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Left sprocket measurements.

Its been about 10 years since I rebuilt a 911 engine and was aligning the sprockets tonight right side is right on with 3 shims. For left side waynes book references adding 54mm to the measurement to determine alignment.. What am I missing here? That doesn't make sense wouldn't I want to subtract? Any guidence for a guy relearning?
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Old 06-05-2018, 06:38 PM
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Timing sprocket alignment.........

Quote:
Originally Posted by mb911 View Post
Its been about 10 years since I rebuilt a 911 engine and was aligning the sprockets tonight right side is right on with 3 shims. For left side waynes book references adding 54mm to the measurement to determine alignment.. What am I missing here? That doesn't make sense wouldn't I want to subtract? Any guidence for a guy relearning?


Ben,

The left sprocket (1-2-3 cylinders) alignment distance is 98.07 mm (+/- 0.25).
The right sprocket (4-5-6 cylinders) alignment distance is 43.27 mm (+/- 0.25).

The difference between left and right sprockets alignment distances is 54.8 mm.

The Bentley SC shop manual has a very nice diagram for reference. HTH.

Tony

Last edited by boyt911sc; 06-06-2018 at 01:59 AM..
Old 06-05-2018, 06:53 PM
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The right side is within .003" to the layshaft.. The left side I am trying figure out how much I need to subtract so I can compare from right side..

Tony is that what your getting at?
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Old 06-05-2018, 07:10 PM
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Show me your data.........

Quote:
Originally Posted by mb911 View Post
The right side is within .003" to the layshaft.. The left side I am trying figure out how much I need to subtract so I can compare from right side..

Tony is that what your getting at?


Ben,

What are your measurement data? The procedure is very simple. Measure the following:
a). Measure the depth of the intermediate shaft face in mm from the edge of the crankcase. Call this A.
b). Use a straight edge to measure the distances of the left and right sprockets. Call the measurements L (left) and R (right).

Calculations:

L - A = is your left side sprocket alignment distance value. Control L = 98.07 mm
R - A = is your right side sprocket alignment distance value. Control R = 43.27 mm

Compare your measured distances to the controls with 0.25 mm +/- tolerance.

Tony
Old 06-06-2018, 02:44 AM
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I was using waynes book as a reference.

I measured layshaft/intermediate 1st

Second I measured right sprocket with straight edge and compared to 1st measurement and adjusted out 1 shim to get them within .003"

3rd measured left side and then stopped.

I will reread it today.. It was a long day and probably just tired..
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Old 06-06-2018, 03:09 AM
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Just re-read the 911 hand book by Bruce A and now makes sense. I will recheck today.
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Old 06-06-2018, 05:31 AM
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Start with 3 shims on the left. It will probably be close with 3 shims.
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Old 06-06-2018, 09:20 AM
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So I have the following measurements



Layshaft=A 2.035"
Right sprocket 3 shims = 2.030"
Left sprocket 4 shims = 4.261"

So backwards to a point but cam boxes and cams are from different engines

Thoughts?
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Last edited by mb911; 06-06-2018 at 12:58 PM..
Old 06-06-2018, 09:35 AM
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Strange numbers you got here.........

Quote:
Originally Posted by mb911 View Post
So I have the following measurements



Layshaft=A 2.035"
Right sprocket 3 shims = 2.030"
Left sprocket 4 shims = 2.035"

So backwards to a point but cam boxes and cams are from different engines

Thoughts?


Ben,

The difference for the left and right alignment distances is 54.8 mm (theoretical). I am not sure where you are doing the measurements but your numbers are way off the chart. What do you mean layshaft = 2.035? How come this is the same as the left sprocket? Please use mm instead of inches for better communication.

Are you aware that the sprocket orientations (offset) when installed are different from left to right? Left sprocket offset facing outward, right sprocket offset facing inward. Take a look at the picture below:



Are we on the same page?

Tony
Old 06-06-2018, 12:15 PM
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Tony the layshaft is being measured via the early way as it a 72 case.
We are on the same page..

I don't have a caliper that measures mm.. Sorry just the starret dial caliper (manual)
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Last edited by mb911; 06-06-2018 at 12:59 PM..
Old 06-06-2018, 12:18 PM
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Here is the reference I am using. Fromt what I am reading is layshaft and right sprocket need to match as close as possible and then take that measurement and add 2.157" or 54.8mm to come up with the left side.

That appears correct. I am closer now.. A little tweaking now. Look at my post has amended measurements. Keep in mind I did this on 6 911 engines in the past but haven't for 10 years so foggy I suppose..

Relearning..
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Old 06-06-2018, 01:02 PM
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Old 06-06-2018, 01:04 PM
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