Shocks

The Cagiva era Morinis
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Shocks

Post by nickst4 »

Yet another query!

I knew from my reading on the subject that some contemporary roadtests were critical of the monoshock, pointing out that the top few coils were very nearly bound at a standstill, and that the rear suspension would then appear to hit the heavy rating of the spring and the linkage geometry, resulting in a very choppy ride. So it seems to be on mine!

I'm about the ideal size and weight for the bike, at 5'6" and 140lbs ready to ride, and I thought the apparently-soft rear suspension would suit me well, but it definitely stiffens dramatically if the bumps are at all sizeable. I enquired of Wilbers as to Dart shocks, and though they do them for hundreds if not thousands of models, they don't offer one for the Dart. I'm not enamoured of Hagon shocks as they often seem to have excessive stiction.

It occurs to me that one might find a linear spring with a rating somewhere between the high and low rate of the progressive-wound OEM one, and just let the shock linkage get on with it's job of providing a progressive rate, if that's the way it's designed.

Any comments? I ride in the real world of bumpy roads, not on super-smooth race-tracks!
morini_tom
Posts: 919
Joined: 05 May 2006 13:47
Location: Northampton

Re: Shocks

Post by morini_tom »

Thought about this myself a few times but never had the time or money to properly sort it.

Given the age of our bikes, a complete new unit probably wouldn't go amiss as I'm sure the damping isn't as good as it once was and they're not really rebuildable.

If you look at eBay there are various aftermarket dampers listed for the freccia- not sure how good any are but got to be better than the soggy 25 year old original! You could then get a damper with some adjustability and with a bit of luck spec more appropriate springs too.

I've held off this because my underseat pipes run very close to the shock and I have no room for a shock or spring which is even remotely bigger diameter than the original and I'm reluctant to purchase an expensive new one and find it doesn't fit. Would be interested in the outcome if you went down this route though...
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

morini_tom wrote:Thought about this myself a few times but never had the time or money to properly sort it.

Would be interested in the outcome if you went down this route though...
I shall take it on as a mission! There's a suspension specialist near me in Stowmarket that's had a lot of my money over the years, and I'm sure they'd be helpful. Having had the spring off the damper, I know it still damps as well as any I've tested, so an alternative spring, maybe with custom spacers that I can make, is worth a try. And having had all the linkages off earlier this year, I know I can easily remove the shock and take it in for MC Technics to check rates and have a look in their store....

Nick
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

Well, I'm glad to say the problem has been dealt with. My mechanic-guru, Carl Harrison in Harleston, Norfolk, says he remembers selling and working on Darts. His general and specific knowledge is awesome, and I recommend him very highly, especially for Italian exotica. Anyway, he pointed out that my bike had way too much static sag at the rear, such that it was running through the linkage ratio and geometry far too quickly. He said I should definitely not look for a different-rate spring, especially with the front suspension being pretty soft. I measured sag at the rear indicators and it was maybe 30mm: not 40mm as he estimated it by eyeball, but still a lot. Although I find preloads versus spring-rates a bit of a black art, I took Carl at his word and wound the shock spring preload up by maybe 6mm, resulting in the static sag reducing to 12mm, and the ride height being raised significantly. Now the bike drops comfortably onto its shock, rather than collapsing as it did before. Pumping the backend now gives a very supple and damped action, without the feeling of hitting the bumpstop. There'll be a bit more angle on the sidestand too, of course.

This has made a significant difference to the ride, and has definitely reduced the stunning kick-up-the-bum when hitting my local backroad bumps that I found so objectionable. On smoother roads, of course, this bike rides superbly. I guess the ride-height change will have sharpened steering responses, not that they needed it, plus given a bit more ground clearance. The chain tension should still be fine, given it was right before. Raising ride-height and retensioning the chain is a quick way to knock gearbox bearings out!

