cam timing question

OldTee · 02-09-2009, 04:34 AM

This may be a dumb question. Timing my 79SC I observed the following. Starting with the dots up on both cams I timed the left side with the pin not installed on the right side. When moving to the right side to time with the left cam at the the 360 past TDC for #1 I had to move the rs cam slightly to get enough lash to install the rocker for #4. I then rotated the engine 720 degrees and set #4 valve lash per the book. Rest of timing went as advertised.

My question is by moving cam slightly did the cams get out of wack with each other. Using TDC and valve lash seems to leave the opportunity to miss time becasuse the shoe at TDC is very large. (ie digital indicator does not move off "0" for quite a while).

I just answered my own question. You are setting TDC valve lash at the point where the valve just closed and it remains closed for a while. There fore the importance of an exact valve lash (1mm) initial setting.

PS I used two digital dial indicators. works great.

BK911 · BK911's Garage

I read your post several times and I am a little confused on what you are asking. Basically, if your valve lash is set correctly, then timing the cams sets their relationship to one another. You are supposed to move each side slightly to get the timing correct. After you tighten everything down, remeasure to verify nothing shifted. If the numbers are within spec, you are done.

2.70Racer · 02-09-2009, 12:12 PM

Old Tee,
When you are setting valve lash, you set the cam at TDC compression stroke.
At TDC compression, both valves have been closed for over 90 degrees and will remain closed for over 90 degrees.
As you can see this position for setting the valve lash is not critical at all.
Once the right and left valve lash has been set then of course you can proceed to timing the cams.
This is accomplishd at the overlap position for each cam.
For the either side the overlap position is 360 degrees past TDC compression.
The cam is then adjusted so the intake valve has opened between 1.4mm and 1.7mm.
Once one side has been adjusted and rechecked, the opposite cam overlap timing is 360 degrees from the first side.
To put it another way, when #1 is at TDC overlap, #4 is at TDC compression, and vice versa.
This is because #1 fires 360 crankshaft degrees from #4.
Probably more info than you were asking.

Rusty 356 · 02-09-2009, 01:34 PM

Do any of you rebuilders set valve lift at the maximum, allowing for chain wear and or stretch?

Flat6pac · 02-09-2009, 05:29 PM

I always set to the high spec as the chain changes length with heat and wear

OldTee · 02-10-2009, 03:59 PM

I understood the answers. My real headache and what disrupted my timing process was the fact that both cams were marked the same. Both said DC13 and both had dots. I got some help and we both discovered that the cams were mis marked. So.... the observation that one dot goes up and one goes down is probably norm but not universal. Grrrrrrr...

2.70Racer · 02-10-2009, 07:35 PM

Old Tee,
My solex cams from Camgrinder are one dot up and one dot down.
It would be nice if they were all dots or markings up.

OldTee · 02-11-2009, 03:51 AM

Quote:

Originally Posted by 2.70Racer

Old Tee,
My solex cams from Camgrinder are one dot up and one dot down.
It would be nice if they were all dots or markings up.

Consistency is only a word it seems, not a practice.