XS650 Clutch Pushrod experiment & tidbits

[Signal]

Thanks for posting. Can you tell me what the diameters of the slave cylinder piston and master cylinder piston are?

 

[ihaxs650]

Signal, Heiden Tuning is selling a separate 11 mm master cylinder for the Heiden hydraulic clutch kit. I am not sure what diameters the slave and master pistons are on the stock kit. I am assuming the 11 mm master is for an easier pull.

 

[Marlin72xs]

This is mostly a 'thought experiment', and a companion piece to the clutch worm experiment:

http://www.xs650.com/forum/showthread.php?t=31554

The XS clutch has the notorious feature of slackening-up when the engine is hot, and the conventional wisdom blames this on differential thermal expansion rates between the aluminum engine case and clutch pushrod(s). This exercise explores the potential relief if an alternate material is used for a 1-piece pushrod. I have never handled, much less seen, a 2-piece setup, which I understand utilized aluminum in the longer of the 2-piece pushrod setup to overcome this expansion problem.

The computations here are rough ballpark, to determine the feasability of using alternate clutch pushrod materials. These alternate material candidates were selected based on availability, strength and thermal expansion coefficients.

Pic #1 - I have a few 5/16" rods of these materials, which are 304 Stainless, Navy brass, 6061 aluminum and 7075 structural aluminum.

View attachment 38352

Considering whether it's feasable to conduct this experiment. Others, especially ME's, are encouraged to jump-in here and comment on this project. I have this in a spreadsheet, but decided to expand it here to improve understanding.

1-piece stock clutch pushrod:
Length = 9.570" (243 mm), we'll use 10" for our rough sample calculations
Diameter = 8mm (.315"), can use 5/16" (.3125)
Material = unknown Carbon steel

Depending on type of clutch worm and stock/aftermarket clutch levers, total leverage multiplier at clutch lever is about 30-50.

Pushrod stress:
At a tested mid-range compression of 370 lbs (stock XS1B) , a 5/16" rod (1/13 sq-in cross-sectional area) is experiencing about 5000 psi of compressive stress.

Normal compressive load distribution can be used when length/diameter ratios are below 6. Special column loading considerations and limits must be employed when the length/diameter ratios are 6 to 60, and especially at 60-120 (severe buckling phenomena). The clutch pushrod length/diameter ratio is about 30. Without going into all the engineering math here, all the selected materials here (within this stress value) qualify for normal compressive stress/strain calculations, without worrying about buckling.

Decided to drop the 6061 aluminum since it would be a slightly weaker and redundant version of the 7075 aluminum.

Coefficients of thermal expansion (within normal engine temperature ranges). Units are MicroInch per °F (.000001" / °F) per inch of material
Engine case Aluminum = 13.1
Carbon Steel = 7.8
304 Stainless steel = 9.6
Navy Brass = 11.8
7075 Aluminum = 13.1

Compute expansion of 10" of material based on 200°F temperature rise (70°F - 270°F)
Engine case Aluminum = 0.026"
Carbon Steel = 0.016"
304 Stainless steel = 0.019"
Navy Brass = 0.024"
7075 Aluminum = 0.026"

However, these candidate clutch pushrods undergo compression during clutch disengagement, and deform (shorten) under stress. The amount of length change (strain) can be predicted using the modulus of elasticity (Young's Modulus) for each material, when stressed below the material yield strength. The higher the modulus, the stiffer the material. The length change (strain) is: stress (psi) / Modulus, then times the overall length.

Rough values of Young's Modulus (in millions of psi):
Carbon Steel = 30
304 Stainless steel = 30
Navy Brass = 15
7075 Aluminum = 10

Compute length change (strain) for 5000 psi stress on 10" rod
Carbon Steel = -0.002"
304 Stainless steel = -0.002"
Navy Brass = -0.003"
7075 Aluminum = -0.005"

Now, compute overall length change (expansion -strain).
Carbon Steel = 0.016" - 0.002" = 0.014"
304 Stainless steel = 0.019" - 0.002" = 0.017"
Navy Brass = 0.024" - 0.003" = 0.021"
7075 Aluminum = 0.026" - 0.005" = 0.021"

Interestingly, the Navy brass and 7075 aluminum are equal.

Now, compute overall length differential to aluminum engine case (0.026" - rod expansion).
The smaller, the better.
Include 30-50 leverage multiplier to show slackening value at clutch lever.

Carbon Steel = 0.026" - 0.014" = 0.012" (0.36" - 0.60" at clutch lever)
304 Stainless steel = 0.026" - 0.017" = 0.009" (0.27" - 0.45" at clutch lever)
Navy Brass = 0.026" - 0.021" = 0.005" (0.15" - 0.25" at clutch lever)
7075 Aluminum = 0.026" - 0.021" = 0.005" (0.15" - 0.25" at clutch lever)

It's winter, too cold to experiment with this now, just throwin' this out there. Anybody else try any of this? I see no issues in at least trying the 304 stainless, but would appreciate any insight.

Just read your dissertation on thermal expansion! Impressive as usual. As a HS Physics teacher in the 80's, we took those same rods, (with the addition of copper), and put them in a steam jacket with a 10:1 indicator and literally watched the rods expand from room temp to boiling temp. Just wanted to say hi. Hope all is well with you.

