Help! Cam Sprocket Alignment
 

This is a little long so I apologize in advance but I am at my wits end and need help.

I just put the cams back in my 1983 911 SC. When I took the car apart I wire tied the cam sprocket, the timing sprocket behind it, the shims, fat washer and sleeve together so that I wouldn't lose track of what came from where and which order they went back. I bagged and labeled each for the side it came from.

I put these components back the same way that they came out, with the right #of shims (4 shims on the right and i believe 4 on the left) in the right locations. The fat washer has the bevel towards the cams. I expected that the alignment check today would be a matter of formality. It wasn't and I am now a little stumped.

I used the stromski racing holder and straight edge to take my measurements and did so a number of times, so I believe they are pretty accurate. I also made several measurements around each sprocket. The below measurements, with the exception of the imtermediate shaft, are from the top of the straight edge so you need to deduct 1.05" (26.67 mm) from the measured numbers.

My measurements were:
Distance to intermediate shaft end from case 0.34 in (8.636 mm)
Distance to the Left Sprocket from top of bar 5.153 in (130.429 mm)
Distance to the Right Sprocket from top of bar 3.03 in (76.962)

Checking these measurements for the right sprocket:
76.962 - 26.67 - 43.27 = 7.022 mm (1.614 mm short)

Checking Left SProcket
130.429 - 26.67 - 54.8 - 43.27 = 5.689 mm (2.947 mm short)

That's a lot to take away. On the right side that is 3 shims and on the left side it is more shims than I have.

I've also noted a few other things. When I tension the chain and measure, it is parallel to the chain guides in each of the housings. The guides are pressed all the way to the back of the housing.

The idlers, which also ride with their busing at the back of the housing are perfectly aligned with the chains. If I move the sprokets back by 1.5-2 mm, it looks like this will effect the positioning of the chain on the idlers. I don't think it will align at all with the idler.

Finally, I took a washer that measures 1.5 mm thick and placed it behind the chain in the left housing to see how much movement the removal of shims would have on the chain and it puts link pin right neat the ribs on the housing wall (See the first picture).

One more thing, when we started the teardown, we took measurements the same way and the new readings are very similar to the originals. Not that that makes it right.

The only thing that would lead me to believe that the sprockets should move back is that the sprocket is riding a bit out on the cam shaft (see picture 2)

http://forums.pelicanparts.com/uploa...1153697625.jpg http://forums.pelicanparts.com/uploa...1153697779.jpg

Thanks in advance
Rick

As a point of reference, the initial reading before teardown were:

Left Cam (5 readings):
131.4
131.25
131.4
131.3
131.25

For an average of 131.3

Right Cam (6 readings)
76.7
76.5
76.7
76.6
76.8
76.9

for an average of 76.7.
Rick

I guess the issue is whether the layshaft is actually within it's 'design' dimension or not, you didn't mention in your second post whether you had measured the distance when you did the teardown. Or if you had the engine completely apart and refurbished/replaced the layshaft etc. Perhaps it is not completely seated?

Rick:
I just did the same on an '82.
It had 4 shims on each side and showed normal wear on the sprockets, so, it was aligned before the tear down.
I used Wayne's book page 158-159 and common sense.
It took a few measurements, and a lot of thinking, to end up with the right numbers in the end.
Consider this: If the sprockets are installed correctly (Left side concave out, Right side concave in) the same shims are used and no changes were made, it has to be the same alignment.
Are you using the old chain sprockets on the I-shaft? Installed new ones?
Did you do anything to the I-shaft? New bearings?

Quote: "The only thing that would lead me to believe that the sprockets should move back is that the sprocket is riding a bit out on the cam shaft (see picture 2)"
No, that's normal; the big washer on the center bolt has to press against the sprocket, not the shaft.

You need to tighten the cam sprockets with the center bolt when measuring.
Is the whole assembly installed as per page 158 in Wayne's book? Thrust plate, gasket, O-ring, fat washer, shims?
Is your case pre- or post 1983 1/2?
The measurement for the right side should be the same as the one from case edge to I-shaft dimension.
On page 159, figure 6-9, which method do you use?
With the depth feature on your caliper, what measurment do you get on the I-shaft in mm?

