K75S Clutch replacement questions

[beetsandbeats]

I believe my clutch exploded on me on the way home, so I'm looking at replacing it. I've never done a clutch before, but I've replaced the transmission so I think I know what I'm in for. I have a couple questions before I get started and hope I can find some help.

• I just changed the engine, transmission and final drive oil in the spring. Will I have to drain any of them for this job? I don't think so, even if it'll be a bit easier.
• I saw someone use a socket wrench piece for clutch alignment. How bad would it be if I didn't buy the tool?
• I'm going to get the clutch kit from kpartsholland (cheapest). But it doesn't include the thrust rod boot and muffler gasket like Bob's does. Any reason to get these?
• Are there any other parts that may have been damaged and need replacement due to the clutch prematurely failing?
• Any helpful tips for replacing a clutch?

[frankenduck]

1 - If you don't drain the final drive then you need to keep it upright. If you lay it on its side then gear oil will leak out the vent at the top.

2 - You can use the transmission as your clutch centering tool.
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/clutchnospecial/clutchnospecial.htm

3 - You usually don't need to replace  the clutch boot. Use zip-ties to keep the clutch arm holding it so that the spring inside of it stays compressed.

[Laitch]

I believe my clutch exploded on me on the way home, so I'm looking at replacing it.

Describe the sound and aftereffect of your clutch's "exploding."

[beetsandbeats]

Describe the sound and aftereffect of your clutch's "exploding."

Good question, and maybe "exploding" was too dramatic a word. The preamble is that I was cavalier with the clutch cable getting too long and subsequently poorly fixing it and I ended up at a few stoplights with the brake on and clutch not fully out. So I know I've recently put a lot of undue wear on the clutch that was my own fault.

As for the actual event, I was accelerating from a stop and let out the clutch after shifting into second. Immediately there was a high pitched grating and crunching sound. I pulled over and stopped immediately and soon turned off the engine because the grating didn't stop. With the engine off, I shifted into neutral and tried started the engine again. It sounded fine, but the crunching returned when I tried pulling the clutch in. I haven't had a chance to look more as I haven't towed it home yet. As a side note, I had no idea it was a dry clutch until this happened and I would have treated it differently if I had known.

[Laitch]

Was this the noise?

[beetsandbeats]

Was this the noise?

I'd say my noise has more lower pitched crunchy sounds happening, whereas that video sounded like mostly a high pitched whine. I'll have another listen with this in mind when I have a chance.

I am concerned I'll buy the clutch kit, take everything apart, and then find out it's something else. However, another problem is that I live in an apartment building so I want to keep the time I have the bike stripped to a minimum.

[Past-my-Prime]

Clutch replacement isn't too bad.

My clutch gave way more gradually, I found that under heavy application of throttle especially in 4th or 5th, it would not accelerate. On the other hand, I never stalled it out after a stop!

Anyway, I bought a replacement clutch, bolts, etc and it took me as very much an amateur mechanic about two days to replace it. I did buy the tool which makes things easier in terms of alignment.

In addition to the suggestion to hold the clutch arm up (which I also did) buying the M8 x 1.25 bolts that I cut the heads off and ground in a slot to screw in: that allows you to remove two of the transmission bolts and put in "guides" that will align the clutch rod. But having the clutch pre-centered makes installation easier. I suspect that what Frankenduck does is lines up the clutch by "eyeball" and doesn't fully tighten the bolts, then slides the transmission in which will line everything up and then you take the transmission back off and tighten it all. 

After replacing the clutch I had to relearn my launch, because it certainly would stall when you have a good clutch.

Finally, when adjusting the cable, follow all the directions carefully: when properly adjusted, everything works (weird, I know!)

[Laitch]

As for the actual event, I was accelerating from a stop and let out the clutch after shifting into second. Immediately there was a high pitched grating and crunching sound.

Any unusual vibration accompanying the crunching and grating?

[frankenduck]

In addition to the suggestion to hold the clutch arm up (which I also did) buying the M8 x 1.25 bolts that I cut the heads off and ground in a slot to screw in

No need to cut the heads off. Just get the trans close and then used hex headed bolts. Much easier to screw in and out.

These are the actual bolts that I use:

[Laitch]

These are the actual bolts that I use:

Wow! If you get a bunch of them and etch into the shafts with your signature, you'll make a killing on eBay!
 

[frankenduck]

Wow! If you get a bunch of them and etch into the shafts with your signature, you'll make a killing on eBay!
 

