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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 12-14-2010, 11:18 PM   #1 (permalink)
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An even more anal way to ensure undamaged rocker spindle O rings

I took my rocker boxes apart on my 71 Daytona this last weekend to fix the famed "Thackeray Problem", having to do a lingering error in some workshop manuals.

In the process I devised a way to easily ensure undamaged spindle O rings. It worked wonderfuly for me:

http://bullfire.net/Triumph/Triumph15a/Triumph15a.html
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Old 12-15-2010, 12:23 AM   #2 (permalink)
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Why didn't the factory do it that way instead of the "special tool" requirement? Pretty sure they had reamers like that back then.
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Old 12-15-2010, 12:59 AM   #3 (permalink)
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A well engineered solution ed h !

My compliments.
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Old 12-15-2010, 11:17 AM   #4 (permalink)
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As usual: well engineered, well executed, and well documented.

Thanx, Ed.
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Old 12-15-2010, 11:24 AM   #5 (permalink)
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I am no expert on Triumphs and I don't have a 500 nor have I ever worked on one. So it is with great caution and some reluctance that I submit the following opinion.

First, I'm curious about those spindle caps. What holds them in place? Are they simply held in by the friction of the o-ring? What stops them from working out the end with time?

And not to rain on your solution, but based on what I see in your photos, I'm not sure cutting a taper on that end does not compromise the overall design of that shaft assembly. That cap serves as the end support for the shaft, which has alternating loads put on it by the rocker arm. With the taper cut, the portion of that cap outboard of the o-ring is no longer supported. The o-ring now can act as a pivot point about which that cap can pivot, due to clearance as the rocker moves back and forth. My guess is it will move and will start to wear that cover hole bigger and bigger. Plus, the cover is aluminum and the shaft is steel. The bore in that cover will increase slightly with engine temp, more than the shaft will expand, providing more room for relative movement betwen the two parts, cap and cover.

My humble opinion is it was a mistake to put that long taper in there and remove the support for what is in essence half the length of the cap, and in doing so, set it up to wobble in it's bore. If it were me, I would not do this to that cover.

Yes, it solves the o-ring insertion problem. But it does not take into account the impact to the system under running conditions.

I think it is just as easy to make a tool with that same taper and equivalent bore to the cover to assist in installing the o-rings.

Respectfully submitted,
Rob

Last edited by Snakeoil; 12-15-2010 at 11:29 AM.
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Old 12-16-2010, 02:38 AM   #6 (permalink)
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Rob--

The spindle caps are apparently a press or shrink fit. They don't separate often, which is why many people assume they are one piece. Once one does separate, though, I suppose it could vibrate out. On the other hand, the spindle doesn't rotate or move, and the compression on the O ring is pretty high. I now wish I'd thought to put some locktite in there. I'll have to keep an eye on it.

I think I see your point on the taper issue, though I don't see the soft O ring being any kind of pivot or fulcrum. At worst, I guess I've reduced the bearing surface for the spindle on that end, but it still might be larger than the smaller diameter bore on the other end.

In any case, I've read in several places that the factory drawings for the rocker boxes actually called for a chamfer in the location we're talking about, but that it was not actually done on some models.
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Old 12-16-2010, 10:59 AM   #7 (permalink)
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Ed,

I truly hope I am wrong about this as far as this causing problems in actual practice. I would want to see the factory dwg regarding that chamfer you mention. A chamfer is really just the breaking of a sharp that edge and has dimensional limits. Normally set at 45 degrees. Most chamfers are no more than 1/16 deep, although the size of the bore would determine the final depth. What you did is make a tapered hole. That's not a chamfer. And there is a tool specifically engineered to assist with the o-ring installation. That alone tells me that the chamfer was to assist in the positioning of the tool and placement of the o-ring, but not meant to work in this capacity by itself. Having been a machinist, I know that chamfers like this are rarely measured. A 45 degree cutter is placed in the toolhead and the operator comes down and kisses the edge of the bore to break the sharp edge. The result is some get kissed a little more than others, especially in production work. I would think this is the reason some did not get the chamfer. They probably did, just not very deep.

