Camshaft Timing Question
 

The engine in question is an ‘82 SC, stock cams. I have already searched the forums about this, along with the tech articles and Wayne’s book. The issue drives me nuts!

How do you keep the cam from rotating from valve spring pressure after you have turned the engine to overlap and reached the desired value? I find there is usually a lot of pressure resisting dowel pin removal, and when it finally comes out the dial indicator reading jumps about half a millimeter.

To me this is the difficult part of 911 cam timing, the rest is straight forward. I must be missing something here; what is it?

I always set up with all rockers in place.
Some just use a single rocker on measuring intake, that must be what you’re doing.
Each hole has a .fifteen variable that’s why you will jump half a mm.
Bruce

This.

So how do you account for setting the clearance on #2 and #3 doing that. Roll the engine through to each position untimed? I always figured the reason for only using one set of rockers, or just the intake, was to prevent potential interference while timing the cam.

if you are timing the valves with the intake lift method, fit 1 intake rocker to the 1/2/3 side only and do the lash. rotate the crank backwards past TDC and then rotate the crank clockwise but about 20° BTDC or about close to where the lift number you need will be at TDC. Fit up all of the drive parts and your indictor. Turn the crank until you get your desired lift. Then pull the pin and rotate the crank either clockwise to TDC or backwards past then clockwise to TDC. Fit the pin. tighten the nut or cam bolt, rotate the crank until you come back around to TDC and see what the lift is. Repeat until you get the number you need. The cam will not move. If it does for some reason, keep fitting the pin, checking and adjusting until you get it right. Remember there will be some play in the dowel pin so you can get the number you need on the nose. Typically if you error on the "hole" just before TDC the slack in the pin to hole will allow you to end on the nose.

If you want, you can remove the rocker from the # 1 cylinder , turn the engine 360° and repeat for the # 4 cylinder. Once the cams are set, you can go ahead and fit each rocker one by one and perform the lash.

A good check once you are all done is to rotate the engine until you achieve full lift on each valve and check against reference marks on the crank pulley. You may be surprised that they are not the same. This can be camshaft errors or rockers are re ground and the faces are not the same. If you see some differences and decide to leave, you can then understand why there might be some idle RPM differences.

There is no interference, just a nice breaker bar for resistance. When I put the heads, sub assembly, on rockers are torqued, adjusted, and complete.
Back crank about thirty degrees from TDC so the pistons are all below the top of stroke.
Install heads, turn cams dot up, advance crank to Z one. Install chain boxes, seal cam thrust, check parallel and adjust, cam wheels on chain, Tensioners in place, pin the cams, set number one,
Match number two
Bruce

As I was explaining
 

http://forums.pelicanparts.com/uploa...1516821405.jpg
http://forums.pelicanparts.com/uploa...1516821482.jpg

Thanks for your input, I will give those ideas a try.

So do you set the rocker arm lash on the flat/ base of the cam?

i've always wondered if it would be an easier way of seeting the valve lash.

You just have to know where you are on your firing order.
Remember the cams turn CCW for firing order and you have to skip the area for the other side heads. Just think about it...
Years ago I recall a shop saying pull the motor once a year for work and set the valves and check the stud torque then.
Bruce

I do it as Bruce, that is the only way for me, one old timer 911 mechanic taught me ...;-)

Ivan

On the base circle of the cam lobe. Valves closed.

Question.

Are these head assy's coming off or going on?

Spent another frustrating morning on timing the left cam for doing the valve clearance check. Didn’t get it done but I think I found an issue, at least for that side. I can’t explain how it got there but it is what it is.

The sprocket on that side fits the cam nose really tight. So tight, in fact, that I had difficulty getting it off when I decided to give up and disassemble things. That at least partially explains why there was so much difficulty adjusting timing as the sprocket wasn’t able to turn freely relative to the cam and change their relationship. Examining the sprocket bore I could feel two high spots on the back edge; tiny but definitely there. Now here’s the weird part. On the rear face adjacent to these high spots are two places where it looks like the sprocket has been struck by something, like a screwdriver blade possibly, that has offset the metal into the bore a little. If those had been on the front side I can see how someone might have tapped them onto the cam, but since they are on the back (at least in the last iteration of the engine) that side of the sprocket is inaccessible to hammer blows.

I’ve been thinking about the frustrations of this a lot. Maybe too much. However in doing so I have conjured up a scheme to assist cam timing that I think will work very well. Your opinion may differ; that's why I'm throwing this out for consideration.

So, here’s my idea.

Additional parts required (“tooling”):

M12 X 1.5 nut (Home Depot, etc.), M12 X 1.5 X 50 bolt that is threaded for the entire length OR
60mm bolt that has more threads than the existing camshaft bolt. It has 30mm worth of threads, we need more than that.

These bolts will involve going to a hardware place a little more specialized than Home Depot.

