Can someone please explain to me what straight cut drop gears are and what they do.
Dad tried to explain what they are but he got way to technical and i kinda lost him.
So what do they do?
What are the difference between these and normal straight cut gears?

I want to know as they are going into the mokes 1360 stroker and i want to know what advantages they offer!

Cheers, Steve

Gday

It's as simple as it sounds, the gears are cut straight instead of angled like helical gears. Cheaper to make, not stronger like every one thinks.

New designs tend to be stronger than originals, plus u can get different ratios, bearings, etc

Cheers
jacob

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'72 Clubman Van - 1022cc, 295 head, 731 cam - Daily Driver
'69 Morris 1100 S - Dinged by a bus, in shed under repair
'64 Morris 1100 - Early 1100, long term project

Thanks Jacob

So all the main gears in the box are straight cut?
They are brand new made in the UK by MED engineering.


-Sorry had to add this, 1000 posts yay thats gone quick

Welcome to the 1k

No, most of the gearbox is helical, only 1st & reverse are straight cut.

Oh, & the whine from most race boxes are from straight cuts

Cheers

Jacob

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'72 Clubman Van - 1022cc, 295 head, 731 cam - Daily Driver
'69 Morris 1100 S - Dinged by a bus, in shed under repair
'64 Morris 1100 - Early 1100, long term project

Thanks Jacob, all makes sence now.

What actual advantage do the straight cuts offer? Faster gear changes?


Steve,

Straight cut gears give a gain in power (well, they reduce the power loss)
When helical gears mesh they try to push sideways, there is a sliding action across the teeth as they mesh.

The drop gears are the three gears that drive the gearbox from the crank, they are not the gears inside the gearbox.

The straight cut gearbox gears only increase power, they don't make the shifts any quicker.

Straight cut gears wear out faster for 2 reasons:
1. Point loading on the teeth- there is only 1 tooth in mesh at any one time, where helical has 2 at least.
2. Materials used now in aftermarket Mini SC gears are poor quality compared to the factory helical gears.

This mightn't matter much in a race car, but in a road car you would expect gears to last.

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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've just spent some time in the past 2 week looking in to getting gears made as some now are NLA.

The factory did use fairly high quality materials and post treatment methods but even these were not as good as they could / should have been and under even moderate use some of the individual gears will suffer fatigue failure.

Some after market stuff these days is little more than rubbish, that is true, however, there are at least a couple of manufacturer's products that are way better than anything the factory made.

Do your homework and looking at price WILL give you a bum steer (the best - off the shelf - I found were not the dearest, by a long way!)

Be warned - straight cuts are very noisy.

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"the best - off the shelf - I found were not the dearest, by a long way"

Well don't keep it to yourself GT Mowog. Do tell.

MiniSport?

The noise of straight cut gears is magical.
To get an equivalent experience, put a car in reverse, open the window and floor it all the way to redline. Thats what you get every time you drive forwards with straight cuts.
They would also wear out quicker as like has been said, a helical gear is stronger, due to having 2-3 teeth in contact, and the size of the tooth can be smaller with helical gears because of this. So replacing a helical gear with an equivalent sized straight cut gear will give a weaker gear.

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Simplify and add lightness

I can't hear anything over my exhaust, I wish I could replicate straight cuts

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You're so square
Baby I don't care

I had a close ratio set of straight cuts in my Cooper S back in 1970 (They would have been the genuine BMC ones back then) and it was a fantastic sound, but the thing I liked most was the extra legs the lower gears had, 1st felt almost like 2nd and 2nd like 3rd, it was magical how they wound out. I ended up running a slightly lower diff ratio as the only down side was with the S diff first gear was a tad high for road use in my opinion, though I did have a friend that ran the straight cuts and the 3.44 diff.

When they decided that carb icing was going to be a problem and spun the engine around 180 degrees the penalty was a 2-3% reduction in efficiency attributable to the additional gear in the drop train to change rotation direction. That was reported in the Automotive Engineer article published in '59 I believe. So 1 extra gear = minus 2% power available at the wheels. You can get some back by making the set SC.

M

The later story was the carb icing was a myth and the truth was that the early gearbox syncros couldn't handle the inertia from the two bigger diameter drop gears. The ealt box was based on existing A-30 internals.

They built cars later on with the SU at the front of the motor, My Austin Montego has an A series engine mounted the other way around with the carby at the front. (ram fed by a cold air intake!)