Broken clutch lifter plate... What next?

[cbxman]

Hi Guys,

The clutch on my 750 K1 was not too good.  It would drag.  Not nice changing gears. So searching on this site revealed some interesting stuff.

Based on some of those threads, I bought a K6 clutch on eBay which had a very nice looking lifter plate on spec......just in case.

I have pulled the clutch today an hey-ho the lifter plate is broken with three of the spring posts having fractures.  I guess this would be a major contributor to my problems.

The steels are quite badly stained.  Maybe not to the point of serious corrosion, so I think I will buy new.

Now having got this K6 clutch assembly, I don't want to break it.  I have read that they can be broken if the pack is not assembled correctly, so care is required here.

I thought I would check the spring lengths and found that all four of them were around 35.5 mm, which would be much too long if the 30.5mm WSM spec is to believed.  I'm wondering if that extra length may have caused the lifter failure.

Any idea what the correct length should be?

The lifter mechanism looks good though

And the friction plates are barely worn.

Photos attached

Cheers,

Jerry

[K2-K6]

The long springs shouldn't be the cause of failure, they are correct-ish specification for F2 that uses the same hardware with manual stating 36.80mm fitment.  It's to give higher preload of spring and greater clamping pressure for high rpm launches on that engine.

Most will be broken by incorrect assembly of clutch pack, then tightened when the pack won't close to working position fully.

Before lift plate is installed you can put a couple of bolts into the threaded holes and pull the rear plate forward with your fingers to check if the clutch pack is going to close completely (no springs or anything installed) which will allow you to check basic alignment without risk.

If that's all okay, then installation of lift plate should be simple, just turn the bolts very slowly and feel the springs compressing (only need a 1/4 drive socket with small handle) if you feel one getting too much significant resistance then stop all, back out and examine again to see if you've snagged something. You can do them 1/4 turn at a time in rotation to tread very carefully  too.

[K2-K6]

To add, you don't need to use the longer springs unless specifically needed to be aggressive with clutch operation, the std length should be fine.

[cbxman]

Nigel
Thank you for the info.  I don’t need drag bike clutch performance, so I’ll try to find some standard springs. They are incredibly stiff.

I have checked the steels for flatness and they all have warps exceeding the 0.03mm limit. The friction discs too exceeds the 0.03mm

So looks like new springs and discs. Ouch!

Cheers,
Jerry

[Trigger]

There are two lengths of springs fitted to the 750. Early ones were short with a thicker dia coil. Later springs are longer with smaller coil 

[cbxman]

There are two lengths of springs fitted to the 750. Early ones were short with a thicker dia coil. Later springs are longer with smaller coil 

Trigger,
Thank you.

Being an American import, this bike could have anything in it!

I have measured the springs that are in it.  They are 35.5 mm long, with 8 turns of 2.6 mm of wire.  Extremely hard to compress by hand.  There's a company called Barnett (sp?) and they produce performance parts.  Their take on the 750 is springs 36 mm long with 2.6 mm wire. I think those springs are the hopped up ones.  Apparently stock Honda springs are supposed to be 31.75mm with 2.54mm wire.. A lot shorter with thinner wire.

Also....Studying the release mechanism a bit more, I noticed that the release bearing was not seated in the release plate.  About a 1mm short of seated.  The release cup which fits into it was not seated either.  They were solid I had to press them out.  I cleaned the faces, greased them and pressed them back in to seated.  How did that happen?  They must have been like that from factory.  I have been trying to figure out what that might mean in terms of clutch performance....maybe nothing other than the adjuster screw might be set further out than normal.

The interaction between the face of the release cup and the release mechanism is unclear.  The adjuster screw seems to just push the release bearing away, which means the face of the release mechanism isn't running against the flat portion of the mechanism...may be that's how it is.. with the nose of the adjuster screw running in the bottom of the cup rather than the flat faces of the two

Baffled, and apologies for the waffling....

Jerry

[Trigger]

As i have already stated, Honda had two types of springs in the 750 and you will not find it in the manuals. Yours are the later type ( longer with thinner wire) . The K6 clutch is the same as the F1 clutch with a double plate.
Early spring fitted to the K1 was 32.50 with a 2.92 wire.

