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1980 Honda Z50r
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Discussion Starter #1
I just installed the TB HD auto clutch kit p/n TBW0971 and ALSO had issues with it grabbing RIGHT above idle. Everything else about it worked right. It disengaged as long as you had the shift lever depressed, it shifted good when moving, it did not slip when kick starting, etc. It just engaged WAY TOO EARLY. I called/ emailed TBolt, but they are not responding due to the COVID-19 thing.

HERE IS WHAT I LEARNED / FIGURED OUT :

1: This is a well built unit, but the parts are not the same as what my stock 1980 z50r auto-clutch came with. This clutch uses stamped metal weights instead of rollers.

2: For some reason, this clutch is designed to work with engines that IDLE way lower than what a 50-70cc motor likes. Because cause of this, it engages JUST above idle.

3: There is a total of 28 weights that centrifugally sling out to engage the clutch as RPM increases above idle. 7 weights in 4 clusters.

4: You can remove 2-3 weights from each cluster of 7 and just add tiny washes to take up the space. You will basically change at what rpm the clutch starts engaging. I believe in “CAR TERMS” they call this “STALL SPEED” rpm (torque converter stall speed) .

5: I removed 1 weight from each cluster of 7 and added tiny washers to take up the space of the removed weights, the difference was noticeable. So I then took it apart AGAIN and removed another 2 weights from each cluster of 7, and added washers to take up the gap. I now have 4 weights per cluster engaging the clutch and 3 washers “doing nothing”. The clutch grabs good and strong, It does not drag, it engages like the stock auto-clutch did.

6: You can also simply just grind off the “heel” that engages the clutch as RPM increases. But if you do that, you cant go back.

Trial and error......

Good luck
 

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Great info to modify your clutch! Haven't had the trouble you describe with their clutches, but have noticed the steel plates are sometimes a little tight where the dogs fit into the clutch basket. Interestingly, the stock clutches use a hollow dowels for the weights, but the ATC70 clutches use solid dowels for better hook-up. One of my buddies uses solid dowels on the clutch of his wheelie bike, and it will pop the wheel up super easy.
 

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1980 Honda Z50r
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Discussion Starter #3
Yes, my stock clutch also had the rollers in it.
I hope this helps people. It seems to be a common problem people have after doing the TB HD clutch install. They put up posts about the same situation and OVER and OVER the responses are:

1: Did you adjust it correctly?
2: Your Idle must be too high....
3: It needs to break-in....
4: That’s how it is, live with it.....I HATE HEARING THAT ONE

Well.....this was the FIX for me.

I will keep watching this thread and post updates regarding if this mod affects the durability/reliability of the clutch. I am optimistic.

Trial and error....

Good luck, keep the little 50 ALIVE
 

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1980 Honda Z50r
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Discussion Starter #4
Update....this clutch is doing great after I modified the weights. Grabs good and strong. I just have to give the engine time to rev down between gear shifts, otherwise - WHEELIE.
 

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1980 Honda Z50r
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Discussion Starter #5
GPS’d 50 miles on it since the install.
Working good so far. If anyone has questions, feel free to ask.
 

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1980 Honda Z50r
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Discussion Starter #7
Do you happen to recall what size washers you used to replace the weights?
They were just small-area washers with 1/8 inch holes in them. I actually went back in and removed them, and reinstalled the original weights after I ground off the “heel” on them.

If you want to use washers, just make sure they are steel and thick enough to take up the slop from the weights you remove. Also make sure they dont not protrude above the original weights.
 

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Thanks for the pics, greatly appreciated.

Let me ask you this: why did you go to Plan B and grind the heels? Too much lateral sideplay with the washers in place?
 

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1980 Honda Z50r
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Discussion Starter #10
Well, I actually went back into the clutch because I decided that I wanted to removed one more weight out of each cluster so that the engagement rpm would be a little higher. At that point I realized that I didn’t want all these thin steel washers spinning at 7000-8000 rpm waiting to possibly take a trip thru my engine.
Also, at that point the “trial and error” part of this project was finished. So, I figured its best to put the 16 original thickness pieces back into the clutch.
So, once again....the clutch originally came with 28 weights ( 7 weights x 4 clusters ).
In total, I eliminated a total of 4 weights (16 total) centrifugal effect from each cluster.

I’m just really puzzled at why I had to modify this clutch so much when you consider it comes from TBolt, and they are really well versed in these little bikes. I have reached out to them via email tech support regarding this matter, but since COVID-19, they are not responding at all.

I see that this is a common problem in the Honda 50 community...its just strange. The only thing I can think of is that maybe they are getting these clutches from a different supplier and/or they are being mislabeled.

Any comments/questions are welcome.
 

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1980 Honda Z50r
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Discussion Starter #11
If anybody wants to do this mod to their TB HD auto-clutch, I can walk them thru it. Or they can send me their unit and I will do it for a small fee:)

I wish I took pics along the way, that’s why I am making the offer.
 

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I am going through this same issue with an 05 crf50. Came to me with a completely smoked stock auto clutch and a host of other issues. I had never used a TB HD auto clutch in a build before but this one seemed like a good candidate. Put it all together and the bike will idle all day in neutral, but stalls out in gear. It feels like the clutch is dragging just enough to not fully release at idle. If I turn the idle up enough to keep it from stalling the bike wants to move on its own. I will probably try this method with the weight delete... But I'm not really happy about it. I'm doing this on a customers bike and losing my @$$ in labor. I hope TB Parts sees this thread and gets this sorted out.
 

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Well I did the mod as described above and... It still acts the same way. I'm going to rummage through my old box of parts and see if I have a Honda auto clutch in good shape somewhere at this point. Pretty irked.
 

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Well I did the mod as described above and... It still acts the same way. I'm going to rummage through my old box of parts and see if I have a Honda auto clutch in good shape somewhere at this point. Pretty irked.
A friend of mine who builds a lot of engines has told me he has had to sand the friction discs with a DA sander, as they are thicker than stock. Also, don't know if you saw the post about the hollow dowel weights on the OEM clutch, but it might be worth a try if you have the stock clutch still. I have used their heavy duty clutch without too much problem other than the fact that it engages a little too firmly unless you drop the RPM's between shifts. Not a problem if you are racing or hammering on your bike, but a little strong for just a neighborhood cruiser.
 

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Swapped the TB clutch out for the original clutch with different used plates in good shape and it just plain works. Hate to say it but thumbs down for this TB product.
 
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