We are not talking huge numbers here. If you can slip that shaft into the cover with your fingers, then there is clearance between the shaft and the bore of the cover. Not much, but clearance nonetheless. That means that the o-ring, although significantly compressed, is still the largest diameter of that cap and hence is the pivot point for any angular movement . Everytime that rocker opens the valve, the shaft bends, an extremely small amount, but bends for sure. When it does, the cap tilts relative to the bore with the o-ring as the pivot point. The shaft also moves up and down perpendicular to the bore due to clearance. So the more surface area supporting the cap, the larger the area across which those forces are spread.

I truly not trying to rain on your parade, Ed. If this was just you and me in your garage, I'd probably never have said anything because it was too late and saying anything would not add any value at that point. But since several have liked the idea and others come to the forum for advice, I felt I should point out why I think this is a bad idea. At least this way, others can see both points of view and decide for themselves.

I base my opinion on good mechanical design practices, formal training as a machinist in my formative years and working working with very large, high tech, rotating equipment for nearly 40 years. It is not based however on any experience with Triumph engines, or specifically the 500 twin.

Again, respectfully submitted,
Rob
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Old 12-16-2010, 02:34 PM   #8 (permalink)
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Rob--

I respect your apparent knowledge in this area and don't doubt some of the effects you describe. I'm just not sure how significant they are. I do enjoy the discussion, though.

You might be interested in a sister thread to this one on another board:

http://www.britbike.com/forums/ubbth...062#Post348062

This is one place where the factory chamfer was mentioned.

Ed
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Old 12-16-2010, 04:00 PM   #9 (permalink)
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Thanks for that link, Ed. I probably should join that forum. Just what I need, another forum. Does help get thru the winter months though. Seems like a knowledgeable bunch, from that thread anyway.

So the chamfer is 15 degrees for an included angle of 30 deg. That's a relatively steep taper as chamfers go. But it makes sense for getting the o-ring to follow it rather than roll and climb up on the edge of the o-ring groove until it gets damaged. The standard 45 deg chamfer probably offers little help. Having not done this yet, I don't have a feel for the task. But from all the comments I've read, I have to believe it ain't easy.

Your reamer is a 10 deg included angle or 5 degrees relative to the axis of the bore. This means you have to go much deeper into the bore to get the correct starting ID for the o-ring, which is something you mention in your write-up. This tends to support my opinion that the angle of your mod, although great for slowly squeezing the o-ring down as it moves down the bore, removes more of the supporting bore ID than the design called for.

What I liked about that other thread was the mentioning of cutting a second o-ring groove in the cap. This would give you both better sealing and greater retention for the cap.

Out of curiosity, I opened up the Trophy 500 Parts manual to see how the rocker shaft is listed. It is shown as a single piece, with the cap as part of the shaft. Makes me wonder what the fit is between those two parts. You said you thought it might be a press fit. I would tend to agree.

I'm not familiar with P-80 lubricant that John Healy mentioned in his post as lube they use for installing the o-rings. I would give STP a try since it about the slipperiest stuff I've ever used.

I'm interested in all this, because the 650 and 750 engines have similar o-rings and I'll be getting into my 650 pretty soon and my 750 daily rider does weep a tiny bit on one of its shafts.

Glad you are taking my comments in the spirit in which they are intended. Not trying to be a know-it-all or come across as a Triumph expert. I still have plenty to learn about these beasts. I too enjoy the discussion because alternate opinions tend to make you think about things you might not consider noodling on stuff all alone in your garage.

Best regards,
Rob
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Old 12-17-2010, 09:23 PM   #10 (permalink)
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Rob--

I remember the thread about the guy who cut additional O-ring grooves in his spindles. Actually, I think he cut two additional ones in each spindle. I really liked that solution. Doesn't help to prevent O ring damage, though.

I haven't used P-80 either, but I know it is a lubricant specially formulated for rubber. I looked for some the day I assembled my rocker boxes, but didn't find it.
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