Gunter, RVP,
I didn't do anything to the intermediate shaft. I only did an uper end job to replace broken studs. While I was there I did the heads and had pitting ground out of the cam shaft but had them ground to stock. Nothing there that should have affected the lateral distances.

Interestingly, if you look at my second post above, the alignment before and after looks very close.

I have the left sprocket concave out and the rigth one concave in. The order of placement was like wayne shows on p. 158.

When I worked the numbers with Wayne's book, I found that I must be post 1983-1/2 because my right sprocket is closer to the 43.27. dimension that he references for post. And the method used was the right picture in figure 6-9.

I shaft measurement was 8.636 mm.

Oh. I did also torque to spec before measuring.

That is good information about the placement of the sprocket on the shaft.

Rick

With chain tension off, do you remember if you had a little end-play in the cams? I.E. could you move them freely back and forth?
Did they turn easily without the chain on it?
If all is well, they should turn easily and have a little end-play.
It is curious that the alignment before and after is about the same which leasds me to believe that the discrepancy is elsewhere.
I remember clearly that my first sets of measurements came out screwy, some more thinking, some more measurements and it turned out that my calculations were wrong.
The same logic: The cam assembly went in the same way it came out, so, it must be right. And in the end it was.
Try a regular straight edge from the case edge and measure to the right sprocket with depth-calipers. Subtract the straight edge from the measurement.
Is that not the same as the figure from the I-shaft to the case as per 6-9 page 159?

Gunter,
Thanks for staying with me on this. Without tension on the chain, both cams turns freely with finger pressure and both shafts do have a little end play.

The inital readinga were taken by my friend with a metric vernier caliper. The final reading were taken by me with an english dimensioned caliper. I thought that I miscalculated the conversion but I have tried the measurements and conversions a number of different ways. I'm not going to rule that out though. I just ran to the shopto check the measurement on the intermediate shaft again. I will be back in the shop tomorrow night and will check everything again.

I think you last question was whether the I shaft measurement and the right sprocket are the same. According to the book that is only on pre 83-1/2 cars

I don't understand the part about measureing to the intermediate shaft end. That is your .34" measurement. As far as I know this measurement has no bearing on the situation. You need to measure the depth to the front sproket on the shaft. There is a hole offset at about the 5 o'clock postition to measure this. The number should be the same as the number to the face of the right sproket.

-Andy

True, but.......................
Try to measure the I-shaft as if you had the pre-1983 1/2 case.
Otherwise, of course, the 43.27 mm come into play according to Wayne's book.
I didn't have to use it with my '82, it was straight forward on the right side; after several tries with a metric vernier, the numbers were the same.
I used a straight edge pressed agains the case.
On the left, the area on the sprocket for measurement is much smaller because of the concave.
See what happens when you try the first method.

Not on later cars, in their case there is a 'design' depth that the sprocket face on the Layshaft to the end of the shaft should be, so you measure the end of the shaft and add the design depth.

Are you sure you have the correct conversion? It is pretty hard to convert inches to metric at those accuracies? Based on your original measurements I woul d think you are OK as they match so closely. In the end if you are taking the measurements the same way, and you get the same readings as you had with the factory setup, you should be good. Since you can't actually measure the layshaft offset you can't confirm that it is to design parameters

Hold the presses. I think I might have found the problem. I have beem walking around all day picturing every detail of the measuring process. I will check tonight and let you know. Not to give it away, but if it is what I think it is, I'm a dope :-).
Rick

