MK III headsteady adjustment

I just installed the spring assy from the MkIII to my MkII but despite reading the MKIII shop manual re adjusting it (basically, don't change it from factory setting - whatever THAT is, and only adjust it with the bike on a cradle or on it's wheels. Fine...but adjust it to what? How much tensions is supposed to be on the springs and how would one measure whether the tension is correct - seems to me that essentially one is trying to get most (all?) of the engine/cradle's weight to be suspended by the springs when the bike is on its wheels. Is there some fairly easy way to determine this?

MexicoMike said:

...but adjust it to what? How much tensions is supposed to be on the springs and how would one measure whether the tension is correct

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http://britmoto.com/manuals/Manuals/850_man.pdf - Section C1, Fig. C1(a).

Thanks, but I have that manual. I don't have any problem attaching and fitting it but unless I'm really blind (possible, my wife says I can't find anything right in front of me), I don't see anything anywhere in the MK III manual that addresses how to know the amount of tension to put on the springs. Section C9 #14 "Important Note" just tells you not to disturb the original setting. But since I'm fitting it for the first time, there is no "original setting."

there is just a length measurement in the manual

AHA...I was about to answer that there was no such measurement but when I looked carefully at the C1a diagram I saw some chicken scratches that when I enlarged them, turned out to be those measurements - 1.47 to 1.53" for the spring coils. There is also another measurement in the low part of that diagram but I can't tell what it's measuring. It looks like .2 Min and .5 Max but I can't tell what is being measured in the diagram.

I just checked Is that 1.47 INCHES? There's no way you could stretch the springs that far.

I recently fitted a Dave Taylor Head Steady that came with the spring assembly for my 73 850.

I am looking, but cannot right now find, the instructions that came with it.

But, I remember very clearly the fiddly difficulty I had in getting the spring hook ends to line up with
the grooves in the bar, had to bend them a bit to make them fit without twisting.

Forget the instructions, I just went out and looked under the tank.

Just keep tightening the nut until the top of the bolt is flush with the top of the nut!!! perfect!

Mex, I hear what you say and I'd suggest that as your bike is not a Mk3, as is mine a Mk2 the addition of the spring support is not neccesarioly dictated by the stipulations of the Mk3 manual. Its easy to tune the spring to what works best on your frame. For example, I find a spring coil gap of 2mm just about the sweet spot on my frame and Iso set up. Wind it in or out go for a ride and feel the differences.

Mick

MexicoMike said:

AHA...I was about to answer that there was no such measurement but when I looked carefully at the C1a diagram I saw some chicken scratches that when I enlarged them, turned out to be those measurements - 1.47 to 1.53" for the spring coils. There is also another measurement in the low part of that diagram but I can't tell what it's measuring. It looks like .2 Min and .5 Max but I can't tell what is being measured in the diagram.

I just checked Is that 1.47 INCHES? There's no way you could stretch the springs that far.

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If you measure from where the springs turn 90 degrees to begin the coil winds, it can be done.

MexicoMike said:

I looked carefully at the C1a diagram I saw some chicken scratches that when I enlarged them, turned out to be those measurements - 1.47 to 1.53" for the spring coils. It looks like .2 Min and .5 Max but I can't tell what is being measured in the diagram

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Unfortunately that appears to have resulted from the copying process, as the diagram shows clearly enough in the original paper copy manual.

The second dimension (.2" - .5") is the allowable distance between the spring bracket and spring trunnion.

Also, the saddle that the springs sits on (on the frame) has 2 notches to locate the spring. You have to experiment to see which location will give you the measurements in the manual.

ML said:

Mex, I hear what you say and I'd suggest that as your bike is not a Mk3, as is mine a Mk2 the addition of the spring support is not neccesarioly dictated by the stipulations of the Mk3 manual. Its easy to tune the spring to what works best on your frame. For example, I find a spring coil gap of 2mm just about the sweet spot on my frame and Iso set up. Wind it in or out go for a ride and feel the differences.

Mick

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Hi I fitted a DT and adjusted the spring thingy until the low frequency vibes were reduced in the rev range I wanted (MKII).

Thanks all; I understand it now. I saw that there are two notches to hook the spring but the book shows it attached to the hook toward the rear of the bike so that's what I did. However, as noted above, it looks to me like mine will need to be at the forward hook in order to achieve the dimensions stated. Part of that MAY be because since I drilled my oem head mount to accept the spring device, I didn't really know how high up/down the front side of the mount to drill the holes. So they may be in a different spot vertically than the oem MK III. I did offset the spring mount appropriately to end up with the trunion bolt centered in relation to the frame.

I have a related oem headsteady question re offset of the engine itself re the headsteady plates. In the parts diagram for the MKII there are no shims shown in the diagram to set the plates parallel when attached to the rubber mounts and the engine head steady mount. On my 850, the left side plate will bolt directly to the rubber mount and to the engine without being angled. However, on the right side, there is a 3/16" gap between the engine mount and the plate with the plate bolted to the rubber mount. So there needs to be spacers (washers) between the plate and the engine mount to keep the plate from twisting the rubber mount. But again, I see nothing in the manual that shows that any shims are used. Basically, the distance between the surface of the rubber mounts is wider than the distance across the engine's head steady mounts. So there is no way to NOT use spacers as far as I can see. But what did the factory do or could the new rubber head steady mounts be wider than the originals?

