Author Topic: CB750 cam quest: Kenny Harmon F?  (Read 838 times)

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Offline PeWe

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CB750 cam quest: Kenny Harmon F?
« on: December 19, 2020, 02:40:30 am »
A friend has a nos unmarked cam. Only markings are the cam cast marks as K134 and more.

The profile look very close to my Megacycle 125-20 that I noticed had number style close to KH F when timing.

Below photos of the unknown cam I believe is a KH F
Measured IN lobe (4) on cam - base:
37.6-28.3=9.3mm

Kenny Harmon F lift on camcard:
IN 0.385" (9.78mm)
EX 0.330"



.

#
#
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Here Megacycle 125-20 vs Kenny Harmon D.
 

EDIT:
I have measured the #1 IN lobe on the other 2 cams with similar fat lobe design. These with known lifts when I timed them.

Megacycle 125-20:
36.5-27.2mm= 9.3mm on cam
Lift when timed: 0.379" (9.63mm)

Kenny Harmon D:
36.75-28.3mm= 8.45mm
Lift when timed: 0.350" (8.89mm)

RC295 copy:
36.1-26.4mm= 9.7mm
Lift when timed:
0.393" ( 9.98mm)

125-20 has  in lift of 0.388" on card and a little bit less when timed. Not 0.338" as written everywhere else.
Typical is the early opening of ex as they all have. KH D too.

RC295 as reference only when measure on cam vs timed value in engine.

I have seen that a cams lift can differ some on 1-4.
Also lower lobe with lower base circle so lift will be OK.
« Last Edit: December 20, 2020, 10:49:36 am by PeWe »

Offline Laids

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #1 on: December 20, 2020, 02:01:14 pm »
In the spring I rebuilt a motor but decided on using the existing head I had as it was done only a few years ago. It had a KH F grind but was showing a little wear. I got a few cams off a friend and one of them had the same profile as the F grind but without the KH markings on the end. I didn't end up using it as one of the lobes was hitting the cam tower while the original KH didn't. The markings on the sprocket plate look like your Megacycle cam numbers.

Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #2 on: December 20, 2020, 10:29:45 pm »
Interesting!
It might be a K/H F cam profile made by Megacycle?
They have a "125-F" in their chart of cams, K/H F profile.

Do you have the possibility to measure the cam lobe on that cam?

For cyl 4, closest to the end marked with notch.
- Total lobe height. You need to set the caliper tighter, rotate cam slow until it open the caliper at highest.
- Base circle. Caliper turned 90 degrees from highest point.

The cam hitting the cam tower had obviously higher lobes. With wider base circle, lift can still be the same as the other cam.

Too narrow base circle also affect the rocker arm and angle how the adjuster screw will hit the valve tip.

I guess many cams are close to hit the tower.
« Last Edit: December 20, 2020, 10:35:47 pm by PeWe »

Offline Laids

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #3 on: December 21, 2020, 05:24:50 am »
I'll have to get the cam as I gave it back to my friend, but I will be over there tomorrow.

Offline gschuld

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #4 on: December 25, 2020, 10:32:08 am »
This is presumably an Kenny Harmon F grind.

George

Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #5 on: December 25, 2020, 11:49:40 am »
Thanks Georg!
All 9mm something are IN lobes, all 8mm something the EX, right?
It seems that the KH F profile was really popular since it was made by different makers.

I read in another thread that all KH profiles were inspired by Ducati cams.

Any experiences of the F cam are welcome too.
Is it a cam that sudden wake up at 6500-7000 rpm? ;)

A decked head increasing the compression might be needed.

Offline Sam Green Racing

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #6 on: December 25, 2020, 01:29:19 pm »
PeWe, the RC 295 cam is still available from Dynoman Performance (DP295) and is a great cam.
What little it looses on top end power, it more than makes up for it with great power from the start and right through mid range.
I had the 125-75 in the auto but changing to the DP295, it knocked nearly a second off the quarter mile time.
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Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #7 on: December 25, 2020, 02:39:13 pm »
This F cam identification for another bike. The owner of that bike has a DP295 in another 836 engine.

 
I used a cam with RC295 engraved on the washer side earlier this year and before that.. Timing numbers matched RC295 too.

I replaced that cam AND the ported head with another head with less chamber volumes. Cam that went in was a used 125-75 billet cam.

Next dyno 10hp more than last dyno a few weeks before. Now 101whp and more torque from ca: 3000 to +9000 rpm  ;)

I'm still curious to use the old cam engraved RC295 since compression has entered the good area.
Tested with cheap compression tester, 197.5-202.5 PSI.

Earlier around 170-180PSI. Leaking valves (carbonized) had reduced cyl 2-3 from the year before when it had 180-190 PSI.

Simple test to see the result of static compression and cam.

Last head not as much ported either. F2 34mm in valves, K stock (KPMI) 28mm ex.

