B40 and B44 motor in OIF chassis

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craigacc
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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.

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kommando
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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.

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gunnag
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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
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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?

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