Degreeing cams?

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PSk
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Degreeing cams?

Post by PSk » Mon Mar 30, 2009 8:05 pm

Tom,

I cannot see how degreeing a twisted cam solves the problem. Surely you can only get some of the cylinders right. Usually when a camshaft is degree'd (I believe) the closest cylinder to the sprocket end of the camshaft is used to set the correct orientation of the cam. Thus if the cam is twisted the last cylinder(s) on that side will still be out.

Surely new cams are required?

Please note I 100% agree that if an engine is rebuilt that the cams should be degree'd, but if the cams are twisted then you can never get perfect cam timing on all cylinders that that camshaft controls the valve timing of.

It's probable too that Ferrari (or whomever) never actually make all camshafts perfect ... I know a lot of time is spent looking for good production cams in production car racing as not all are good.

Best
Pete

Rudy van Daalen Wetters
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Re: Degreeing cams?

Post by Rudy van Daalen Wetters » Mon Mar 30, 2009 9:32 pm

Yes, I don't really understand that either. If one lobe is off
four degrees how is resetting that one going to affect all the other
cam lobes?

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 GT s/n 8705

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Yale
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Re: Degreeing cams?

Post by Yale » Mon Mar 30, 2009 10:22 pm

Two weeks ago Tom was saying to me about how he had written a post about the degreeing situation with the cams on the car they were working on and then stripped all that part off because he felt there would just be a bunch of comments debating this. I was thinking what the hell is Tom talking about, hah! Best, Yale
1964 330GT #6097

Rudy van Daalen Wetters
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Re: Degreeing cams?

Post by Rudy van Daalen Wetters » Mon Mar 30, 2009 10:25 pm

Bring it on!!! Maybe we can surpass the thread on detailing horns...

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 GT s/n 8705

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tyang
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Re: Degreeing cams?

Post by tyang » Mon Mar 30, 2009 10:41 pm

Hi Guys,

Yes, Degreeing the cam will let you know how much the lobes are off, and a correction can only applied as a compromise. If you want everything to perfect, perfect, you'll have to regrind and weld new lobes.

The front lobes closest to the drive gear is checked, while the rear most lobe is also checked. If there is a discrepancy, then a compromise is set.

Tom
'63 330 America #5053

Rudy van Daalen Wetters
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Re: Degreeing cams?

Post by Rudy van Daalen Wetters » Mon Mar 30, 2009 10:52 pm

My thought is that a four degree variance would warrant a new or
replacement camshaft.

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 GT s/n 8705

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tyang
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Re: Degreeing cams?

Post by tyang » Mon Mar 30, 2009 11:29 pm

Rudy van Daalen Wetters wrote:My thought is that a four degree variance would warrant a new or
replacement camshaft.

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 GT s/n 8705
That's up to the customer. It might not be as bad as it sounds since it's a 4 cam engine. The exhaust cam has the discrepancy, so we'll see how well it runs with the cam adjusted to make the difference.

Tom
'63 330 America #5053

kare
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Re: Degreeing cams?

Post by kare » Tue Mar 31, 2009 1:59 am

PSk wrote:I cannot see how degreeing a twisted cam solves the problem. Surely you can only get some of the cylinders right. Usually when a camshaft is degree'd (I believe) the closest cylinder to the sprocket end of the camshaft is used to set the correct orientation of the cam. Thus if the cam is twisted the last cylinder(s) on that side will still be out.
Every cylinder adds load to the shaft and if it starts to twist I am pretty sure it all occurs between the drive and the first cylinder where the load is at max. I am not sure if the shaft really twists or the chain wheel gets dispositioned to the cam.

FWIW, I've seen old steel keys that have been in use for 100 years and have twisted 90 degrees and show no trace of cracking...

Best wishes, Kare
250 GT 2+2 3197/GT

PSk
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Re: Degreeing cams?

Post by PSk » Tue Mar 31, 2009 3:32 am

Yale wrote:Two weeks ago Tom was saying to me about how he had written a post about the degreeing situation with the cams on the car they were working on and then stripped all that part off because he felt there would just be a bunch of comments debating this. I was thinking what the hell is Tom talking about, hah! Best, Yale
:), heck it is very interesting stuff.
Tom wrote:Hi Guys,

Yes, Degreeing the cam will let you know how much the lobes are off, and a correction can only applied as a compromise. If you want everything to perfect, perfect, you'll have to regrind and weld new lobes.

The front lobes closest to the drive gear is checked, while the rear most lobe is also checked. If there is a discrepancy, then a compromise is set.

Tom
Okay that makes sense. Appreciate the answer. I guess it depends on the depth of the customers pockets and also whether this car has to see off a competitors one at the next Goodwood meeting or not :wink:

BTW: I believe with high powered drag cars that they design cams, etc. expecting the crank to twist by a certain amount during the run ... crazily complex I imagine.
Pete

kare
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Re: Degreeing cams?

Post by kare » Tue Mar 31, 2009 5:27 am

PSk wrote:BTW: I believe with high powered drag cars that they design cams, etc. expecting the crank to twist by a certain amount during the run ... crazily complex I imagine.
Not as complicated as you might think; when you know how much torque the engine will be putting out, it will be pretty simple to find out how the crank twists under said load. They did this without compures in the inline 8-cylinder engine era...
250 GT 2+2 3197/GT

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carello
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Re: Degreeing cams?

Post by carello » Tue Mar 31, 2009 8:40 am

It would be nice to see a plot of the cams for the engines discussed. The only project i have at hand is shown below. Anybody have a cam plot they can share?
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