Cam Chain Guide Mod

Jim, if I may, some additional info.

Took some measurements of my 256 camchain and my SR500 guide. Wanted to see the seating depth of the camchain onto the center-ribbed SR500 guide.

SR500-GuideFit02.jpg
SR500-GuideFit03.jpg


0.057" depth of the rollers, 0.059" rise of the center rib.
Pretty close.

It appears that the camchain rollers AND sideplates will likely be in simultaneous contact with the SR500 guide. This could be a good thing since there's no concentrated loads, they're all distributed.
 
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Now, here's where it gets fun.

As 5twins has been advising, centering of the front guide should be considered critical. Without this centering, the camchain will definitely abrade the guide's lateral confinements, be it the channel type, or this center rib type. Right now, centering the guide in the cylinders is the procedure. But, this relies on "blind faith" that things will eventually line up so that the camchain is centered on the guide.

For reference, here's dimensions of a 256 camchain fitment into a MikesXS -01 channel guide.
XS650-GuideFit02.jpg
XS650-GuideFit01.jpg


The total side clearance of camchain into guide channel is 0.42" - 0.38" = 0.04" (1mm).
The total side clearance of camchain onto the center rib is 0.184" - 0.154" = 0.03" (0.8mm).

This whole guide alignment thing is new to me, coming from the 256 flatland. So, this is just a thought experiment. If one wanted to be assured of true centering of the camchain and guide, perhaps an additional step could be added to the engine assembly procedure. For example (simplified):

- Assemble and center the guide in the cylinders.
- Install the cylinders and head.
- Install the camshaft, its bearings.
- Install (temporarily) the ungasketed cam endcaps, to center the cam.
- Install camchain (or the other method, camchain on cam first, then bearings).
- The camchain should be tight, else add the tensioner and adjust.

Now, using some sort of peek-a-boo divination, peer down into the camchain tunnel to see if the camchain is indeed centered on the front guide. If not, loosen the front guide bolts and tweak the thing 'till it IS centered.

For the sake of sanity, I hope that preliminary centering of the guide in the cylinders guarantees the desired result, a guide that is centered and aligned with the camchain. If not, maybe could consider this rethink...
 
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Been contemplating a kind of "cheater" alignment tool. Imagine a long strip of brass or steel, somewhere in the 0.010" - 0.016" thickness range, formed into a channel shape that fits into and hugs the camchain and guide protrusions, like these. Red lines represent the cross-section of the cheater strip.

XS650-GuideFit01b.jpg SR500-GuideFit01b.jpg

The cheater would need to be at least a foot long, and extend to both sprockets. With the front guide's attachment bolts loosened, this would force the guide into alignment with the sprockets and chain.

Again, just a thought experiment...
 
Yup- I was day dreaming about something like that on the way home from work yesterday 2M.

That tool would be pretty whippy though (being so long and thin) so I’d wonder how feasible it would really be.

Hmmmm....:umm:
 
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How about something like a piece of UHMW plastic the full width of the cam chain tunnel, machined with a raised centre strip to fit in the guide channel?

Use this when installing/centering the guide. Would be too thick to verify chain alignment but if you knew the guide was for sure centred may not be as important? The curved guide face may pose a problem in machining this centering jig though.
Just throwing out ideas.
 
The difficulty is that the chain is in there at the same time and so there isn’t much room for any sort of tool to hold against the guide before tightening the mounting screws.
 
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Well, you need to install the cam chain guide before the cylinders are re-installed so that centredness/plumbness can be measured at the top and bottom of the guide, so I guess this jig would just be doing your measuring for you.
Edit: Or used before cam chain is rejoined so there's enough slack / clearance.

You're right Pete, won't solve the alignment check problem once everything's back together with the chain.
 
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Yup - centring the guide in the cylinder barrel is important but that doesn’t necessarily guarantee that it will be centred on the chain itself (and THAT is what really counts). If the cam or the crank is off just a bit relative to the barrel....well, there ya go. Anyhow, we’ll do our best and see what happens.
 
You guys really are perfectionists! This all makes me wonder how Yamaha assembled these motors in the first place. Did they have an alignment tool, or just "eye"-crometers? With all the 'tweaking' going on, there's going to be some exceptionally "perfect" motors out there... (I know... nothing's "perfect"). So many superior aftermarket parts/products now exist, addressing any 'shortcomings' the Xs had, that this really is a marvelous machine. :wink2:
 
Robinc's comment mentioning the full width of the tunnel got me thinking. What's the purpose of the guide anyway? A chain run between two sprockets should have precious little sideways movement, so is it just to control chain slap? Or is there a real risk of the chain jumping one of the sprockets?
 
