've never seen any (documented) claim that the straight-cut gears add anything other than that noise.
To draw an analogy, there are folks who swear the intake roar from sparrow-strainer air cleaners must mean more power; I'm waiting for the evidence.
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Harlan Halsey
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Re: Stripped cam gear

#39 Post by Harlan Halsey »

A few years ago I was Pitted across from Bob Kahn. He started the engine in his Speedster, and the racket was so bad that alarmed,I ran across and said shut it down. Bob yelled not to worry, that was the sound of the straight cut cam gears!

Steve Douglas
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Re: Stripped cam gear

#40 Post by Steve Douglas »

My friend had his engine stop on the way home from North South, the engine is now at Jacques's and it has been torn down, the only failure seems to b the cam gear loosing a bunch of teeth. Any ideas on what happened ?
The engine is a Stoddard exchange rebuild, 912, with maybe 25,000 miles.
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C J Murray
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Re: Stripped cam gear

#41 Post by C J Murray »

What does Jacques think?
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Steve Douglas
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Re: Stripped cam gear

#42 Post by Steve Douglas »

He is puzzled too. He said he hasn't seen one this bad without a lot of damage to other parts. The case is off being cleaned maybe then the gear size can be measured. It was a -2 gear that failed.

Richard Leonetti
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Re: Stripped cam gear

#43 Post by Richard Leonetti »

The crank said "Go" and the cam said "NO" :cry:

Dave Erickson
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Re: Stripped cam gear

#44 Post by Dave Erickson »

A washer or a weak tooth on the cam gear are possible causes.

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mario musto
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Re: Stripped cam gear

#45 Post by mario musto »

How does the steel gear on crank look? Did cam rotate freely with gear off and no other foreign items found in case?

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