The older head with larger chambers has KPMI 5mm stem valves 34/28.

I have another head going on with KPMI 33.5/28.5 valves to be refurbished. I'll make sure that compression will not be less than 200PSI with same tester.
I'll change base gasket to thinner, now RCS 0.020", 0.010" ordered. This is my 1005cc billet block engine.

Then a new dyno with that head and 125-75 to hopefully reach a few whp more.

After that another test with the RC295.

The DP295 I helped to time a few months ago.
IN had really good lift, 10.12 mm at 0 lash. (Not with same tool as I use)
My RC295 "only" 9.98mm (0.393").
0.390" is the specified lift.


I timed my RC295 @0.04" lift
In 25/55 degrees
Ex 55.5/22
Lift: 9.98mm (0.393")/ 9.22mm (0.363")

125-75
In 26/55
Ex 55.5/23
Lift: 10.0mm (0.3937")/9.4mm (0.370")

Similar numbers but lobes different. RC295 has fatter, more rounded.

I look forward to coming spring.
Waiting for the other head and new base gasket.
 A little bit higher compression and hopefully better flowing ports. ;)
« Last Edit: December 26, 2020, 11:05:07 am by PeWe »

Offline Sam Green Racing

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #8 on: December 26, 2020, 04:37:58 pm »
PeWe, it depends what you want the cam for.
There's plenty of cams that make high power for speed but the 295 gets you there quicker over a shorter distance like on the drag strip.
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Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #9 on: December 26, 2020, 11:36:34 pm »
Hi Sam, agree about the RC/DP295 cam.
Most likely one of the most useful hot cams to use for any bore size. High lift, relatively short duration/overlap and nice idle.

I have had thoughts to get an DP295 just for sure! But my RC295 marked one is probably enough. I have other stuff ongoing from Dynoman so still time to add ;)

BUT, it is tempting to get a welded one to later be compared on dyno with my billet 125-75 for the graphs sake ;) ;D
(My K6 with 1005cc has welded rocker arms.......)

The question about F only to identify an unmarked cam and hopefully get riding experiences too.

Offline Laids

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #10 on: December 27, 2020, 11:30:20 am »
So PeWe, I measured the KH F look alike cam.

Lobe           37.21
Base Circle  28.1

I found another cam which had numbers on the sprocket holder 12535, the weird thing is it looks like the lobes are turned 180'.

The pic with 3 cams is from the left, the could be megacycle KH F, centre a stock cam and to the right a mystery cam

Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #11 on: December 27, 2020, 02:03:57 pm »
Thanks for the cam data! ;)

Your photos and data together with George's photos and data help to indicate the cam I syarted this thread with to be a possible KH F profile.

125-35 seems to be a beast!
Megacycle number.
High lifting cam. >0.400" on both IN and EX.

I think that the notch is on wrong side. Use the horisontal lines parallel to cam holder with notch down at cyl1:4 @ TDC as initial setup when timing.

I have a Megacycle cam where that notch is wrongly placed. The horisontal line OK. See photo below.

I think MRieck used that 125-30/35 profile recently in his 1005cc CB750 F digging out 106whp on std gasoline if I remember correctly.

(30 means hardwelded cam, 35 billet)

Megacycle cam data here:
http://satanicmechanic.org/megacyclecam.shtml


« Last Edit: December 28, 2020, 10:57:52 am by PeWe »

Offline Don R

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #12 on: January 04, 2021, 09:37:01 am »
 I read that the KH/F cam increases the open time (duration) on the exhaust side to help cool the valve for  endurance racing.   Mine is welded for sure, you can see the weld buildup on the sides of the lobes. I'm curious about overlap.
« Last Edit: January 04, 2021, 09:38:35 am by Don R »
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Offline PeWe

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Re: CB750 cam quest: Kenny Harmon F?
« Reply #13 on: January 04, 2021, 10:45:14 am »
I read that the KH/F cam increases the open time (duration) on the exhaust side to help cool the valve for  endurance racing.   Mine is welded for sure, you can see the weld buildup on the sides of the lobes. I'm curious about overlap.
Hi,

I have read that too somewhere.
Don R,  do you have a photo of it to attach here?

125-F  cam card
Lift @0 lash, open/close @0.04"
IN 0.385"  28/62
EX 0.330" 69/29

Overlap 57 degrees
(In open + Ex close)
In need of higher compression than 10.5:1 pistons. Shave the head 0.25mm might be enough.
Same as using MLS 0.03" (0.75mm)  instead of 0.04" (1mm thick).

Stock head height 71.2mm if I remember correctly.

(I let a head to be shaved 0.5mm ro reduce chamber volume by ~1.6cc. Chamber diam 65-64mm.)

Probably slightly different numbers when timing a real cam.

This cam seems to have been a common grind since it is made by different companies/ grinders.