B25T Gearbox Clicking – What Sound is This?

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B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Sun May 17, 2020 5:08 pm

If a picture is worth one thousand words, what is a video worth then?
BSA B25T Gearbox Clicking
Of course I'm not talking about the sound of the chain, I mean the much lower frequency click/clunk. The video was taken with the bike on a stand. It makes the sound spinning the wheel forward or backwards. It's definitely coming from the engine/gearbox end, not the wheel/brake. I noticed it the other day when I was just pushing it around the barn. We haven't drained the gearbox oil, but I think we will later today.
Also, my Dad is reporting it has been popping out of 4th gear. He hasn't reported problems with any of the other gears, but I haven't ridden it in some time (it's his bike, but I'm the one who knows how to use the forum and I'm his mechanic :mrgreen:). I don't know if the popping sound and the 4th gear thing are related, but it's ironic he reports the 4th gear thing and the next time I push the bike around (in neutral of course) I hear this. Hmmm.
So, anyone want to take a stab? Ideas? Thank you!

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Re: B25T Gearbox Clicking – What Sound is This?

Post by minetymenace » Sun May 17, 2020 7:34 pm

Video runs a bit fast, maybe you could say how many clicks you get each time the shaft rotates. Does it happen with the rear wheel still and the gearbox turned with the kick start?
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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Mon May 18, 2020 3:53 am

Alright, since it's difficult to actually see how many turns the countershaft sprocket turns, here's what I did:
Turned the rear wheel five times. Heard 31 clicks. The bike uses 14/54 tooth sprockets, so for every one rear sprocket turn the countershaft sprocket turns 3.857 times. Therefore, the countershaft sprocket turned 19.286 times – which still equates 31 clicks. Therefore, it's right about 0.622 countershaft sprocket turns per click, or the inverse, 1.6 clicks per countershaft revolution.
We did drain out the gearbox oil. No big chunks. There was some shiny stuff.
IMG_8319.JPG
I don't know about these bikes, any other gearbox oil from bikes I'm used to seeing shiny stuff. I didn't check the noise with the wheel still and turning the gearbox with the kick starter. Will check that tomorrow.

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kommando » Mon May 18, 2020 10:03 am

You are going to have to open the gearbox and inspect all the parts, I would be looking first for missing teeth. Even in neutral the gears rotate but transmit no power so my guess is a missing tooth on one of the gears or one side of a gear tooth is eroded.

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Re: B25T Gearbox Clicking – What Sound is This?

Post by koncretekid » Mon May 18, 2020 2:15 pm

Layshaft pinion gear (the one that's always engaged with the sleeve gear) is the gear that wears the most. Ratio is 22/14, or 1.57. Sounds pretty close to 1.6.
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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Mon May 18, 2020 3:01 pm

koncretekid wrote:
Mon May 18, 2020 2:15 pm
Layshaft pinion gear (the one that's always engaged with the sleeve gear) is the gear that wears the most. Ratio is 22/14, or 1.57. Sounds pretty close to 1.6.
Tom
Wow, that does sound HIGHLY suspect. I've attached an annotated screenshot to demonstrate what's being discussed.
Screen Shot 05-18-20 at 09.51 AM.JPG

So, it looks like a look see into the gearbox is pretty inevitable now. It probably wouldn't be wise to continue to operate as is...
I looked through the manual and it looks like the gearbox can be disassembled without removing the entire engine from the frame. Any recommendations for or against doing this disassembly/inspection in frame?

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Re: B25T Gearbox Clicking – What Sound is This?

Post by minetymenace » Mon May 18, 2020 3:19 pm

Remove battery.
Drain gearbox oil.
Put a block of wood/plastic/stuff behind the clutch adjuster cover to hold the clutch in towards the gearbox.
Lie the bike on its LHS
disconnect clutch cable
Remove Exhaust (if it is in the way), gear change lever & kickstart.
Disconnect points cable
Brake the taper on the auto A/R
Remove outer cover
Remove all loose kick start bits
Remove split pin (UK version) or cotter pin (US Version) from cam plate pivot, remove cam plate pivot.
Remove nut on end of mainshaft and rest of kicker bits
Unscrew ALL screws from inner cover (don't forget those little ones at the front at the bottom!)
Pray.
Simply pull off inner cover leaving all gearbox bits in situ.
QED

The mainshaft stays in place, but you should be able to remove the layshaft, Reassemble in reverse order, a bit fiddly, but possible. If you can't get it back together, you may need to remove the clutch and pull the mainshaft, which is easier to do right at the start!!!
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Re: B25T Gearbox Clicking – What Sound is This?

