Topic: Kenny Harmon F cam, Ride report.

[Don R]

I have an old  kenny Harmon F cam going into the 836. Does anyone have a cam card for one or know the timing specs?

[Jerry Rxman Griffin aka MuthaF'er]

Isn't Megacycle doing these now?

[scottly]

The specs are on the Satanic Mechanic site:


                                                                    In o/c
                                                                    Ex o/c
         Valve   Durat-                                             btc/abc
Cam      lift    ion       Description                              bbc/atc
---------------------------------------------------------------------------
D        .345    277       A famous grind. Excellent for a major HP  32/65
         .325    294       increase, yet a wide range of use. Long   77/37
                           exhaust duration for sustained high speed
                           cruising without excess combustion chamber
                           temperature. May be used with stock
                           springs if desired.
---------------------------------------------------------------------------
F        .385    295       For the greatest HP possible, consistant  35/73
         .330    290       with sustained use. Extra long exhaust    82/38
                           duration for efficient temperature con-
                           trol. Best choice for Road Racing. Best
                           power 7-11,000 RPM. Should be used only
                           with Racing Valve Spring Set.
---------------------------------------------------------------------------
Super F  .405    308       DRAG RACIN ONLY. ABSOLUTELY NOT FOR       42/83
         .370    279       STREET USE. Over 300 intake and "short"   73/25
                           exhaust timing. This cam is not suitable
                           for sustained use, only with Racing Springs.
---------------------------------------------------------------------------

[PeWe]

I scanned my old docs from Action Fours with their cam data and installation guide line.
Published here: Action Fours - Cam spec.pdf
http://forums.sohc4.net/index.php?topic=123458.msg1400942#msg1400942

19-103  D
19-104  F

[Don R]

Thanks for the link. It's copied and ready for when my gaskets arrive.

[Don R]

OK  The specs vary, one says open .020 at 38* one says 35* I wouldn't mind if it was advanced a bit to lower the torque curve. I got the opening at .020 and 36.5* it closes a little early making the duration about 4* to 8* shorter than advertised depending the card you look at, That would be OK too.  The exhaust number was way off because the degree wheel had slipped. I'm thinking slap on the cover and carbs and call it done.
 
The Action 4's directions assure me the cam is ground to very accurate specs and this is more than needed. I'm wondering if they just got too many calls from people asking WTF?

[Big Jay]

Thr rocker arm ratio vary. You will almost never find the cam/s in a rocker arm motor being exactly what the card says. Just use the lobe centers that are on the card.

[MRieck]

Thr rocker arm ratio vary. You will almost never find the cam/s in a rocker arm motor being exactly what the card says. Just use the lobe centers that are on the card.

 Thanks for that Jay. I have many people ask this question for all cams....not just a Harmon cam. All the arms vary....period. Great post sir.

[bwaller]

Makes sense to me.

[Don R]

Thanks Guys,

I found out how to calculate the lobe centers, It's not written on the old info I got. I'll make a better degree wheel holder and have another go at it. Sometimes patience is not my strongest trait. I may pull the dyno cover so I've got something more precise than the kicker to turn too. I'd like to check the duration at .040 and .050 so I can compare to modern cams too.  I'm betting the numbers aren't so radical when it's apples to apples.

[Big Jay]

Do it at .050"  .020" is too innacurate.   Lobe centers.  Intake opening number plus close number plus 180, divide by 2, subtract smallest number.

Exhaust the same. The smaller number will probably be open on intake and close on exhaust.

[MRieck]

Do it at .050"  .020" is too innacurate.   Lobe centers.  Intake opening number plus close number plus 180, divide by 2, subtract smallest number.

Exhaust the same. The smaller number will probably be open on intake and close on exhaust.

Gospel.

[MRieck]

Makes sense to me.

What do you know?

[Big Jay]

When Eraldo Ferracci was drag racing Hondas ( bet many of you didn't know that ), he had a special fixture he made that could check sohc 750 rocker arms to find the ones with the most favorable ratios.

[Jerry Rxman Griffin aka MuthaF'er]

While you're at it and making this look easy would you also explain 'rocker arm ratios'?

[Don R]

I can get this one.

The effective pivot point is moved, so for each increment of movement at the cam the opposite end at the valve moves more, giving the effect of a bigger cam.
 Like a lever.
 My big block is 1.7-1 my old small block had rockers with an offset pushrod seat that you could turn 180 and change the ratio from 1.5 to 1.6 to one.
 On a pushrod motor the pushrods can work at various angles so it's easier to move the pivot points around.
 My buddy has a small block Chevy with offset shaft rockers and offset lifters so he could move the pushrod out of the port area and make the port bigger.

 In our case if the rocker shaft was closer to the cam it would change the ratio to provide more valve lift at the same lobe lift.
Did I explain that right guys?

[MRieck]

When Eraldo Ferracci was drag racing Hondas ( bet many of you didn't know that ), he had a special fixture he made that could check sohc 750 rocker arms to find the ones with the most favorable ratios.

Right...they would go through a bucket of arms.  And I did know that about him and dragracing Honda's. An interesting history on Eraldo on how he came into Ducati. I do not profess to know everything BUT I do know somethings.

[bwaller]

Makes sense to me.

What do you know?

Hey Rieck, have you heard it yet today? 

[754]

So a checking fixture could easily be made, so what are you looking for,. Consistency, i would think..not necessarilly highest lift..but that may help... In a stock parts only scenario..

[Don R]

I love a thread where I can learn something. Thanks so much for chiming in.

Just so I'm sure, I check the intake degrees at .050 opening,  then .050 from closing noting the degrees at each then put the CL 1/2 way in between. Then check the Ex. to see if it is close.

[Don R]

And if I understand the rocker arm theory, a person could also hardweld the rocker arms and regrind the radius of the rocker to move the contact point on the cam to provide a bigger ratio?  I realize it's easier to just get a bigger cam.  As long as you're not bound by rules to stock parts. 

[754]

 I think the pivot has to move for that..ie, move the pivot in the line between lobe and stem..results in ratio change.. .
 Selecting through a bunch of rockers. To get the closest  together group is blueprinting anyway.... Imo

[Don R]

OK. So the centerline on the cam card isn't a magic number derived by computers or voodoo, it's just the cam company doing the math for you?

[754]

Re the ratio post, i suppose you could weld up rocker pad and by grinding the radius centre further from pivot.. Change the ratio .. But in certain motors, moving the shaft hole , or exccentric shafts are easy to do..

[Don R]

 I can see where the cam contact point could be manipulated to a small degree.

My big block chevy has T&D shaft rockers, due to the splayed valve arrangement each rocker has it's own shaft. The intakes share a solid stand, the exhausts have individual stands, making it easy top move things (geometry) around. My buddies small block has T&D's with a single shaft with all of the intake and exhaust rockers on it. Like the Hondas except for the pushrods. Underhead cam. LOL.