Or I could etch BMW roundels into them, give them an eleven digit part number and then sell them at BMW dealers for $150 each.

[sooprvylyn]

No need to cut the heads off. Just get the trans close and then used hex headed bolts. Much easier to screw in and out.

These are the actual bolts that I use:

I used these (link below) and cut em to 100mm long...the upper one needs to be a bit shorter to fit.  Much easier than dealing with those hex heads. You put the rods in before you pick up the transmission and slide the tranny right on. Less fiddly

uxcell M8 X 160mm Tight Adjustable Push Rod Double End Thread Stud Screw Bolt 5pcs https://a.co/d/5pGcsRn

[sooprvylyn]

Also, the clutch assembly is a balanced unit. Use a sharpie to mark all the parts BEFORE you disassemble them so you can put them back together the same way you took them apart. You'll get a bad vibration if you don't, and good, good, good, good vibrations is all we like.


Also proper form says replace the stretch bolts on your clutch. There are 6 of em. Technically you shouldn't reuse them, but some do anyway. It's a little risky because they aren't designed for reuse. You can also use hardware store bolts and lock tite like I did. Iirc they are m6x20mm or maybe 25mm. If you do locktite just remember you did for the next time and you'll need heat to loosen later.

If you stick w the oem stretch bolts, make sure everything is lined up perfect BEFORE torturing the 6 bolts to spec. Once tightened to spec, they aren't supposed to be reused because you've stretched them as designed. Further torquing can cause bolt failure...which means complete disassembly to remove the broken bolt.  Just use hardware store bolts and locktite, they don't have this problem.

[Past-my-Prime]

No need to cut the heads off. Just get the trans close and then used hex headed bolts. Much easier to screw in and out.

Cutting the heads off allows me to completely remove the transmission, change the clutch, and reinstall the transmission, without running the ris of bending the clutch rod. I don’t know why BMW doesn’t make a special tool for this.

[Laitch]

I don’t know why BMW doesn’t make a special tool for this.

If that's dry humor, it's on the Arid end of the scale. 

[frankenduck]

Cutting the heads off allows me to completely remove the transmission, change the clutch, and reinstall the transmission, without running the ris of bending the clutch rod. I don’t know why BMW doesn’t make a special tool for this.

Good luck bending a clutch pushrod. They are tempered steel and very tough. I done many dozen transmission removal/installs and never bent one.

You don't even really need to use the bolts. They just make life a little easier.

BMW doesn't make a special tool for this because it's not necessary.

[frankenduck]

Also proper form says replace the stretch bolts on your clutch. There are 6 of em. Technically you shouldn't reuse them, but some do anyway. It's a little risky because they aren't designed for reuse. You can also use hardware store bolts and lock tite like I did. Iirc they are m6x20mm or maybe 25mm. If you do locktite just remember you did for the next time and you'll need heat to loosen later.

If you stick w the oem stretch bolts, make sure everything is lined up perfect BEFORE torturing the 6 bolts to spec. Once tightened to spec, they aren't supposed to be reused because you've stretched them as designed. Further torquing can cause bolt failure...which means complete disassembly to remove the broken bolt.  Just use hardware store bolts and locktite, they don't have this problem.

The BMW shop manual makes no mention of not re-using those six bolts. It does however note that you should use a new main clutch nut every time you install the clutch housing (basket.)  If those six bolts needed to be replaced then don't you think BMW would note that in the shop manual like they do for the clutch nut?

[frankenduck]

Also, the clutch assembly is a balanced unit. Use a sharpie to mark all the parts BEFORE you disassemble them so you can put them back together the same way you took them apart. You'll get a bad vibration if you don't, and good, good, good, good vibrations is all we like.

Only if you are re-using those parts. He's replacing the clutch parts with new.

I assume this is what he ordered:
https://kpartsholland.com/products/complete-clutch-kit-k75

For new parts the manual notes: "Insert the pressure plate (3), clutch plate (2) and housing
cover (1) in such a way that the colour marks are offset by
app.120°. "

[Laitch]

You don't even really need to use the bolts. They just make life a little easier.

Yes, they make the job easier, and more efficient too. So does jacking up the transmission up for alignment if you're working by yourself or are new at this in general; however, I acknowledge that ease and efficiency aren't for everybody.
 

The OP is under the gun in this situation trying to get it all together so the OP's landlord and neighbors aren't bothered too long by the repair, or parts lying out get stolen. I'm just not certain of this problem's source. What would be helpful is if the OP recorded the troubling sound with a phone recorder uploaded the file into a YouTube public video then posted YouTube link here.

