Topic: What sort of mileage have you gotten out of your CB750 clutch?

[AwesomeCB]

I searched low and high for an answer. Assuming typical driving style and conditions, how long can one expect a clutch to last? My K6 has only 14,500 miles and I can feel the clutch starting to slip. I don't know anything about the prior ownership and how that person rode, but 14.5K seems early too me.

[tlbranth]

My '70 has about 60,000 miles and the clutch works fine. I have never had a wet clutch wear out. My GL1500 has close to 150,000 miles on the original clutch. Are you using that newer high mileage oil?

[70CB750]

Following

[Don R]

 In case you haven't adjusted the clutch lifter, do that and then re adjust the cable. I learned how to do it the hard way, on a trip in a motel parking lot. In the rain.  Actually on the cb750 world relay tour.

[PeWe]

Adjust the clutch inside the clutch dust cover fastened with 3 screws. Make sure the arm has a play when cable has a slack or even better disconnected.

Unlock the nut, unscrew the lock screw just a little, max 1 turn out. Tighten the lock screw until it stops and open back out again by 1/2 turn. Lock screw by its nut and attach cable. Adjust cable at the bottom so you have adjustment at the handle bar lever that should have a small play too until it start to move the arm.
Play change with hot engine compared with cold

I have got slips due to this arm with no play. I had opened it only 1/4 turn which changed later, maybe when warm. 1/2 turn will give a safety margin.

You can check play again when engine is hot just for sure and see that there is a play. This way made me to always go for 1/2 turn, not less. 1/4 turn out can work if you stop tighten the screw at first resistance.

[AwesomeCB]

Thank you. I'm mainly interested in getting a general idea about clutch life.

I know how to adjust a clutch. I'll also take the plates out and measure thickness and warping before concluding I need to replace them. Just wondering what mileage people typically get...

[trigger]

I searched low and high for an answer. Assuming typical driving style and conditions, how long can one expect a clutch to last? My K6 has only 14,500 miles and I can feel the clutch starting to slip. I don't know anything about the prior ownership and how that person rode, but 14.5K seems early too me.

If the clutch is original, that means the plates are 43 years old and will most properly gone hard and brittle. So, it doesn't matter how many miles.

Here is a picture of once they are old and start to fail 

 

[AwesomeCB]

If the clutch is original, that means the plates are 43 years old and will most properly gone hard and brittle. So, it doesn't matter how many miles.
 

I did not know this, so you're saying I should redo the clutch? Would you happen to be familiar with this kit?
https://www.ebay.com/itm/HONDA-CB750K-CB750F-CB-750-K-BARNETT-made-with-KEVLAR-CLUTCH-KIT-1969-1978/281769681300?epid=1260954616&hash=item419ac82194:g:Lp4AAMXQWuRQ9gML:rk:1:pf:0

[trigger]

If the clutch is original, that means the plates are 43 years old and will most properly gone hard and brittle. So, it doesn't matter how many miles.
 

I did not know this, so your saying I should redo the clutch? Would you happen to be familiar with this kit?
https://www.ebay.com/itm/HONDA-CB750K-CB750F-CB-750-K-BARNETT-made-with-KEVLAR-CLUTCH-KIT-1969-1978/281769681300?epid=1260954616&hash=item419ac82194:g:Lp4AAMXQWuRQ9gML:rk:1:pf:0

I can't see that this clutch would fit all CB750's from 1969 to 1978. There must be at least 6 different clutch baskets between those years. A EBC CK1145 will do the job at less than half the price 

[ofreen]

The clutch on my ‘75 750F has a little under 164,000 miles on it and is doing fine.

[ekpent]

 Never replaced one yet on multiple different 750's. My one I ride the most,a K4, has around 25,000 miles on it.

[seanbarney41]

Same here...but lots with around 50-80,000 miles.  Once, I thought I was gonna have to replace one.  After a day at the dragstrip, that was just me, and a dozen or so other guys, so few that I was basically doing dragstrip run after run for about 2 straight hours, my clutch was slipping a little at full throttle in 4th gear.  I re-adjusted it, changed the oil, and it was good again.  That engine got sold about 4 years ago.  Recently popped up for sale on facebook swapper...no mention of clutch replacement or the need for it. lol

[pmanning]

I replaced the original clutch on my K5 at 91,800 miles.  It was not crying for replacement but I had the engine apart for an overall freshen up so it seemed like a convenient time to do it.

[kpier883]

I have replaced springs more than the clutches.  Replaced springs in my CBX a couple of years ago due to slippage.  Same on a kz And CB750. 

Also noticed the oil question, but didn’t see an answer.  It is a good question.

[kpier883]

I don’t like Barnett clutches. Tried one on th KZ 1000 in the late 80’s and it slipped when cold.  Changed back to stock with new springs and never had any more problems.  Others may have had better results.

