Additional Clutch plate?

This topic has been raised before, but I would be grateful for help on two points.
The Atlantic Green website (thanks for the reference which I picked up from a previous thread) has the following paragraph:

"

Clutch Stack Height


Since the easiest clutch is when the clutch diaphragm spring is about .68” of deflection (175 lbs) and clutch pull is about .1”, the engaged position should be around .58” of diaphragm deflection to get the sweet spot. Therefore, the diaphragm appears to be about .03” inverted beyond flat (.55”) when engaged. The problem is how do you get the diaphragm to be at a certain position when assembled? You adjust the internal clutch stack height, the diaphragm is usually extended a bit to much. Therefore, you add thickness to a component in the clutch stack height. You could have a custom (thicker) backing plate made to be placed in the rear of the clutch basket, or you can add a clutch steel plate .080” thick. You can see using a straight edge on the diaphragm, if it is flat, extended or inverted. It is interesting to note that as the clutch wears, it always gets harder to pull until it finally gets to .40”extended. Then its up to 325lbs of pressure! I don't necessarily endorse this as a must do modification. But you should understand what is happening if you decide to go through with it. The lowered clamping pressure may cause slipping. "

Click to expand...

I have to change my clutch plates, and have bought a set of Barnett plates (including the steel plates). So I will have my old thin steel plates left over when I install the new ones, and could insert an extra plate, as is suggested as a possibility by Atlantic Green. I contemplated purchasing a thicker back plate from CNW or RGM, but rejected that on the basis of cost for the moment.

Has anyone installed an additional plate, and if so is the issue of clutch slippage significant? I don’t really find the current clutch pull difficult, and so don’t want to do something that is a real pain for not too much benefit.

Where would you put the additional plate? I am guessing that it would go right before the diaphragm spring, so that you would have two steel plates against each other; but you could put the additional steel plate against the backing plate, so that you have backing plate, steel plate, friction plate etc or would it be possible to put the additional plate behind the backing plate? I would guess that would be a bid idea, but will ask anyway. Thanks.

But, have you measured the stack height of the new plate assembly?

L.A.B. - as usual asking common sense questions.

No - at this stage I have not measured the new clutch stack; I thought I would delay all the measuring until I have the clutch apart and am in a position to put the new plates in, so that I can test them in situ; it may be that there is just no room for an additional plate - in which case the issue is moot.

I am pretty much relying upon the information on the CNW website; and the Atlantic Green website that suggests that the stack can be made thicker by either an additional plate or different (thicker) backing plate (and I am therefore assuming that the new clutch stack will allow some room to do this); but am hoping to gain enough knowledge that I can make some informed decisions at that time, rather than disassemble; then gain information and reassemble some time later.

I've mix and matched types of plates plus an extra steel plate doubled up against back of basket and they all felt the same perfect light function as long as I got the stack height so the spring just slips in its groove w/o any effort but nil slack to go in more than that. I never bothered to measure knowing it'd confuse me no end till DynoDave specs came online to see down/dirty lands in propper measure.

Also various pressure plate thickness and materials are available and even a novice like me has 3 of to mix and match for sweet shade tree clutch I basically forget about for a few years at a time now. ATF in primary not a bad id either. Call Barnett to check that they told me to wet new or resurfaced plates with ATF then wipe off excess to prevent chattering on inital bedding in.

If ya abuse yours like I did Peel you will see slippage wear at back of alloy belt baskets where its metal on metal in one of my stack ups. Note which way the plates edges stamped out with blunt sides inward.

I tried an extra barnett steel plate in my clutch which measured to normal stack height, and it slipped so much I could not even tighten the center nut. It sure pulled easy though.

Dave
69S

This is one of Fred's great articles. Add one of Dyno Dave's seals and a teflon lined cable from Venhill and your clutch is totally pimped. I mean farkled.

http://www.oldbritts.com/ob_clutch_info.html

http://www.venhillusa.com/

Chris
Hi,greetings from Sydney.
I have just done all this.I installed a set of Barnett plates into my 850 with an extra steel plate plate right at the back.
As per the Old Britts article I used 65 thou extra plate ,when all this was assembled the height of the clutch plates stack came up to the bottom of the circlip groove,so it was perfect.
You might need a different thickness of extra steel plate as every bike is different.If you need a special thickness of plate,try someone local with a surface grinder and magnetic table to grind it down for you.

