Cam Timing question, What do you think of these numbers?

[pano]

I just measured my cam timing.

To set the #1 piston (left side when sitting on the bike) on TDC, I used the positive stop method and confirmed it with the dial indicator.

I then measured my IN and EX cam lobe centers by zeroing the indicator on the spring retainer when the valves were closed (cam engaging rocker on base circle no lift position)

I measured twice and again double checked the TDC measurement.

I got the following numbers and used the following equasions;

IN numbers 0 and 59, so ((59-0) + 180) = 239, and 239/2 = 119.5

EX numbers 33.5 and 14, so ((33.5-14) + 180) = 199.5 and 199.5/2 = 99.75

Am I doing something wrong or do I have massive cam chain stretch???

 

[pano]

According to my manual and my measurments of the cam chain, it has stretched beyond servicable limits.

Do you think a chain stretch would push my lobe centers to where they are which to me seems way off?

 

[gtsg01]

I think that your numbers are off due to your methodology.

The numbers in the book are for the camshaft itself. In order to use the retainer as a measuring point, you must first set the valves to 0 lash. This will give you an accurate picture of your camshaft.

Also, you must subtract the BTDC value from the Intake and the ATDC value from the Exhaust. In this case;

Intake; 30+180+70=280/2=140-30=110 ATDC

Exhaust; 63+180+25=268/2=134-25=109 BTDC

Go back and get the the actual numbers from your cam and rerun the numbers. I think that you will still have a split in the IN/EX from chain stretch.

Forgetting to remove the ATDC and BTDC values is a common mistake, but once you understand it, it's pretty simple.

 

[massakins]

There may have been some room for error in the method used to determine TDC. If the stop or dial indicator were used to find TDC on their own at the top of the piston's travel you may have included some inaccuracy.

I was taught to use a stop that contacted the piston before TDC; the crank was turned until the piston touched the stop, degree wheel reading noted, then the crank was turned in the opposite direction until the piston touched the stop again and this degree wheel reading noted. TDC was halfway btween these two readings. I'd adjust the degree wheel to indicate TDC at this point and recheck to verify.

If a stop is used at the top of the piston travel only you'll find that the crankshaft can rotate several degrees without the piston moving. Plus the piston can rock in the bore and cause erroneous readings as well.

I try to adjust my cams to +/- 1/2 degree or less of the target readings and ensure they are repeatable when finished.

 

[pano]

I am using a positive stop to set TDC. I checked it with the dial indicator and agree there is some ambiguity with the dial indicator as the needle stops and does not change direction for several degrees on the degree wheel.

I have a book that says to put the indicator on the valvespring retainer, set the dial indictor to zero and turn in crank in the direction of normal engine operation. When the needle hits 1mm or .040 I take a reading off the degree wheel. Then continue to turn the crank until the dial indicator reaches the same .040 position on the way back. Then take that number.

I use those 2 readings from the degree wheel to figure cam timing.

It seems there are a few forms of the same equasion that get you to the same result.

I will redo every thing again today.

 

[BadBillyB]

Pano, Your method is correct, your math is correct, and since both are retarded about 10 degrees, you probably do have a stretched chain. The valve clearance does not affect the measurement of the centerline angle. I have found on my own bike that the factory TDC mark under the ignition cover to be "dead on" with the degree wheel after finding TDC with a piston stop tool......I check centerline a little different though. I zero my indicator at max lift, then mark the degree wheel at .040 before max lift and then .040 after max lift. Your centerline is half way between these points.......count the number of degrees from this point to TDC......BadBillyB

 

[gtsg01]

Link to WEB CAM

http://www.webcamshafts.com/degreeing.html

 

[pano]

Thanks for all your input.

I have read through a few cam degreeing websites but that is the best written one yet.

I will re check the timing using several indicator placement points, I want to try BadBillyB's. I think they should all be about the same result and I will finally stick to one method and use it.

I am making my baseline measurement before I put the slotted sprockets in.

Thanks again.

 

[BadBillyB]

I think that your numbers are off due to your methodology.

The numbers in the book are for the camshaft itself. In order to use the retainer as a measuring point, you must first set the valves to 0 lash. This will give you an accurate picture of your camshaft.

Also, you must subtract the BTDC value from the Intake and the ATDC value from the Exhaust.

Forgetting to remove the ATDC and BTDC values is a common mistake, but once you understand it, it's pretty simple.

Setting the lash to zero is needed to give you an accurate picture of the camshaft as far as duration and opening points goes, but it not necessary for determining lobe center.....And his figure for BTDC is zero, so......

0+59+180=239
239/2= 119.5
119.5-0(figure BTDC)=119.5
Seems right to me......BadBillyB