Eagledriver hit on it. The face of the drive sprocket on the intermediate shaft is THE dimension.
Whatever you measure thru the access hole to the FACE of the sprocket is where you set the FACE of the right hand cam sprocket.
You don't care about inches and millimeters. Same dimension.
Now the left side. 54.8mm further than the right side.
So what's that in American? 2-5/32" is within ONE thousandths of an inch of 54.8mm.
54.8mm=2.157 inches, 2-5/32"=2.156"
Get it there and call it perfect.
So lets say your measurement happens to be the "design" number, 43.27mm. Great, whats that in American? How about 1.70 inches.
Thats where the face of the RIGHT side cam sprocket goes. Yes 1.70".
Add 2.157" plus 1.70" equals 3.867" American. That's where the face of the LEFT side goes. Remember this is for the "design dimension".
If your measuremnt thru the hole is different than 1.70" then IT IS the right side dimension. Add 2-5/32" and you have the left side.
The difference between the right and left will always be. 2.157"=2-5/32". Simple.
Don't let the conversion get you lost. You've got it in American now.

Actually, the origin is English. And what a mess when you get into how many feet are in Nautical Miles vs. Land Miles, etc,
(Or Withworth threads, LOL)
In Engineering, we worked with both, millimeters and inches, and it quickly became apparent how superior the metric system is.
We have to thank Napoleon for this one.
Strangely enough, the American military, and pharmaceutical industry, adopted the metric system years ago, so, why not the whole country?
Anyway, waiting with anticipation for Rick to report back on the mystery.

I found my mistake. I misread the caliper when measuring the thickness of the straight edge. I read 1.05" and it should have been 1.005". The difference was 0.045" or 1.14 mm.

When reading the right sprocket, this measurement was used once. So with the correction, I am off by 0.47 mm.......1 shimmust be removed.

For the Left sprocket, this measurement was used twice. So sith the correction, I am off by 0.667 mm........1 shim must be removed.

Sorry for the confusion but thank you all for helping me think it through.

By the way, I rechecked all of the measurements last night and it checked out.

Final question: This car existed with this shim configuration for the last 23 years without failure or evidence of adverse effecs. If there was any chain stretching, wouldn't it have occured already. I am not replacing the chains. Is it really a good idea to remove the shims and change the stresses on the existing chains?? or is 0.5mm so small a difference that it is not even worth thinking about any further?
Rick

Good news: I thought it would be something simple; most standard straight edges are 1" = 25.4 mm.
Keep in mind that for these measurements, the end play on cams and I-shaft has to be considered.
Both shafts are either all the way "In", or all the way "Out" for the alignment to be correct.
The alignment has no real effect on "Chain-stretch".
If it is off, it'll show as wear on the sides of the sprocket-teeth.
In my case, according to my measurements, one shim should have been removed on the left side.
But I left it thinking that it run fine before and the end-play-float will take care of it.
You can remove the shim if you are sure of your measurements.
Good thing you didn't replace the chain.
Replacing the chain without new chain sprockets is a disaster waiting to happen; search for one of my posts on this subject.
Best wishes.

Rick,
I'm sure you are getting anxious to get your car up and running. I would replace the timing chains, unless you are anticipating getting back in your motor in the next year or so.
If you think you can get the sprocket alignment better, do it.
I enjoyed your question and I understand all this better because of it.
Gunter, since we Americans are among the last in the world still clinging to the old archaic English system, which even the English have disavowed, I'm calling it "American". Kind of my commentary.
Converting everything just adds one more layer of BS before we get answers, eh.

This has certainly been a learning experience for me.

Now, I know I said one more question, but I have one more. In my last post I was kind of asking the question: if it ain't broke why fix it. but it sounds like I can answer this question myself by examining the spocket wear. If there is wear on the side of the sprocket facing me, I assume that is indicating that it is shimmed out too much. If there is wear the the other side (facing the cam towers) then I need to add shims. I'm thinking more in terms of validating my measurements than using it to make the decision.

Does that sound right?

I know I show some wear on the side facing me so if the above is true, it would validate the measurements that suggest I need to remove shims.
Rick

Rick,
Sounds right to me.

I removed Thank you all again for your knowledge and support.

Let's try this again.

I removed 1 shim from each side tonight and rechecked all measurements and I am now where I need to be.

Again, thanks for all the knowledge and support.
Rick