Clunky Forks on early Strada

[FatherB]

My 1975 Strada has very clunky forks at low speed. I've checked and rechecked everything and nothing is amiss. I saw Paul Compton's reference to an approved Marzocchi modification but when I stripped mine to carry it out my dampers were very different to the ones Paul referred to. Apparently mine are very early Marzocchi's fitted in '74 and '75. Does anyone have advice about curing low speed clunking in these early Marzocchi's which have a ball valve inside the top end. I've tried different weights of oil( 10w, 15w and 20w) and changed to Hagon progressive springs but the problem persists. Any advice or knowledge would very welcome. Thanks, Brian

[MickeyMoto]

Are you sure the forks are Marzocchi? I thought earlier bikes had Ceriani.

How are your head bearings?

[George 350]

Hi Brian,
You say "clunky at slow speed". What exactly do you mean by this, as speed shouldn't really affect fork behaviour.
Do you notice it most with small bumps or after light braking from example? Putting it on/off the stand?
How much preloaded are on the top nuts? ( ie. How far do you have to push down on the nut to get the thread to engage in the top of the stanchions?
As Mickey says, are your steering head bearings OK?
Are all the mudguard mounts fully tight? (DON'T overtighten them though!) as that can cause an alarming amount of noise.
If everything is seemingly in good order though, try raising the oil level slightly, say 10cc per leg and see if it improves things.
Keep us posted.
Regards,
George

[FatherB]

Thanks for the suggestions so far. The head bearings are correctly adjusted. They're taper rollers with custom made holders. All good there. It did the same with the original cups and cones. I've tried some extra oil, going up to 220cc per leg- no difference. The Hagon springs have significant pre-load, protruding about 25mm above the stanchion before the cap nuts are fitted. The mudguard bolts, torque stays etc are all tight and been rechecked several times. Nothing else is loose around the front end. I've been over everything several times. The brake and speedo cables are secured in their guides with cable ties. The clunking does not happen when pushing the forks up and down at a standstill with or without using the brake. It's only noticeable at low speed going over imperfections or small holes. It's a clunk or 'clashing' as if the spring were not under compression and suddenly being jarred to take up the slack but they are definitely under considerable pre load. It did the same thing with the original springs and spacers. The article Paul Compton referred to posted a modification for the later Marzocchi's but my dampers are different. They're earlier types referred to in the manual but not illustrated. They're definitely Marzocchi's and not Paoli's or Ceriani's or anything else. I've owned the bike since 1985 when I bought it with 8,000 miles on it and lived with this issue since then. I'm looking for advice from someone who's overcome the problem on these early Marzocchi's. Thanks.

[huub]

Sounds like the forks topping out because of too much spring preload ,
For ride height you should have the front end sag about a quarter of the suspension travel with you sitting on the bike.
if the preload is OK, get thinner oil , and add until the front end dive when braking is acceptable.
Personally i dont like aftermarket springs , they are usually too stiff.
keeping the original springs and adding a spacer to tune the ride height usually works for me.

[FatherB]

It's not 'topping out'. It happens on sudden compression at lowish speeds up to about 30mph when encountering road imperfections such as a speed bumps, change in surface level, shallow potholes etc. The Hagon springs now fitted are longer than the originals by about 100mm and protrude about 25-30mm before the top nuts are fitted. This also happened with the original springs and spacers. Sag seems about right with me on the bike at about 20mm. At speeds above 30-35 mph ( going by the Vagliar speedo!!) the forks behave very well. The action, damping and road holding are excellent as we'd expect on a Morini. Trying different weights of fork oil from 10w to 20w has not cured this low speed 'clashing' noise. My own sense is that the dampers are not reacting quickly enough on sudden compression at low speeds. At higher speeds where there is more force on compression this slow reaction is overcome by increased hydraulic pressure and they work fine. The modification shown by Paul Compton and approved by Marzocchi themselves involves filing a chamfer on the topmost hole on the damper rod to cure the problem. However my dampers are an earlier version than the one in Paul's post and don't have a top hole in the same place. They're quite different. There are two top holes but they are partially obscured by a top piece which contains a ball valve. I've tried to upload photos of my dampers here but apparently that file is too big. I'll try and find some way of posting the photos. I'm really looking for someone who has successfully modified these early Marzocchi dampers to overcome this problem.

