Sunday, December 6, 2009

Lightning Cam Pics?

In my last post I featured a Leineweber # 5 Knuckle cam. This elicited a response from a reader, Jim Franco, saying that he has a cam that recently came out of a Knucklehead hillclimber with lobes that looked quite similar. He was kind enough to send me some pictures of the cam, which I have posted here. The holes in the drive gear immediately bring to mind the legendary Knucklehead "Lightning" cam. Contrary to what seems to be popular opinion, I do not believe that the Lightning cam was the only factory cam to have these holes.

As can be seen in the above picture, the lobes do have the radical shape similar to the Leineweber #5. I have heard the Lightning cam referred to as the "banana lobe cam." I am not sure if this was a common slang term for it or not, but one can certainly see where the name came from.

I ran a factory Knuckle cam which had holes like this in my street bike for a few seasons. The lobes did not visually appear any different from any other stock Knuck cam, and it did not perform noticeably better. I also do not remember a keyway, like the one seen in the above picture.
Barring someone with more knowledge of the elusive Knucklehead Lightning speaking up, I am very inclined to conclude that Jim has himself a genuine one here!


Jim Franco said...

Lee: some measurements on the (?) "Lightning Cam".

Height of lobe .465"
Base Circle (bottom of lobe circumference) .840"
Width (Diameter) of drive gear 2.750"

Now, I also have a stock lightened knuck cam (? of late-model 1936 vintage) with the following measurements....

Height of lobe .370
Base Circle (Bottom of lobe circumference) .870
Width (Diameter) of drive gear 2.74

Best I can do Lee, getting varying measurtements the more I doubled check! Used a digital verier caliper. work your magic......


Jim Franco said...

If I misunderstood and didn't get the measurements you need Lee...shoot me a pm...I'll correct it.


St.Lee said...

Hi Jim, Sorry it took me a while to get back to you. Snow here. I take it you are measuring the lobe height differently from what I expected. If you measure from the highest point on the lobe across to the opposite side of the cam (same height as the base circle) it would be about 1.220 on a stock Knuck cam. Subtracting the base circle from that will give the cam's lift (also the valve lift since rocker ratio is 1:1). Or is that what you already did in giving the lobe height?

Andrews lists their "stock replacement" Knuck cam as .348 lift. I am not sure if that cam is a replica of the original or not, but it would be good to know.

When I asked the gear width, I was curious as to whether the gear might be thinner, since I have seen a significantly narrower circuit breaker drive gear with holes in it. I am guessing that since you have a stock knuckle cam to compare it to, you would have noticed any difference there.

I am still researching, and hopefully more to come. Too bad we don't have an old time hot rodder to enlighten us!

Jim Franco said... ARE correct...the gear width is different from .570" stock cam to .525" for the "Lightning cam".

Again, you are correct, the Stock cam lobe height is: 1.220" vs "Lighning" cam at 1.285".

Lee...So, does that make the "Lightning" cam lift dimension .475 if other documented Camshaft diameter meaurements attribute the base circle at .81?

Cool.....hoping you can verify my math ;)


Jim Franco said...

By the way, Lee...I get the .81 base circle data from Bruce Palmer's book. My actual measurement of the base circle (and again I could have measured incorrectly!) is .84 for the "Lightning Cam vs. .87 for the stock cam....obviously changing the "Lightning" Cam to a lift of .440 ......


St.Lee said...

The .810 figure from Palmer' book is the diameter of the shaft that rides in the bushing, not the base circle. He also has a lobe width listed of .875 which must be an awkward way of saying base circle. (note its very close to your measurement) Your cam works out to about a .445 lift. That would lead me to suspect that it is an early aftermarket item, although I have no reason to think that except my assumption that the Lightning cam would have had close to stock lift. Don't let my suspicion dishearten you; I could very well be wrong about that.

Jim Franco said...

Nope...not disheartened, Lee! I'd rather run the .445 lift than the stock .348 anyway, I already have a stock .348 cam and this motor is going in a bar-hoping Bobber. I hear the sounds she throws out is "race-cool"! I'll get pics to ya when I'm done, promise.

The guy I bought this motor from, took the vl framed knuck down his dirt driveway before the motor was removed from that VL frame...his words, "That thing hits a mean lick"!

I'm OK with aftermarket in this case! Thanks for all your info.....great talking with 'ya! I'll be hanging around to learn more from you.


Jim Franco