cam sprocket alignment

[burgermeister]

I cannot get repeatable readings for the cam sprocket distance. The main issue is that the case has about a 0.2mm step at the parting line of the 2 halves. So obviously if I use just 1 case half, I get a rather small span on which to lay the straightedge, and based on that span my readings vary. If I use both case halves, I can get almost any reading I like based on where I set the straightedge.

Certainly neither method is repeatable within 0.25mm, though if I pick the exact same spot for the straightedge, I am usually within 0.05mm, so the repeatability issue is not with the operator or his equipment.

I am curious if anyone else has experienced this, and what you might have done about it. You'd think the surface would have been machined with the 2 halves clamped together, but obviously this was not the case (haha pun intended ...)

My solution has been to just use the same number of shims the factory did. The camshaft position is set by the chain housing, and since I have not switched cases or chain housings, I see no reason why the cam sprocket alignment should have changed.

[yelcab1]

Of the engines I have redone, the factory shims have always resulted in good cam sprocket alignment especially if the cam towers are not changed.

[hcoles]

I'm no expert, my 1 cent.

When I redid my top end I spent way too many hours using the Stomski tool and straight edge/etc. along with a spreadsheet to measure what shims I should reinstall. After all that the shims originally installed were correct.

I've often wondered is +/- 0.003"? over a distance of say ~1 foot really going to make any difference? And it is on the tension side, the slack (feeding) side is not constrained very well as is comes off the "floating" tensioner arm. Seems like the feed side would be the important one.

[KTL]

I think you're just fine putting the shims back the way they were originally installed, as long as the parallelism measurement checks out reasonably well.

I agree that the parallelism is a proper thing to check. However it's not absolutely critical that it be dead nuts on. I found on my '87 3.2L rebuild that the 4-5-6 cam sprocket had been installed backwards by somebody. The parallel measurement was way off (can't recall by memory) and the cam sprocket showed some side wear on it, which obviously should not come as a surprise. But my point is that the engine showed no ill effects in terms of noise or massive wear on the sprocket.

I only did the top end so I don't know how the intermediate shaft sprocket or the shaft bearings look. Engine continues to run fine to this day, 15K miles later.

[AlfonsoR]

Originally Posted by hcoles

I'm no expert, my 1 cent.

When I redid my top end I spent way too many hours using the Stomski tool and straight edge/etc. along with a spreadsheet to measure what shims I should reinstall. After all that the shims originally installed were correct.

Would you mind explaining in more detail? I was thinking of buying the Stomski tool to do my first engine, but if you are saying that it was troublesome to use, then I would look for a different way to do this.

Was the tool difficult to use? Why did you have to spend so many hours analyzing the data?

Thanks

[afterburn 549]

3 shims are the "Norm" but not against any known law to do other wise...

[Smoove1010]

I was very careful to keep all of my gears, sprockets, shims, etc. together when I did my tear-down. Only last night when I re-installed the cams did I notice that the right and left side both had 3 shims each while the reference material calls for four on the right side (1987 3.2)

Is it possible it came from the factory like that? I saw no obvious signs of the engine ever having been opened up before. Has anyone run into this?

I'm now searching for a caliper to borrow, but given the difficulties some have posted about being able to get conclusive, repeatable measurements, I don't want to create an issue where there is none.

GK

[KTL]

I use a simple straight edge (not even a precision one) and have been able to get results I feel are accurate and repeatable. It's nothing more than a long ruler (literally, it is a long measuring ruler) that is reasonably straight. I hold it on the intermediate shaft bore and take my measurements accordingly. Seems to have worked OK for me over the years.

[Smoove1010]

KTL - I planned to use a simple straightedge (a long carpenter's square) across the front surface of the engine case, but don't you need a precise depth from the straightedge to the IMS, and to the sprockets? They've got to be within .25 mm, correct? I'm looking for a caliper that has a good depth gauge to get that measurement.

Also - assuming that the shims turn against each other, sort of like a bearing surface, I lubed them with assembly lube. Was I correct in doing so? The reference books say nothing about this.

Thanks,
GK

[KTL]

Yep, use a good pair of calipers with a built in depth gauge. I have a nice Starett caliper that I use.

No worries about lubing the shims. The shims get splashed with oil anyway during engine operation.

[AlfonsoR]

A carpenter's idea of precision and an engine builder's idea of precision are in two different leagues. I once tried to determine how flat a cylinder head was using a 36" carpenter's square. By my measurements, it seemed the head was warped by about .020".....it was not, the machine shop declared. The carpenter's square is just not that precise.

[Smoove1010]

I got myself a digital caliper with depth gauge last night - probably not the best quality one available, but choices are limited when you go to local retailers. I took measurements of arbitrary things with it, and found that it was repeatable, and since I was looking for distances of objects that were relative to each other, I felt that it would do the job.

I used a carpenter's square after holding the edge down against my granite counter, and it was flat all the way across - no daylight. If nothing else, I proved that my square and my counter were both equally straight, or equally warped.

I measured the depth to the IMS and the right and left gears. Bentley's diagram on this was most helpful to me as it lists the expected delta between the measurements. I took the IMS depth, added the delta for each side, and created a range for each that took into account the .5mm margin for error.

The tough part was getting repeatable measurements to these points, holding the square in position with one hand while holding the caliper squarely against it, and sliding the moving part of the caliper with the other. After some practice, I got a range of measurements for each reference point that were within +/- .3mm - I used the IMS measurement that was in the middle of that range as my reference point.

After doing the simple math, I was satisfied that the left and right were within spec, so having 3 shims on the right was intentional, whether done at the factory or by another wrench.