Post by Mr Mike » Mon May 18, 2020 8:33 pm

Been into quite a few gearboxes using the above procedure. I put the bike on my homemade lift so everything is right in front of me. Don't take the engine out. Leave chain on so you can turn gearbox easily after fixing to check for sounds. You'll fiddle a bit getting it all back in but once you get the hang of it, it goes pretty easily.

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Mon May 18, 2020 8:47 pm

Thank you both very much! I was going to ask about lifting the thing up on a stand instead of laying it on its side, but it sounds like that'll work fine.
I'd rather put this off and work on some of my other junk, but my Dad is really chomping at the bit so I'm sure I'll get roped into it very soon. I'll keep this thread updated and report what is found.
Thanks again! You guys are the best!

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Re: B25T Gearbox Clicking – What Sound is This?

Post by koncretekid » Mon May 18, 2020 9:53 pm

If you need parts or help, Ed Valiket is only 2-1/2 hours from you in Howard City. See link at top of the page.
Tom
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Re: B25T Gearbox Clicking – What Sound is This?

Post by Mr Mike » Tue May 19, 2020 2:08 am

Ed V probably knows more about these bikes then all of us put together.

Koncretekid, been to your province three or four times. Always loved it. My mom was from PEI. I always get some cod fish cakes or poached cod when I go up there. Reminds me of my mom. It was regular table fare for me growing up. Hard to find salted cod down here now.

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Tue May 19, 2020 3:23 am

koncretekid wrote:
Mon May 18, 2020 9:53 pm
If you need parts or help, Ed Valiket is only 2-1/2 hours from you in Howard City. See link at top of the page.
Tom
Yes, we are quite familiar with Mr. Ed V! We've had him so some smaller stuff for us and we've bought many parts from him. I've been to his shop once. He's a great guy and has been a huge help to us throughout this project. And yes, he is an immense wealth of knowledge. I'm sure we could have called him on this, but he always has a lot of work to get done (not that he's ever indicated he minded helping us out) so I thought I'd post it here. Plus, I do appreciate keeping a relationship with you gentlemen. :thumb

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Thu May 21, 2020 9:49 pm

We've got the oils drained (gearbox and engine) and Dad removed the outer timing cover the other day. He made the first discovery: The mainshaft nut (and lockwasher and kickstart spring) were sitting in the bottom of the outer timing cover. The treads on the nut are pretty nasty so we'll be getting a new one of those (along with the lockwasher and kickstart spring), but the threads on the mainshaft look fine. But, with the nut temporarily stuck back into its proper position there is still that clicking, so we'll be going all the way it looks like.
IMG_8370.jpg
IMG_8369.jpg

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Sun May 24, 2020 5:11 pm

First, big thanks to minetymenace and Mr Mike! The gearbox came apart exactly as they said it would. Quite easy, actually. It looked like the exhaust wasn't going to interfere, but as the inner cover began to slide off it was apparent it was going to be in the way of the clutch cable boss. The one more piece of information that may help a future reader is removing the cam plate pivot after removing the cotter pin. I'll double check, but I believe I used an 8-32 in screw to thread into the end of the pivot and this gave me something to grab on to and pull it out.
Next, kudos to koncretekid! We've definitely found the problem, and it is exactly like he said. Surly a missing tooth from the layshaft pinion gear. Here are a few pictures:
IMG_8383.jpg
IMG_8385.jpg
IMG_8384.jpg
So, on to repairing and putting it back together. From what I can see, the 22-tooth mainshaft top/4th gear looks fine. No damage. Would it be acceptable to reuse this if no visual damage is seen? In addition to the layshaft, we're definitely going to replace the mainshaft nut, washer, and spring. I think this nut being out of place resulted in the mainshaft being shifted to the left from its correct position was causing the popping out of 4th gear thing.
In other news, as you can see from the overview picture we discovered a very questionable weld repair on the case around the main bearing. This winter we already planned to tear this engine back down to have Ed balance the rotating assembly and fix other miscellaneous stuff (questionable oil leaks, etc.) so we will just swap out the cases then. Already ordered a new pair from bsaunitsingles. Sort of a shame because right now the engine and frame number match.

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Re: B25T Gearbox Clicking – What Sound is This?

Post by kgubert » Sat Aug 15, 2020 4:54 am

Not to resurrect a "thread from the dead," but I wanted to give this one closure.
Per all the wonderful knowledge shared here (and parts from Ed V.), we got her reassembled. Apparently there are better sealants/gasket makers, but I had a tube of Permatex Motoseal that I use on the center cases of bikes... from another country... about 45 years newer... that have one rear shock... point made. Anyway, it seems to be working great. One thing more we did is clean up the Mainshaft Nut and corresponding Mainshaft threads well and use blue Loctite there before tightening. I think my Dad has probably ridden the bike 3-5 ours since we got it back in service. Working perfectly!
Thanks again to all!

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