Anyone use a non-conformist path to set cam sprocket alignment?
 

Laying a straight edge on my '85's intermediate area to set sprocket alignment doesn't look good. My case appears far from "perfect" in that area. My 4-5-6 side of case is slightly proud there. And, the rear edges have not been machined. Have heard others say the same of their cases.

My sprocket on the 4-5-6 side is also clearly worn, on the flat side of the sprocket in particular. This wear is where the sprocket's teeth sides engages the chain---the links have been chewing the sides of the teeth. Suggests to me the sprocket had been positioned too far back (too many shims.) That said, the procedure to set that sprocket where it had been could have been done by "the book." My concern: the case in that area potentially being an inaccurate reference.

Had I been conscious of this matter when my case was split, I'd have had the case exterior around the intermediate shaft area machined 90 degrees to the shafts bore.

As it stands, am wondering if anyone else has considered this situation and taken an alternate route to the mounted straight edge path?

I'm thinking to feeler gauge the chain and sprocket but can't say for sure that will work---have yet to try it. Premise is, with slack out of the chain and having the chain settled into place (after a few rotations) there should be close to an equal gap on both sides of the sprocket to the chain when the cam sprocket is aligned to the intermediate shaft sprocket.

Thoughts?
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Go off one side of case or other @ intermediate shaft and split the difference. You’re over thinking it.
How do you know the wear is from misalignment? Could be from worn out chains, sprockets, too much slack in chain et.

I have found several of my cases were as you described, not perfect where you would put a straight edge at the intermediate shaft cover. The method I have settled on was to make a second adjustable support that threads into a cover bolt for the straight edge out past the outer sprocket. I then adjust its position so that the distance reading on the near and far side of the sprocket are the same. This way I know the straight edge is parallel to the sprocket. From here I can measure the intermediate shaft distance and adjust shims as needed.

john

I have a potential solution I plan to use on mine. My case had a fair bit of corrosion here,.and I would rather measure from the face of the shaft rather than the lip of the case.

http://forums.pelicanparts.com/uploa...1677873377.jpg

So I made what I am calling a 'datum' extender for just this issue.

http://forums.pelicanparts.com/uploa...1677873511.jpg


http://forums.pelicanparts.com/uploa...1677873553.jpg


http://forums.pelicanparts.com/uploa...1677873862.jpg

Turned this from a scrap of hot rolled steel, and then slapped it on the surface grinder, top and bottom face ground parallel within .0001". This fits lose in the bore, and does not rest on the case edge.
My thought was I could clamp this up under the Stromski tool and then I am measuring the intermediate shaft just like I did on the surface plate ....

Dp... agreed on those as possibilities for wearing the sprocket. My conclusion is from looking closely at how the chain makes it's full transition onto the sprocket (during a slow rotation. There's minimal slack in chain. Stomski's tensioner is used. Chain's new.) On the passenger side where the sprocket is worn on the side that faces out from the cam, on close inspection I found the chain being pushed further away from the cam when entering onto the teeth. This "push" continues along the side of a tooth until rotation moves the chain fully onto the sprocket. The result is the teeth on the sprocket are now beveled in towards the center of the sprocket towards the tips of the teeth. I contemplated getting new sprockets but since these are already nicely beveled, perhaps they should stay in service.

Don't have the measurements I took of the chain I.D. and sprocket O.D. but as I recall there is 0.5 mm clearance given between the chain when on the sprocket. In a perfect world, I'm thinking alignment between the intermediate sprocket and cam sprocket would be proven when the chain enters the cam sprocket with 0.25 mm between the inside of the chain and sprocket on both sides of the sprocket. At a minimal, entry of the chain onto the sprocket would be so the chain is not pushed over in the least by the teeth.

I tried to get a feeler gauge in between the sprocket and chain but that's no simple matter... so...

Took all the shims out (on passenger side.) Doing so resulted in the best entry of the chain on the sprocket. But, when doing this, the chain does not seat on the rail / ramp (when the rail is engaged as it should be on its posts.) Clearly, the chain is too close to the cam for the likes of the rail with zero shims.

