Murena high fifth gear

[JL]

Hi Jon
If you are unable to machine the gears normally, another thing you could try is something that I used to do on Simca gearboxes when I could not get the correct ratios. The teeth of the gear and part of the outer gear were ground off just leaving the centre of the gear; we then had another gear made which had a centre which was an interference fit on the old part of the gear that was left. The two pieces were then submerged arc welded together. With your situation you could remove the centre of the new gear and grind the teeth and part of the old gear and then combine the 2 pieces that would then fit your gearbox

I have attached a quick drawing to try and help my explanation.

The down side is that the gears do need heat treating after the machining but we never had a failure of the gears.

Regards
John

[Jon Weywadt]

Well, the gear box is reassembled and back in the car, with its new 2. gear synchro ring. Its like having a new car. 
I have put off the 5. gear replacement until after the summer holidays. I will have the gear shaped to look like the original, such that it fits with the original bearings. I will also have a shim ring made to fit over the gear/synchro assembly, since this is 3,5 mm narrower than the originals. The shim will have to be hardened, I think.

[Jon Weywadt]

Well, the gear box is reassembled and back in the car, with its new 2. gear synchro ring. Its like having a new car.  
I have put off the 5. gear replacement until after the summer holidays. I will have the gear shaped to look like the original, such that it fits with the original bearings. I will also have a shim ring made to fit over the gear/synchro assembly, since this is 3,5 mm narrower than the originals. The shim will have to be hardened, I think.

Well it is almost time.

Jan has turned the Fiat gear for me so it now has the dimentions of the original Murena gear. It turns   out that the gears, even though hardened, can be turned on a lathe with a tungsten-carbide bit.

If you look back to page 9 in the post, there is a photo of the two gear sets and the difference. Here you can see the modded gear.

Since the indention in the gear rests on the center ring of the bearing, it has no wear due to friction against other parts. The other side had to be turned 1mm down. It is held by the nut which turns with the shaft. Again no wear. I am therefore not worried about any reduction in hardness on the surfaces that were turned. The whole gear did not get hot enough to reduce the hardness of the teeth, which is what matters.

The other gear wheel, with the synchro, is not as wide as the original and requires a shim (3,5 mm thick). This gear turns on the inner bushing, which is a fraction wider than the gear. Thus when the nut is tightened against the shim, which tightens against the synchro, which tightens against the bushing, (I think that is the order  ) the gear can still turn freely

I will bring the gears to the Danish meet on the island of Fyn this weekend (tomorrow). There is not enough time to fit them before that.  I would have loved to test the difference on the long haul there.

[Oetker]

Super.
Now to find a shim that meet all sizes.
Think that has to be made seperately.

[Jon Weywadt]

Super.
Now to find a shim that meet all sizes.
Think that has to be made seperately.

Already done.
Jan turned a couple that we will harden and grrind to the correct thickness.

[Oetker]

If possible, I like one to.
That will save me work this winter.
Ofcourse payed for.