Thought I would bring this question over here from my build thread for a bit more coverage.

Basically have myself two x 22G1921, 3/4'' 4 Synchro Flywheel Housing cases which I need to choose between the two for my engine build.
Only difference from what I can see is that the left one is Non Vented (BIRMAL stamping), and the right one is a Vented unit (DIEKAST stamped)

Both are in good condition and ready to roll after a bit of clean-up!
So, what's the difference, what engine were they fitted to? Cant imagine a 998/1098 needing the extra venting, maybe they do? 1275 perhaps?
Any advantages/disadvantages using one over the other.

Anyway, which one should I use for a 998 standard engine rebuild?
Any light you can shed would be awesome.

Thanks for looking,
Cheers

The vented one would be off a non-S 1275, probably.
You can cover that hole up if you want, I use a cover plate off a Mini steering rack. Slot the screw holes a little and it fits good.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I have a 77 with a 998, twin carbs and extractors, electronic 45D. The non vented housing is standard fitment, and hasn't proved to be a problem using it as a daily driver. It travels on the highway and the city without problems. The clutch is three years old and has no problems.

Hope this helps.

Mark.

Thanks fellas, I'll conjure something up to cover that hole then if no real advantage having it there.

Cheers.

if Matt Read chimes in, he'll explain that the transfer housing needs to match the gearbox case so that the idler gear and outrigger bearings are aligned properly

The best one to use is the one that came from the factory with the gearbox casing, but it's probably too late for that

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did I tell you that I won a trophy?

No, not yet. The Non Vented housing in this pic is the one from the gearbox I'm rebuilding. But did intend to use the other. Interesting.

Wouldnt mind some other feedback if this is the case (case, gearbox ahh you know what i mean)

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Soooo they line bored the the transfer case and gearbox case???? Never heard that before....

Cheers, Ian

Yeah I've heard of it, as a machinist, I'd like to see how they did it though! it's a blind hole, on the outside.
I reckon they had jigs, and they were interchangeable when built, but not 10 years later if you tried to mix fit older and recent ones.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I don't believe this to be the case either.
Every Gearbox case was sold as a spare part with its matching Diff housing.
It was not sold with the clutch housing bolted on as well.
So one would thing that they where not machined as one unit.
It really isn't that hard to drill and bore a series of holes in a housing like that and get them in exactly the right place, keeping in mind that it has 2 dowel pins to locate it correctly on the gearbox and one hole has to line up with the primary gear, which is part of the engine.
Just my thoughts and logic, could be wrong
Dave

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"Every Gearbox case was sold as a spare part with its matching Diff housing."

very good point Dave. None of my NOS gearbox cases have the clutch housing supplied but do have diff housings.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.