...Added 1 shim. Chain meeting sprocket is still good but rail is still not seating on the rail. It's possible to manually push the chain down onto the rail but did this only to get some idea what's going on.

Finally at 3 shims the chain is seated on the rail. And the chain is slammed against the sprocket's side but still enters the teeth well.

For comparison, my straight edge bolted to the case at the intermediate shaft area called for 6 shims. I did check my measurement taking relentlessly before concluding there must be a better way. Am not suggesting every 3.2 case by the intermediate shaft is useless to use for this alignment. Am saying I don't like my case for this. Other cases may be perfectly suited for an accurate "edge" alignment.

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That's a clever solution John. Will have a go at that and see how the math stacks up to eyeballing the entry of the chain onto the sprocket.

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Reclino, fine way to skin this cat! And nice tool you made. Your case being proud on the passenger side is exactly like mine.

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I don’t know much about chains on 911 engines, other than to set them up by the book. However, on other chain applications, such as motorcycles and farm machines, if you get a wear pattern on one side of a sprocket, that’s a primary indication that you need to change the alignment. So if it were my engine, I would add at least one shim.

I was going to suggest the same as reclino. A bearing race of appropriate size could serve the same purpose if you don't feel up to making a custom spacer.

Have run with John’s suggestion. Is most direct means to sort out sprocket alignment given what I have to work with—measure opposite ends of the sprocket until the straight edge is parallel to the sprocket. Shim is put between straight edge and case by the intermediate area with shim thickness as needed. Am fastening “L” straight edge to case using the intermediate fastening points.


http://forums.pelicanparts.com/uploa...1678639605.jpg

It’s been commented that 3.2 cases (perhaps other liter cases) are proud on the passenger side at the intermediate. Mine was. I leveled this area (seen above) so the intermediate cap now sits flush to both sides of the case—will be putting Mopar between cap and case to back the o-ring up—a personal pref. If you’re thinking I just F’d up my case in regard to using it for straight edge referencing… indeed. Bear in mind I didn’t trust my case here for sprocket alignment to start with. Are ALL 3.2 cases not to be trusted? I can’t imagine so since the factory recommends the case be referenced for sprocket alignment. By default then, 3.2 cases should be considered accurate. Looking at my sprockets and looking at my pre-leveled case, I couldn’t ignore what I was seeing. I had to go down the rabbit hole on this one to empirically sort this sprocket stuff out---or live with some never-ending doubt. (Not a place I want to be.)


http://forums.pelicanparts.com/uploa...1678639697.jpg

Straight edge is 2 ½” x 2 ½” x ⅛” “L.” Beefy. I put this aluminum section on a granite slab beforehand and it looked good to my eyes and didn’t deflect. Absolutely perfect? Can’t say that. Is good enough to get on and see how this approach pans out. There are usually refinements to be made so am considering this a “beta” as I move forward.


http://forums.pelicanparts.com/uploa...1678639754.jpg

To baseline this, all shims behind sprocket were removed and “L” is fastened directly to “leveled” case. (“Level” does not mean "perpendicular.") Hole in "L" just beyond nearest bolt is access to measure depth to intermediate shaft. There are two holes further out on "L" that exist to avoid interference to chain house studs. Straight edge to sprocket is way off. Feeler gauge was used to incrementally sort out what shim value worked to parallel the straight edge to the sprocket. Have ended up with 0.5 mm shim. (I take measurements until there’s relentless repetition.) Can see feeler inserted between case and “L” on the driver’s side here. In other words, edge needed to be moved closer to the sprocket. Considering I removed more meat from the case on the passenger’s side than the driver's to level the case, rabbit hole deepens.


http://forums.pelicanparts.com/uploa...1678639914.jpg

Moving the setup to the driver’s side, am faced with an instant problem. Vernier won’t reach the sprocket with the 2 ½” edge. I went to a 1 ½” “L” with—notably—a 1/16” wall. Did so only because this is what was on hand. This section of metal was not straight, could easily be bent and twisted… ultimately I abandoned this after fiddling with it. Fiddling being to sort out where the short comings in the program (as I'm working it) are.

