Stack Height

Hey,
I'm a little dense, ok a lot dense when it comes to determining stack height.
I've watched some videos on the subject but I just can't seem to comprehend how to go about it. Help?

Mix and match clutch plates to obtain the correct distance below the circlip grove.. ?

john robert bould said:

Mix and match clutch plates to obtain the correct distance below the circlip grove.. ?

Click to expand...

Yep, I got that part. So I can use my mike to measure it? You Know what it's supposed to be off hand? If not I can always look it up.

lwmcd1 said:

john robert bould said:

Mix and match clutch plates to obtain the correct distance below the circlip grove.. ?

Click to expand...

Yep, I got that part. So I can use my mike to measure it? You Know what it's supposed to be off hand? If not I can always look it up.

Click to expand...

Setting the stack height can depend on the depth of the clutch housing concerned, so it isn't always a matter of arriving at a particular stack height dimension.

http://atlanticgreen.com/ndnsclutch.htm
http://atlanticgreen.com/clutchpak.htm

lwmcd1 said:

john robert bould said:

Mix and match clutch plates to obtain the correct distance below the circlip grove.. ?

Click to expand...

Yep, I got that part. So I can use my mike to measure it? You Know what it's supposed to be off hand? If not I can always look it up.

Click to expand...

'Just went through this myself. Using a straight edge across the face of the drum , measure the depth to the spring next to the outer circlip. That's your "zero". From the same straight edge, measure the depth next to the center hub. Seeing that every other finger is staggered, I averaged the two. What you're looking for (in theory) is to have the spring close to flat across the face in the fully engaged position. Looking at http://atlanticgreen.com/ndnsclutch.htm, notice where the transition point is indicated to the left of the "Flat Diaphragm" point. By their numbers on the cool spring rate chart, I'm running just below flat, which should put the spring pressure in the neighborhood of 250/275 pounds. As noted in note #3, "Flat Zone .45” to .55” of Deflection—The Flat Zone is when the diaphragm is approaching flat. This occurs when the two tiers of the clutch fingers are half (9 fingers) inverted and half (9 fingers) extended." That made a world of difference in the clutch pull, and stopped the slipping.

Nathan

Ken Canaga recently mentioned that he found one of his clutch baskets depth didn't match DynoDave references for good stack height - so did like hobot - [on his own] - mixed matched various things till clutch had nice action - then measured for fun to report - as no set height that works best for all cases. Same thing for ignition timing, get right first by actually run testing then measure for good public reputation instead of by gosh and by golly shade tree.

Nater_Potater said:

'Just went through this myself. Using a straight edge across the face of the drum , measure the depth to the spring next to the outer circlip. That's your "zero". From the same straight edge, measure the depth next to the center hub. Seeing that every other finger is staggered, I averaged the two. What you're looking for (in theory) is to have the spring close to flat across the face in the fully engaged position.

Click to expand...

I use a slightly different method.
With all the clutch plates in position including the pressure plate, the diaphragm spring is set to flat using the standard clutch spring compressor, then installed and the circlip fitted (but without releasing the compressor, after) and the distance between the spring and the underside of the circlip is measured.
The dimension between the flattened spring and the circlip will be the amount by which the stack height needs to be increased for the spring to be flat at the fully engaged position.

Old Britts shows something similar:
https://www.oldbritts.com/ob_clutch_info.html

Can you tell us why you are asking about stack height?
If clutch pull is pretty easy and you have no clutch slipping then you should be good to go.
However if clutch is a hard pull it can indicate the wear of the fiber clutch plates has allowed the clutch pack height to sink low enough that the hard pull is needed because the spring has over released.
If so you can get a selection of different thicknesses of clutch pack spacer plates from OldBritts and modify the stack height so you get a reasonable clutch pull. Two finger pull worked for me. If one finger pull I suspect you will get clutch slippage.
The un used plates can be returned to OB.

rx7171 said:

Can you tell us why you are asking about stack height?
If clutch pull is pretty easy and you have no clutch slipping then you should be good to go.
However if clutch is a hard pull it can indicate the wear of the fiber clutch plates has allowed the clutch pack height to sink low enough that the hard pull is needed because the spring has over released.
If so you can get a selection of different thicknesses of clutch pack spacer plates from OldBritts and modify the stack height so you get a reasonable clutch pull. Two finger pull worked for me. If one finger pull I suspect you will get clutch slippage.
The un used plates can be returned to OB.

