Cam Timing Questions

[magic930]

This is my first time timing cams and I want to be sure I do this right...

First problem is my three pin cam tool does not seem to fit very well... do I file the pins until it fits snug or are there only a few positions where it actually fits and seats properly?

Setting the initial position for the CAM to be "straight up" is really guesswork and could easily be off by a few degrees. I assume this is the purpose of the exact timing which is measured by the dial gauge. Is the process of setting the valve clearance then measuring overlap repeated until both the overlap and clearance is correct?

Seems like using the dial gauge is a much more accurate way to measure the rocker clearance than a feeler gauge. Or is there too much slop in the elephant foot to do it this way?

When adjusting the cam timing with the Dial guage in place the rebuild book mentions holding the cam while turning the crank such that the cam and therfore the dial does not move. I can see how this turns the cam sprocket to a new position but on my '87 cams which are held by a 19mm bolt there is no way to hold the cam in place while you do this. Once the pin is out all bets are off. Am I missing something here?


Any help appreciated.

[ChrisBennet]

Originally posted by magic930
First problem is my three pin cam tool does not seem to fit very well... do I file the pins until it fits snug or are there only a few positions where it actually fits and seats properly?
I've bought 3 of these tools over the years. 1 fit great, 1 didn't fit (sent if back), 1 fit OK. I'd send the tool back and try again.

Setting the initial position for the CAM to be "straight up" is really guesswork and could easily be off by a few degrees. I assume this is the purpose of the exact timing which is measured by the dial gauge.
Yes, the "both up" position is just the rough timing setting.

Is the process of setting the valve clearance then measuring overlap repeated until both the overlap and clearance is correct?
Just set the valve clearance and leave it. The overlap region (where neither rockers are not on a cam lobe) is pretty wide.

Seems like using the dial gauge is a much more accurate way to measure the rocker clearance than a feeler gauge. Or is there too much slop in the elephant foot to do it this way?
I've never tried it but it seems like a pain and you can't do it in the car.

When adjusting the cam timing with the Dial guage in place the rebuild book mentions holding the cam while turning the crank such that the cam and therfore the dial does not move. I can see how this turns the cam sprocket to a new position but on my '87 cams which are held by a 19mm bolt there is no way to hold the cam in place while you do this. Once the pin is out all bets are off. Am I missing something here?
I just put the bolt back in and give is a little pffft with the impact gun. Then use the bolt to turn the cam.

The essence of measurement is consistancy. If you turn the motor over 6 times and get something other than "zero" at TDC (every other revolution) on the dial indicator. Change your chain tension, see if you have too much assembly lube on the cam, etc

-Chris

[Jim_0068]

Your best bet is to do these few things:

1) go buy Wayne's "How to rebuild and modify...." book. It is only $30 or so and comes with a great CD if you order from pelican parts

The whole procedure is simplified and is easy to understand. I was confused before i got that book. Basically what you are going to do is only install the rockers for cylinder #1, make sure the cam is positioned so that the punch mark on the cam is at 12 o'clock, tension the cam with some vise grips against the case, make sure #1 is at TDC, adjust the valves for #1, then go through the procedure for setting the cams in the book

The best tool for this is the Z-block that holds a dial indicator exactly parallel to the valve. This is also available from pelican parts for like $25 i believe.

[Tim L]

As far as the cam turning with the pin and bolt removed it doesn’t move in my experience.

Tim

[magic930]

I do have the book and the correct tools I was just a bit confused. I have the #1 and #4 rockers in place and hope to finish the timing in the next few evenings.

The CAM bar is particuarly irritating because it does not seem to fit in most of the holes or where it might fit there are studs in the way on the chain housing. Holding it steady while tightening the bolt is another challenge and seems to be a place where error is easily introduced.

In particular the process for insuring that the cam remains vertical or is truly vertical to begin with and stationary while tightening or moving the crank is difficult. Once the 19mm bolt is on, all markings are covered. So how critical can "vertical" be or is "truly vertical" the postion which the process trys to achieve?

[hobieboy]

With the pin & bolt removed, mine actually "jumped" just as magic930 experienced/speculated.

Luckily, it only happened on the left CAM. I used the 2 bolts in the front of engine for mounting the scavenge pump as levers to hold the cam in position.

I think what you can also do is to use the 19mm bolt, thread it all the way in then use that as lever, assuming your CAM does not have enough lift at this point.

HTHs...

[Jeff Alton]

My cam tool did not fit that well either. A little touch up with the Dremel and it works like a charm.

Jeff

[ChrisBennet]

Originally posted by PatrickT
With the pin & bolt removed, mine actually "jumped" just as magic930 experienced/speculated.

When I want to move the pin I turn the engine backward a 1/4 of a turn to take the pressure off the rocker. This way the cam doesn't want to spin when I remove the pin.

I realize there are probably better ways but the method I've come to use is simple and methodical and avoids the slipping cam.

Step 0) First I mark the initial pin hole with a crayon.

Step 1) Rotate the motor one revolution to TDC and check the reading.

Step 2: Turn motor backwards a little to take pressure of the rocker, remove the pin, rotate the cam just enough that I can put the pin in adjacent hole, put the pin it and write it down it's position relative to the initial pin hole ("2 holes counter clock wise").
Then I turn the engine forward to TDC, and look at the indicator.

Step 3a) If the indicator is reading in the ballpark, I remove the bolt, put the big washer on and put the nut/bolt back and tighten it up.

Step 3B) If the indicator is not reading where I want it, I repeat Step 2.

Step 4) Turn through 2 rotation and read the indicator. If it looks close, I torque the nut or bolt to spec and then check the settings several times (i.e. 3 times = 6 revolutions).

-Chris

[magic930]

Thanks for all the responses and advice. I spent a half an hour filing my CAM tool to fit properly then went at it. After actually doing the timing it now makes more sense then just reading about it. I did not have any trouble with the CAM slipping as I thought would happen.

I had read that with SC CAMs on the 930 .9-1.1mm gives mid and upper range power and 1.4 to 1.7 is for low end power.
So I managed to get the CAM set to exactly 1.4mm (SC CAMS) on the left side and will do the other side tomorrow.
Anybody else with a 930 and SC cams? What overlap did you use?