The difference is amazing,the clutch pull is so light now and no it is does not slip.
I also have the clutch nut with the sealing o ring and a teflon lined cable.
Brett

I've made that mod also, and found that .005" makes a difference. Too much makes the clutch slip under load. .065" worked on my 850 with original bronze plates. Old Britts I think will sell you a set in .005 increments and buy back the ones you don't use.

drc

This dimension is the one to adjust. From the top of the diaphragm spring to the bottom of the spring clip groove should be .030" to .050". Anything over .065" (although somewhat acceptable) will start getting heavy in the lever.
Courtesy of Old Britts,


The other issue is the aspect of the diaphragm at rest. There are curves and calculations the show the best of both world, effectiveness of the clutch vs ease of operation. I found that the position of slightly concave, ever so slight less than flat, offered me a 2 finger clutch that will not slip under full load in any gear.

What we're trying to do here is to achieve the right amount of leverage against the raised area of the pressure plate and ideal amount of resistance from the diaphragm. This relationship is the true lever of the clutch which is transmitted to the handlebar lever. This dynamic relationship is neither Zen nor a dark art and once visualized is not that hard to understand or to achieve.

I also purchased a thick alloy anodize pressure plate from RGM. I adjusted this by machining the outboard side to preserve the anodized surface against the clutch reshaping the raised area slightly. This was a little trail and error not wanting to take off too much at first. As my fiber friction plates wear, my clutch will increase in resistance and I will replace these 5 fiber plate when needed. They still look good and the function has not diminished after 3 full seasons .

Frankly I couldn't make any sense of the Old Britts description when I measured my stack height. There is essentially a shelf running around the inside of the clutch housing that the diaphragm sits on. It looks to me like the photo is showing the measurement from that shelf to the slot! It is assuming that the diaphragm is completely flat and in contact with the plates, therefore it has no bearing on the height of the stack, which isn't that hard to calculate by adding together the individual widths or just measuring the complete stack.

It's just me but if I were going to add an extra plate to add height to the stack, I would put it as close to the bearing as possible, and I would remove as much material as possible by enlarging the center hole, drilling holes or both to keep the extra weight down. Essentially it is just a shim.

Russ

rvich said:

Frankly I couldn't make any sense of the Old Britts description when I measured my stack height. There is essentially a shelf running around the inside of the clutch housing that the diaphragm sits on. It looks to me like the photo is showing the measurement from that shelf to the slot! It is assuming that the diaphragm is completely flat and in contact with the plates, therefore it has no bearing on the height of the stack, which isn't that hard to calculate by adding together the individual widths or just measuring the complete stack.

Click to expand...

Unless the stack height is low, the diaphragm spring should actually rest on the raised ring of the pressure plate (you can see it in the Old Britts photo where the circular cut-outs are). With the diaphragm held flat (by the release tool) you will be measuring the distance between the top of the stack height (+ spring) and the slot.

LAB, I agree with what you are saying above. But just turn the clutch tool a turn and measure it again. Somebody commented that .005 inch makes a difference. It is nearly impossible to tell your diaphragm is that flat.

I had much better luck measuring the height of the stack. I then put the retainer into its slot while the basket was empty and measured its height from the bottom of the stack. Comparing the two gave me the measurment I needed. I just think the other method is prone to mistakes in measuring. If you need .065 added to your basket, chances are the diaphram will not be laying on the pressure plate.

Russ

OR could just put in the stack ya got on hand and see if prevents spring to seat in slot or leaves too much slack beyond slot then mix/match/sand down items so spring just slips in nicely then p\ull the stack out and measure it. Similar to best ignition timing go by feel and response then put numbers on it how ever ya like. Following this subject for over a decade now by seasoned Nortoneers, most refer & prefer to vary the pressure plate thickness. I'm going to try to thin stack plate and pressure plate to fit 7 elements in if I can.

In the end this is a real man's motorcycle hobby, both by the physical powers involved and the mental and financial and time needed to get a fully fettered Cdo.