Mike, you should find that the 850 steady has the bolt holes offset to allow the side plates to align, the same way the front and main ISOs are offset. I replaced my old cracked 750 part with an 850 for a few years and the holes are about 3/16" offset to the right looking from front. Mk3 seems to be same part as mine has the holes for the spring device.

The distance (width) between the mounting surfaces of the rubber mounts (where the side plates attache) on my 850 frame is a hair less than 2 11/16" inches; the width of the headsteady mounting surface where the sideplates attache to the engine is 2 1/2" So there nearly 3/16" of an inch to be made up either by shimming the plate or just tightening the plates and letting the upper mount rubber on the right side twist as I tighten the lower bolts. The left side rubber/plate/head mount on engine lines up. I just can't see this as being correct, especially as the shop manual does not call for shims "as needed." But the headsteady on the engine is the correct one.

Mike,

Each of the springs have a spring constant of 140 lbs/in. As they are in parallel, you need to insure that the adjustment produces a 1/2" exension in the coil length, to produce a net of 140 lbs of force along the jug axis. This approximately unweights the isos, as the engine cradle assembly weighs 140 bs. There's nothing like an orderly universe were motorcycle technology actually makes sense. I had to use the second detent on the frame piece to get my Mk3 into adjustment.

MexicoMike said:

Part of that MAY be because since I drilled my oem head mount to accept the spring device, I didn't really know how high up/down the front side of the mount to drill the holes. So they may be in a different spot vertically than the oem MK III.

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The mounting bracket should be fixed so that its lowest point is level with the bottom of the steady.

If it was positioned higher, then I expect you could have problems setting the spring length correctly. I also have to fit the spring onto the forward location in order to gain sufficient adjustment.

I apologize if I'm being unclear by mixing two different headsteady issues. I understand the springs and the fact that I will need to move the spring to the second hook to get the proper stretch re the 140 lbs - thanks.

The issue I am wondering about is not related to the spring mod at all and it has always been this way. But I want to at least understand if it is normal or not.

Re the diagram - Part 4 (sideplate) bolts to part 1 and part 6 (Ignore part 5 - their position in this figure makes it appear as if they go between 4 and 1 but, of course, they do not. THey are "inside" part 1). If I bolt part 4 to part 6 on both sides, part 4 will touch part 1 on the left side as it should but there will be a 3/16" gap between part 4 and part 1 on the right side. Therefore, to avoid twisting the rubber of part 6 on the right side, washers have to be inserted between part 4 and part 1 on the right side. The distance between the mounting surfaces of the two part 6's and the distance across part 1 is different by 3/16" so no matter what, the sideplates cannot be mounted without shims or bending the right side rubber rather badly. I'm wondering if the original factory part 4 was slightly narrower than the replacement parts which are the same as those used for the exhaust mountings. Since no shims are speced in the parts diagram, I ASSUME that from the factory the width across the the two rubber mounts and the width of part one where the sideplates mount was the same. The only way this could be the case is if the original rubber mounts weren't as wide as those supplied now.

MexicoMike said:

If I bolt part 4 to part 6 on both sides, part 4 will touch part 1 on the left side as it should but there will be a 3/16" gap between part 4 and part 1 on the right side.

I'm wondering if the original factory part 4 was slightly narrower than the replacement parts which are the same as those used for the exhaust mountings. Since no shims are speced in the parts diagram, I ASSUME that from the factory the width across the the two rubber mounts and the width of part one where the sideplates mount was the same. The only way this could be the case is if the original rubber mounts weren't as wide as those supplied now.

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Possibly? But my MkIII's steady assembly is exactly the same as you've described it, with a 3/16" gap between the side plate and the steady box on the right side when the plate lower mountings are loosened.

the sideplates cannot be mounted without shims or bending the right side rubber rather badly.

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When the fittings are tightened, the rubber mountings (mainly the R/H one) appear to compress, but I can't see that the R/H one bends much?

Well that's interesting and I had never thought about it. It seems to me that both rubber bushings should be "loaded" (compressed) the same amount so I was trying to put no compression on both rubber mounts when the bike is in an upright position. I guess it doesn't matter...

MexicoMike said:

The distance (width) between the mounting surfaces of the rubber mounts (where the side plates attache) on my 850 frame is a hair less than 2 11/16" inches; the width of the headsteady mounting surface where the sideplates attache to the engine is 2 1/2" So there nearly 3/16" of an inch to be made up either by shimming the plate or just tightening the plates and letting the upper mount rubber on the right side twist as I tighten the lower bolts. The left side rubber/plate/head mount on engine lines up. I just can't see this as being correct, especially as the shop manual does not call for shims "as needed." But the headsteady on the engine is the correct one.

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Had the same issues, 850 Mk2 and found that the side plates would need thick washers to make up the gap otherwise one of the side plates will pull in out of the vertical and that is noticeably negative on vibration. It just seems obvous that the rubber buffers must not be preloaded in any plane and I spend a lot of time centralising the headsteady and symmetry of the side plates, carefully tightening the nuts up and then finally the winding down the spring trunnion. By the way, do all of this with the bike not on the centre stand. I'm real happy with the feel of the setup but it did take a few goes to get it right.

Mick