Clutch spring plate: what is the function

[PanPal]

When I put my 59 back together, I ordered glued clutch plates to replace the original riveted plates. The new set did not have a disc with a pad on one side and a spring plate on the other side. Last night when I reassembled the clutch, I took out one clutch plate and installed the spring plate with the others. What is the function of this spring plate? Should I take it back out and put the disc that came with the set back in ???

[DanM]

I think the purpose of the spring plate is to smooth out the engagement and eliminate chatter. In a car clutch you will see springs the size of valve springs placed around the center- they do the same thing.

Dan

[Plain]

PanPal:

Very interesting question. I have no hard answer on this, but will throw out my opinion and the logic that led me there for inspection and correction by others. The clutch morphed a number of times in the '36 - '40 period. A big problem during this time was clutch failure due to clutch spring failure due to heat. Problem was the most severe in police traffic and commercial machines which saw a lot of hard clutch action.
The '36 clutch system contained fiber disks, steel disks and a "humped" disk. Around '37 or '38 the humped disk was replaced with a flat steel disk and the first use of a "sprung" disk, The sprung disk was a half steel, half fiber and placed in the position against the pressure plate. It was originally notched so that it did not turn, or could not turn, against the drive disk. It is my opinion that the sprung disk was an attempt to provide cooling, or reduce heat transfered to the pressure plate, and the clutch spring heat failure problem. Around '40 the clutch was redesigned again and the notches on the inside of the sprung disk disappeared. Sprung disk became known as the "Spring" disk. '41 the design changed again to what was used with minor changes until around '64 or whatever year it was that major redesign occurred.
If you study an OEM spring disk, and look at the grooving, it would appear that the function was intended more for cooling than for friction or clutch engagement considerations. How important the spring disk was for cooling is a good question since when the major redesign occurred it was replaced with a double sided friction disk.
I have used both types over the years, and cannot tell that there is any better or worse clutch spring life between the 3-1/2 plate setup (3 friction disks and the spring plate) and the late design. Back in the day, the word was - do not mix. That is, either use the 3-1/2 plate setup, or the late setup, but don't mix the disks. Never had it explained to me as to why, just did it. I find five Alto red bonded fiber disks and four steel plates create a clutch pack heigth that is correct and I prefer it to the old 3-1/2 plate setup.
There is a LOT of variation in thickness in the various bonded fiber plates. There are a LOT of sorry excuses for new steel plates. Check some and you will see a lot of variation in the thickness of the plate. Use good steel plates and check your total clutch pack height when using the late setup.

So, I say that the spring disk was for cooling of the pressure plate/clutch springs. Hopefully, sharper minds will agree, or set me straight and keep me from wallowing in ignorance

[VintageTwin]

The plate you are referring to is the outer most plate and called a half-plate (37950-41), because there is fiber on the inboard side and plain steel on the outside. You can still get a half plate with some clutch replacement drive (steel) discs and friction discs. There are three fiber discs and three steel drive discs and one half-plate. I prefer the "Police Service" bonded fiber discs from V-Twin. You can't kill them if you keep oil away from them. I also prefer the non rattle-ball or Barnett smooth steel drive discs. The measurement between the flat outside surface of the outer disc and inside edge of the pressure plate is still 31/32. A guide to clutch replacement and hub liner tools and riveting is outlined in our book. The rivet tool isn't cheap, but boy howdy...it works. It will fasten a hub liner better than a shop will attach it without this aircraft tool.

[King]

Over the years a lot of strange stuff has ended up in my clutch basket. The mix/match seems to work well but I'm curious, what is the proper clutch pack height when using a stock preasure plate???

Thanks,

King

[VintageTwin]

The only measurement I've found called out in the shop manuals is 31/32".

[Cotten]

I think the 31/32" measurement was drempt up by some engineer to keep technicians angry.
It is far more important that the plate travel in and out squarely. If it don't,...then tighten and loosen the adjustor nuts until it does.
(Five-stud hubs make this a bit more difficult, with no other benefit.)

