Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles Genny shovel cam vrs knuckle cam

Genny shovel cam vrs knuckle cam

Post Mon Feb 09, 2009 9:53 am

I'd explain where the errors are, but it's the same thing I explained the last time... oh, wait it was the last 5 times.

Here's the new deal: you won't listen, and I won't speak. You won't learn anything, but no one's delicate feelings will be hurt - and isn't that the highest goal?
Much better.
Last edited by panic on Mon Feb 09, 2009 6:33 pm, edited 2 times in total.

Post Mon Feb 09, 2009 1:22 pm

Posts: 152
Location: Carver, MN

Ok, I know I am risking being proved a fool by disagreeing with you Panic, but Boring the Knuck heads for the Pan firering is indeed like shaving the heads .200". Both the Knuck and the Pan share the same stroke, rod length, and piston compression height. Unless the distance from the centerline of the crankcase to the cylinder base gasket surface on the case is different from Pan to Knuckle (and I don't think they are), that means the top of the piston is coming to the same place on either. On the Knuck it is coming (roughly) to the head gasket surface on the cylinder. On the Pan it is coming to the top of the firering, or .200' above the head gasket surface. Obviously if you remove the firering, you will need to add a .200" stroker plate to keep the piston from coming .200" out of the top of the cylinder. But if you bore the Knuck head for the firering you have lowered the head .200" in relation to the dome of the piston as compared to setting on top of a Knuck cylinder. Am I wrong?

The pushrod angle when using Knuck heads with shovel cam and lifters is far better than the angle with stock Shovel heads. In fact, just eyeballing the Knuck head/ Shovel lifter block combination (with no covers), the pushrods appear to be perfectly straight in line with lifters. The problem is that the lifter blocks are machined at angle for the cork to seat on, that is different than the angle of the lifters. (Come to think of it, maybe all it would take to make the covers seal would be to re-machine the seat for the cork in line with the lifter.)

As to how good (or bad) and engine with Knuck heads and Shovel cam and lifter blocks will run, all I can give you is my own personal experience. AMRA "Street Racer/FL" National Champion 1986 and AMRA "Pro Stock" National Champion 1987. Throw in the 7 National Record certificates hanging on my shop walls, and I think you would have to admit the loss of performance from mismatched parts is within acceptable limits for most street use.

Post Thu Feb 12, 2009 1:11 pm

Posts: 152
Location: Carver, MN

Wow, Panic; So if someone disagrees with you, you just go back and edit your post so that future readers can't read it and decide for themselves who is correct.

Let me try one more time. Mock up your engine with the piston at top dead center in a Knuckle cylinder. The piston will come to the top of the head gasket surface. Now take the Knuckle cylinder off and put on a Pan cylinder. The piston will be in the same place; the top of the firering. (The distance from the top of the firering to the base gasket surface on the Pan cylinder is the same as from the top of the cylinder to the base gasket on a Knuck cylinder.) Now, if you you bore a Knuck head for the Pan firering and put it on a Pan cylinder, it becomes fairly obvious that it will set down .200" (the height of the firering) lower than if on a Knuck cylinder. The piston will protrude .200" further into the combustion chamber. That is why I said to think of it like shaving the heads .200". In reality it is exactly like shaving the cylinder .200" but leaving a firering so that the piston does not protrude.

Of course none of this will work if you are smarter than everyone else in the world. But for the rest of us, it may be useful info, especially since you get similar results from using a bored out 61" Knuck cylinder on a 74" motor. The only difference is that the firefing already fits in the head and the firering is only .125" tall.

I hope no one's "delicate feelings" were hurt here, and I apologize if that is the case

Post Thu Feb 12, 2009 2:26 pm

Posts: 530
Location: Ogden, Utah, USA
Just a note: Or two... boring the fire ring clearance into the head will result in a larger combustion chamber, not smaller. Other note: Pan cylinders are shorter than knuckle cylinders. I don't know anything about shovel cylinders so won't stick my nose in that direction. Knuck rocker arms are 1 to 1 and pan shovel are more like 1.5 to 1. spacing was changed inboard to outboard on the cam when harley changed to the pan. resulting misalignment caused by that idea is not a step forward. And last bit from me...oil return from heads is gravity on pan and shovel. Vacuum on the knuck. So you can make it work if you want. How bad do you want to make it work? How much are you willing to spend? Will the results be worth the effort? Your choice. Yes there are lots of heads modified to take pan cylinders. That is what folks did when there were no knuck cylinders any where.Yes some have modified cams to obtain lift and timing that was not available any other way. We don't need to do it that way any more. Be sure that what you want to do will work for you. I don't even know if knuck lifter blocks can be fit into a pan or shovel case with out a lot of work. But even if you did the spacing issues would remain. Tiped pushrod covers wold be hell to seal and no vacuum would make for a messy and smoky motor. I have seen external drain lines run to the case from the heads on the primary side below the number boss. I was told that worked. You would need to use a knuck breather to make the case suck at the right time. I don't know if a knuck breather will fit in to pan or shovel cases. So ask the questions and makeup your own mind but I gotta say it will be a bit of work. Only you can say if it is worth the effort. :D
Steve H

Post Thu Feb 12, 2009 3:08 pm

Posts: 152
Location: Carver, MN

boring the fire ring clearance into the head will result in a larger combustion chamber, not smaller.

That is correct if you are just cc'ing the head, off the engine, however nearly all of that extra space that you bore out of the head will be filled with the firering and piston, so the final result is a big increase in compression ratio.

Post Thu Feb 12, 2009 6:30 pm

Posts: 123
Location: Mpls. area
Lee, just curious, did you ever work for Kokesh MC in Blaine? Mike

Post Thu Feb 12, 2009 8:30 pm

Posts: 152
Location: Carver, MN

Hi Mike, yes thats me.

Post Thu Feb 12, 2009 10:14 pm

Posts: 123
Location: Mpls. area
You did the "super stock port and flo" on my evo back in 96, very impressive...Mike


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