Definitely getting there! :D

Nick
EVguru
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Re: Shocks

Post by EVguru »

Some of the early road tests appear to have been done on pre production machines. These weren't proper Darts, but Freccia frames with the Morini engine. The factory brochure (the one with the big picture of Massimo Tamburini) definitely shows one of these. The tubing that hangs down from the main frame rails is different. What other differences to production machines there were i don't know, but the Freccia springs are different. Both front and rear are stiffer than the Dart, the front pre-load spacers being shorter. One of my Darts arrived without spacers and I had to make some (I gave the measurements to Rob at NLM). The Dart also has fork extenders of about 30mm length and the rear shock is (usually) mounted the other way up. These are Cagiva machines and build quality was not the best.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

I had a nice quick ride on the Dart last week; probably one of the last this year 'cos the roads get filthy with mud and salt around here. Anyway, I was reminded of my intention to pursue better springing for the shock, so I removed it pretty easily (taking the battery carrier out helped a lot) and took it into MCT in Stowmarket. Darren put the spring on his Ohlins testing rig and did lots of arcane stuff with strain gauges and travel measurements. His measurements determined that the close-wound section that binds very easily is at 10kg rating (sorry, I don't know exactly what the units are) and the rest is at 13.

My theory was that it might make more sense to have a linear spring rather than a progressive (or what Darren determined was more nearly a two-rate one), with a rate between the current two and hope that the linkage would provide a progressive action. Darren agreed, and has supplied me with a WP 11kg spring of the right length. The diameter is a few mm larger than the Marzochi original, so it needed a couple of spacers to fit. Now back together, I shall get it back onto the bike in the next day or two and hope the weather is favourable for a test-ride. I only need to run the first mile of my country road to see if there's any improvement!

Nick
mantaray
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Re: Shocks

Post by mantaray »

Very interesting Nick
Always tought the spring is too weak
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

So far, in the garage, the results are very promising! Pumping the bike from the grab handle gives a beautifully-supple feel without the abrupt halt it had before, and very good rebound damping (the original shock). Set up with about 10mm static sag, it drops another 10mm or so with me on it, instead of going straight through the first rate of the old spring. Again, bouncing my weight in the saddle doesn't give the bottomed-out feel like before.

Maybe the heavy overnight rain will stop and the roads dry out enough for a ride later!

Nick
morini_tom
Posts: 919
Joined: 05 May 2006 13:47
Location: Northampton

Re: Shocks

Post by morini_tom »

Nick,

Intesresting developments!

We seem to have been doing a bit of research on this in parallel, although I'm yet to actually do anything on the bike.

I'm limited by how much I can do with the oem damper as mine is certainly not damping as well as it used to, so I was keen to replace. I also have a space (and heat!) issue causd by my underseat pipes, so I can't go up in diameter on the spring.

I contacted Wilbers who list a shock for the freccia, and they were happy to build one to spec for the dart. I sent them measurements of the original dart spring, and they are making a progressive spring to that spec, although I've asked them to go down from 72mm OD spring to 68mm whilst maintaining spring rate to give a bit more clearance to my underseat pipes.

From my fag packet calcs I reckon my dart spring is 80N/mm in the first bit of travel and 160N/mm once the progressive section is coilbound.

The damper I've ordered is a 631 which also has adjustable compression and rebound damping.

Hopefully it'll arrive in a few weeks and I'll keep you updated.

Tom
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

Hi Tom,

I asked Wilbers about a Dart shock and they couldn't help, though I didn't suggest the Freccia option. I hope you'll have success. At least you'll have supple damping, but to my mind it's the spring that's the problem. Getting them to make a spring to those same rates sounds like an expensive mistake!

By the way, the WP spring I fitted and hope to test today cost me £70+VAT, but the chance of finding something s/hand of the right size is slim, and Darren had done all the testing on his machine so I couldn't back out. Lengthwise it's perfect, but is 75mm OD rather than 72mm, hence the need for extra adaptors for the seats. Also, being finished in a nice metallic grey, it doesn't look as daft as the OEM red one! I hope it lives up to expectation...

Later,

Nick
EVguru
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Re: Shocks

Post by EVguru »

Fundamentally, the requirements for a motorcycle damper are the same as a car. The damping rates are matched to the spring and the bump:rebound ratio is the same. Why then do motorcycle dampers cost so much?

I suspect the answer is because they can.

Kawasaki went to a single linkage operated coil-over simply because they could then use a Koni F1 unit with all the sophistication that was missing from motorcycle units at the time.

