7 replies to this topic

[ben.mini]

Hi all,

looking for some views/recommendations. I am rebuilding a gearbox, I have two gear sets to choose from.

The engine is an MG metro, been bored +20thou, Gt spec Head, lightened flywheel. Final drive is 3.4, primary gear 29 teeth and input gear 28.

The engine came with a double groove gear set, before the engine work the car drove well, and pulled well in all gears, but 1st gear was really short. As in you would be changing up in seconds.

I have a second gear box case, came with a single groove gear set.

How big of a difference is there between these gears from a drive ability point of view? Would a single groove set be better?

Cheers
Ben

[KTS]

the single groove gearset has a significantly taller 1st gear than the double groove (3.65:1 vs 4:1) so you don't need to rev the nuts off it to avoid bogging down in 2nd

 

2nd gear is pretty much the same (2.13 vs 2.18) and 3rd gear a bit taller (1.36 vs 1.43)

 

if you use the standard primary (29tooth) and eco (28tooth) input you end up with effective gearbox ratios (i.e. Crankshaft to Mainshaft) of :

 

1st :   3.52:1

2nd :  2.11:1

3rd :  1.38:1

4th :  0.97:1

 

..which is not too far off what the S/GT gearsets were (3.33, 2.09, 1.35, 1)

 

to visualise the difference, check out the excellent Guessworks page below : 

 

http://www.guess-wor.../Tech/ratio.htm

Edited by KTS, 03 January 2023 - 05:22 PM.

[Spider]

Here's a table of all the Factory Helical 4 Synchro Gear sets, part numbers and ratios;-

 

 

I'd suggest as KTS has, going to standard ratio drop gears (ie, 1:1).

With your Cam and also depending on what final drive ratio you setting on, I'd suggest the (original) Cooper S Gearset and if I can also suggest, a 3.44 final drive.

[ben.mini]

Thanks both,

Spider, when you say 1:1 ratio, is that as simple as getting a 29 tooth input gear to match the primary? Or is other fettling required?

[KTS]

 

I'd suggest as KTS has, going to standard ratio drop gears (ie, 1:1).

With your Cam and also depending on what final drive ratio you setting on, I'd suggest the (original) Cooper S Gearset and if I can also suggest, a 3.44 final drive.

 

i was actually trying to suggest retaining the existing drop gears as they have the effect of making the single groove gearset ratios closer to the S gearset (..1st gear is still a bit shorter..) but without having to spend a load of cash on a new set of gears and laygear.

 

agree on the 3.44 final drive though

[ben.mini]

Thanks KTS.

 

 Your suggestion is looks like the most cost effective. I have been looking at the S ratio's but is giving me more questions. 

 

Minispares sell a S Ratio (18 Teeth) first motion shaft for 18mm nose shaft (DAM3167), and the layshaft to match as 22G1040. I would then need the 2nd and 3rd gear to match the layshaft, from spiders table above.

 

So the main question I have is, the 22G1040 lay gear, uses a pre-a-plus single step layshaft (C-22A1738). The cases I have are A+ DAM 5626. Would this layshaft fit in a DAM 5626 case?

 

My thoughts are yes, from what I have read, as it was the smaller bearing area that was increased not the part that passed through the case to the locking tab. Would different thrust washers be need as well?

 

Would the smaller layshaft be introducing a weakness? 

 

All of that above though does make me lean to your suggestion KTS. I will be sticking with the 3.44 ratio as well.

 

Thanks

Ben

Edited by ben.mini, 03 January 2023 - 09:39 PM.

[Spider]

Spider, when you say 1:1 ratio, is that as simple as getting a 29 tooth input gear to match the primary? Or is other fettling required?

 

Yeap, just a matter of getting a fairly common 29 tooth Input Gear.

 

 

Thanks KTS.

 

 Your suggestion is looks like the most cost effective. I have been looking at the S ratio's but is giving me more questions. 

 

Minispares sell a S Ratio (18 Teeth) first motion shaft for 18mm nose shaft (DAM3167), and the layshaft to match as 22G1040. I would then need the 2nd and 3rd gear to match the layshaft, from spiders table above.

 

So the main question I have is, the 22G1040 lay gear, uses a pre-a-plus single step layshaft (C-22A1738). The cases I have are A+ DAM 5626. Would this layshaft fit in a DAM 5626 case?

 

My thoughts are yes, from what I have read, as it was the smaller bearing area that was increased not the part that passed through the case to the locking tab. Would different thrust washers be need as well?

 

Would the smaller layshaft be introducing a weakness? 

 

All of that above though does make me lean to your suggestion KTS. I will be sticking with the 3.44 ratio as well.

 

Thanks

Ben

 

Yes, that Laygear and 1st Motion Shaft are part of what you'd need. You'd also need a 2nd and 3rd Gear.

I have built up quite a few Gearboxes, based on the DAM5626 Case and these Gear Sets. There's not problems, quite straight forward.

The Earlier 2 Step Layshafts are prone to wearing on the small end, but, if a decent quality EN36C Shaft that's hardened to at least 64 Rc is fitted up with decent bearings (be aware, there's loads of cheap rubbish out there), you can expect to get quite decent life from them, as long as there's always some oil in the gearbox.

 

I've not (yet) run the numbers on the 29 / 28 Tooth Drops, but I'm not crazy about them as they are all over-drive sets and so increase losses.

[ben.mini]

Thanks both for the input. I have managed to source a GT clubman box with a DAM3168 gear set. Mostly usable apart from a chip on the first motion ion shaft as per my other post.

Plan is to transfer this into a DAM5652 case. Also came with a 29th tooth input gear, so 1:1 drop gears as a suggested. I have a 3.44 final drive and cross pin diff for it as well, so hopefully a nice little set up moving forward.