And if your hotdog motor can spin the plates on accelleration, just tighten the nuts some more.
The design and assembly ain't rocket science! It's downright dinosaur, and very sturdy. Even the 5 plate design was a step backward.

RE: springs fatigueing
They last forever if you loosen up the footclutch dampener!
(Leaving the pedal up like a sissy fatigues them fast by keeping them under compression, And the lack of feel makes you slip and burn instead of engaging smoothly.)
The outer spring plate is VERY important for smooth operation.

[VintageTwin]

In practice though, the 31/32 measurement is amazingly consistent when measured at three points (the three stud areas). Within 1/64" run-out with the old OE/re-pop junk I ran in mine. Pix show it in our book. All you need is a pocket slide rule. 5-plate I don't know about. I love rebuildable stuff though.

[Plain]

Cotten:

I am replacing the three post clutch hub in my '59 pan with a five post. Logic told me that this was an improvement and would adjust more accurately than a three post. Logic has failed me in the past, and part of this may have to do with just wanting to try something that I have never had before. Therefore I am interested in your comment concerning the five stud hub. Am I taking a giant step backwards?

BUT, you got me with the statement "The outer spring plate is VERY important for smooth operation." Then left me hanging. I am wallowing in ignorance here. Expand. Details! What is it, how is it, that the spring plate effects operation.

Thanks-----Plain

While we are at it, back up to King's post on clutch pack height. I'll take a swing and the rest of you help me out of the wallow. Where clutch pack height is concerned, whether using a five plate (late) or 3-1/2 plate (early) it seems to me that the clutch pack height is a function, or should be a function of the height of the drive lugs on the side of the clutch basket. I like to see the top of the last steel drive plate approximately 1/8" below the top of the drive lug. In most clutch packs, 5 or 3-1/2" that equates to a clutch pack height measured from the bottom of the first fiber disk to the top of the last steel drive plate of 1-1/2". This does not consider the last fiber plate in a five plate setup, or the spring plate in a 3-1/2 plate setup. My logic (maybe failing me again) is that there needs to be a small safety factor in the ability of the last steel drive plate to move towards the top of the drive lug when the clutch is fully released - hence the 1/8". If the last steel plate is placed too close to the top of the drive lug, there is the possibiity of binding on the top part of the drive lug when fully released (more so with plates with antirattlers than without). Most clutch baskets will measure approximately 1-3/4" from inside bottom surface of clutch basket (where the first fiber plate rests) to the top edge of the clutch basket. Most drive lugs will measure 1-5/8" from the bottom of the surface to the top of the lug.

[King]

Cotton

Like Plain I could benefit from some clutch adjustment advice. I’ve pretty much ignored the old dinosaur as long as I can get a good starting kick and it pulls me up the mountain, but more smooth in the shift would be appreciated.
I certainly agree that toe-down is the way to spring longevity even when setting at a red light I slide her into neutral, but I have to keep my rocker relatively tight to keep it toe-down or it will vibrate up and start to disengage the clutch.

Plain

Thanks. Your logic sounds good to me. Next time I pull it down for a de-glaze I’ll check out the relationship of my plates to the lugs.

King

[Plain]

And I could use some additional advice. As I am assembling my new clutch from scratch I have chosen to use the long "cram in" clutch hub bearings pioneered by the belt boys. Also intend to use the Nylatron clutch hub friction disk. Got a friend that swears by both of them. Any opinions?