What you do with these items is run the nut up on the M12 bolt as far as you can, screw the bolt into the camshaft as far as you can, then run the M12 nut down and tighten securely against the cam nose. (This can be done with a pair of 19mm combination wrenches but if you wanted to get fancy you could get a cheap 19mm wrench, heat it with a torch, and bend it to fit the space better.) Now you have a tool you can use to either hold the cam still while you turn the crank (sprocket pin out of course) or just turn the cam itself. Once everything is indexed where you want it, undo the jam nut, remove the bolt, and replace it with the regular heavy washer and factory bolt.

My original thoughts on this were to just use the regular cam bolt with the nut run up on it. However it’s not long enough and thread engagement in the camshaft is insufficient.

You're correct that the fit of the sprocket over the cam snout needs to be loose enough that the two can rotate independently. If they are too tight because of the black stuff applied to the cam, you need to clean that off. We need them to be free or else you can't re-index the vernier assembly to allow the pin to be placed in a different sprocket hole.

You don't need to get another bolt and a nut. Just tightly bottom the original bolt in the snout of the cam and use that as your way of rotating the cam. Then cam can be turned with the bolt head. You just have to strategically install the bolt in the cam at the right time, w/out the big fat washer in place. Basically you use the specialty counterholding tool to hold the cam (with the indexing hub + woodruff key, chain sprocket and retention pin in place) and then snug the bolt all the way into the cam snout to create thread interference like double-nutting.

Once you've done that, pull the pin and use the tools to rotate the cam as desired to change the TDC overlap lift amount. Then hold the cam with the nut, put the pin in whatever hole will take it, put the sprocket holding tool back in the sprocket, remove the bolt so you can install the big washer, put the bolt back in torqued to spec, rotate engine 360 degrees and check your lift spec. Repeat as necessary.

I guess I was lucky, and everything worked out fine timing my cams to Bentley.

Will say this though, I studied the methods many times not fully understanding. But, when I blindly followed what the Bentley stated, it made total sense.

I understand the method fine, but the darned parts won’t cooperate! Technique is straight forward (if a bit fiddly when compared to the way 95% of the rest of the industry does it!).

I considered bottoming the bolt but worried about boogering (good technical term there) it up and thought thevjsm nut method would be more conducive to being able to turn it in both directions.

Isn't the sprocket flipped around if you move it from LHS to RHS? Maybe the sprocket was on the other side in the last life?

all i could say-add is ,pictures are worth 1000 words..so Steam lets see what are you doing there?

Ivan

Boogered is the proper engineering term for damaged threads or cylindrical deformations.... ;) :)

The new cams have the small bolt in the end of the cam and unlike the older cams, I could not get the bolt to hold the cam while removing the pin like Kevin suggested. For some reason, I could not get that to work.

On the old cams you had a tool that would hold and rotate the end of the cam. Not so on the newer cams.

The only way I could do it on my motor was to stick a small fillips screw driver in an adjacent hole when I removed the pin. I could then use that screwdriver to rotate the cam in relation to the chain sprocket.

Yea, yea, I had all the rockers in, etc, etc. Now my motor has a high lift cam with racing springs, so that added to the problem.

I use the screwdriver method too. At least on one cam, on the other you can hold it by the bolt..

Relative to a reply above, the sprocket was installed on the same side it came off of when I disassembled the engine. I marked and bagged them as I did so. So the boogered side was towards the heads and thus in accessible.

I will post some pics this afternoon or this evening. Inaccessible (not on this device) at the moment.

Late cams
 

I use a simple method for the bolt drive cams, if it’s a new assembly I install rockers on one cyl. With the key ways up on both cams and at Z1 pin both sprockets, say your timing spec is 6mm, roll it through and if you see it’s going to be more than 6mm at one revolution stop at your timing value, unpin the sprocket and continue the crank to Z1 then repin and you will be very close, If you are short of your timing value (within reason) go beyond Z1 to your value and unpin and back the crank up a bit beyond Z1 then in normal direction aproach Z1 and repin. That way you aren’t sticking screwdrivers etc. in the pin holes and wrecking them.
Hope this helps, Mike Bruns

OK, you asked for them, here are a couple of images of the damage to the sprocket:

http://forums.pelicanparts.com/uploa...1517002730.jpg

And here is a second image that shows the shiny spots on the inner bore a little better:

http://forums.pelicanparts.com/uploa...1517002730.jpg

Now here's a bonus. I just ordered the replacement parts from our host yesterday (1/25) and not early in the day either. THEY ARRIVED THIS AFTERNOON! I don't think I've ever had service like that before. I did not select or pay extra for expedited shipping either. The difference between the new parts and the old ones are pretty amazing as well; here are a couple of images of that:

http://forums.pelicanparts.com/uploa...1517002730.jpg

http://forums.pelicanparts.com/uploa...1517002730.jpg