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CA72 (250) clutch problems

Oln600

Member
Joined
Sep 7, 2021
Total Posts
46
Total likes
9
Location
Nijmegen, The Netherlands
Hi all,

Driving my CA72 (engine revision done past year) I feel the following:

When I open the throttle and it revs to higher rpm, suddenly it feels like the clutch plates are slipping: during acceleration, it suddenly increases rpm more, but no expected speed gain.
The first bit, I actually gain speed, but later not anymore, although the rpm increases. The clutch plates were replaced by new ones, as were the springs. I cannot remember the exact assembly anymore, as it was in different phases due lack of time..

Who could help me diagnose this gremlin?

Thanks in advance

Olivier
 
Hi all,

Driving my CA72 (engine revision done past year) I feel the following:

When I open the throttle and it revs to higher rpm, suddenly it feels like the clutch plates are slipping: during acceleration, it suddenly increases rpm more, but no expected speed gain.
The first bit, I actually gain speed, but later not anymore, although the rpm increases. The clutch plates were replaced by new ones, as were the springs. I cannot remember the exact assembly anymore, as it was in different phases due lack of time..

Who could help me diagnose this gremlin?

Thanks in advance

Olivier
Yes, it sounds like it's slipping. First thing is to do a proper clutch cable and lifter adjustment so that you are sure that the clutch is fully engaged. If there is no free play at the lever then it may not be releasing fully.
 
Hello Ballbaerian,

After disassembly, the following seems to be the situation: i replaced the center of the clutch during revision. I accidentally replaced it with a different model: the one that need the two iron wires on it (as seen on exploded view 1), where my engine was always set up with the clutch centre without those (exploded view 2) and with only 4, instead of 5 friction plates.. So I drove around with the clutch center with the two grooves in it, meant for 5 plates, with only 4 plates. Could this have been the problem? If so, will it be solved with an extra friction plate? The dimensions appear to be the same.

1)


CA72-2.gif

2)
CA72-1.gif





ca72-3.jpg

ca72-4.jpg

Description:

Left center is the one without the grooves with 4 plates
Right center is the one with the grooves with 5 plates

Diam = 109mm
H1 = height from top till bottom exl. the center where it seats the gearbox
H2 = total height incl seating with the gearbox
Hinside = heigt inner center from bottom seating till top seating.

As you all see: highly comparable.

What do I miss?


Thanks again, hope to hear you all soon.

Gr. Olivier
 
Hello Gr. Olivier,
Sorry for the delayed response, it's been busy here.
There were changes to the clutches that were only partly noted by the parts catalogues and part number application as per engine numbers. It took me awhile to figure out the differences and which parts were compatible. I would try to use the later parts, which do take an extra pair of discs and plates.



From post 416 through 479, I have some pictures and explanation of what I found and did. Mine is a 305 but your 250 may very well be exactly the same.
I did go further than the stock set up and utilized some friction discs with a larger friction area, as well as adding another steel to make 6 pairs, instead of the stock 5 pairs.
Pay attention to any spacers behind the outer basket that may need removed if changing to the later style which has a longer hollow portion against the main shaft bearing. You want your primary chain to be in alignment with it's crank gear first, then figure out the clutch disc possibilities. The fit and location of the circlip will be affected.
The thin wire plate separators are to help with clutch drag but are not essential. I have removed mine and it is no problem.
 
One nice thing about these bikes is you can install the cable and clutch lifter mechanism with it's rod on the right side and observe the plates being compressed or released on the left side with it's cover off.
 
We had contact before about my cb450 BB restoration project. The Netherlands is small, almost everything is nearby :).
You got me in the right way. I'll might contact him again. Met him on an other forum, didn't know he was here as well.
 
We had contact before about my cb450 BB restoration project. The Netherlands is small, almost everything is nearby :).
You got me in the right way. I'll might contact him again. Met him on an other forum, didn't know he was here as well.
Look around at other threads here, Jensen is usually involved in DOHC 450 threads like the Black Bomber.
 
Spoke with Bill Silver by the way; he told me I drove with a clutch center for a later model with the wires on it. It is meant for 5 plates, I drove it with 4 (early model) thick plates (5mm), which explains the slipping. The clutch housing stayed pretty much the same, which makes it interchangeable. I'm now going for the 5 plate (CB and CL) setup. Found a 40 dollar 2nd hand CB72/77 clutch on ebay for the other spacer-plates (Ax1 + Bx4).

It is nice to see all this time made available by you to help me out here. Most appreciated!
@ballbearian I enjoyed your thread about your build up. Beautiful work.

I'll keep you posted.

Gr
 
So, back again. My 2nd hand cb72 clutch arrived. Got new friction plates, but gonna use the steel (b-)plates. Question: how do i revise them? Clean them obviously, but then?
 
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