John, if you’re following along, your idea is excellent provided the right tools & process. What I’m missing is a long enough (200 mm) depth gauge and a true (beefy) straight edge. In my approach, I question how reliable the shim process that I used is. To split hairs, am thinking after the fact that the fasteners that hold the straight should be torqued equally for each install of the edge. I did not do this. (Case and feeler were cleaned at each move.)

For exploration, am having a stab at Reclino's datum insert-on-the-intermediate-plate idea. Refinements in my gear will accompany this. Among them is a longer vernier that is a genuine depth gauge with a 4” footer. A rectangular metal channel rather than an “L” will be used. And that piece of metal will be machined so the datum faces at both ends are parallel. Finally, aluminum plug within intermediate shaft will be removed to drill & tap it entirely through. Can see that aluminum plug in the first pic above. There’s currently only about a ¼” depth of thread in that plug—bore does not go entirely through it. Using the entire plug’s length to bolt into will roughly double the threads for fastening into. Point is to get a solid connection between the straight edge, datum insert, and the intermediate shaft face using the aluminum plug to torque into. (This ALL relies on the face of the intermediate shaft being perpendicular to the shaft and the intermediate shaft sprockets being perpendicular to the shaft.) Take me a few days to put the gear.

If you see anything odd, or have ideas, sing out.

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http://forums.pelicanparts.com/uploa...1679657086.jpg

Cut from steel rod.


http://forums.pelicanparts.com/uploa...1679657086.jpg

Intermediate plug. 901.105.275.00. Going to drill this through and continue the 6mm threads the factory put half way through. Might not need to bother with this. I plan to put some torque on the joining nut and don't want to see doing so yank out the threads. Crossed my mind to JB Weld the hole afterwards. Sketchiness of having "JB part" inside the engine doesn't bode well (with me.) Will replace plug with new afterwards.


http://forums.pelicanparts.com/uploa...1679657086.jpg

Bolt run through plug and plug reinstalled. There’s a small step on the bore in the case that’s just proud of the intermediate’s face. Datum is made no larger than intermediate’s face to avoid it getting hung up on that step.


http://forums.pelicanparts.com/uploa...1679657086.jpg

Tight clearance between bolt and datum is intentional---keeps datum centered / away from step.


http://forums.pelicanparts.com/uploa...1679657086.jpg

Will suggest the key to this sprocket alignment approach is making sure all tooled working surfaces are parallel. Aluminum arm had to be machined for this—raw, it was off.


http://forums.pelicanparts.com/uploa...1679657626.jpg

http://forums.pelicanparts.com/uploa...1679657626.jpg

Once intermediate nut is tightened, arm is solidly part of engine. 150mm caliper works on passenger side. 200mm is called for on driver’s. First check is to see if arm and sprocket(s) are parallel. If not, suk is the word. Both are parallel. ⅝” total depth of datum allows arm to clear studs.


http://forums.pelicanparts.com/uploa...1679657626.jpg

This tool is better than dedicated depth caliper as it offers flexible positioning—can be positioned coming or going on caliper’s leg. $19 on Amazon.


Credit to Reclino for this idea. I modified the tooling some but the premise of referencing off the intermediate shaft to determine sprocket alignment… a stroke of genius on his part.

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Nice, this looks like a very stable way to measure this.
David
Performance EngiNerding

I made a simple tool that to position the straight edge out at the cam sprocket.

http://forums.pelicanparts.com/uploa...1679686000.jpg

One end is a aluminum tube that is threaded to screw into timing chain housing stud. Bolt with nuts screws into other end of threaded tube. When installed it looks like this.


http://forums.pelicanparts.com/uploa...1679686178.jpg

My straight edge rests on the bolt and sits between the nuts on the bolt so I can position the straight edge and also keeps the straight edge from moving when measuring.


http://forums.pelicanparts.com/uploa...1679686322.jpg

The other end of straight edge is held with bolt and nut against the case. I adjust the position of the straight edge out at the cam sprocket until measurements on either side of the sprocket are the same. This way I know the straight edge is parallel to the sprocket. Now and I can then do my depth measurements knowing everything is parallel.

john

A fine idea you conceived David! Thank you. Worked out very well.


One more way to skin this cat. Thanks John.

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