harleyKmodel

Does anyone have any "factory" information on the J/M cam combination?

Interesting request, as I never knew there was an “M” exhaust cam, as such information seems to be absent from the usual on-line sources of KR cam info. I was aware of the -69R part numbers for J/K cams (25499-69R) and J/L cams (25498-69R), but was unaware of the J/M cam set. Might you have a part# for the J/M cam set or know anything else about it? I suspect it must be for a dome piston engine since it seems to follow the alphabetical naming sequence of the other -69R cams?

Since information on the J intake lobe is well known, I suspect your inquiry relates to only the "M" exhaust lobe. Over the entirety of the KR reign, my read of the published data suggests there were only subtle changes made to the exhaust cam, and by the mid 1960’s to the end there were basically 2 profiles used, as shown in the table below (opening/closing data at 0.010” lift with zero lash). According to Jim Leineweber the longer duration exhaust cams in the table (J/L combo) were primarily used for road racing with close ratio gear boxes, whereas the shorter duration exhaust cams (J/K combo) were used for flat track racing. How the "M" lobe fits into this mix is anybody’s guess, but based on the existing design progression I suspect that any change would be incremental at most.

KR Exhaust Lobe Timing Data

J cams time in at intake 66-66, 312 duration, 90 lobe center .395 lift, and exhaust at 65-40, 285 duration, 102.5 lobe center, .395 lift,
K exhaust is 58-42, 280 duration, 98 lobe center, .395 lift
L exhaust is 65-40, 285 duration, 102.5 lobe center, .395 lift
M exhaust is 60-42, 282 duration, 99 lobe center, .395 lift, so the same as J exhaust (why the change in designation?)
I have Ms in Reiman's 1969 Daytona motor
The J/K combo are the H cams with less lift. ( intake .440, exhaust .405)

hugoct wrote:J cams time in at intake 66-66, 312 duration, 90 lobe center .395 lift, and exhaust at 58-42, 280 duration, 98 lobe center, .395 lift,
K exhaust is 58-42, so the same as J exhaust (why the change in designation?)
L exhaust is 65-40, 285 duration, 102.5 lobe center, .395 lift
M exhaust is 60-42, 282 duration, 99 lobe center, .395 lift,
I have Ms in Reiman's 1969 Daytona motor
The J/K combo are the H cams with less lift.

Thanks for the new information on the “M” exhaust lobe. From the opening/closing numbers you provided sounds like it falls right in between the J/K and J/L cam sets.

Not being nit-picky or argumentative, but some of the numbers you’ve quoted above do not agree with the published data I’ve seen on the KR cams. Specifically, the exhaust numbers I see posted for the 1967 J cams, 25499-67R, do not agree with yours, as the numbers I see are 0.395” lift, opening-closing of 65-40, 285 duration, and 102.5 lobe center. The numbers you’ve quoted for the J cam set is actually the data I see for the J/K cam set 25499-69R (as shown in the table posted above).

I believe we could also say the J/L cam set, 25498-69R, is possibly the same as the J cam set, 25499-67R, since the timing numbers are the same.

Although I use the opening/closing numbers for a given KR cam profile to extract all the same info you do, I have to admit I've never had the opportunity to degree any KR cam with the exception of the KHK, which I believe to be the same profile as the -53R cam, but with 0.375” lift rather than the KR cam with 0.395” lift. I am therefore always concerned when performing these extrapolations from only 0.010” lift opening/closing numbers, i.e., suggesting 2 cam sets are the same, assigning lobe centerlines and lobe separation angles, overlap, etc, since the low lift opening/closing tell us almost nothing about the actual shape of the lift curve, i.e., the lobe symmetry, the lift rates on the opening/closing flanks, etc. I wish I had a pile of KR cams to degree and overlay the lift curves to see how they actually compare, but alas, have never had the opportunity and know nobody that has such information available. I do have a set of J/K lobes to mount so will at least have the opportunity to measure these later in the year. Do you by any chance have any actual lift curve data on KR cam sets?

What sources are you using? The data I've posted are from the HD supplied tech manuals for the KRs, except for the Ms which are stamped on the lobes and appear on some Race Department Motor Test cards. The H & J data is from one iteration of the manual and the J/K and J/L are from the last iteration.

WZ507, could ya explain how to check a cam, for lift and duration? I have 3 sets I need to check. I put on cam in my lathe and put a dial indicator on it, Zero'd at the base of the lobe and turned the chuck 180º, to the highest position on the lobe. The cam lifted .325

hugoct wrote:What sources are you using? The data I've posted are from the HD supplied tech manuals for the KRs, except for the Ms which are stamped on the lobes and appear on some Race Department Motor Test cards. The H & J data is from one iteration of the manual and the J/K and J/L are from the last iteration.

You clearly have superior sources for your cam data, as yours is from factory race manuals and mine is off the internet, so have no idea where it actually originated. The only thing I can add is that all the i-net sources were consistent, which means nothing, but at least did not raise any red flags with me. I’m curious, what cam related information did the factory race manuals provide, i.e., opening and closing timing only, duration at any higher lifts, or what?

Regarding your query about the sources of cam data, I’ve seen KR cam data posted at the following locations.
1. The “frenchowl”, a member of this forum, had KR cam data on his website, but I don’t believe that website is presently available. Perhaps he’ll chime in and let us know.
2. Victory Library posted KR cam data here - http://victorylibrary.com/tech/KR-cam-c.htm
3. Enfield Racing posted some KR cam data here - http://www.enfieldracing.com/page/28565-H-D-Cams (lower left side of page has link to Table of Specs)

The Factory Manual (more like a handbook) gives part number, lift, running tappet clearance, and opening-closing numbers +/- 2 degrees.
Duration and lobe centers at the given timing marks are the readers calculation.
That's all you got back in the day.
Some guys advanced or retarded the cams for different effects.
Most guys just bolted them in on the marks and went to the track.

Although a wee bit lumpy, I love the. 420" E set in my mod KHKs, Yes! Erik

Collected by myself and Jim Haubert over the years, this is what I had on my web site on KR cams:











Patrick