Topic: When Installing a Performance Cam

[Ellz10]

It might be time to call your cam manufacturer if your confident your measurements are accurate.

I once ordered a .670 lift intake cam and received a .520 lift cam shaft with the .670 lift’s number on it.
With the same manufacturer received a cam with one bearing journal considerably larger and wouldn’t fit in the sbc block.

Check your .050 intake opening and closing and see if it is any where near your 268* total duration.

Doesn’t matter whether it’s 25*btdc - 59* abdc or earlier or later. Just the total is close to 264*.

Yeah im gunna give them a call today and see what they deal is. Maybe they can provide some insight.

[Ellz10]

Am I supposed to be adding a set number for some reason or anything like that? I don't understand. This is the only thing keeping me from finishing this motor rebuild.


EDIT :

I finally figured out the problem. After a call to WebCam Racing and a few pictures back and forth, we were able to determine that my understanding of "zero valve lash" was incorrect 

I was under the assumption that zero valve lash meant that the tappet screw was not to touch the top nub of the valve. So after correcting that and re-doing the process, I was able to achieve. 375" which is still .010" off but I'm assuming it's user error or an error in reading of the indicator.

I'm going to go ahead and read all of them and make sure they're correct and if they are then I'm moving forward!

[Don R]

 George Bryce is on facebook explaining cam timing now, it will be available to watch after it's done live. He is a bit of a guru on Suzuki dragbikes and V twins. 

[Ellz10]

George Bryce is on facebook explaining cam timing now, it will be available to watch after it's done live. He is a bit of a guru on Suzuki dragbikes and V twins.

Too bad I don't have Facebook!

[Ellz10]

This is what I got now. Much better. My intake duration is off by 4° and my exhaust duration is off by 7°  -  my intake lobe center is 2° advanced while my exhaust lobe center is 0.5° retarded. Is my duration off due to my lobe centers being off a couple?


Intake #1

21° BTDC

59° ABDC

Duration at .050" : 260°

Lobe Center : 109°



Exhaust #1

23° ATDC

62° BBDC

Duration at .050" : 265°

Lobe Center : 109.5

[Don R]

George Bryce is on facebook explaining cam timing now, it will be available to watch after it's done live. He is a bit of a guru on Suzuki dragbikes and V twins.

Too bad I don't have Facebook!

 He posts them on youtube too. Tech Talk Tuesday. I'm not sure it would help. In case anyone wants to figure out what he's saying.

[Tracksnblades1]

This is what I got now. Much better. My intake duration is off by 4° and my exhaust duration is off by 7°  -  my intake lobe center is 2° advanced while my exhaust lobe center is 0.5° retarded. Is my duration off due to my lobe centers being off a couple?


Intake #1

21° BTDC

59° ABDC

Duration at .050" : 260°

Lobe Center : 109°



Exhaust #1

23° ATDC

62° BBDC

Duration at .050" : 265°

Lobe Center : 109.5

Your measured intake duration is off by 4* because your intake valve wasn’t open .050 at 25* btdc. It's .050
opening as you recorded it was 4* late (retarded) at 21* btdc, but closed right on cam card 59*abdc.
260* measured duration vs cam card 264* difference of 4*

Your measured exhaust .050 opening occurred at 62* bbdc, 4* after the cam cards 66* went by..
Your exhaust recorded .050 closing occurred at 23* atdc, 3* before the cam cards 26* made it to the pointer.
Measured duration 265* vs cam card 272* difference of 7*.


I would try setting your indicator (with the shortest extension) up on #1 intake’s retainer at Honda T mark/ true TDC degree wheel and carefully Preload indicator to  .500. Zero the indicator.  Loosen jam nut on intake #1 rocker arm and turn lash adjuster screw in until Indicator needle starts to move. Lock jam nut on Intake #1 rocker arm without moving indicator’s needle. This should get you really close to zero lash and take up all the clearance (slack) in rocker-arm bore to pin and pin to holder bore. Recheck intake opening and closing and see if you get 260* total duration again for the intake or whether it shows closer to 264*…I don’t think the cam grinder machine’s tolerances would allow a 4* duration error on the intake and a 7* duration error on the exhaust. 

[Don R]

 I was wondering if the valve could be at zero lash but already partially open?

[MRieck]

I was wondering if the valve could be at zero lash but already partially open?

That is why I always time cams at the running lash. If....for example....the intake valve is supposed to open at 20 degrees BTDC BUT you .005" of lash. Your opening will be delayed by 5 degrees and you will get the number on the cam card at 15 degrees BTDC. I never like that zero lash as I have seen people preload the valve which Don is alluding to.

[Tracksnblades1]

I was wondering if the valve could be at zero lash but already partially open?

That is why I always time cams at the running lash. If....for example....the intake valve is supposed to open at 20 degrees BTDC BUT you .005" of lash. Your opening will be delayed by 5 degrees and you will get the number on the cam card at 15 degrees BTDC. I never like that zero lash as I have seen people preload the valve which Don is alluding to.

That elusive and subjective zero lash is what brought the lobe center methods.
Less chances of set up and read errors…

[Don R]

 It can be difficult subject to wrap your mind around. I took a week off and came back to it last time.

[HondaMan]

I've always done it by measuring what the cam has on #1 cylinder, then on #4 cylinder. Too often I have found (except on Megacycle's cams) that I have to 'split the difference' between them, as they were not identical.

This said: the modern cam-grinder machines (CNC) should not have this issue today. Still, I find it once in a while: many of the performance cams we find in these engines now were made long ago...