Tim, Jim, et Listers,
I hope you don't mind my forwarding to the List your reply to my question
about your "average" TDC statement, but I thought it was too interesting
not to share. After you explain it, it seems rather obvious, but this is
the first I've heard of this particular issue. Also, since Tim doesn't
mention it in his instructions, I thought it was particularly relevant. I
would have thought that, although cast or forged cranks may have some
dimensional variations, this would be nullified during the machining step.
I have heard that in the process of "nitriding" a crank, which requires
pretty high temperatures, that the crank can become distorted. There are
newer processes that use ion plating that don't heat the crank up much. I
believe I have read where this type of process is used in production
engines on high specific load surfaces - e.g., cam lobes.
I suppose +/- 1.25 degrees wouldn't be a really big deal for most motors,
unless you are operating at the extreme limits or after the last 1% of
performance. How much variation was there in deck height and/or stroke
between the eight cylinders?
TTFN,
Bob
>Bob,
> A standard production engine's crankshaft is made by giving a few twists
>to a hot piece of "taffy" and allowing it to cool. When I told my machinist
>I planned to dial-in the cam, but first I wanted to know where TDC really
>was, he said "you're nuts! It will drive you f...ing crazy!" ...and
>he was right.
> The crank TDC's varied by almost 2 1/2 degrees, so I averaged them and
>set the degree wheel accordingly. I didn't trust the timing marks on the
>damper (until proven) and they turned out by chance to be spot-on, for the ave
>rage TDC, but not for #1 TDC. Did I mention the stroke of each crank throw
>was not quite the same resulting in a slightly different volume swept by each
>piston? These are a few reasons a real racing crankshaft is so costly, and
>it is one step toward how pro engine builders get dependability and real
>horsepower from an engine. I may still have the story I wrote about this for
>PTC on disc, and if I find it I'll zap it to you.
>Jim
At 11:40 AM 10/18/99 -0500, Ronak, TP (Timothy) wrote:
>Listers,
>It appears that there is some interest in Degreeing a cam so I thought I
>would pop in my thoughts.
snip, snip, snip, . . . .
Robert L. Palmer
UCSD, Dept. of AMES
619-822-1037 (o)
760-599-9927 (h)
rpalmer@ucsd.edu
rpalmer@cts.com
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