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[cbxman]

Thanks Trigger,

More confused now..  Hondaman was staying 31.75 with 2.54mm for the early clutches.

However, my bike is a K1, built Nov 1970.  The clutch could be from anywhere after 50 years, so you could be right, and maybe the UK market and US markets had different setups, although the parts book would have you believe there are no differences.

I guess I'm at the mercy of whoever supplies the springs.  I suppose I could use the current ones.  They are almost exactly the same as each other, although intended for the later clutch.

Ho-Hum,

Cheers,
Jerry

[Trigger]

It all depends on what spring hondaman is measuring 
CB750 K0 to K6 springs were superseded so many times 
22401300000
22041300000
22401368000
9501475140
22401275000
22401369000

[cbxman]

Trigger,

He was measuring an early Honda item and a Barnett item.

See:

http://forums.sohc4.net/index.php/topic,182424.msg2115426.html#msg2115426

Jerry

[cbxman]

Just an update on the broken clutch.

I should have said "Broken Pressure  Plate", not "Lifter Plate".  Silly me.

I sourced a partial clutch basket, which had an intact pressure plate.  The basket and hub was from a pre K6 bike but fitted on to a K6 'Driven Sprocket'.  It was bit chewed up at the back where the circlip portion of the shaft had ground its way into the back of the basket.  Still it is OK so I have spare basket, and hub which will fit the K1.

After many hours of searching about broken 'lifter plates' and 'pressure plates' It seems that there is no defined procedure to follow.  There were two well defined issues with installing these 750 clutches...

1 Misaligning the hub with the pressure plate.  The pressure plate can only be fitted to the hub in only 2 of the four possible positions. The splines must fit into the splines of the pressure plate, or you will break the pressure plate.  This is what had happened to my bike by some PO.

2. The 'Lifter Plate' is a favourite for breaking.  It is said that the uneven tightening of the four fasteners through springs will cause it to break.  The spring posts slot into the reverse side of the lifter plate towards the end of tightening down.  If the sequence is uneven, the plate can tilt and then hang up on the edge of one of the spring post.  Further tightening will crack the lifter plate.

However, I have found another failure mode, which I have not seen posted anywhere, so I thought I would mention it here.

3. I was tightening the post fasteners and one became harder to turn than the other three.  Using a small angled mirror and a torch, I could see under the lifter plate and saw that the end of one of the clutch springs had dropped into the groove on the reverse of the lifter plate where the post should go in.  Had I carried on tightening that fastener, it would have snapped the lifter plate.

So these clutches are really tricky to install.

Having said all that, I'm happy to say that after a test ride this afternoon the clutch was working well....I could actually move to neutral from 1st whilst stationary!!  Changing up and down the box was excellent.

I hope that helps someone who is considering working on their clutch.

Cheers,
Jerry

[Lobo]

Not quite the answer we’d all like, but rebuilding the clutch with the engine in the (clutch) vertical plane solves the issues.
Have just had my ‘750 engine rebuilt on a very nice jig that rotated the engine anyway-up, with Lindsay (rebuilder) commenting on how easy it is to damage clutches if doing so in the normal orientation.
A fair amount of jiggling, tightening, jiggling still involved…

[cbxman]

Lobo,

I agree.  if the clutch is lying on its back, then the springs will naturally keep straight.  I expect that most people will be servicing the clutch with the engine still in the bike though.  With gravity trying spoil your day!

Cheers,
Jerry

[Lobo]

As an aside, Lindsay (Donai) is a fairly well known (Period 2) sidecar racer here in Oz, and primarily raced Honda 750 rigs some 40+ years. He builds / modifies all his own bikes / engines etc, inc engineering some extremely fancy exhaust systems. ANYWAYS, whilst rebuilding my clutch he pointed to a shelf of nothing but CB750 clutches, and commented that a ‘750 clutch assy will typically last one day on the track. Bloody hell.

And of course, they’ll be changed in the ‘normal’ position, so I guess the engine on its side in my case was here nor there to him!

[cbxman]

Lobo,

Being aware of these pitfalls means you can relax when re-installing them.

I was being ultra cautious as these parts are getting really hard to get.

I could so easily have broken that lifter plate if I had not stopped and checked.

Cheers,

Jerry