[disco]

I searched low and high for an answer. Assuming typical driving style and conditions, how long can one expect a clutch to last? My K6 has only 14,500 miles and I can feel the clutch starting to slip. I don't know anything about the prior ownership and how that person rode, but 14.5K seems early too me.

If the clutch is original, that means the plates are 43 years old and will most properly gone hard and brittle. So, it doesn't matter how many miles.

Here is a picture of once they are old and start to fail 

 

I similarly had a 40 something year old clutch fail. Cork departed metal as per pics. I replaced clutches on all my 750's after that. The risk is that some of that cork clutch material gets ground up by gears etc and is then small enough to make it past the oil filter screen. Once that happens it's only a matter of time before the oil orifices get blocked & you got a catastrophic failure due to lack of oil.

[70CB750]

Also noticed the oil question, but didn’t see an answer.  It is a good question.

Second that - what oil are you using?

[AwesomeCB]

Also noticed the oil question, but didn’t see an answer.  It is a good question.

Second that - what oil are you using?

I meant to answer about oil, sorry. I have 10w/30 dinosaur oil in it.

[kpier883]

Your dino oil COULD be part or all of the problem.  Newer oils have more oil modifiers and less ZDDP than oils of the 70's and 80's.  The friction modifiers MIGHT be causing your clutch to slip.  Lack of ZDDP MIGHT cause increased wear, especially in the transmission.

JASO is the Japanese equivalent of the U.S. SAE body.  JASO sets the oil standards for various applications for Japan.  I will attach a reference link that explains JASO oil specifications.  It is best to use a JASO MA rated oil in wet clutch applications such as our CB750s.  This ensures that the clutch and transmission requirements for the oil are satisfied for our use case.

There are some oils that could probably pass the test to be certified for JASO MA, but have not gone through the process to achieve said certification.  One example is Shell Rotella T4 dino oil.  It does not have the certification symbol, but states on the back that it is compliant.  See attached pictures for evidence.  I use Rotella for this reason. 

The search function in the forum, or a google search on oil and clutches with this added to the search criteria: "site:sohc4.net" (see third picture below for example) will yield many discussions for oil.  Probably better to do that than get into all the nuances of oil in this thread. 

References:
https://en.wikipedia.org/wiki/Zinc_dithiophosphate
https://www.oilspecifications.org/jaso.php
https://en.wikipedia.org/wiki/Friction_modifier

[AwesomeCB]

Thanks for the links re: oil and clutches. I know it's been discussed extensively here. This is my third CB750K and I've always used 10/30 oil (different brands) without any issues. On the next oil change, I will make sure it's JASO MA rated.

What I would like to know: How many miles is typical in the life of a clutch? Some people have mentioned that it's not miles but age that matters, suggesting that after 42 years, it would be time to rebuild it.

[kpier883]

Can’t help. Have only put 20,000 miles on my CB750, and it is the only SOHC Honda I have owned. 

I put about 70k miles on an 82 KZ1000 and handed out much more clutch abuse than I have on my Honda’s.  I replaced springs on it after trying Barnett, went back stock with the stronger springs. 

[754]

 Awesome before you pull anything apart, just do the adjusting procedure.
 I like Barnetts, a nd slipped the he'll out of them , for a very long time,  but quite a few people don't like them.. 
 I used them very hard..

[Old Scrambler]

80,000 miles on original with first adjustment at 76,000..............clean oil helps..........parked for years in dirty oil not so much

I use a stock clutch for landspeed racing with Barnett springs...............so far OK

[paulreade]

I've recently purchased a k6 and the clutch was on its limits at a mileage of 16k. I spent a fair bit of time on this forum and the U.K. Forum pooling ideas from members. I eventually too their advice on a ck1145 kit, set of new standard springs and it's all good now. I believe the plates had become brittle causing the slip. Check the threads on this - opened up some interesting thoughts from those that are in the know. Overall an easy job to do once you have the kit.

[PeWe]

Thanks for the links re: oil and clutches. I know it's been discussed extensively here. This is my third CB750K and I've always used 10/30 oil (different brands) without any issues. On the next oil change, I will make sure it's JASO MA rated.

What I would like to know: How many miles is typical in the life of a clutch? Some people have mentioned that it's not miles but age that matters, suggesting that after 42 years, it would be time to rebuild it.

10W-30 oil in a CB750 is wrong oil. That kind of thin oil is for newer engine constructions with much tighter clearances.
Your crank bearings must get scuffmarks when that oil runs hard in warm temperature and the oil will collapse?

Any motorcycle oil of correct viscosity will work much better. 10W-40 when ambient temperature is around 15C and lower, 20-50 when warmer. You'll feel how the gearbox work.

My K6 got 20W-60 when ambient temp climbed to around 30C which I tested last summer. Another guy on this forum had good experience of 15W-60 due to the warm weather.