MKIII spring on 70 bike

I've got all the parts for the spring assembly and attached it to the bracket I am planning on using for the Taglieri type heim head steady. It looks like I can't get the threaded bracket as low as it is mounted on the MKIII boxed head steady. Picture is with the spring as tight as I can get it and it barely pulls the front iso up. I'm wondering if I can cut the bolt that's welded on that bracket and turn over the bracket to get another inch or so of spring action. I'd have to re-bend it. Any grand ideas? Also where can I get some longer 5/16-20 Allen bolts for the head? I think that's what they are. Certainly can't find them at Ace.





Dave
69S

DogT,
Just make a new angle peice and mount it upside down with a through bolt any thread pitch will do just use a self locking nut then you should have plenty of space to get the correct spring tension.

DogT said:

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The spring needs turning around, so the open ends of the spring trunnion hooks are at the front (well....that's how it's drawn in the MkIII manual and parts book :wink: )

Get rid of the angle bracket and the spring bolt bracket and bolt and use a stepped straight bracket

Explain stepped straight bracket? And if I don't use the bolt/bracket how do I attach it to the spring/round gizmo with the hole in it?

Like this? I really don't have any way to make one of those.



I need to go to town, I'll see if tractor supply has anything.

The OB site shows the spring with the opening to the rear. I wouldn't think it matters much, maybe the best way it fits?

Dave

MIght consider also making the top of spring seat higher off the tube.
Also what is the extra fastener seen next to the breather fitting?

Actually if I use a straight bracket in place of the angle one, and a 3 1/2-4" bolt, that would give me all the pull I want. If I bend a piece of 3/16 AL to match the angle will that weaken it too much? I could use a piece of 3/16" steel. That wouldn't get stressed, especially if I heat it.

Don't see any extra fittings that I know of. There's the hose clamp next to the angle breather or the nut at the front of the engine? It came that way.

Dave

DogT How would it be if you turned your right angle attachment bracket upside down. You'd need to use counter sunk screws to keep flush with the angle aluminum. just a thought. Cj

I found a piece of steel laying around the barn so I whacked off about a 2" square piece. Drilled 2 holes, one offset 1/8" and at an angle, put a carriage bolt in it and now I can tighten the blazes out of it. How simple can that get? The iso still doesn't do much. I wonder if the rubbers in the iso have already taken a set in only 2 years. I guess the only way I can find out is...... If I put a hammer handle between the frame and the bottom of the engine, I can just get the iso centered if I put a bunch of weight on it, with the spring.





Ludwig only uses a spring giving him 20kg on his setup, that's 44lbs. I would think the spring would want to pull the full weight of the engine/gearbox/cradle?

Any ideas on longer 5/16-20 Allen heads? I don't want to ride it with this little amount of threaded into the head. I might try Rocky Point.

Dave

DogT said:

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Is the bike resting on its wheels?

The spring should be tensioned so the distance over the coiled sections measures 1.47" - 1.53" (spring still fitted back-to-front)

Yes, on the wheels and prop stand. I just don't see if it matters, the engine is suspended in the frame, so what ever is done to the frame, the engine/etc. weight is still there. I'll try on the centre stand just for drill though.

I found the nut much easier to turn with a spanner if the opening is to the rear.

DogT said:

Yes, on the wheels and prop stand. I just don't see if it matters, the engine is suspended in the frame, so what ever is done to the frame, the engine/etc. weight is still there. I'll try on the centre stand just for drill though.

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Acording to the MkIII manual (OK I know yours isn't a MkIII and has the frame mounted stand) it states: "Prior to checking adjustment or dismantling note that Mark III models must be supported by a stand or strong box placed below the main frame tubes with the centre stand folded."

I put it on the centre stand. No difference. Remember my stand is attached to the frame, so there should be no difference if it's on the stand or on the wheels. There might be a slight difference if I would sit on it because it changes the geometry because the shocks are a bit compressed, that's all.

Dave
69S

DogT said:

Remember my stand is attached to the frame, so there should be no difference if it's on the stand or on the wheels.

