Camshaft Sprocket Alignment

[patkeefe]

Hi all:
I have an engine which I built like 10 years ago. It has been sitting sealed up in the basement. This is an older 7R 2.7 case, and it was basically a basket of parts I rounded up and built the engine from (except for the thousands of dollars worth of new stuff). I think there is an SC oil pump in it, but I don't remember. I have no inclination to take this apart to verify anything. I am now going to use it, and I had Mr. D. Elgin regrind some old "E" cams to a Solex profile. I just put these cams in, and I am aligning the sprockets. I am having some issues of the head scratching variety.

Using Wayne's book as an example:

I have measured the case face to drive sprocket dimension, which is 2.030". Measuring with a vernier and straightedge to the right side sprocket, I am getting 1.870". Hmmm. There is no way I can remove all of the shims to get to the 2.030" dimension )which would indicate to me that the sprockets are parallel in the same plane).

Since I built this so long ago, I do not remember any details of the chain drive sprockets. Is there something in the drive sprockets that could cause me to be almost a quarter inch off in my measurement? The chains look fine when I assemble it with 3 shims on the left and four shims on the right, but this measurement is disturbing.

Anyone got any light they can shed on this?

[boyt911sc]

Pat,

What is the distance of the driver side sprocket from the crankcase edge? Passenger side? How deep is intermediate shaft end from edge of crankcase? These are the three (3) measurements you need to determine the alignment.

Could you measure them in metric? I will give you an example of my recent cam alignment data:

Driver side (using a 1” Stomski straight edge) = 132.10 mm
Pass. side (using the same straight edge above) = 77.10 mm
Intermediate shaft depth from crankcase edge = 8.26 mm

Computations:

DS sprocket:
132.10 mm -(25.4 mm) - (8.26 mm) = 98.44 mm (spec.= 98.07 mm)

PS sprocket:
77.10 mm - (2.54 mm) - (8.26 mm) = 43.44 mm (spec. = 43.27 mm).

The delta from spec:

DS = 98.44 - 98.07 = 0.37 mm
PS = 43.44 - 43.27 = 0.17 mm

If you have any question about the computations, please let me know.

Tony

[r lane]

Gotta ask, but are the cam gears facing correctly. One flush, one concave.

[Walt Fricke]

My first thought also.

[patkeefe]

Tony, I will measure it and convert to mm later tonight.
And, the cams are assembled as they should be. But, there is something wrong, hopefully something silly.

Also, I call the drive sprocket the sprocket on the intermediate shaft. The cam sprockets are the driven sprockets. And, drivers side is left, passenger side is right?

[Phillip_G]

I just did this a couple of weeks ago and ended up purchasing the Stomski tool because I was getting measurements all over the place trying hold my strait-edge and caliper perpendicular. The tool made it a lot easier. My previous cam installations had using the reground original cams, so original shims were within spec (3 on left, 4 on right) but this time went with new DC-40 cams and ended up needing an extra shim on each side.

Also, another tip is to tap the cams and intermediate shaft forward with a plastic mallet before taking the measurement. There is a bit of fore/aft play on the cams.

Phil

[boyt911sc]

Originally Posted by patkeefe

Tony, I will measure it and convert to mm later tonight.
And, the cams are assembled as they should be. But, there is something wrong, hopefully something silly.

Also, I call the drive sprocket the sprocket on the intermediate shaft. The cam sprockets are the driven sprockets. And, drivers side is left, passenger side is right?

Pat,

Double check the cam sprockets’ orientation.
Cylinder 1-2-3: concave face towards rear bumper.
Cylinder 4-5-6: concave face towards the front bumper.

You could easily commit his blunder until you do the alignment measurements and find the mistake. Let’s see your measurements and analyze where the discrepancy occurs.

Tony

[patkeefe]

OK,here are the net dimensions:
Center drive sprocket is 50.75 mm
Right side is 46.25 mm
Left side is 107 mm

So, when we measure the center (drive) sprocket face, it is 50.75 mm from the case, with the face of the case being the reference. The right side should be also 50.75 mm. For the chain to be running "straight", the depth of the drive sprocket and the depth of the driven sprocket should be identical. This is assuming the intermediate shaft can be installed only one way. It is possible the intermediate shaft is from, say, a 3.0L which may or may not be dimensionally different from a 2.7 intermediate shaft. But, I don't know. I will have to research the parts further.

BTW, the left side sprocket cannot be installed with the concave side facing to the front of the car...interferes with the chain box gusset, and will not allow the cam to turn.

[boyt911sc]

Pat,

You need the measurement of the intermediate shaft front to crankcase edge. Without this value you can not calculate or compute for the alignment of the camshaft sprockets. Take the measurement point from the flat side near the gear teeth for both sides to the straight edge (ruler) minus the depth of the intermediate shaft front.

How many shims do you have at the left and right side respectively? The left side is very close to my calculation but the right side is about 5 mm short. Are you sure you had the thrust washer installed?

Do you have an Bentley SC Service Manual? Take a look at page 102-31 (Engine Disassembly and Assembly).

Tony

[patkeefe]

Hi Tony. I got your message, Let me look at the Bentley.

[patkeefe]

So, it seems I have been measuring from the wrong spot. The reference measurement, according to Bentley, is the face of the intermediate shaft, which is around 0.340" from the face of the case. This is per Bentley illustration page 102-31 (duplicated on 151-10).
My previously measured dimension "B" is 1.87". Bentley says it should be 1.70" +/- 0.01". So, by screwing around with the shims, I can get a net dimension of 1.71" by using three shims on the right side. I haven't done the left side yet.

So, yes, I was doing something incorrectly. Sincere thanks to Tony D. for pointing this out to me.
Now, I have to find my depth micrometers to do the right side, as my Vernier caliper is not long enough.

[boyt911sc]

Originally Posted by patkeefe

So, it seems I have been measuring from the wrong spot. The reference measurement, according to Bentley, is the face of the intermediate shaft, which is around 0.340" from the face of the case. This is per Bentley illustration page 102-31 (duplicated on 151-10).
My previously measured dimension "B" is 1.87". Bentley says it should be 1.70" +/- 0.01". So, by screwing around with the shims, I can get a net dimension of 1.71" by using three shims on the right side. I haven't done the left side yet.

So, yes, I was doing something incorrectly. Sincere thanks to Tony D. for pointing this out to me.
Now, I have to find my depth micrometers to do the right side, as my Vernier caliper is not long enough.

Pat,

If you use metric measurement, we will be in the same page. I calculated the left side cam sprocket of your engine and came up very close to “spec.”. It is only the right side that needs special attention. Last night, I went down to the basement to do some measurement with the intermediate shaft and compared your data. There was a 5 mm discrepancy between your data and the spec. That’s the reason I was asking about the thrust washer. You should be good now.

Tony

[patkeefe]

Tony,
I finished screwing around with alignment just now ( I have to fly up to NY this afternoon, for a week, so I wanted to get this done).
Left side is now at 98.04 mm using five (5) washers.
Right side is 43.43 using three (3) washers.
I am calling it good.
I'll time the cams when I get back before Christmas, because I likely need one full uninterrupted day to do those.
Thanks again!
Pat