Ok, there has been some questions raised about the Mikes XS cam chain guide mounts that go on the front of the barrel. The question is whether Mikes replacement has a longer threaded portion and whether it protrudes into the cam chain tunnel.
4C2DE747-60A9-4487-9805-40B66ADD6F3E.jpeg


I measured a new replacement set against two stock original sets I had on hand. The results are the Mikes units measure 12.4mm from end to end and the stock units measure 11.5mm
E8D73255-BF93-4878-80A5-81A4FE4C9347.jpeg


Stock on the left, Mikes on the right
9B58CF2E-C79F-4A50-9B59-9BA583B7AF83.jpeg


I then mounted a stock unit and a Mikes unit in my barrel, complete with a new copper washer and took measurements. The Mikes unit extended 3mm beyond flush into the tunnel and the stock unit extended 2mm.
AAB716F5-C751-4AE6-A456-0D4185FBA300.jpeg


I guess the question is, does that one millimeter make any difference?
 
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Bob, how thick is the copper washer? Would putting 2 washers on a bushing instead of 1 be a viable workaround?
 
I think it could. The guide will be further in and pressed into the chain more. That could cause increased guide wear, especially with a new, tight chain. Personally, I wouldn't use them. Honestly, this is a part I've never found the need to replace. I don't usually even remove them from the cylinder. Why would you? If they're installed, still in good shape, and not leaking? And, I don't think you'll get comparable chrome quality on the repro part, if it's anything like the chrome quality on their topend hardware kit. That chrome just plain sucks, lol.
 
The washer I used is a new replacement, also from Mikes, ( I bought a whole top end washer kit) the new washers are 1mm thick. That’s twice the thickness of the stock ones I had. They measured out.5mm

I honestly don’t know how doubling washers would work.
 
I think it could. The guide will be further in and pressed into the chain more. That could cause increased guide wear, especially with a new, tight chain. Personally, I wouldn't use them. Honestly, this is a part I've never found the need to replace. I don't usually even remove them from the cylinder. Why would you? If they're installed, still in good shape, and not leaking? And, I don't think you'll get comparable chrome quality on the repro part, if it's anything like the chrome quality on their topend hardware kit. That chrome just plain sucks, lol.

I had two stock sets. One set had been left in the jugs and were pitted from media blasting. Then I had a nice shiny OEM set , which I temporarily lost. That’s what prompted me ordering replacements. For what it’s worth I put the factory ones back in.
 
I'm telling you, use your originals, not that new junk. New can be good or better, but in this case, I don't think it is. Same goes for that fitting at the bottom of the oil pipe. I know they are often rusty, but a wire wheeling and some silver Testor's model paint fixes them right up. Why bother? Because that "new" replacement is REALLY junk. This is the "new" one my buddy bought. It was so poorly threaded, we couldn't even install it .....

pluFl0L.jpg


Another junk part we encountered during that rebuild were the banjo bolts for the top fittings on the oil pipe. The head twisted right off one before it was up to the torque spec, which isn't that high, only about 14 pounds or so.
 
You guys really are perfectionists! This all makes me wonder how Yamaha assembled these motors in the first place. Did they have an alignment tool, or just "eye"-crometers? With all the 'tweaking' going on, there's going to be some exceptionally "perfect" motors out there... (I know... nothing's "perfect"). So many superior aftermarket parts/products now exist, addressing any 'shortcomings' the Xs had, that this really is a marvelous machine. :wink2:

"eye-crometer" he sez. I'ma steal that one!
 
... What's the purpose of the guide anyway? A chain run between two sprockets should have precious little sideways movement, so is it just to control chain slap? Or is there a real risk of the chain jumping one of the sprockets?

The chain is tightest at the front, and would prefer a straight run. But, a tiny bit of front/back or side deflection translates into a large increase in the chain tension, challenging its life expectancy.

Visualize the strings on a guitar, and their tensions. It's very easy to apply a little bit of deflection in the middle of the string, resulting in a relatively large increase in the string's tension. A large leverage.

If you could eliminate, or reduce, any form of chain deflection, slap/whip/snatch, there's a good likelihood that chain life will be increased. Not to mention sound reduction.

Consider that camchain life on the early, type "A" flat guide XS1's, was relatively poor, as compared to the reported 30k+ mile expectancies of the later 447 bikes.

You guys really are perfectionists!
... With all the 'tweaking' going on, there's going to be some exceptionally "perfect" motors out there...

Haha, it gets worse, Tebo.

An even more tedious method of guide alignment could be done in a "dry fit" scenario.

Before attaching the pistons and any gaskets, and minus the camchain, fit the cylinder (with a loosely attached guide) atop the case. Add the head, camshaft/bearings, and the end caps. Now, a larger, thicker, cheater alignment bar could be slid down the tunnel, engaging both crank and cam sprockets, and engaging the front guide. The front guide will now be aligned with the sprockets, and can be tightened down. Then everything is disassembled, leaving the pre-aligned front guide affixed in the cylinder block.

If you want to get really anal about this, consider that the crank and aluminum cases will thermally expand at different rates, moving the crank sprocket rightward (relative to the case) by several thou when the engine reaches operating temps. The alignment cheater bar would need to have this preconfigured....
 
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