Single best upgrade under $30!

Got a stock '73 850 Mk2 in pretty good condition, gets ridden every weekend and I've always thought the handling reasonable, but not as firm as my previous '73 Bonnie. I've been thinking about a top Iso or Dave Taylor head steady but recently I had to opportunity to fit a Mk3 spring steady off a re-build project. Well, what an amazing difference! There was an immediate improvement all round. The Isos smoothed out earlier and the front end feels lighter. Going into bends is sharper and more stable, powering on in the bend is solid.

The benefit is conveyed from the dual spring exerting a lift on the motor, I believe this to be around 50Kg - 120Ibs and also resisting the tendency for the motor to tilt over when stressed in a bend. I'd have to recommend this as the single best frame improvement to the pre-Mk3 series models. The stock box head steady is used - with the Mk3 bolt on angle bracket, dual spring and spring retainer saddle. Thats about US$30 of parts. Note the two attaching bolts of the Mk3 angle bracket are off set 1/4" to the timing side when drilling the head steady.

Mick

head steady

I would say that 36 years later it was long overdue I don't know any rubber that would last that long even if the machine was parked for 36 years any parts that include rubber should be replaced.

ML said:

The stock box head steady is used - with the Mk3 bolt on angle bracket, dual spring and spring retainer saddle. Thats about US$30 of parts

Mick

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Where do you get these parts for $30.00? I always thought the Dave Taylor would be the least expensive.

A couple of answers may help, the frame has been upgraded to vernier Iso's for ease of maintenance and the frame rubbers (all 8 of them) have been replaced in the past 2 years, so its in pretty good condition. Swing arm is good and I always take a lot of trouble to line up the box head steady so handling is as best as one could expect from a stock 850 Mk2.

Obvously a proper top headsteady such a Norvil, Old Britt, Dave Taylor or Ludwig's design would be the best solution, but this subject is about a very low cost off the shelf bolt on improvement. I discussed the differences with a friend who has Mk3 and he puts in big mileage, serously 1,000Kms in weekend is normal for this guy. He rode both Mk2 and his Mk3 and declared he can detect the firmness and smoother Iso in the Mk3. I suggested that the spring steady resists (not prevent) the tendancy for the head to tilt under cornering stress.

The parts are Mk3, - Retainer 06-5585, Spring 06-5454, Trunnion 06-5456, and Bracket 06-5458 priced from Norvil's latest catalogue 9th January 2009 at US$27.95 less postage.

Mick

Now that I compare the part #'s with the parts diagram I see what you are talking about. I think I'll try it. Thanks for posting.

That's pretty interesting. Any chance you can post any photos of the completed setup?

Does the saddle just mount on top of the large head steady bracket?

Thanks.

trinorman said:

Does the saddle just mount on top of the large head steady bracket?

Thanks.

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Here's an image from a parts diagram.



I'm not sure where the "saddle" (retainer) mounts because if the bracket mounts to the front of the "Box Section" that bolts to the top of the head (large part on the lower right of the diagram) then the "saddle" would be too far forward to mount to the 2 outward Box Section screws. It would almost have to mount to the coil bracket. You have to wonder - at which point does all this cease to be "isolastic" and become more or less - rigid. I would think the "saddle could more or less just hang there as the springs should bear the load.

It does mount to the coil bracket, And there are parts in the system that are not in the drawing. You still have two plates that have rubber buffers that bolt to the small tube. I will try to find a diagram, Chuck.

Horton is correct. You have your stock late 750 or 850 box head stead assembly as is, to which you add the four Mk3 parts. Remove the side plates and head steady. Assembly is self evident once you have the Mk3 parts. Note early 750's had non-box, but a flange type head steady. I guess the later box is more rigid so worthwhile upgrading to that.

Match up the Mk3 trunnion angle bracket to the box head steady front face. Note the 2 fixing holes are to be offset to the timing side. Find the centre line and move the angle bracket not more than 6mm to the timing side. Its not super critical, the springs have some sideways latitude of movement. Drill the box head steady with the matching drill size for the bolt holes. Use Allen (cap screws) inserted through the interior of the box head steady so the nuts are on the outside of the angle bracket. Attach the angle bracket with the trunnion bolt facing upwards. Refit the box head steady onto the cylinder head and take care with alignment. Torque down evenly. I chose to keep it as rearward as possible and make sure the rubber bungs and side plates are parallel and evenly spaced. I use washers either side to ensure this.

The spring saddle fits onto the lower frame rail above the coil brackets. Push the wiring harness out of the way. The fixing holes align with the rear most of the coil bolt holes and you simply undo them, slip the saddle on and refit the bolts (nuts underneath are welded so no need to fiddle with a 2nd spanner).

Slip the spring over one of the two saddle retainer lips. I used the front most one, don't know if it makes any difference. Hook the springs onto the trunnion and gently wind down the trunnion nut. I found removing the right hand coil allowed better spanner reach. The spring tension is adjustable to suit the affect you are comfortable with, so try to start with around a 2mm gap on the spring coils.

I'd be very interested to hear others results, I guess the factory knew what they were doing on this subject but on the road responses are what matters 36 years later.

Mick