play in top shock mount - Skorpion with 2400km

[Petrolhead]

Hi folks, I was tightening up the back wheel nut and as I levered upwards with a extension bar I was surprised to find that there was a slight clonk from the top shock mount. I looked more closely and it does go up and down around the bolt ( which is tight) by 1 to 2mm.

Bike has only covered 2400km is as new, has anyone had this and what sort of fix can I do? Seems like the quality of some cycle parts is iffy

[mincehead]

Open it out to the next diameter bolt size, and / or sleeve it, a relatively simple engineering fix.

[Petrolhead]

Thanks for the suggestion, I measured the bolt od and its 11.87mm and the id of the sleeve is 12.47mm o it looks like manufacturing error on the shock. I spoke to my friend who has two Vincent Comets and a Black Shadow and is used to making bits up for them, he says to get a bit of SAE660 phosphor bronze round bar 3/4 inch about 19mm which approximates to the od of the shock sleeve of 18mm.

So I am going to drill it centrally to 11.50 mm and then ream it out to size which should sort it. Alternately I have two sintered bronze Oilite bushes on order OB121820 which I can install side by side as a sleeve and their as supplied finished inside diameter is 12mm +/- 0.02mm. The Oillite bushes are less strong than the phosphor bronze bar as they are made of compressed spheres of phosphor bronze , the gaps in between the granules to retain oil.

Methinks this might sort it when I press out the old steel sleeve and press in the bronze one .It sure is going to be fun doing it......thanks again Mincehead

[Dicer]

I should stop reading these posts. I thought I would just check my Tour after seeing this since it was sitting there on the centerstand...and it's the same.

So what takes the rotational movement at the top shock joint? Surely it isn't supposed to rotate on the bolt. From what I can see, it looks like some sort of Metalastik type rubber bush around the bolt.

According to the parts list, the lower joints on the dog bone linkage have ball and needle bearings.

http://www.grahamsmotorcycles.com/web/M ... _Shock.htm

[Petrolhead]

Dicer, the suspension linkages all have good bearings suitable for the moving parts to have no play for a good while as long as they are greased up, from what I see. I am a newbie to the MZ world so am finding my way along it But the shock top mount metalastic bush seems to have a generous clearance to its bolt which transmits to quite a movement when relayed to the end of the swing arm, so being a perfectionist I want to eliminate it. The shock oscillates slightly back and forth on the top mount bolt as the swingarm compresses and rebounds. There's no needle bearing at the top end of it, so its grease which keeps it good. If I can , i'll drill and tap the top shock mount to take a grease nipple.

My bike has been through four mots like that and it did not fail , so I don't see a problem there. Its just means to me that the rear wheel does not track the road as closely as it could. Sometimes its just to make a good bike better which drives me The hole was not oval or was the bolt so it must be just how they are made from new.

[Dicer]

Hi Petrolhead, thanks for the reply. I just got a chance to have a better look at this after I pulled out the upper shock bolt. BTW, I'm also new to MZs but not to motorcycles or automotive work in general.

The bolt shank measures 11.89mm OD and shows no wear (17,000miles on the bike) but there was movement of the bush on the bolt before I loosened it. IMO, that bolt is supposed to be reefed up tight and any movement of the shock, which is minimal anyway, ought to be accommodated by the rubber in the Metalastik bush. This is exactly the same way as most automotive shocks and suspension arms are located.

I agree, the clearance between the bolt and the inside bore of the bush seems to be excessive. And, I measure about .012" sideways play between the bush sleeve and the frame clevis before the bolt is tightened. So for now, I'll insert a shim washer and tighten it up solid. The inner sleeve of the bush should be solid with the frame. I definitely don't think you'd want to install an oilite bush or any grease fitting there.

Regarding all the pivot bearings on the dogbones, I can't see how they are supposed to be lubricated. The handbook just states "assembly grease" but there's no obvious means to apply it other than disassembly. Maybe someone else can chip in.

[Petrolhead]

Sorry about the delay in replying, its been a bit hectic. Yes, the pivots on the shock bottom mount and dogbone ends seem to be a strip and grease when apart affair, this is the same as the Honda Prolink I have.

IMO though, if the top shock bush is held tight at its metal centre, the outer rubber portion would resist the slight rocking motion of the shock adding torsional value to the spring rate and wear on the internal bushes in the damper. My take on it would be to make a bush with a close sliding fit to the central bolt and also a close pivoting fit to the frame lugs.

I don't have much experience of mono shocks , my Hornet 919 has free moving bearing pivots on its monoshock both top and bottom and the old seventies Honda CB750 Four has a free pivoting top mount by virtue of a shoulder on the top shock frame mounts to stop the dome nut and its thick washer clamping the top shock central bush tight.

Only my opinion mind i'll be happy to stand corrected by the other more knowledgeable users here. I am a MZ novice after all

[dandywarhol]

If the top bush is metalastic then do the final tightening up with your weight on the bike - otherwise the bush gets a harder time on full compression.

[Dicer]

If the top bush is metalastic then do the final tightening up with your weight on the bike - otherwise the bush gets a harder time on full compression.

The rotational movement of the top joint is almost nil so I doubt it makes a difference. I've put a few miles on my bike after I tightened my own top bush and it's remained tight, no play. I understand your concern though because it's a common mistake for some people when installing Metalastic bushed auto suspension to tighten it all up while it's still on the axle stands. In some cases the car will end up sitting an inch or so too high.

[Petrolhead]

I think that's been very helpful, thanks all. Just a word of caution, the steel inner sleeve of the metalastic bush is bonded/vulcanised to it and the rubber shreds when you try and press it out. Fortunately I have a nylon bush of the right id and od off a 4x4 leaf spring kit, which will do the job along with my made up phosphor bronze sleeve.

[Dicer]

Just a word of caution, the steel inner sleeve of the metalastic bush is bonded/vulcanised to it and the rubber shreds when you try and press it out.

That's the way Metalastic bushes are. If you want to press one out without destoying it, you need to use a mandrel just a fraction smaller than the outer metal sleeve (which is also bonded). But generally when changing them, the rubber has usually perished and it's necessary to saw out the outer sleeve and collapse it after removing the rubber etc. Incidentally, the inner sleeve is usually longer than the outer one for the simple reason that it is supposed to be tight so the outer part can still move. Maybe yours had worn down from being loose.

[Petrolhead]

Thanks for that info, I now know a bit more about these type of bushes In the end I decided to bite the bullet and get a Hagon stainless body variable damping shock. They are £295 incl UK postage .....here's a link
https://www.hagon-shocks.co.uk/catalog/ ... tno=M67080