Finally bought one: 1971 B25T

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Finally bought one: 1971 B25T

Post by kgubert » Sun Aug 12, 2018 8:34 pm

As indicated in the title, my Dad and I finally found one that's pretty much perfect for what he's looking for (project, a couple mild trail rides a year).
It's originally a 1971 B25T, actually matching numbers. Definitely Betor forks, and possibly Betor shocks as well. I can't positively ID them, but that's my best guess so far. Does anyone recognize them? It also has 18/21 in. Rickman rims and hubs. Just identified the carburetor yesterday as a Mukuni MIC 28 mm unit (I'm likely going to start another thread to discuss that). It has a Preston Petty MX rear fender and an unidentified fiberglass front fender.
The bike needs a considerable amount of things to be ready to ride. It pretty excessively leaks oil, so a gasket kit is on its way. The carburetor was kind of held on with a piece of tube and zip ties. I suspect the bike was recently stuck back together just to sell because a lot of fasteners are just not tightened (including front axle, swing arm pivot, footpegs... you get the idea).
Anyway, we got it started. It doesn't smoke at all, but during my short trip around the field it appeared to be very down in power. It quit on the way back due to the carb falling off the rubber tube holding it to the jug :lol: . Also, right now it has a 16/50 tooth gear setup. Much, much too much for offroad. We're going to order a 13 tooth front sprocket and go from there.
So, that's where I'm at so far. Neither of us has a ton of time for a project, but we're both really enjoying working on it, planning, discovering, and learning. It's really great to have a project together. I'm really glad I found this site/forum and I hope posting about B25 stuff isn't frowned on too much (it doesn't appear to be based on other posts).

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Re: Finally bought one: 1971 B25T

Post by Canberra » Mon Aug 13, 2018 12:43 pm

Hi Kgubert, Looks like a good start. Is the front wheel 20 or 21 Inch?

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Re: Finally bought one: 1971 B25T

Post by kgubert » Tue Aug 14, 2018 9:46 pm

Thankfully, they are 18 in. rear and 21 in. front.

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Re: Finally bought one: 1971 B25T

Post by kgubert » Mon Sep 10, 2018 6:02 pm

Since it's been a while, it's definitely time for an update. We had the engine torn mostly down, save for primary drive and splitting the cases (didn't have the special tool for unbolting the clutch springs). As soon as we removed the rocker box inspection caps I knew we were in for a long haul. The exhaust spring/retainer had worn significantly into the rocker box. It would definitely be boring if I went through every little wrong we found, but to summarize this is a list of the current parts being replaced:
  • 1. Replacement head - the original may be savable, but we found one in much better shape literally 10 minutes away
    2. Replacement rocker box - inspection cap threads were not in great shape
    3. New piston and sleeve - original sleeve had already been bored once
    4. New connecting rod - original small end did not look good
    5. Haven't inspected the big end yet, but I'd be surprised if it doesn't need to be cut
Of course, there are a bunch of small parts (fasteners, crank bearings, etc.) in addition to that list.

I actually had a question, and maybe I should start another thread for it(?)... Right now the bike had 16/50 tooth sprockets. Being that it is strictly a trail bike and the primary rider is not and has no desire to be fast, I've purchased a couple gearbox sprockets: a 13T and a 12T. I'd like something like a 25:1 first gear (just comparing to certain red 250 I have).
Of course the primary drive is 23/52T and first gear 2.65:1. My original thought was use the 12/50T combo, but I thought it'd be better to go with a 13/54T combo. Both would be about a 25:1 first gear.
Anyway, I was looking at the currently installed 16T gearbox sprocket. Gosh, it looks like even the 16T piece doesn't leave a lot of room between the inside of the chain and the gearbox. Has anyone installed a 13T or a 12T sprocket on one of these? I'm afraid once installed the chain will contact the gearbox...

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Re: Finally bought one: 1971 B25T

Post by minetymenace » Mon Sep 10, 2018 9:44 pm

Couple of pages that might be of interest:
Ratio Page
B25 Speed Calculator

You should be able to get a 17T gearbox sprocket on there without trouble
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Re: Finally bought one: 1971 B25T

Post by Ian Hingley » Tue Sep 11, 2018 9:22 pm

Special tool for unbolting the clutch springs?? It's called a screwdriver...
66 BSA Victor Enduro, 72 BSA Lightning, 62 BSA B40 trials, 89 H*nda Bros 650, 96 Aprilia Moto 6.5, 2000 Aprilia Moto 6.5

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Re: Finally bought one: 1971 B25T

Post by kgubert » Wed Sep 12, 2018 3:38 am

minetymenace wrote:Couple of pages that might be of interest:
Ratio Page
B25 Speed Calculator

You should be able to get a 17T gearbox sprocket on there without trouble
Thanks, that's a handy table. So, according to that table, the gearbox will accept down to an 11T sprocket? If so, I should be fine with a 12T or 13T it would seem... I was just worried about the chain getting too close to the gearbox in the inside diameter. By the way, when I was mentioning a 25:1 first gear that was simply [primary ratio]x[first gear ratio]x[sprocket ratio]. So for a 13/54T sprocket combo, (2.261)x(2.65)x(4.154)=24.89.
Ian Hingley wrote:Special tool for unbolting the clutch springs?? It's called a screwdriver...
Yes, you're right. I know it's only a flat head screw driver with a slot in the middle, but I didn't feel like sacrificing one of my big flat heads.

Would I redeem myself if I mentioned I spent the time instead welding up and grinding the massive wear spot on the kickstart spindle where the kickstart cotter contacts it? :mrgreen:

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Re: Finally bought one: 1971 B25T

Post by koncretekid » Sat Sep 22, 2018 2:25 pm

"Ian Hingley wrote:
Special tool for unbolting the clutch springs?? It's called a screwdriver..."

