Measuring Sprocket Alignment

88911coupe · 09-26-2008, 05:28 AM

I can't seem to find this issue addressed in other threads so I'll ask here. I can't seem to get a consistent measurement for the face of the IMS spacing on my '88 3.2. Using picture 6-9 on page 159 in Waynes book for reference, I get different measurements at different spots on the face of the thing attached to the IMS with a circlip. Is there one "spot" it needs to be measured from, i.e. the spot in Wayne's pic? I also lightly tapped it with a socket to make sure it's seated and I'm still gettting variations, obviously not much but enough to confuse me.
TIA

hcoles · 09-26-2008, 06:24 AM

what tools are you using - Stomski block and straight edge bar?

88911coupe · 10:04 AM

Nether apply for this particular measurement. I'm measuring the distance from the case "face" back to the end of the IMS. If you have Waynes book handy it's picture 6-9 (page 159)it's measured using the other end of the caliper used to measure the "depth" of the spacing. I have a straight edge to measure the sprockets but this particular measurement does not need them.
Thanks for the help

Bobboloo · Bobboloo's Garage

Actually the straight edge does apply since it supplies the reference point for the cam timing sprocket.

I would think your best off measuring from the place where the straight edge rests on the case.

I would also turn the crank clockwise to get the IMS to find the position it has when the motor is running. Tapping it will take it out of it's rotating position.

euro911sc · euro911sc's Garage

If you are using a vernier caliper with depth measurement from the protruding shaft you can get some variation due to not being at 90 deg. Its hard to get the end of the caliper to be good on the slight surface to measure the intermediate shaft depth. You may wish to invest in a depth gage which has a much larger surface to keep it steady and at 90 deg. to your hole. I took 10 measurements and averaged thinking I would error on a normal distribution

Had the same problems using a straight edge to get cam sprocket measurements... no Stomski tool, just an AL construction level...

Best regards,

Michael

hcoles · 09-26-2008, 12:32 PM

okay, I need to go look at that page and see if I have any intelligent comments.

Bobboloo · Bobboloo's Garage

Quote:

Originally Posted by euro911sc

If you are using a vernier caliper with depth measurement from the protruding shaft you can get some variation due to not being at 90 deg. Its hard to get the end of the caliper to be good on the slight surface to measure the intermediate shaft depth. You may wish to invest in a depth gage which has a much larger surface to keep it steady and at 90 deg. to your hole. I took 10 measurements and averaged thinking I would error on a normal distribution

Had the same problems using a straight edge to get cam sprocket measurements... no Stomski tool, just an AL construction level...

Best regards,

Michael

You could also set the straight edge across the face and measure 90 deg. down to the shaft. Then measure the width of the straight edge and subtract it from the number you got.

88911coupe · 09-26-2008, 12:42 PM

I took the average which was about 8.5 mm for the IMS section. I'll Us the straightedge as well and see if that helps to give a more consistent depth reading. Using the average I was coming REALLY close to where it needs to be. It seems the more carefully I measure the closer it gets to where it needs to be. I've kluged together a way to keep the straight edge pushed up solid against the face of the engine so I'll see if my measurements are still coming close to where they need to be.
Thanks for the help.

88911coupe · 09-27-2008, 03:12 PM

I decided to leave 4 on the left and 3 on the right which is how I found it. I ketp doing the measurements and would get close then it out get out of spec. I then calculated what would happen if I put 3 on the left and 4 on the right and they both would have moved away from being close to perfect. Chris's comment on another thread that he's seem nearly all 4 on the left and 3 right helded my decision.

KTL · 09-28-2008, 07:55 AM

I found one of my sprockets installed backwards when I did the top end @ 78K. I put about 15K on the engine before I did the top end. Didn't fail, even with some hard use at probably a dozen track events? I'm certainly not endorsing sprocket misalignment. Just pointing out that as long as you've got the sprockets oriented right and get a close measurement for shim count, you should be okay.

hcoles · 09-28-2008, 08:03 AM

Kevin, I've thought the same thing... we are talking 0.004" or something like that over a length of 1.5' on the tension side of the chain. That works out to a very small angle. On the loose side the sprocket is supposed to self align. If you look at how much the tension sprocket can move in and out.. e.g. when braking or ? the 0.004" shim seems like nothing.. I would say this super measuring of the shims is a lot about nothing originating in Germany 40 years ago by some guy trying to justify his place on the production line. Just my conjecture.

88911coupe · 09-28-2008, 05:38 PM

OK...hate to admit it but I was thinking the same thing. The amount of stress if this was off .5mm seems to be really small. Still though, I did everything recommended to get it to measure in spec as closely as possible.

hcoles · 09-29-2008, 03:48 AM

since we don't really know the root of why this needs to be so close - we do as they say.
It also adds to the fun of reading about rebuilds. once yours is up and running without obvious issues. Now that you mention stress....it brings up a good point I didn't think of... could be we are not just worried about sprocket/chain wear but also should be worried about the cam or layshaft always being "pushed" to one end.

304065 · 09-29-2008, 05:46 AM

Guys, don't second guess the factory. The reason the maximum allowable alignment error is 0.25mm is because the shims are 0.25mm thick.

Buck, remember that what you are measuring is the sprocket-to-sprocket alignment. I did this process over the weekend and I measured from the aft intermediate sprocket face to the the protruding end of the intermediate shaft, and then set the Stomski straightedge across the end of the shaft to establish the reference plane for measuring to the cam sprocket face.

First couple times I did it, I got outrageous errors that made me check my math-- like 4mm. Turns out I didn't have the port cam sprocket all the way seated up against the shims. A couple taps seated it so I could see the woodruff key and the measurement came out at 0.25mm.

Now I can't remember if the intermediate shaft sticks out on the later engines, I think it does?

hcoles · 09-29-2008, 05:56 AM

Quote:

Originally Posted by john_cramer

Guys, don't second guess the factory....

sorry - my job is to second guess any and all designs and suppliers. In fact my current responsibility is to "second" guess the engineering of a large German company. I find "holes" all the time. In this case, I didn't advocate not following the "factory" because we don't know the complete story.

All that being said.. yes it takes a bit of practice to get good measurements, got to be careful about banking all the parts one way or the other/etc.

KTL · 09-29-2008, 06:09 AM

Intermediate shaft does not stick out on later engines.

My backwards'd sprocket shows some side wear, but nothing alarming like a groove. Just a brighter finish, indicating some rubbing.

I don't think the Stomski straightedge is a must. I think Stomski came up with that nifty tool so you could do the measuring on your own without the help of another set of hands. I had a friend hold a long steel rule (like a drywall square w/out the "T") I bought to measure the parallelism. Worked good since I was able to get repeatable measurements.

hcoles · 09-29-2008, 06:28 AM

I agree.. you can get some ground stock and if you have someone to hold it against the case you can make measurements

88911coupe · 09-29-2008, 07:57 AM

I managed to put together a way to solidly press a straightedge up against the face. I kept getting really close to the correct measurement and several times got nearly dead on. My real concern was that when I took my engine apart I had 4 on the left and 3 on the right, which was opposite of what Wayne's book says is standard. I began think somehow I'd put them in the baggies and mismarked them but that seemed really unlikely considering how thorough I'd been. Then Chris, in another thread, mentioned he's seen nearly all with the same situation as mine, 4 left, 3 right. Just to make sure I redid all my calculations to see what woud have happened if I'd move one shim over to the left. The resulting range was further away from where I needed to be so I feel comfortable with how it is now.
Thanks for the input.