Do some clutches have non-adjustable thrust pins? I am having trouble with what looks like a home-made pressure plate. Without any way of adjusting the pins I have to get the total thickness of clutch plates exactly right or the clutch will either not lift or not bite. It is driving me potty, can anyone help? Do I need a new pressure plate with adjusting pins in it? Advice please!
Someone will know the historical sequence of the plates with adjustable and those with non adjustable lift pins, but my own experience is that the non adjustable pressure plates are perfectly good and I changed to use one from an adjustable one. The reason for the change was that my dad offered one of the stiffer pressure plates he made and they are not adjustable. Since setting it up i have only had to adjust the lift once and now it’s a very good clutch. If you are trying to use the build up thickness of your clutch plates to give you the correct adjustment then you are going to be very lucky to achieve success unless you are simply rebuilding a previously functioning setup. Otherwise you should build the clutch up exactly how you want it and then either modify the pins you have or make some new ones out of 3/8″ silversteel bar. I got a short length off eBay for a few pounds and made them up using a hacksaw,file and emery cloth. I make the ends convex, but they didn’t take long to make and there wasn’t more than a couple of thou between them. I didn’t give enough end float initially … around 0.010″ was soon worn when plates bedded in. I’m pretty sure I gave it another 0.015″ clearance and it has been perfect since.
Thanks Richard, very helpful.
Alan Noakes can provide adjustable clutch plates. His contact details are on the back page of Yowl.
I don`t know when the adjustable pins were introduced but 27/28 Flyer clutches certainly had non adjustable pins, the problems start when the plates wear and the clearance dissappears at this point owners would grind down the pins without being very accurate about keeping to the same length and at a later date when plates get renewed owners find they cannot get full lift to free the clutch. While adjustable pins can answer most of the problems sometimes previous owners have shortened the pins on a badly worn clutch, and also standard pins seem too short for a present day refurbished clutch, I always advise owners to sand new fibre plates by .020″ if they are fitting one of my alloy pressure plates. I have been asked about supplying new adjustable pins recently, if no one else has these available I will consider making some please let me know if there is any interest. Alan Noakes. email@example.com
It all gets more complicated than it seems at first glance because the earlier clutches also came in a ‘slim’ version, with one less friction plate and one less plain plate. These need different springs and different adjustable thrust pins. A while back I sent samples of both to Graham Moag. The factory used to supply sets of three of the solid type non-adjustable pins in various different lengths and from memory these went from about 3/4″ up to 1-1/4″, in increments of 1/16″. However they are easy to make out of 3/8″ diameter silver steel bar, as Richard Moss has described, even if you haven’t got a lathe, and the length and end profile can easily be adjusted just by holding them in the chuck of an electric drill, against an abrasive surface. I personally don’t make them concave on the ends, but do put a small radius on them to stop them from ‘digging in’. I also heat-treat them after making them, by heating them to Cherry Red and dropping them into a small tin of old sump oil. (Do that outside !!)
Lots of food for thought here and thanks again to everyone for the advice. The nice new bonded plates I bought are too thick so I have gone back to old cork plates with only a little binding and no slipping (so far). One stupid question: do the adjustable plates have pins which bear on the original thrust pins? If so I would need pins, Alan. I have yet to enjoy stripping a clutch completely so I am ignorant of that area. The quick thread does seem in good shape though, plenty of lift.
Cork clutches are very sweet, and will tolerate a lot of oil without slipping, but will not tolerate any abuse, ie. excessive slipping of the clutch, and once the surface of the cork gets burnt/charred they are useless. The Ferodo type circular inserts contain copper wire inclusions which reinforce them and conduct away heat. They will tolerate a lot of abuse and will not burn. They just quietly wear away ! If the Saftek friction plates are too thick you can still use them…
Just omit one friction plate and one plain plate, and then try assembling it. Typically when a clutch is assembled the outer raised lip of the pressure plate should be somewhere close to being level with the outer edge of the clutch housing/basket.