I found that a 1/2" socket, can't remember if 6 or 12 point, captures the screw and actually turns it. It's a great help to get them started, especially with stronger springs and 6 disc clutch.

I now buy some nice stainless steel hex head clutch screws from "bsanut" on ebay. You can really lean on them to get them started.

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Re: Finally bought one: 1971 B25T

Post by Ian Hingley » Sat Sep 22, 2018 10:23 pm

koncretekid wrote:I now buy some nice stainless steel hex head clutch screws from "bsanut" on ebay. You can really lean on them to get them started.
Hi Tom.

Was doing this job only today. Absolutely hate it!

So I'm definitely gonna try these hex head versions. Thanks for the tip!

Past couple of times I've taken the little hex level screw from the gearbox drain plug and screwed that into the slotted clutch screws to help get them started. Seems to work.

Cheers

Ian
66 BSA Victor Enduro, 72 BSA Lightning, 62 BSA B40 trials, 89 H*nda Bros 650, 96 Aprilia Moto 6.5, 2000 Aprilia Moto 6.5

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Re: Finally bought one: 1971 B25T

Post by minetymenace » Sat Sep 22, 2018 11:42 pm

Clutch nuts eBay item number:382395213049
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Re: Finally bought one: 1971 B25T

Post by koncretekid » Sun Sep 23, 2018 3:24 am

Yes, those are the ones. Springs seem to be good as well although I have not actually checked their strength.
Tom
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Re: Finally bought one: 1971 B25T

Post by kgubert » Wed Oct 03, 2018 2:53 am

Time for an update, I think. And of course, more questions.
The engine is at a shop in London, ON, Canada right now getting machine work done and assembly. My Dad and I went back and fourth about having them do the assembly or just the machine work and us do the assembly. Unfortunately being very short of time lately, we elected to have them do the assembly. Should have it back in another couple weeks or so.
First question is about an oil filter. As delivered, this bike didn't have the original oil filter. It still had the screen above the oil sump (mostly blocked with gasket maker and other garbage), but no external filter. What's the best external filter to use? Of course one option is the original style, like this one:
BSA 250 Singles B25 Oil filter assy complete FB994 (82-8903)
I've also read of some using an automotive style filter, possibly like this one:
Oil Filter Kits
Or are there better options?
My other question had to do with the triple clamp and the travel stops, but I think that one is better held for now. I'm going to take a video of what the problem is with the Betor triple clamps (I think) and the original travel stops and interference.
As always, thanks everyone!

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Re: Finally bought one: 1971 B25T

Post by minetymenace » Wed Oct 03, 2018 7:57 am

The oil filter was an option (on most bikes, standard on <12fs FS). The original oil filter is OK if you are going for originality, but a modern spin-on filter is more convenient and easily available. Traditionally they are fitted in the return side of the oil system, and it is arguable whether this is the best place for it, but without substantial modifications there is little choice. Is it worth it? I think some oil filtering is better than none, but BSA did think about clean oil and there are a number of "filters" in the system already. They are:
1. The sludge trap in the crank. A centrifugal particle collector, very efficient (worth checking that your engine builder cleans this out). On a B25, the engine will probably need stripping before this is full (being second cousins to hand grenades :shock: )
2. A screen at the bottom of the tank (frame), pretty useless, it stops big lumps of detritus and pebbles which might have fallen into the oil tank from reaching the engine.
3. The "settlement tank" (rear part of the frame), an area of low flow which allows heavy lumps to settle out. There is a service sheet that tells you, when changing the oil, to drain the rear of the frame. On an old bike, it likely that previous owners neglected this instruction, and you may find a lot of crud here. I used a circulation pump to clean mine out with various solvents earlier this year, and was surprised how little muck I manage to extract from here.
4. The screen at the bottom of the engine. This stops the largest lumps of metal reaching the oil pump when the engine goes bang, thus saving the oil pump when the barrel, head and cases are wrecked when the con-rod breaks! It also acts as a separator, allowing oil (rather than mist) to collect in the sump so that the oil pump can pump oil rather than air back to the tank.
There are many topics on oiling, please try the search function and look in the Tech Pages on the main site. The key to oiling on the B25 is to keep the pressure up on the big end, and change the oil regularly. Tightly toleranced parts, well put together are key to a reliable B25. An oil filter helps, and is a "nice to have" but is not something to loose sleep over.
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Re: Finally bought one: 1971 B25T

Post by tridentperu » Sat Oct 06, 2018 11:57 am

Good luck with your project, it sounds as though you are learning about the technicalities of these little BSA engines fast!

re external oil filter, it's prob the best mod you can do to ensure continuing engine health. I use a small filter from Dave Madigan in California that is just great. It is small, tucks away up behind the gearbox, and the filters are cheap Ho~~a ones.

pic attached hopefully
PB080009.JPG
Enjoy

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Re: Finally bought one: 1971 B25T

Post by kgubert » Mon Oct 08, 2018 6:02 pm

Thank you both for all the information! Yes, learning the technicalities of these things is a lot to learn, but we are having fun learning everything. I have been scrolling through the Tech pages. Yes, a lot of good information there.
That little filter housing really looks clean! Even better if it uses a commonly available element. I searched for his name, but I didn't come up with anything. I assume he doesn't have a site, direct contact only?
Thanks again!

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Re: Finally bought one: 1971 B25T

Post by koncretekid » Tue Oct 09, 2018 4:50 am

David Madigan

MagnoUnderscoreGrailAtYahooDotCom Edit by MM..Coded the email address in an attempt to reduce spam

Contact Dave and he will email you a price list.
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