This killed a solid hour of my evening Porsche-time, but it was an hour well-spent. One less thing to worry about when getting ready to hit the ignition key...

GK

[Rusty 356]

I have used the Stromski kit on the last several engines built and as stated in an earlier post, if taken apart and kept together the measurements are usually less than the 0.25mm variance. My next Stomski tool will be the DigiDix for setting cam timing. As our hobby becomes more expensive it is nice to have tools that really work.

[88911coupe]

This was one of the handful of things on my rebuild that really was not fun...the other being the cam timing. Anyway, I wondered how critical the extreme measurements were on this then I recalled KTL's story about someone installing the sprocket backwards...with minimal damage. If I ever do another rebuild this is one of those things I'm not going to lose sleep over. I'll save that for the cam timing, and case sealing.

[Smoove1010]

Originally Posted by 88911coupe

This was one of the handful of things on my rebuild that really was not fun...the other being the cam timing. Anyway, I wondered how critical the extreme measurements were on this then I recalled KTL's story about someone installing the sprocket backwards...with minimal damage. If I ever do another rebuild this is one of those things I'm not going to lose sleep over. I'll save that for the cam timing, and case sealing.

Indeed, and keeping in mind that the tolerances here are pretty broad, Porschey-wise, since the adjustments are in .5mm increments. My value-priced calipers measured them out to be between .49 and .51, BTW...

[KTL]

Originally Posted by Smoove1010

The tough part was getting repeatable measurements to these points, holding the square in position with one hand while holding the caliper squarely against it, and sliding the moving part of the caliper with the other. After some practice, I got a range of measurements for each reference point that were within +/- .3mm - I used the IMS measurement that was in the middle of that range as my reference point.

Good job. Sounds like the same hand-eye precision measuring coordination trick i've used for the job.

It's one of those things when you're done, you say "I could really use another set of hands...." Often times when I employ the wifey for those second set of hands, I end up regretting it.......

[Walt Fricke]

I drove my self nuts using a modified carpenter's square (short leg cut off). The square was fine as a straightedge, but you really need four hands this way. My first effort led to me making a scatter diagram and finally picking one in the middle. Normally, the IMS protrusion from the case stands a bit proud of the two machined edges for the motor mount which are farther out. Very easy to rock the straight edge so it is pressed against two supports on one side, or two on the other. What you want is to have it resting only on the two sides of the IMS case protrusion.

I really like the Stomski tool. I had purchased a set of depth micrometers (actually, one mike and a bunch of extensions), but found that my digital dial indicator was long enough, and stable enough, even without the nifty base plate I bought for it. And the first time I used the Stomski I found I was already right on. I've got 4 motors (3 for one race car, one in the SC), so I go through this often enough to be happy I paid the $ for the Stomski (which is much like the tool the factory shows in its manuals).

One of my race motors was made from two different case halves (one motor blew up one side, the other the other, I guess), but the machinist who did the work got it to work out just fine. No issues with that. However, on my first rebuild of the motor (I bought it with about 25 hours on it), and getting to setting parallelism, I found that the outer (motor mount) protrusions stood proud, at least on one side, of the IMS seal plate area. Aaaargh. Eventually I used the die grinder so that the straight edge sat true on the IMS stuff, and I could get a feeler gauge under it at the motor mount area.

But without a tool, I think it is very very hard to get a relatively thin edged straight edge to work well. It wobbles up and down, as well as the problem of not being sure what two points side to side it is resting on. Though a helper can make up for all that.,

[yelcab1]

[QUOTE=KTL;7413609]...I found on my '87 3.2L rebuild that the 4-5-6 cam sprocket had been installed backwards by somebody. ..QUOTE]
You know that the 1-3 side has the spocket facing out, while the 4-6 side has the cam sprocket facing in, right? It is supposed to be that way !

[Walt Fricke]

I would venture the guess that Ken knows that. Backward on the right side would have the sprocket facing out.

Once you realize the relationship between the cams and the cylinder banks, with left forward, and right back, and that the cam wheels are to be installed to minimize this offset, you won't make the mistake. Of course, Wayne's or Bruce Anderson's books make this very clear with diagrams and such.

I am interested to hear that the misinstalled gear actually worked pretty well. A mechanic/machinist buddy once told me that if you were two shims off you could tell while hand rotating the engine with the covers off that things weren't meshing right. I've tried looking at how parallel the links are, especially on the idler. But not to the point of being systematic about it, so I can't say as this is a valid test or not. I thought I saw something, but not sure.

[burgermeister]

Thanks for all the replies! I ended up finding a feeler gage that matched the mismatch of the case halves & taping it to the case where it meets up with the engine mount. This made it fairly easy to make the measurements. I'm using a 24" Starrett straightedge (they're 1/4" wide, so they are easy to keep square) and a 6" HF digital caliper. I hold the caliper so the edge of it rests against the straightedge (so looking along the caliper, the caliper and the straightedge make a "T", not a sandwich) - this minimizes measuring error if I'm not holding everything perfectly square.

Ended up with 3 shims per side. I t appears that the chain has about 0.75 mm slack sliding side - side (fore-aft relative to the car) on my cam sprockets, so that would also be an indicator of the degree of precision required - if the IS sprockets have a similar amount of slack, one could be off +/- 1.5mm without the chain needing to run uneven.... not suggesting one should try that, but it does indicate the +/- 0.25mm is a bit excessively anal.

There was a comment re. cam timing being difficult - that's one thing I've never understood. Cam timing is one thing that always seemed a breeze to me - takes me 20 - 30 minutes for both sides. Everything else I do seems to take double or triple what the Dempsey books say it should, just not cam timing... I always have been an oddball I guess