I have earlier called the Scott clutch “The Achilles heel” of the Scott. I still think that this is an appropriate description. On two of my Scotts – 1936 and 1938, I have bonded friction plates and new plain plates. Gearboxes have been overhauled with new main-shafts and oil seals. I use Castrol R40 oil. In spite of oil seal, oil is leaking into the clutch, especially if the bike is leaning on its side stand on the clutch side. The oil acts as a glue between the clutch plates, and when you use the clutch, it will often lift the whole clutch basket instead of separating the plates properly – especially when starting. A wobbly clutch basket means a very difficult start. It now takes me ca. 1 1/2 hours to take the clutch to pieces, wash plates and basket with brake degreaser, and reassemble.
I have found no other solution. Maybe I should use ordinary mineral oil instead of R40, or maybe I should do something with the oil seals. Maybe also retrofit old fashioned friction plates with Ferodo buttons which probably will not cling to oily plain plates in the same manner as the bonded plates. I need to have a strong clutch, since both engines are very powerful, having been gas-flowed and equipped with Roger Moss Hi-compression heads.
Just to confirm, a later pressure plate with adjustable pins can be retro fitted to an earlier clutch with loose pins, having free play in the cable does not mean that you have clearance on the pins. Oil on the plates is a problem, on new type fibre plates I make radial grooves in line with the tangs on both sides hopefully these grooves collect oil and centrifuge it out through the slots, I find using Castrol D140 oil reduces oil loss from the gearbox while Castrol R is an excellent oil it does absorb water over time, I am of the opinion that any oil leaking from the mainshaft/ clutch nut seal does not get into the clutch, the problem is that the splines on the sleeve gear get filled with oil and leak through the joints either side of the clutch backplate and using a sealant here on assembly will save a lot of problems. Alan Noakes. firstname.lastname@example.org
I use a thixotropic oil/grease in my gearbox. It’s got the standard felt seal, a rather rusty shaft and I’ve never had contaminated clutch plates or slipping clutch. The bike gets left, sometimes for weeks, on the side stand. I’ve got Pierce clutch plates but still ferodo inserts in the basket. The springs are Fanny Barnet 250 as the club ones were too heavy with the thicker, modern plates. I must just be lucky 8)
As Alan says, the oil is stopped from passing through the middle of the high gear bush by the felt (or rubber) seal in the clutch centre nut. There is no seal however behind the nut, and oil will pass back through the splines. I use sealant here with good effect.
On the occasion that we have had sticking plates due to Castrol R, we just stick a tray under the gearbox and one of us pours petrol over the clutch whilst the other holds in the clutch and spins the back wheel (in gear!). I wouldn’t do it on ones new handmade herringbone brick driveway, but it always works.
Having realised that the thrust pins are a simple push fit (thanks Alan) I shall order some silver steel bar as advised by Richard Moss and see if I can sort it out; if not then it will be a new adjustable pressure plate so light at the end of the tunnel.
Re sticky oily clutches I have a petrol resistant spray bottle which I use the same way as Richard, seems to work well and nice and quick and easy.
I have some 00 semi-fluid grease, does anyone else use it for their gearbox? At present I am using SAE 50, not overfilling and it seems ok.
It should be noted that there different SAE grades for engine oils and gearbox oils. An SAE 40 grade engine oil suits a Pilgrim Pump or drippers nicely. For the Scott three-speed gearbox a 140 grade gear oil is about right.
For many years people have tried Shell Tivela compound A, a thixotropic grease/oil and while it works well initially in reducing leaks, it tends to emulsify with traces of moisture and cause corrosion, which is NOT a good thing…. The Scott gearbox has no drain plug, so it is quite a job to clean it out !
The late Roger Lane gave me a 25 litre drum of 140 grade gear oil, which I have been using and giving away at Scott Rallies for a few years, but it is now all given away or otherwise used. I’ve just had a quick look on t’Internet and there are several listings for 140 grade gear oil, so it is readily available even if your local garage or motor factors doesn’t have it in stock. On eBay Castrol Classic D140 can be had for less than £11-00 per litre including postage, and a litre should last you for years !
In my Scott TT Rep which now is ready for the road after a total overhaul of engine and gearbox, I have chosen to use Shell Dentax 140 to lubricate the gearbox, to see if it will behave differently from Castrol R40. I used this oil successfully in gearbox and differential in a Bugatti Type 30 for years, and still had some 10 litres left in a 25-litre drum bought 30 years ago. It will be interesting to see how it behaves.