k piston

[jug]

any body out there have the dimensions of the k model pistons? the distance from pin hole to top is the main thing as I am thinking of using them when I rebuild my servi this winter.

[Rubone]

They are taller from pin to crown and won't fit your Servi without head modifications.

[kitabel]

Depending on the manufacturer, up to +1/8" on the compression distance, with a shorter skirt. The weight is different, but IDK how much.
Part of this excess height is useful in reducing the quench clearance, which is too loose in stock 45 engines. It's probably 1/16" down from the deck @ TDC now, you want closer to .015"-.025" below the deck to achieve .035" minimum clearance.
The remainder can be made up with a fabricated stroker plate, or Bridgeport a shallow cylindrical relief in the head's gasket surface deep enough for .035" clearance and slightly larger diameter than the dome OD, like 2-7/8". The relief is the better method but will be more expensive.
All methods increase the static compression ratio.

[jug]

Do I have to machine heads if I use no 6 heads

[Rubone]

Yes, the area in question is the same on all heads, the flat portion above the piston. If you are not trying for the extra squish why not just use 45 pistons? And without other breathing mods there would be minor gain.

[kitabel]

A bit of trivia for your amusement: the only head that is both "immune" to machine work and has your 45 bolt pattern is the 1948-52 WR, which has a K-style pop-up relief, but:
1. $$$$$$$$$$$
2. you can't get the head on, your exhaust valve will crash the head - it's in a different place than yours

[duffeycycles]

Do I have to machine heads if I use no 6 heads
The #6 would need more clearance made than the others.It is already shorter/lower/tighter.I agree with Robbie,use 45" pistons not high top.

[Rubone]

Illustrations tend to help clear things up. Left to right, NOS #5 head, #6 head, WR head



From the other side, not the piston interference area is the same on 5 or 6, just a slightly smaller combustion area. The casting is the same just machined thinner for a 6. WR head illustrated the pocket needed for pop-up K pistons.



The difference in height is obvious, 45 left, K right. Skirt is actually the same length but is radiused for flywheel clearance.

[jug]

thanks for all the info you guys sent my way. I am sure I will have more questions later. any other things you guys think of about the heads and anything that helps me get a little more out of the old 45 send it . thanks to all

[jug]

Rubone, great pictures. helps a great deal. keep the good stuff coming.

[kitabel]

All non-pop-up 45 heads (1929-73 D, R, W, G; iron or aluminum; regardless of compression ratio) have the quench ledge in exactly the same place: milled flat with the head gasket surface.
Milling the head increases the CR but does not change the P-H clearance.
Milling the cylinder (head gasket surface or flange) does both.

Harley-Davidson intended all sidevalve engines including UL, VL, K, etc. to have quench (1923 Ricardo patent), which was the advantage that made the previous IOE (JD etc.) engines obsolete and permits reasonable compression ratios. There is nothing dangerous, radical, or experimental about it.
The sloppy factory tolerance made this distance too large to be fully effective. Getting it down to .035" increases:
1. torque
2. chamber turbulence, squish, and mixture homogenization
3. engine vacuum
4. gas mileage

Reason not to do this: money.

[duffeycycles]

WLD cylinders have a machined flow to the piston from the valves that helps.Tom Sifton style.

[Rubone]

WLD cylinders have a machined flow to the piston from the valves that helps.Tom Sifton style.

Actually WLD do not unless it is tuner added. WLDR does though, although they are extremely thin on the ground as '41 was the last of them.

NOS WLD cylinders