Thanks-----Plain

[Cotten]

The only real disadvantage of a five-adjuster hub is that you need a five-hole puller to remove it.
A three-adjuster is easier to square up the plate action for the same reason it is easier to level a three-legged chair than a four legged one. Five makes it a little tedious.
Hair-splitting on the distance from plate to spring retainer is just that. Worn discs can easily stack up to 1/32" less than fresh,... weakening the tension... but still have many seasons left in them.
The idea is to get sufficient pressure on the plates to stay hooked up, yet not so much that a hand clutch can't work it comfortably. (A footclutch can handle even super-heavy die springs!)
And of course, the springs should not coilbind when the clutch is fully disengaged.
Anywhere in between is fine!
The springplate encourages the plates to disengage. It smooths out the action dramatically by giving a progressive tension to the springpack. Thus chatter and noise is reduced incredibly. (When aluminum housings came along, the Factory apparently felt they cut cut costs by eliminating it, since it is hard to hear what's going on in there.)
ALL clutches should pull themselves into engagement, and stay there. If vibration disengages it, there is either not enough tension in the springpack, or the linkage is not allowing the pedal/mousetrap to go over-center of its bellcrank pivot.
If your springpack is wimpy, you lose "feel", particularly with a pedal. It should be like working a clutch on a car.
This will make carrying a passenger on a buddyseat easier as well, as you will merely have to press upon the heelpad with your toe, and not depend upon your ankle to move in an arc it was not designed to,...when you are sitting far forward to accommodate a healthy payload.
There are far more serious concerns that spring tension.
The travel of the pushrod/pressureplate should be minimized, as the entire clutch drum (or 'basket') can walk in and out accordingly, wearing out the primary chain sideways. This is of a particular concern for footclutches, as there is rarely a built -in stop for the pedal, other than the footboard.
The nylon roller retainers work well!
My first '65 came with a pin installed in the extra hole of the pedal, acting as a detent between the rolled edges of the bracket support. I believe it was Factory, and it makes adjustments much more accurate, because the pedal is! If no footboard is used, it is critical, as it will prevent the pedal from completely flipping.

[VintageTwin]

Go nylatron 0n the hub liner. You got a rivet squeezer? You'll need one. The rivet head goes in back. the peen on the liner side. If you're going to rivet it on with a hand peener, expect to have the liner somewhat loose when you finish. It will still work, but persnickety people won't like the results of hand peening. Too bad the club can't have a tool room with loaner tools like the USATCO peener. You'd put up a deposit and use the tool then send it back. If you damaged the tool, your 3 times the original cost deposit would be forfieted. some kind of neat penalty like that, where it hit you in the pocketbook for being careless.

[Plain]

Cotten:

I feel better about my spiffy new five post hub. If the worst objection that I am facing is a five hole puller and tedious I can handle that. I am a pretty tedious old fart myself. One of the reasons that I opted for a five post over a three post is that I have never liked the spring layout on a three post. Three springs between two posts, two springs between two posts, two springs between two posts. It seemed that the post - spring spacing on a five post was more logical and would be more accurately adjusted. We shall see.

I agree on the 31/32". I start there and adjust down accordingly for bite, bearing coil bind in mind. For me, 31/32" has always been a starting point. I should add that whether using the five plate setup or the 3-1/2 plate setup, I stay with the short fat springs. Never cared for the ling skinny late springs. Stock motor to mild stroker I stay with regular springs and avoid the heavy duty springs. Heavy duty just increases the pull on a hand clutch and I don't think they are needed until the motor starts getting really strong or your riding style is smoking it out of the hole, in which case you will need more than just heavy duty springs.

Minimum travel of the pushrod/pressure plate. I agree completely.

"The springplate encourages the plates to disengage. It smooths out the action dramatically by giving a progressive action to the springpack." Hummmmmmmm. I am sitting here looking at a spring plate, oem, well worn, trying to get my head wrapped around this. I cannot visualize it or understand it yet. This is going to be a real butt scratcher. Tell me, are the grooves in the steel side of the spring plate that extend out to the edge for cooling, or does this contribute to the progressive action, and if so, how? Thanks.

Plumber:

Thanks for the vote on the nylatron. I have an old stand riveter that must date back to the civil war. It is a huge beast. I think that you could rivet the wheels onto a railroad car with it. It will put all the squeeze required on a hub liner rivet and then some. I'd be glad to rent it out but we would probably have to have a crane to load the old behemoth.

Adios----Plain

[Plain]

I say Cotten. See post above. You are leaving me twisting in the wind here. Details please.

Adios-----Plain