Click to expand...

My clutch is very easy to operate. I think I may be just a tab obsessive compulsive. I've never actually got a very good reading in my attempts to measure it and I would just like to know how others do it satisfactorily.

Duh, ya mix and match &or machine till sweet and easier as any similar size craft then take the stack out to put a number on it that really only applies to yours during its long interval of wearing to much. One reason for my repeated pleased clutch action on 2 Combats *might* be I leave gaskets out of tranny. This didn't occur to me till just now so not sure if it actually affected stack function, but mention it in case others run out of gaskets and eager to ride.

I'm impressed with by making a thin spring groove spacer ring, a new solution to me that may become another factory acceptable upgrade.

Hm I've '72 Trixie pack out so will measure it for comparison. I know what a stiff action clutch feels like, from bad routing or wearing of cable or lever pivot and at times on/off feathering 2000ish rpm to lean a 260' sharp lean while climbing a 25' hwy entry slope where gravel collects and close by blind bend traffic suddenly appears so can't creep onto road like an old lady but smoothly accelerate with max tire edge traction and not have clutch grab so much it spins out or stalls engine and not think twice about the effort to modulate varying squeezing/releasing of level effort but do get sore jaw grit muscles blocking out memories of the many accidents and my close calls right there in middle of nowhere several times daily routinely. I seek nothing better. My SV650 is more squeeze effort and less sure feathering, to point I only ride it when feeling like could take another crash while Trixie refreshes me when feeling too weak fearful otherwise.

Total stack + pressure plate = 1.158"
Plate stack + residual ATF pressed tight = 0.8000"
Pressure plate = .358"

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By David J. Comeau 24 Aug 2000- Rev. 29 Dec 2004

There are basically two variations of clutch pack in the Commando.
First is the early style THICK friction plates and are used with the THICK pressure plate.
Next is the late style, which used the THIN friction plates and the THIN pressure plate.

Plain Clutch Plate
Both clutch variations use these steel clutch plates 06-0746=.080” thick
Early Qty =3
Late Qty=4
Barnett #524-S

Friction Plate

Early-thick .145” friction plates Qty =4
Thru 70- bonded segment 06-0749
71-72- solid fiber 06-1339
Barnett- bonded segment-thick # 524-68

Late-thin .125” friction plates Qty=5
73-75 Bronze 06-3741
Barnett-bonded segment-thin # 524-73.

Pressure Plate

Early THICK pressure plate 06-0745 =.347” thick

Late THIN pressure plate 06-3768 =.227” thick


STACK HEIGHT
To derive the full clutch height you add all the separate components including the FULL height of the pressure plate.
This is the FULL dimension filled by STACK HEIGHT of the components, between the backing plate in the clutch basket out to the diaphragm. From an engineering stand point this is the correct number.
Early clutch, original stack height=1.167”
Late clutch, original stack heigth=1.172"

.....N.B. Ken Canaga and Hobot I do NOT give a "recommended stack height" but only that the stack height is the sum of the height of all the clutch components

STACK HEIGHT
To derive the full clutch height you add all the seperate components including the FULL height of the pressure plate.
This is the FULL dimension filled by STACK HEIGHT of the components, between the backing plate in the clutch basket out to the diaphragm. From an engineering stand point this is the correct number.
Early clutch, original stack height=1.167”
Late clutch, original stack heigth=1.172"

the above colored part is a gentle jab at Fred since the stack height fills the whole basket up to the bottom of the diaphragm spring. You will note his # does not do this, IMO due to the inappropriate dimensions of both his pressure plates


Clutch basket depth:
Measured from the bottom up to the land that the diaphragm sits on ..............NOT the circlip groove.

If the full STACK HEIGHT is equal to the Clutch basket depth (ignoring free play clearance) the diaphragm should sit flat if both are equal. Determining "FLAT" or zero is what allows the diaphragm chart to be meaningful since the graph is an analysis of the spring all by it's self.
FWIW even though BDM and I have had a few "go arounds" and mostly him calling me names etc., I do believe him... that there are 3 different diaphragm springs. So you can't totally go by my chart with only 2 samples, but the characteristic shape of the 3 different springs remains the same. Referencing the "flat" is the place to start to tune toward the overcenter feel for ease but hopefully not going to far or you loose to much clamping pressure and it may slip if engine torque exceeds the clutch holding power.