 

[TwoManyXS1Bs]

Hey, Marlin72xs. Thanx.
My hat's off to all you physics instructors.
To capture interest, my first instructor used drag racing to demonstrate accelleration physics.
A real fun guy...

 

[gggGary]

Just wanted to pat myself on the back for wading through this entire thread in one sitting.
Caviat; the coffee pot went dry.

 

[TwoManyXS1Bs]

Congrats, gggGary.
I fully understand the challenges of grinding thru some of these marathon threads.

Last week I tried to re-read Mailman's entire XS2 restoration thread,

Didn't make it...

 

[peanut]

Congrats, gggGary.
I fully understand the challenges of grinding thru some of these marathon threads.

Last week I started to re-read Mailman's XS2 restoration thread,

Didn't make it...
View attachment 140721

I see that you are into metal recycling in a big way 2M..........thats very commendable

 

[TwoManyXS1Bs]

Status update.
I've been running the 1-piece 7075AL pushrod for almost 5 years now. Clutch action has been great, absolutely no adjustments have been necessary to take up pushrod wear, and no adjustments have been needed to accommodate thermal expansion. Hot or cold, the clutch slack remains the same.

So, time to pull and inspect it.

The dimpled ends, where the balls have settled in, have remained the same since the inspection of 3-1/2 years ago. Post #133.
http://www.xs650.com/threads/xs650-clutch-pushrod-experiment-tidbits.32267/page-7#post-465210

However, the part of the pushrod that rides in the mainshaft bushing is starting to show wear, mostly where it touches the outer edge of the bushing at the 2.1" location, enuff to feel with a fingernail.

The wear line at the 1.9" location is where the pushrod rides in the oil seal, and so far is just a blemish, non-detectable with a fingernail. There's been no oil leakage.

The other end is showing slight blemishing at the final 1/2", when it runs alongside an oiling hole in the mainshaft. Can't detect any wear with a fingernail.

Decided to retire this pushrod, replaced with a new one made from higher quality 8mm stock...

 

[peanut]

thats impressive performance 2M but I suspect a lot of that is due to your meticulous preparation and installation detail.

How much of that wear is due to eccentricity of the worm gear action ? have you done any tests on worm gear concentricity ? I have no idea what the tolerance is meant to be .

 

[TwoManyXS1Bs]

Thanx, peanut.

..How much of that wear is due to eccentricity of the worm gear action ? have you done any tests on worm gear concentricity ?

Yeah, good point. My worm and pushrod are misaligned about .007"-.008".
From here, Post #83.

http://www.xs650.com/threads/xs650-clutch-worm-actuator-experiment-tidbits.31554/page-5#post-323154

It would be nice to have the worm assembly and mainshaft in perfect alignment. That should eliminate any side loading and wear on the pushrod. Cogitated on making an alignment jig, but my head exploded...

 

[peanut]

Cogitated on making an alignment jig, but my head exploded...

i want to know where you find the get-up-and-go to do all this stuff 2M ..... whatever you're on ....I want some of it

I was thinking more of the degree of elliptical motion of the wormgear when operated being imparted to the rod at the bush

 

[gggGary]

2M I use the TDS on the seal, chuck the solvent dried shaft in the drill press or lathe, apply powder to the spinning shaft with a rag to the wear areas. then use grease powder mix...

 

[TwoManyXS1Bs]

I used the grease/powder mix in that area, but having a rethink on your idea of surface application of the WS2 to the shaft.

It'd be great if that would arrest the wear in that area.

Cogitating on some sort of wear tester, plain 7075AL vs coated...

 

[gggGary]

 

[ReycleBill]

I used the grease/powder mix in that area, but having a rethink on your idea of surface application of the WS2 to the shaft.

It'd be great if that would arrest the wear in that area.

Cogitating on some sort of wear tester, plain 7075AL vs coated...

Great thread!

So do you have any of these shafts available and if so, how much mailed to North Carolina? And do you accept Paypal or should it be paid some other way.

 

[TwoManyXS1Bs]

Hey, RecycleBill!

I'll PM you...

 

[TwoManyXS1Bs]

After 1-1/2 years, decided to pull and inspect the 7075AL pushrod.
Just blemishes around the seal/bushing area, can't feel it with fingernail.

... chuck the solvent dried shaft in the drill press or lathe, apply powder to the spinning shaft with a rag to the wear areas...

Ok, did just that.

Burnished some WS2 onto the shaft, in the seal/bushing zone.
Almost can't tell, just a tinge of amber color there now.
Applied a WS2/grease mix in the seal...

 

[dps650rider]

I did mine with a steel insert at the end where it runs in the bushing. Been in there for years now and no problems, and no change in adjustment with temperature. A very good modification and highly recommended.

 

[joebgd]

I did mine with a steel insert at the end where it runs in the bushing. Been in there for years now and no problems, and no change in adjustment with temperature. A very good modification and highly recommended.

Can you post a pick?. Wouldn't you need a thinner rod to accomplish that?

 

[TwoManyXS1Bs]

Yes, Dps650rider posted his modded/sleeved pushrod way back in post #66.

http://www.xs650.com/threads/xs650-clutch-pushrod-experiment-tidbits.32267/page-4#post-346794