B25T Rear Chain Oiler – Cap Off?

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B25T Rear Chain Oiler – Cap Off?

Post by kgubert » Wed Aug 28, 2019 3:45 am

We've got the project '71 B25T is decent running condition. After the first ride around the field we discovered primary chain oil leaking out of where the rear chain oiler assembly was supposed to be. Of course, the assembly is missing, leaving only the hole. It'll just be a trail bike for us and it's using a gold D.I.D. 520 MX chain. We have no need for and don't really want the chain oiler. It would be nice to just cap this off, but I was hesitant because wouldn't that leave no place to vent the primary chain case? I've read of the hole being capped off on B50s, but don't they have other means of venting the B25s do not? I know it gets pretty warm in there, so it seems leaving it with no ventilation would be a very bad idea.
Can this be capped off? What about ventilation? What''s the recommend solution?
Thanks in advance for any assistance.

In other news, my Dad wants to create a list of everything we've done to the bike, been through since acquiring it about a year ago, and of course pictures and post it. We're working on that.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by BSA_WM20 » Wed Aug 28, 2019 8:13 am

Drill a tiny hole in the chain inspection cap
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Re: B25T Rear Chain Oiler – Cap Off?

Post by kommando » Wed Aug 28, 2019 9:57 am

Block it off and no need for a vent if your crankcase seal is good.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by minetymenace » Wed Aug 28, 2019 10:16 am

My B25 has the oiler hole blocked with a short bolt, no vents in the caps and no oil leaks. I guess there is a vent path through the bush into the gearbox, but there is a large volume of air in the primary drive, it would only take a small hole somewhere to equalise the pressure.
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Re: B25T Rear Chain Oiler – Cap Off?

Post by BSA_WM20 » Wed Aug 28, 2019 10:19 am

One of the bikes had a vent via an inspection cap.
I have some kicking around with a hole in them.
All in exactly the same place.
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Re: B25T Rear Chain Oiler – Cap Off?

Post by kommando » Wed Aug 28, 2019 1:07 pm

From what I have seen over the years only the Triumph 250 left the factory with a vented cap and these leak a small but annoying amount of oil. I have blocked off every chain oiler as they are impossible to tune to get the right amount of oil on the chain, a good aerosol of chain lube is easier and less messy.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by midgie » Wed Aug 28, 2019 3:45 pm

None of the 250 or 500cc oil in frame singles ever left the factory with a chain oiler, it was blocked off with a fibre washer and a 1/4" unc x 5/8" setscrew. The bsa badged oif 250cc machines also had qty1 screwed breather plug fitted as std. The b50 of course didn't need it with the breather already on the top of the chaincase.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by kgubert » Thu Aug 29, 2019 12:37 am

You guys really are great. Thank you so much!
Yes, I took a closer look at the parts book today and I see they actually list a part number for the chain oiler blanking bolt and the fiber washer (I've attached a snapshot of this). Yep, it does look like a 1/4-20 x 5/8 in. bolt and a 1/4 in. fiber washer. I found both in stock locally. I think we'll use a button head allen bolt.
I also looked at the parts list, and sure enough there is a 70-9800 p/n listed for a breather cap! I think we'll probably try and duplicate this by drilling a tiny hole in one of the standard aftermarket caps we have.
Thank you again very much!
Screen Shot 08-28-19 at 07.26 PM.PNG

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Re: B25T Rear Chain Oiler – Cap Off?

Post by minetymenace » Thu Aug 29, 2019 9:17 am

I seem to recall that the brand T covers had the hole and a piece of gauze behind held in with a perforated spring disc sort of thing...
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Re: B25T Rear Chain Oiler – Cap Off?

Post by kgubert » Fri Aug 30, 2019 3:50 pm

minetymenace wrote:
Thu Aug 29, 2019 9:17 am
I seem to recall that the brand T covers had the hole and a piece of gauze behind held in with a perforated spring disc sort of thing...
I was searching around and I found this picture from bsaunitsingles. It sounds like that's what you're referencing.
70-9800.JPG
70-9800.JPG (47.74 KiB) Viewed 652 times
Rather than using up NOS parts, drilling a small hole, then gluing a small piece of foam behind to prevent anything from splashing out seems like it'll work. I'll post pictures of what we come up with.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by minetymenace » Fri Aug 30, 2019 4:11 pm

Yarp, that's them there. Wouldn't bother with the hole....might save a bit of weight though :roll:
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Re: B25T Rear Chain Oiler – Cap Off?

Post by tridentperu » Fri Aug 30, 2019 6:42 pm

When you blank off the hole just make sure the screw doesn't protrude too far and foul the outer chaincase gasket surface and thus prevent it sitting properly - it will leak like hell if it doesn't! Loctite the bolt in place and forget it.

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Re: B25T Rear Chain Oiler – Cap Off?

Post by Jeff K » Sat Aug 31, 2019 4:10 pm

kommando wrote:
Wed Aug 28, 2019 1:07 pm
From what I have seen over the years only the Triumph 250 left the factory with a vented cap and these leak a small but annoying amount of oil. I have blocked off every chain oiler as they are impossible to tune to get the right amount of oil on the chain, a good aerosol of chain lube is easier and less messy.
I bought a new Norton 850MKIII in 1976. They finally removed the oiler and included a small spray can of chain lube in the tool kit from the factory. Sad, BSA got it right in 1971 and so did Norton in 1976 and it was their last year for both.
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Re: B25T Rear Chain Oiler – Cap Off?

Post by kgubert » Wed Sep 04, 2019 6:31 pm

Alright guys, I wanted to give an update. Thanks for the note about making sure the blanking bolt doesn't protrude into the gasket/cover. As can be seen here, the 5/8 in. screw is absolutely perfect.
IMG_5529.jpg
From the other side, I think a button head allen screw fits like a glove for this application. Because the surface where the fiber washer rests against is recessed into the casting, I think a regular hex head bolt might be difficult, especially in the somewhat tight area.
IMG_5530.jpg
Finally, we did make one of the caps a breather cap. It's nothing more than a 1/16 in. hole drilled in the center and a [somewhat] round cut piece of foam glued in/on the backside (only glued around the sides/perimeter). We were discussing where to install the breather cap. Initially it seems the higher hole would be better, but I think the hole over the center of the clutch might be better because at that point all oil is being flung away from the breather. The upper one is right beside the chain.
IMG_5531.jpg
IMG_5532.jpg

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Re: B25T Rear Chain Oiler – Cap Off?

Post by minetymenace » Wed Sep 04, 2019 8:49 pm

If the foam survives, would you let us know what sort of foam it was please? (Whenever I stick foam anywhere near the engine, it mysteriously disappears :shock: )
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Re: B25T Rear Chain Oiler – Cap Off?

Post by BSA_WM20 » Sat Sep 07, 2019 11:33 am

Air filter foam should be fine provided it does not do a swan dive into the primary.
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