Topic: More Cam Timing

[Rocketman]

Putting my 550 back together after an off season refresh.  I have timed my cams before, but was never sure when making changes whether to advance or retard the cam.  So, I did both and noted the changes.  Now I know which way to rotate the cam to get the result I want.  There are detailed discussions of cam timing on the forum and each cam manufacturer also has instructions on their websites. Here are some pictures of how I do it.

Using a piston stop and degree wheel to find Top Dead Center.  The degree wheel is mounted to the original rotor bolt by drilling and taping a 6mm hole in the end.  There is less chance of a valve hitting the piston stop if this is done before the rocker assembly is mounted.





A flat piece of stock is needed for the base of the magnetic dial indicator holder.



I like to mount the dial indicator so that the face is visible while turning the crank from the right side of the machine.  I remove all lash so the valve clearance is zero and rotate the crank to 1mm (.040") of lift.





Hear are the specs for the cam I am using.



Since I have been using this cam I was able to install it and line it up with the witness marks on the sprocket.  My first attempt looked like this.

Intake  0 lash  1mm lift

23.5° BTDC
55°    ATDC
180°
258.5/2 = 129.25 – 23.5 = 105.75°

Exhaust  0 lash  1mm lift

52°  BBDC
24°  ATDC
180°
256/2 = 128 – 24 = 104°

Advancing the cam causes the intake number to increase and exhaust to decrease.

Intake

19° btdc
59.5° atdc
180°
258.5/2 = 129.5 – 19 = 110.25°

Exhaust

47 bbdc
29 atdc
180
256/2 = 128 – 29 = 99°

Retarding the cam causes the intake number to decrease and exhaust to increase.

Intake

28° btdc
50.5° atdc
180°
258.5/2 = 129.25 – 28 = 101.25°

Exhaust

56° bbdc
20° atdc
180°
256/2 = 128 – 20 = 108°

Where I ended up.

Intake

24.5° btdc
55° atdc
180°
259.5/2 = 129.75 – 24.5 = 105.25°

Exhaust

53° bbdc
23.5° atdc
180°
256.5/2 = 128.5 – 23.5 = 104.75°

Not exactly as called for on the cam card, but as close as I could get it.  The differences could be due to measurement error or manufacturer error.

I then set the lash at .004 IN and .005 EX to see what effect that has on timing.  It did have a very small effect, but again that could be measuring error.

Intake

23° btdc
53° atdc
180°
256/2 = 128 – 23 = 105°

Exhaust

50° bbdc
20° atdc
180°
250/2 = 125 – 20 = 105°

[flatlander]

that looks very good. i don't think anyone can get more accurate than that!

[bwaller]

Done & done! Obviously that one does the job but one suggestion for the future, look for a larger degree wheel, larger the better. It will simply help you with accuracy.

Did you need to replace anything in your refresh?  When is your first outing?

[MRieck]

Done & done! Obviously that one does the job but one suggestion for the future, look for a larger degree wheel, larger the better. It will simply help you with accuracy.

Did you need to replace anything in your refresh?  When is your first outing?

Head was checked over Brent. New springs and exhaust valves....pulled great vacuum on the Serdi....good to go.👍

[Rocketman]

All that is left is to seat the rings.  Will do a 3 short runs on the stand and then 3 progressively longer runs on a go kart track.  Can’t really get much out of 1st gear, but the acceleration and de-acceleration in 1st loads the rings and seems to do a good job seating them.  Best of all the track fee is $10 for the day!  First race on the schedule is Heartland in Topeka, KS with AHRMA at the end of May.  Shooting for New Jersey in June and Mid-Ohio in July.  Barber with AHRMA is in October, so looking for something in between.  Wish Mosport was still at the end of August. 

[MRieck]

All that is left is to seat the rings.  Will do a 3 short runs on the stand and then 3 progressively longer runs on a go kart track.  Cant really get much out of 1st gear, but the acceleration and de-acceleration in 1st loads the rings and seems to do a good job seating them.  Best of all the track is fee is $10 for the day!  First race on the schedule is Heartland in Topeka, KS with AHRMA at the end of May.  Shooting for New Jersey in June and Mid-Ohio in July.  Barber with AHRMA is in October, so looking for something in between.  Wish Mosport was still at the end of August.

I am planning to be at New Jersey in June Martin.

[bwaller]

Hummm, Jersey in June. What's the date?

Mosport is Aug 5-7th.

[slikwilli420]

June 16-19 Brent. I'll be there with George as well. That's means you have to be there! SOHC reunion!

[grcamna2]

subscribed

[Ramrod_Racing]

June 16-19 Brent. I'll be there with George as well. That's means you have to be there! SOHC reunion!

Well shoot. I'm planning to skip NJ this year to spend all my money out west

[slikwilli420]

June 16-19 Brent. I'll be there with George as well. That's means you have to be there! SOHC reunion!

Well shoot. I'm planning to skip NJ this year to spend all my money out west

That's a tough call either way. I would love to do the double header out West but that's an investment I just can't stomach this year. The Ridge looks incredible though.