[George 350]

Hi Brian,
Unfortunately there isn't an 'exploded diagram' of the early Marzocchi forks in the Morini parts list, but the later forks have a small spring between the damper bush and damper piston that allows a softening of the topping out action.
See:

Screenshot_20250317_180456_Drive.jpg (365.23 KiB) Viewed 3521 times

and the spring arrowed. The Paioli forks also have something similar.
Do your forks have this? Does anyone know if there should be something similar on earlier Marzocchis? If it is there, has it been assembled in the correct order?
If there should be a spring and yours were missing or below the bush instead of above, then it might well be the cause of your issue.
Just a thought,
George

[norbert]

It may sound a bit strange, but are you absolutely sure that the noise come from the fork? I´ve had a similar noise for years. In the end it was the tank

[FatherB]

Thanks. I'll recheck the tank mounts but they were all replaced a couple of years ago and are still good. I'm 99% certain the noise is in the forks on compression.

[3potjohn]

Is there any wear in the sliders with the stanchions i.e. with wheel removed and mudguard mounts loose?

[FatherB]

There's no wear. Stanchions were rechromed by Nottingham Hard Chrome Plating and Grinding and are a nice snug fit in the sliders. They move beautifully with no play. I have the forks stripped at the moment and have double checked that. All good there. I really think it's something to do with the dampers as set out above which is why I was asking if anyone had cured this problem in these very early dampers.

[mad muller]

Have you checked the brake caliper the pads can rattle a bit , and disc is not loose I had a snapped bolt in there that did similar noise the disc was moving a bit , and caliper bolts to fork leg were not tight , if you have brake drum set up check all springs are on the shoes and nothing catching the brakeplate worth a look , cheers muller

[FatherB]

It's an early Strada so has the 200mm Grimeca 2LS brake. It's all good. I've been over the torque arm, mudguard bolts etc several times and they're all tight. Shoes have been relined, springs are good and the brake is really good. There are no clearance issues which would show up without fork compression and none under braking at any speed. The clashing noise only happens at low speed under about 30mph when I hit a sudden change on the road surface such as a shallow hole or speed bump and the fork suddenly compresses. At higher speeds the forks are fine.

[FatherB]

Latest update.
Forks stripped and thoroughly cleaned.
Stanchions are an excellent fit in the sliders with no seals fitted and a light smear of oil. They move fully up and down with no sticking or tight spots.
One SKF low friction oil seal fitted in each slider. One of the old seals had its spring removed and trimmed internally of its sealing lip so it now acts simply as a spacer on top of the new seal and under the circlip. Circlip ends reground to sharper profile and debunked to make insertion and future removal easier. Hopefully I won't have to do that again! In the 1970s two seals were used as seals weren't as good then. As Dave Richardson points out in his tome 'Guzziology' nowadays one is sufficient as quality is much better. Less friction on the oil seals means improved fork action and less stichion. The SKF seals were recommended as the best for low friction in an article recently by a suspension rebuild expert in one of the classic bike mags. I got mine from Simply Bearings.
I tidied up the two oil ports at the top of the damper rod and put a 6mm chamfer on their lower edge similar to the one recommended by Paul Compton a while back for the later dampers.
Forks were now spotless internally so were rebuilt very carefully with careful light oiling of the seals and stanchions.
Bottom allen bolts fitted with new, anneal copper washers and tightened. I always anneal even new copper washers as the manufacturing process can harden them. Some people like Paul prefer 'Dowty' rubber bonded washers. Both work well.
Next stage will be to fit the springs. As they're Hagon progressive springs and slightly larger in diameter the standard top sleeves don't fit. A local suspension expert here in Northern Ireland who rebuilds competition Forks for a living, Mark Arnott, agrees with me that the probable cause of the clashing noise I was hearing was the springs rattling against the inside of the stanchions. I asked him if fitting a piece of bicycle tube over spring might stop this. He said it had been done on some bikes he'd come across and seemed to cure the problem. He recommended a length from the top of the spring about 2/3rds of the way down the spring as most of the noise comes from the middle section. He suggested holding it in place by feeding the top end through the centre of a large washer and folding it out so it sits under the top nut and is held there by spring pressure. I might also glue it with impact adhesive. The lower end is secured by a 2" piece of shrink wrap. I'm off to the bicycle shop tomorrow to get some inner tube of the correct size, an easy pull fit over the spring but not too loose. Butyl rubber used in bicycle tubes should unaffected by fork oil. I'll put it all together then and report back. It sounds a bit 'Heath Robinson'. It may work but it may also go Pete Tong ! I'll let you know in due course.

[FatherB]

'deburred' not debunked !