I just put bath scale on Trixie's clutch lever to depress fully to see between 25-30 lb needed with a few lb let off after spring break over plates freed. Scale reads a bit off depending on how un-skewed I can aim scalle. Trixie's holely front brake starts to test tire grip about 35 lb lever pull. I grip test folks for neuro injury court cases to find women average around 40-50 lb and men 80's to 120's #. Highest I've seen was a few lb over 150 and my best was just above 140. There is some sliding scale on actual grip test d/t the size of the gripper set vs hand size plus will power of the gripper. I also test a series of grip as the first 2-3 may be ok then drops off dramatically as injured nerves and muscle chemistry fatques out abnormally but missed if not looking a bit deeper.

rvich said:

LAB, I agree with what you are saying above. But just turn the clutch tool a turn and measure it again. Somebody commented that .005 inch makes a difference. It is nearly impossible to tell your diaphragm is that flat.

Click to expand...

I've had some fairly consistent results doing it that way as long as a reasonable amount of care was taken to set the diaphragm flat.

L.A.B. said:

rvich said:

LAB, I agree with what you are saying above. But just turn the clutch tool a turn and measure it again. Somebody commented that .005 inch makes a difference. It is nearly impossible to tell your diaphragm is that flat.

Click to expand...

I've had some fairly consistent results doing it that way as long as a reasonable amount of care was taken to set the diaphragm flat.

Click to expand...

Good to know. I was probably being overly careful. Carry on!

i'm a HUGE advocate of the old britts kit they sell. It's a fantastic service (you pay $135 and they send you all the plates, find what works, mail the rest back for a refund, minus the plate you used) i kinda ignored the measurements a bit and went with feel by trying to get the splines on the pressure plate to sit as flush as possible to the splines of the clutch drum. when i started working on the bike i thought "this clutch must be wrong, i'm going to break my hand!" between the extra plate from old britts and a venhill featherlight cable i don't even think about the clutch. I usually leave the bike in first gear with the clutch held in at red lights so i can take off if anyone decides they want to try and run me over, and it doesn't bother my little lady fingers at all

oh another thing i found helpful when dealing with this (which might help you if you don't want to bother paying shipping back to the US for the old britts machined plates) i used a caliper that has the little end that pokes out when you open it (see photo...) i would assemble the friction and pressure plates in the hub, then put that little end against the friction plate and close the caliper till the end of it hit the splines of the drum. that measurement on the caliper turned out to be dead on to the thickness of the plate i need from old britts to make things sit just flush

thanks for all the input; some really useful stuff. There is obviously a chance that when I get the clutch apart I find that the additional plate that I have is too thick; it will be interesting to see. Hopefully I will get to it this weekend; family obligations permitting...

A couple of other points of interest. Based on previous threads I would probably have soaked the friction plates in engine oil, or automatic transmission fluid. The Barnett website says to soak them for installation in a wet clutch and leave them dry for installation in a dry clutch. I asked Matt from CNW what he does; and I hope that he is not offended if I paste his response here:

I would recommend to install the clutch plates dry into the basket.

Even though the Norton primary is somewhat wet since the chain is lubricated, the clutch itself is actually not since it isn't soaked in oil

I use engine oil, 20-50 in my chain primaries. I have heard of many using Transmission fluid but engine oil is a better lubricator in my opinion

Click to expand...

.

And in response to those who have suggested that I instal a Dyno Dave type seal; I have got the RGM version of that ready to go in.

CNW:
I use engine oil, 20-50 in my chain primaries. I have heard of many using Transmission fluid but engine oil is a better lubricator in my opinion

Click to expand...

Interesting.

Chris T said:

And in response to those who have suggested that I instal a Dyno Dave type seal; I have got the RGM version of that ready to go in.

Click to expand...

You may find the RGM seal is no good-unless they have changed the design-which I doubt somehow, as they don't appear to think there's a problem. If it doesn't fit, please be sure to tell them.

850-clutch-t5995-15.html#p59449
clutch-nut-with-oil-seal-t14843.html

In the case of chain ATF works better and racers runing above 20 wt in primary had chain failures - as reported years ago on Brit Iron list while bantering on this subject. Do online searches on chain efficiency and get back to us on it please.

No clutch even those designed for oil do better dry and engine oil is one the worst to put on plates as filled the pores and cooks in to either slip when hot of bind/stick when cold. Call Barnnets on this - they say use ATF on even dry clutches
and just wipe off the wet excess.

Thank goodness I've never had to measure anything but sense fit of the spring as there's always been enough adjustment fudge its a non issue to me. Getting a bit quilty this year as only had to adjust drive chain while clutch remains thoughtless.
AFT leaved less mess too.