Added though related more to the previous clutch thread:FACT...
The release cams (atlas and commando) are both basically LINEAR and have NO effect on over center feel which is entirely a diaphragm spring effect.

I found a shielded Venhill clutch cable works great for easy lever pull. My clutch action is smooth with no slipping. I never measured my stack height. It works as is.

by phillyskip » Tue Sep 30, 2014 3:29 pm
I found a shielded Venhill clutch cable works great for easy lever pull. My clutch action is smooth with no slipping. I never measured my stack height. It works as is.

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Nope that will not fly here, some clutches don't get any better with better cable, so go out and measure your stack and basket depth and type of spring, so we can get a sense to shoot for in relation to what DynoDave and hobot found.

I tried the OB extra plates, but my clutch stack height was already within DD's spec, so I was wasting my shipping charges. Like I said I still have a space between the circlip and the plates, but if I remove it, I get slippage. I think there's differences in the machining of the groove for the circlip and the diaphragm pressures per bike. I could just never improve on my clutch without it slipping so I left it as is. 15K and still the original clutch pack. Plus leave the primary a bit looser than you want to tighten it and it shifts like a dream. No klunking like I hear lots of other bikes going down the road (not Nortons).

phillyskip said:

I found a shielded Venhill clutch cable works great for easy lever pull. My clutch action is smooth with no slipping. I never measured my stack height. It works as is.

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That's two of us, for sure.

JimC said:

phillyskip said:

I found a shielded Venhill clutch cable works great for easy lever pull. My clutch action is smooth with no slipping. I never measured my stack height. It works as is.

Click to expand...

That's two of us, for sure.

Click to expand...

I have not had to do much to my stock clutches as you guys also experienced.
The main reason I first examined my first "clutch" was in my norvil belt drive in about 1989. That is when I figured out the diaphragm operation with a brief primer from Les Emery. His aluminum clutch basket was not the same as stock. I ended up remanufacturing the plate at the bottom of the basket .050" thicker and installing it. I did not obsess any further on clutches.
Over the years, I saw, read and heard guys talking really stupid crap about the commando clutches..such as "your clutch slips because the plates get worn" so I finally broke down in 1997 and did a 15 minute experiment in my 25 ton press and wrote a quickie article which is the basis for what is now on my site.

I can add that the mechanical advantage is approx 2.75 so 200 lbs of push rod effort gives 550 lbs of clamping force. Increasing the pressure plate contact circle diameter increases the clamping pressure.
Also changing clutch stack height has 2.75 times the effect on the diaphragm shown @ the push rod...which is how my chart is displayed.

dynodave said:

.....N.B. Ken Canaga and Hobot I do NOT give a "recommended stack height" but only that the stack height is the sum of the height of all the clutch components

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Just to be absolutely clear, it was hobot who talked about your "recommended stack height", not me. I thought I finally made it clear in the other clutch post that I just used the info you provided (and which I much appreciated) to do some experimenting with the clutch pull on my bike. I'm only repeating that here because you seem to be a bit touchy on the subject. No offense intended, but I'm pretty touchy about people misquoting me too.

Ken

I made my own clutch pushrod. If its length is wrong (pushrod too short) the angle of the actuating lever inside the gearbox can make the action heavy. As far as 'stack height' is concerned, surely all that matters is that full spring load is applied to the stack without the pressure plate/diaphragm bottoming out ? If you have a look at the gearbox in the earlier Triumph twins, the angle at which the lever stands out is important. If it is too far in towards the cover, the action becomes very heavy. If you have this problem, sometimes you can fix it by inserting a !/4 by !/4 bearing roller in between the two halves of the pushrod - mine has a mushroom headed end piece which bears on the pressure plate.

OK, I'm set straight on your article's measuring semantics now Dave. In past forums when I said I don't measure but mix and match till spring just clears seating into groove, I was scolded with your measures held up as what a proper B.I. mechanic should obtain first then install. Only time i ever measured was a few days ago to find Trixies sweet set slip or progressive slippage till locked tight stack, its 'significantly' shorter than Dave's range.

Will keep the bigger spring OD contact pressure in mind for Peel.