B40 and B44 motor in OIF chassis

Here you can talk about all kind of TECH for the B50 B44 B25 And Other BSA unit Singles

Moderator: minetymenace

Post Reply
craigacc
>10
>10
Posts: 12
Joined: Sun Jun 02, 2019 9:22 am
Has thanked: 0
Been thanked: 0
Flag: Great Britain

B40 and B44 motor in OIF chassis

Post by craigacc » Sun Jun 23, 2019 9:51 am

Hi all,

I'm planning to fit an ex war department B40 motor into an OIF B25/T25T chassis. I also plan to use a B44 motor in the same chassis at a later stage.

Any tips, warnings or things to take into account when doing this? I'm already aware of the need for rear engine mount spacing, as the pre OIF engines have a much narrower rear mounting lug.

All thoughts gratefully welcomed.

The bike will be used for long distance reliability trials (over night orienteering on small roads, with several very steep off road hill climbs thrown in). Advice re appropriate sprocket sizes would be welcome.

Craig
Cornwall, UK.
Triumph T25T 1971.
Ongoing B40 and B44 engine projects. Plus several other British Motorcycles
Cornwall, UK.

User avatar
kommando
>1400
>1400
Posts: 1817
Joined: Mon May 24, 2004 8:41 pm
Location: Scotland
Has thanked: 1 time
Been thanked: 25 times
Flag: Ireland

Re: B40 and B44 motor in OIF chassis

Post by kommando » Sun Jun 23, 2019 12:00 pm

The B40 gearbox sprocket will need looking at if its pre the circlip retaining the gearbox main bearing and the sprocket datum point moved by 40 thou. Both B40 and B44 will need work on the oil manifold as it will foul on the frame tube under the engine, or relocate the frame tube. Exhausts and silencer mounts will also need work.

User avatar
gunnag
>740
>740
Posts: 749
Joined: Fri Oct 01, 2004 9:32 am
Location: farnham surrey
Has thanked: 0
Been thanked: 0
Flag: Great Britain

Re: B40 and B44 motor in OIF chassis

Post by gunnag » Wed Jul 03, 2019 9:36 pm

I once fitted a WD B40 engine into an OIF B25 frame, my thoughts are as follows:-
- the rear engine mount needs spacers fitting as already mentioned
- the frame cross member will foul the oil manifold as Kommando mentions, easiest solution is to cut out the cross member, it doesn't affect the frame integrity or strength
- WD B40 engines used a close ratio gearbox which is great for off road use but a pain on the highway. Sell the close ratio gears for profit, these are highly prized by trials riders and fit standard B25 gearbox parts.
- consider fitting a 28 tooth engine sprocket to reduce engine revs and convert the clutch to 5 plates using sureflex plates
- buy the Rupert Ratio unit singles manual which has some great advise on engine upgrades
- use electronic ignition and ensure the alternator is in top condition
- fit a new amal premier carb for reliability
- use an oil filter in the return line

Just my tuppence worth.

mlb50
>180
>180
Posts: 193
Joined: Wed Jun 25, 2014 4:25 am
Location: Perth, West Australia
Has thanked: 0
Been thanked: 2 times
Flag: Australia

Re: B40 and B44 motor in OIF chassis

Post by mlb50 » Sun Jul 07, 2019 2:54 am

Measure the height of the motor from bottom mounting hole to top of the rocker box and determine how much clearance you get between the underside of the top frame tube to the top of the head.
Then see if that clearance will permit removal of the rocker box and the head in-situ. Otherwise you have to take the whole lump out to do top end work. Not a great prospect for sporting usage in the field.

A common mod for B50's is to remove the roocker box head studs and helicoil them to allow bolts to be used instead. On a good day you can have the head off in 30 minutes.
B50 @ 10:1 - what's a leg between friends?

craigacc
>10
>10
Posts: 12
Joined: Sun Jun 02, 2019 9:22 am
Has thanked: 0
Been thanked: 0
Flag: Great Britain

Re: B40 and B44 motor in OIF chassis

Post by craigacc » Sat Jul 27, 2019 10:24 am

Thanks for the replies re this. All concur with what I've discovered so far and I appreciate the input.
Rear engine mounts need spacers as mentioned, I'm having these made at the mo. Plus new rear engine plates, as the much wider rear engine mount casting on the OIF motors has the bolt hole placed further rearward than the one on the B40 lump.
Regarding removing the frame tube that fouls the oil manifold, given the proximity of the bottom engine mount, which also provides strength to that part of the frame, I agree that frame strength would not be compromised. But the issues that arise from removing it could be crushing of the lower frame rails when bolting on the footrests, plus twisting of these rails when standing on the footrests while riding off road. Do folk have any opinions here?
As an alternative, I'm thinking of modifying an oil manifold, so the inlet/return pipes clear the frame tube. Has anyone done this?
Regarding the height of the B40 motor, there seems to be clearance, though I've not fitted the top end yet. Correct me if I'm wrong, but isn't the B50 motor taller than the B40/B25 lump anyway?
Any comments will be welcomed.
Currently, the bike is being fitted with the original T25T motor refurbished. This to get it registered with an age related plate - the engine and frame numbers match. (The bike is a USA import on NOVA only) I'll get some enjoyment from the standard bike before fitting the B40 motor for some trials events next year.
Triumph T25T 1971.
Ongoing B40 and B44 engine projects. Plus several other British Motorcycles
Cornwall, UK.

User avatar
kommando
>1400
>1400
Posts: 1817
Joined: Mon May 24, 2004 8:41 pm
Location: Scotland
Has thanked: 1 time
Been thanked: 25 times
Flag: Ireland

Re: B40 and B44 motor in OIF chassis

Post by kommando » Sat Jul 27, 2019 11:37 am

B44 and B50 are long stroke and taller than the other short stroke motors including B40.

User avatar
JB
>440
>440
Posts: 451
Joined: Tue Jun 15, 2004 8:32 am
Location: Devon, England
Has thanked: 3 times
Been thanked: 5 times
Flag: England

Re: B40 and B44 motor in OIF chassis

Post by JB » Tue Jul 30, 2019 1:00 pm

craigacc wrote:
Sat Jul 27, 2019 10:24 am
But the issues that arise from removing it could be crushing of the lower frame rails when bolting on the footrests, plus twisting of these rails when standing on the footrests while riding off road. Do folk have any opinions here?
The OIF footrest bolt is a complete pita,it's a known weakness, especially if you do a lot of feet up riding as the 3/8 "bolt" is simply not up to the job, it is why the footrest locating slots wear on the frame and the footrest. My advise would be to tap the frame 7/16 UNF, drill out the footrest hangers and fit a 7/16 UNF bolt to each footrest; a far better setup and it also cures your problem about removing the frame tube for the oil lines :ban

User avatar
SteveS
>460
>460
Posts: 469
Joined: Mon Jul 10, 2006 8:28 pm
Location: Nuneaton, Warks. U.K.
Has thanked: 0
Been thanked: 4 times
Flag: England

Re: B40 and B44 motor in OIF chassis

Post by SteveS » Tue Jul 30, 2019 7:20 pm

.
I didn't go as far as tapping out to 7/16", I just used a 3/8" bolt, one for each footrest, but I'm only a little fella :smile: Also welded heavy duty washers to the cut ends of the tube
.
Underside B50 OIF frame with B44 round barrel motor.JPG
Underside B50 OIF frame with B44 round barrel motor
Steve Sewell

Post Reply