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I'm not sure I entirely agree, as there must be some shift of the Iso. loading-depending on whether the weight is resting on the wheels (or rear wheel) or not.

OK I now see its just the top front case through bolt, sorry.
If ya think about the purpose of the spring, which is to nullify its gravity on the isolastics then optimally one should adjust spring tension to just support the engine so it essentially centered on the iso cushions. I was going to ask why not just a straight plate extension to see you solved it that way and likely what I'll have to do to my Peel to adapt to her top link base plate. Two socket head top bolts have a rare fine thread that about nothing else has on a Commando. Fortunately they are not a hi load item so SS or what ever sourced should work out, or might counter sink their seats a bit to gain a few more threads. Their loads are shear type. I've had a terror of a time getting some out and one center one failed shearing off flush, but not really needed. Anywho its one area I definitely use silvery anti-sieze or pink Milk of Magnesia d/t the hi heat they endure.

Dave,
With the stretch showing on the spring as fitted to your latest bracket, i suggest it is way too much. The stock 850 setup generally allows a 2mm gap at most between spring coils. The idea is not to 'lift" the motor off the front Iso, only to reduce the load. I could not see anything wrong with your 1st setup.

Mick

L.A.B. said:

I'm not sure I entirely agree, as there must be some shift of the Iso. loading-depending on whether the weight is resting on the wheels (or rear wheel) or not.

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I know others disagree with me on this. My thinking is the engine/gearbox/cradle/swing arm/rear wheel is suspended in the frame with the isos. Now yes, because the rear wheel is in the equation, there will be some weight taken off the isos when the rear wheel is on the ground, but it's so far away from the bulk of the weight (engine) and behind the rear iso that I would think it would be nearly unnoticeable at the front iso. If anything one would think weight on the rear of the frame would lever the front iso up. Just about any weight placed on the frame would still not change the balance by much unless it's placed totally in the rear or totally in the front.

Right now I have a jack under the front engine iso to center the iso stud. I thought I'd leave it like that overnight and see what happens. Probably nothing. Next thing I'll do is take the front iso off, it's not that hard and see what it looks like in there. I suppose I could take the exhaust dog leg bracket off too or at least detach the silencers, that may contribute to weight shift.

Like hobot says, I would think the optimal situation would be the iso stud would be centred in the iso assembly when the spring is taking the proper amount of weight off. I never knew what was going on until I took the gaiters off. I do notice with the spring on, the isos are more centred side to side than before. I can rotate both side tube caps by hand which I couldn't before.

Yeah, I used nickel anti-seize on everything.

Dave
69S

Power unit pivots on rear iso like a teeter totter. Rear tire striking road lump or cargo on back forces front iso downward, power thrust of rear lifts loads off front iso to point can even wheelie. Spring helps the crank throws not thrust downward much more than upward d/t gravity assist on downward stroke. Springs are said to reduce low rpm vibration isolation to disappear earlier than w/o it. Ideally should just suspend full weight so iso mostly centered at rest. On throttle blips the engine jerks back and upwards off front iso, so angled forward spring tends to resist that too.

hobot said:

Springs are said to reduce low rpm vibration isolation to disappear earlier than w/o it. Ideally should just suspend full weight so iso mostly centered at rest.

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That's what I'm aiming for.

Dave

I'm not sure what I accomplished today, other than take the front iso off and put it back on. The outside rubbers are slightly compressed at the bottom, so I turned them over and re-installed everything. Funny thing is when I removed the collars and tube caps and the mount was sitting there with no bolt through the frame, the centre of the iso was in front of the frame holes by about 1/2". If I loosened the spring, the center of the iso mount would fall down below the holes in the frame. If I tightened up the spring as tight as I can, it just came up almost level with the holes in the frame. I'm not sure what this means. I didn't mess with the rear isos at all.

When you guys put your engine in the frame, do the isos line up pretty good with the frame? I always have to push things around a bit to get things to line up. Like 1/2" or so.

Anyhow, I'm going to straighten out the wiring, bolt this thing back together and at least try it with the new spring to see what happens. Then I have a few more little projects for it. I've learned, one thing at a time.

Dave