SOHC.co.uk Forums > CB750
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 ;)
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