MKIII spring on 70 bike

DogT said:

Also where can I get some longer 5/16-20 Allen bolts for the head?

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Hello Dave
Maybe you've already resolved the bolt issue but:
I just checked the threads on the head steady bolts on my 70 model (it's not together yet - main bearing fiasco nearly resolved, just waiting for old britts shims to arrive in mail), and the pitch is actually 22 tpi, which is BSF. Just to help you avoid confusion, given that access to suppliers may not be plentiful in your vicinity.
Looking at the flat steel plate that you made to attach the engine spring to, it worries me a bit that it's cantilevered off that single bolt.
I hadn't given any thought to the head steady before now. The ideas sound good, but it's nearly spring in oz and i've got to get this bike back together. Any mods will have to wait.

Cheers
Martin

I've been working on the Taglieri head steady in concert with the spring and am waiting for parts right now, so it's on hold for now. I may be able to incorporate the spring attachment with the head plate, not sure until I get the heim joints and start hooking things up. I did find some old threads on the MK3 spring which were helpful.

Yes, I finally figured the bolt as 5/16-22 BSF. Actually Walridge has them in steel so if I need a longer one I can get it there, certainly not at the local hardware.

I've been looking at ludwig's head steady also, I may try that one just for fun. It's much simpler and appears just as effective at stopping side play. It requires cutting 3/16" steel which may be a problem for me although I could cut it with the torch, but it's messy. Or there's a shop not far away they may make the parts for a reasonable price.

Dave
69S

Dave,

The Mk3 headsteady spring is set up to provide 145 lbs of tension with 0.5" extension. This approximately unweights the isos if the spring closely follows the jug angle, and this is possible only when, as Les has pointed out, the spring is attached per the manual. If you want to duplicate the Mk3 spring action, you will have to adjust your geometry to preserve the nearly vertical (10 degrees or so) spring angle and the 0.5" spring extension. I seem to recall that the box headsteady design of the Mk3 evolved to correct the metal failure that was present in previous designs; this part sees a vibrating 145 pound mass.

I wonder if I'm fighting an uphill battle here. I did turn over the spring, but I'm still sorting where I can attach it. The strange thing is, if I remove the front iso mount, completely, including the 1/2" iso bolt, and let the front float with only the center iso holding things together, and I put the front mount back on with out the collars and bolt, the frame mount hole is 1/2" behind the motor mount hole and about the same above it. It doesn't seem to matter if I put the spring on or not, the front motor mount location doesn't change much, maybe 1/8" higher. Even if I jack up the front motor mount, it takes quite a bit of force to get it to come up near the frame hole. Then it's still 1/2" in front of the hole. It takes quite a bit of pushing and pulling to get things to line up to get the 1/2" iso bolt in. It's like all the isos are always under some tension no matter what I do, spring or no, head steady or no. I even took off the exhaust mounts and it doesn't make any difference. I don't understand what's holding the front motor mount down so far, you'd think it would just flop around with things taken off.

I'm wondering if something isn't bent on this frame. I didn't have any way to check the mounting points when I was rebuilding it. I've tried different settings with the front and rear iso vernier and nothing seems to make any difference at all.

Dave
69S

This misalignment is on the centerstand, on the ground, or raised on a bike lift?

There must be frame specs somewhere. You had better look.
I cannot imagine a layout tht is loaded that much. Makes no
sense but then who am I?
Stuff breaks when it isnt neutral at bolt up usually.

If there is weight on the rear wheel then its leverage through rear iso pivot would tend to push the front of engine down and forward. If things bend out of line enough for 1/2" misalignment then would not be able to assemble at all. Try bungee cords around rear rim or block under rear tire to hold that end upward and see if don't align from mount better.

grandpaul said:

This misalignment is on the centerstand, on the ground, or raised on a bike lift?

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Any way I do it, on the center stand (which is on the frame) on the side stand, or just holding it on the tires. It really doesn't make much of a difference. Even if I sit on the rear of the frame putting pressure on the rear wheel.

I'm thinking I'm going to remove the exhaust, loosen the shocks, take off the carbs, take off the front engine mount again, and only have the engine/cradle/gearbox/rear wheel supported by the iso at the top of the z plate and see what is going on. I have the frame dimensions in the manual, and if I find a couple of longish 1/2" rods, I can put them in place of the iso studs and try to measure what is specified in the book for the iso stud holes. I never did check the dimensions when I had the whole thing apart. Another mistake undoubtedly.

If the isos are compressed by 1/2" by just mounting the engine/etc. I probably could never get the isos to work right and may be the reason I find no difference adjusting the vernier for clearance.

Dave
69S

<I never did check the dimensions when I had the whole thing apart.>

You and me both. Ideally you build up the whole bike and get it sorted then take
it all down again and do the cosmetics.
...another reason not to use powder!

I have found the powder to be reasonably flexible.

Dave

Well I mean it is a tough touch up and like your welding fix another
break in the coating job.
Some of my bike is powder just as an experiment. I like the fast
turnaround time on it though.

I use black rustolium out of a can for repairs. So far all of them are in places that are covered up, so it really doesn't matter.

I actually found something useful at Tractor supply today (very unusual). They had a 3' piece of 1/2" steel tubing. I'm going to remove the exhaust, and all the other parts I mentioned, leaving the engine suspended only by the central iso to see if the front mount will come up anywhere near the frame holes. Then I'm going to replace the iso stud and front bolt with a 1 1/2' piece of the rod, letting it stick out where I can measure it and see what the dimensions are. I may be bending my frame soon if it's out.

Dave
69S