Excessive timing chain slack?

[Kgreenhaw]

Wow! Thanks for all of that! So maybe I really didn't need to pull the top end apart, bummer.

What do you think about modifying the front guide, maybe it's doable? I could grind down the mounting boss until it matches the original... And I could get that damper for the tensioner or maybe just replace it. I found a few on ebay.

 

[TwoManyXS1Bs]

Wow! Thanks for all of that!

Sure! It's not everyday that I can ramble in XS1 land. Still learning about this stuff myself.

So maybe I really didn't need to pull the top end apart, bummer.

Well, look at it thisaway. (*Warning* - drifting off into mathland)

The center-to-center spacing of the 256 crank and cam is supposed to be the same as the later 447. What's different is the sprocket teeth counts, the chain pitch and link counts. We can try to calculate the effective straight-section chain lengths by removing the circumferential component of the chain path around the sprockets.

256 camchain = 102 links x 8mm (0.315") pitch = 816mm (32.126") total length
256 camdrive = 17T crank sprocket, 34T cam sprocket
8.5 + 17 = 25.5 links used by sprocket outer circumference,
Leaving 76.5 links in the vertical path = 612mm (24.094")

447 camchain = 106 links x 7.774mm (0.3061") pitch = 824mm (32.447") total length
447 camdrive = 18T crank sprocket, 36T cam sprocket
9 + 18 = 27 links used by sprocket outer circumference,
Leaving 79 links in the vertical path = 614mm (24.179")

So, there's supposedly an extra 2mm of chain in the vertical path (1mm per side) in the 447 engine, versus the 256 engine. Even with this extra length, 447 engine overhauls still incur tight camchain installation. So, your report of new camchain looseness seems odd.

What do you think about modifying the front guide, maybe it's doable? I could grind down the mounting boss until it matches the original... And I could get that damper for the tensioner or maybe just replace it. I found a few on ebay.

Totally clueless about your front guide. I have no idea of what interference you're talking about. If anything, the mount boss of the later arched guide is smaller than my rev -00 flatguide, and even much more smaller than your super-early version. Maybe you could clarify?

 

[Kgreenhaw]

Interesting... yeah, according to your math the 256 should be even harder to install.

Now just to clarify, I installed the master link after the two ends of the chain are pulled up over the cam gear. I think I saw a few instances where guys were joining the chain and then trying to pry it over the cam gear. When I was joining the two ends there wasn't extra slack at that point, I could still only barely get the master link in, it just wasn't that hard.

As far as the front guide goes, when I attempted to install it, the bottom end of the guide was hitting something and would not seat against the ends of the guide bar nuts. The bottom end of the new guide was about a half inch or more longer than the original. It's as if the angle when installed kicks out the bottom of the guide and wedges the chain against the crank sprocket. That's the best way I can describe it. Also, when the two guides were laid flat on the table on their mounting bosses, the new guide was taller.

With the early center guide/slipper in place, the front guide shouldn't fit though, right?

 

[Kgreenhaw]

I looked back through your pictures of the guides side by side and that's how mine looked. It must not have been a half inch longer, it just seems like I cut a lot off to match the length of the old one. And according to the diagram of the tensioning system the bottom of the front guide would've been wedging the chain against the center guide, not the crank sprocket. The new front guide definitely protruded further towards the cylinders than the original.

 

[TwoManyXS1Bs]

...according to the diagram of the tensioning system the bottom of the front guide would've been wedging the chain against the center guide, not the crank sprocket. The new front guide definitely protruded further towards the cylinders than the original.

Is this what you're talking about?



If so, yes, I can see that as a problem. The arched rev-01 front guide does indeed set a little more rearward in that area compared to our original flat guides. I've not installed one of those new guides yet, and never thought that it would cause a problem.

Good catch.

Sounds indeed like a job for some precision skimming of the guide's mount base. Not sure, though, if that skimming should be at a slight angle, or stay at the original angle.

Gotta think about that for awhile...

 

[TwoManyXS1Bs]

This is a closeup (from my album) of the bottom/exit end of the different front guides, match aligned.
Two new guides on left, old/original flat guide on the right. There is indeed a height difference.
Still cogitating...

 

[Kgreenhaw]

That's definitely the issue I seemed to be having and you can see the difference in your photo. Yes, the question is how to grind the mounting surface and have it work properly. Without having a cross sectional view of the engine, I don't know whats going on in there... I 'm not sure if I want to experiment on my baby!

I thought it was strange that the guides have such soft rubber on them. I feel like the chain would just shred them. My original one is rock hard, but I assume it's because of everything it's been through. How hard does the chain rub against the guides?

I took the new guide to the disc grinder and just tried to match the stock one. I'm not sure how far to go, if I remove too much material I pretty much defeat the purpose of having a front guide. If I don't grind enough I will be promoting excessive wear. I stopped where the center sticks up a bit higher that the original, but the ends still drop a little lower. It seemed to me like an equal trade off as far as keeping the same amount of contact.


I ordered that damper for the tensioner, the one that's in there now has a huge crater from that pin wearing into it. At this point I think I'd be better off just using the original front guide, tensioner and nos center guide/slipper. Nothing seems to have that much wear and there are no signs of delamination. All the rubber is pretty much petrified though, is that a problem?

 

[TwoManyXS1Bs]

Yeah, I fully understand the 'no experimenting' mantra.
My front guide is also hard, but it's always been thataway, goin' back to 1974.