A progressive linkage isn't necessarily what you want. They were often used just for packaging reasons, but became the 'must have' technology.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

OK, job done. The balance of the suspension now feels just right, and the slight increase in rate of the new linear spring over the soft part of the old one is such that I certainly wouldn't want it any harder. The big difference for me today was that I didn't get the 'OMG; what-did-I-just-hit/which-way-is-up?' feeling as I went over road irregularities, so I can now ride the back-roads of East Anglia without cursing continually! The essence of the problem is, of course, the quality of the road surface: if you only ride on smooth high-grade roads, (or you weigh so much that you need the higher rate of the OEM spring), you can probably get by without worrying...

Not much left to do on my Dart, but having a reliable neutral light and a functional fuel light would be helpful!

Nick
morini_tom
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Joined: 05 May 2006 13:47
Location: Northampton

Re: Shocks

Post by morini_tom »

Nick,

I'm glad to hear that the spring has made a good improvement to your dart. Interestingly, Wilbers came to almost the same solution for my spring rate as Daren spec'd for yours- I've got a 115N/mm linear spring. It's reassuring to know that two different methods of spec'ing the spring have come to almost the same answer. Hopefully when I get round to fitting and roadtesting it (after the winter I suspect) I'll be as happy as you.

For anyone else interested, I ended up getting a wilbers 630 (not the 631 I originally wanted because wilbers think the remote compression damping reservoir has a clearance issue in the cagiva freccia- I reckon I could have made it fit but didn't want to take the risk as it would be a very expensive mistake!)

The 630 has 22 click adjustable rebound damping (631 gets high and low speed compression damping too) and weighs 1.8 kilos including spring (dart original shock is 2.8kg) Importantly for me the spring diameter is 4mm less than the OEM spring which will give me some extra clearance on my exhaust. Total cost delivered to the UK was just a shade over £300.

Below is a photo of the dart original and wilbers side by side.

Tom
Image
nickst4
Posts: 185
Joined: 31 Oct 2011 06:55
Location: Diss, Norfolk, UK
Location: Norfolk

Re: Shocks

Post by nickst4 »

Excellent, Tom, and I'm rather relieved on your behalf because I'm convinced that a linear spring is best. From what I read, Ohlins prefer linear springs, and no-one would question their skills in suspension technology. With my shock fitted, I can't now see all of the spring but I do recall noticing 115 written on it somewhere, maybe on an end face, so it would appear to be an identical rate to your Wilbers one! Wilbers are very nice quality shocks: I put one on my Monster 750 and that has just the one adjustment so is probably their 630 too. It'd be nice to be able to play with the rebound damping on my OEM Dart shock, as it seems quite strong in comparison with my other bikes. Then again, softish springs and good damping have worked for a lot of light vehicles in the past, Lotus in particular. At least one doesn't get catapulted into the air as the suspension returns to the normal position.

It looks as though you may need some packing for the eyes of your shock, as they appear narrower than the Marzocchi?

I look forward to hearing your results! Maybe we've cracked one of the few criticisms levelled at Darts by contemporary roadtesters. When I was researching them, I found at least two reviews which said that, essentially, the Dart was a hastily-cobbled-up job that ought not to have worked but in fact did, rather superbly. Add all the technical interest and the (to me) exquisite styling, and you have a very special little bike! :D

Nick
morini_tom
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Location: Northampton

Re: Shocks

Post by morini_tom »

So, the Wilbers is now fitted.

Out with the old. Front paddock stand and a ratchet strap looped round the rear and suspended from a stepladder work well for me:
Image

Not much room for the damper because of my exhaust. The OEM spring runs incredibly close to the pipes, luckily the wilbers is a few mm narrower. Not ideal for keeping the shock cool but no room for pipe lagging. One day I may replace that section of pipe with an oval section for a bit more room but so far I've not noticed any significant change in damping after a long ride:
Image

In with the new:
Image

I'll have to wait until after the winter before I get to road test now, but in the garage at least it feels miles better with supple damping and no soggy initial travel.

Next job, new throttle cables as I never got a decent routing with the Mito top yoke and forks. Then a belt and oil change, general clean up and new tyres, perhaps a bit of fiddling with the front suspension (mito forks on mine which I never really got set up properly on the dart) and then I should be good for 2013...

p.s. Nick- in answer to your previous question, the shock eyes are the same thickness (22mm) I think it's just an optical illusion in the photo. I was very particular in giving Wilbers every possible dimension to be sure of correct fitment, even though in theory they should have had all the info as the Freccia shares the same damper (at least dimensionally if not in damping).
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