[sooprvylyn]

The BMW shop manual makes no mention of not re-using those six bolts. It does however note that you should use a new main clutch nut every time you install the clutch housing (basket.)  If those six bolts needed to be replaced then don't you think BMW would note that in the shop manual like they do for the clutch nut?

They're stretch bolts. If you go to any parts fiche it says recommended to replace them. When you torque em you indeed deform them slightly, hence stretch bolts. I actually had one sheer off on me when I tried to reuse it. That was fun. I have to check if my clymers said to replace them, I think it did tho.

I know plenty do reuse them, but there is a risk.

[frankenduck]

I don't have a lift or use a jack. I just sit under the rear frame. A transmission only weighs a little over 30 lbs so it's not really that heavy. If you sit like this and place your elbows on your knees you can slide it off and on.

This where I sit to remove/install the transmission. (This pic is not me. It's a friend I that was helping do a spline lube.)

[Laitch]

I don't have a lift or use a jack.

Well, we all have free will.  I'm sure Richard Simmons would have been impressed.   

[frankenduck]

They're stretch bolts. If you go to any parts fiche it says recommended to replace them. When you torque em you indeed deform them slightly, hence stretch bolts. I actually had one sheer off on me when I tried to reuse it. That was fun. I have to check if my clymers said to replace them, I think it did tho.

I know plenty do reuse them, but there is a risk.

It's shear, not sheer. Shear is tangential sideways force which is different from torsion so you did not shear the bolt that failed on you. It failed under torsion.

Shear vs. torsion:
https://link.springer.com/chapter/10.1007/978-3-031-09312-8_15#:~:text=Shear%20deformation%20can%20be%20observed,other%20force%20factors%20are%20absent.

I've re-used those bolts all of the time (torqued to 19Nm per spec) and never had one fail. In order for one to fail when riding then all six of those bolts would need to fail from shear simultaneously as well as the three hardened guide pins. Not gonna happen. In all my years of K biking I have never heard of that occurring to anyone and it doesn't worry me one iota. If it mattered they'd mention it in the manual like they do for the clutch nut. (I've re-used those too without indident. )

Not that it really matters but neither the Clymer nor Haynes K bike manuals mention replacing the six clutch bolts.

Anyhow, that's just me and my personal experience with lots of K bikes. Other people can do whatever they want.

[sooprvylyn]

It's shear, not sheer. Shear is tangential sideways force which is different from torsion so you did not shear the bolt that failed on you. It failed under torsion.

Shear vs. torsion:
https://link.springer.com/chapter/10.1007/978-3-031-09312-8_15#:~:text=Shear%20deformation%20can%20be%20observed,other%20force%20factors%20are%20absent.

I've re-used those bolts all of the time (torqued to 19Nm per spec) and never had one fail. In order for one to fail when riding then all six of those bolts would need to fail from shear simultaneously as well as the three hardened guide pins. Not gonna happen. In all my years of K biking I have never heard of that occurring to anyone and it doesn't worry me one iota. If it mattered they'd mention it in the manual like they do for the clutch nut. (I've re-used those too without indident. )

Not that it really matters but neither the Clymer nor Haynes K bike manuals mention replacing the six clutch bolts.

Anyhow, that's just me and my personal experience with lots of K bikes. Other people can do whatever they want.

Ok

[daveson]

 I really don't think they're torque to yield bolts, probably just bolts. Torque to yield bolts have some typical characteristics that these just don't.

If a bolt breaks that doesn't mean it's torque to yield, probably it was just sheer bloody bad luck. There could be many different reasons for bolts being described as single use. Wearing my cynical hat for a mini, if the person telling you to replace them is the person trying to sell them, that's a hint. Sometimes it's good form to replace cheap parts with new if they're in difficult to get places, which applies in this case. Sometimes lock washers are considered single use, and since these lock washers are also captured washers, that might apply in this case.

In the photo is a Long torque to yield bolt, and two clutch bolts from a K100. The K bolts are marked 8.8 so they're high tensile, good for 800MPa tensile strength. If you just get bolts from a hardware, they might be 4.4 or less, they might just be plain Jane mild steel, they might just stretch or break.

The torque to yield bolt has a non threaded section, and part of that is reduced in diameter, that prevents any stretching from occurring in the threaded part, which we obviously don't want.


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