The two critical items are:
Delamination
Wear at the top (where the chain flings off the cam sprocket)

I'm working on two possible mods that would allow use of the new front guide.
Both are lousy, in their own way.

Here's Option 1, using the new front guide as-is.

 

[TwoManyXS1Bs]

I would imagine that the chain does a significant amount of rubbing on that front guide, compared to almost none (except at the top) with our flat guides.

A mod promoted here is to polish the edges of the camchain's sidelinks, to reduce any abrasion.


(Working on pics for option #2, a variation on yours, will take awhile...)

 

[Kgreenhaw]

So do you think the reproduction guides use a softer material than what Yamaha used? Have you encountered reports of new guides wearing prematurely? I still don't see how you would retrofit an early engine with new guides and tensioners, don't the type B tensioners have a six hole pattern? And even those are no longer available. So putting a new front guide and new center slipper still needs to have an early tensioner?

Your mod seems like it would work in theory, but it is hard to know exactly what to change... I wouldn't say they're lousy.

Have you ever worked with delrin? I've made bushings out of that stuff, I wonder if a copy of the front guide could be machined completely out of that? It seems to hold threads pretty well.

 

[TwoManyXS1Bs]

So do you think the reproduction guides use a softer material than what Yamaha used? Have you encountered reports of new guides wearing prematurely?

It sure feels softer. And, there's many threads in here about self-destructing front guides.

I still don't see how you would retrofit an early engine with new guides and tensioners, don't the type B tensioners have a six hole pattern? And even those are no longer available. So putting a new front guide and new center slipper still needs to have an early tensioner?

In mid-production of the '71 XS1B, Yamaha changed the camchain tensioner system to the upcoming XS2's type "B". All 3 tensioner components were implemented, as they won't mix/match with type "A" parts. My later-version XS1B has this system. Strange looking, as it has the 6-hole tensioner mounted on the older 4-hole cylinder. The position of the outer 4 bolt holes is the same.

Your mod seems like it would work in theory, but it is hard to know exactly what to change... I wouldn't say they're lousy.

Haha, that's yet to be seen. Will be posting the Option 2 info after this.
Net difficulties this evening are hampering this.

Have you ever worked with delrin? I've made bushings out of that stuff, I wonder if a copy of the front guide could be machined completely out of that? It seems to hold threads pretty well.

This is an active concern. Have a look into these threads:

http://www.xs650.com/forum/showthread.php?t=18711
http://www.xs650.com/forum/showthread.php?t=38751

 

[TwoManyXS1Bs]

Here's the Option 2 thought experiment. It shaves the front guide's mount boss surface, similar to what you were doing. But, instead of a parallel setback, it is done by pivoting the guide about an imaginary point about an inch above the top of the guide.

This would preserve as much of the new guide's chain contact area as possible. And, would reduce the amount of material removal by about half. It essentially re-angles the guide by about 1°.

The next few pics are an attempt to show how it could be done on a table sander.

 

[TwoManyXS1Bs]

Here's the type "A" tensioner/guide parts in their respective relative positions. The primary point of interference with a new front guide and the original center slipper is at the upper/front of the center slipper, which is about 2" below the centerline of the front guide's lower mount bolt. We'll use these as the primary reference points.

 

[TwoManyXS1Bs]

To establish the baseline reference points, the type "A" front guide is marked to show the centerline of its lower mount bolt. Then the guide is placed on the disc sander table, its mount boss surface is firmly against the sanding disc.

A perpendicular line is drawn on the sander table, under and aligned with the guide's lower bolt hole.
Then, another perpendicular line is drawn 2" left of that. This is the location of the primary interference point.

 

[TwoManyXS1Bs]

Now, while keeping the guide pressed firmly against the sanding disc, a reference rod is placed against the guide surface, at this 2" interference zone line. A clamp is fitted to the table, pressing this reference rod toward the guide surface, all while keeping the guide pressed/aligned to the sanding disc.

This establishes the original type "A" guide's slipper surface position, where the primary interference with the new guide would occur. Basically, we want to sand/shave the new guide enough to re-establish that surface position.

 

[TwoManyXS1Bs]

Here's the fun part. On the new guide, a pivot arm/point must be fashioned, to the top end of the guide. Here, I'm just using a scrap bracket to represent a way to establish the pivot. Some creativity needed here.

 

[TwoManyXS1Bs]

Close-up of the tentative pivot bracket. The actual pivot point needs to be about 1" extended from the guide's top.

 

[TwoManyXS1Bs]

Now the sanding/grinding occurs. Keeping the new guide pressed to the pivot point, the guide is swung in to the disc sander, and a bit of material is removed.

Then the machine is stopped, guide pressed against the pivot and sanding disc, and the reference rod is placed between the prepositioned clamp and the guide's surface.

Note the progress. Continue the material removal until the reference rod fits in there.

I suppose a little extra could be removed, not sure about that...

 

[Kgreenhaw]

I took a look at those threads, I didn't realize so many others had issues with the re pop guides! That'd be cool if someone made a working prototype, it looked like at least one member had started machining one. It seems like the biggest hurdle is finding the correct material...

And nice write up! I used the same type of sander, but with much less of an "engineering" approach. I just eyeballed mine, haha! I'm not sure ill ever try to use it in a motor. It would be great if someone could manufacture a superior alternative to what's currently available. What are guys using in the racing world? Anything different?

 

[TwoManyXS1Bs]

...What are guys using in the racing world? Anything different?

As far as the XS650 is concerned, stock factory slippers and guides is all I've heard of...