Toying with idea of taller Metro 5th gear (to go with the already taller final drive)

[Big Dave]

Gearing is an effective strategy if your engine has enough torque at the target RPM to push the car through the air at the desired speed.

This a no-brainer for diesels. They have mondo torque at low RPMs, but gas engines are highly resonant and that RPM may depress volumetric effiency to the point the engine simply cannot make enough torque, and she lugs excessively.

My engine will idle (650 RPM) down the road but I have a pretty big engine.

[MetroMPG]

Re failed gears: I wonder how many miles the chopped tandem Metro XFi has on it - he machined his own 5th gear set:



1989 Geo Metro Gets 75 mpg

I've had poor luck getting replies from the owner's son (who made their web site - owner doesn't do computers).

[MetroMPG]

So... slowly moving forward (the speed of all my projects)...

This is the "test" I got back from the old school machinist:



He put the whole thing in the lathe (gripped it by its teeth, I assume) to trim some of the taper around the shaft area, then used that new surface to hold it in a chuck and remove the teeth.



Here's what it used to look like. The modified gear is the output one (on the left) in this pic of Ben's:



So the word from my brother is the machinist is willing & able. So I'll go out to see him with the rest of the parts to talk turkey. And money.

[Christ]

Don't look like you'll get too awful far in 5th gear now, D...

[Formula413]

He's making it into a CVT

[MetroMPG]

It would be a truly manual CVT! Swap cogs... I mean pulleys... and belts as needed.

[janvos39]

I made gear modifications more then once in the same way. Works out well if there is enough material left under the new teeth ring. Press fit and some weld spots will do the rest. Are you going for spur gears with lower friction?

[MetroMPG]

No straight cut gears for me - I'm going to re-use helical cut gears from a 2nd gear pair.

I like the idea of press fit and spot welds or pinned, even. The Ford ZX2 owner with the welded 5th gear set believes it may have been the continuous welding bead on both sides of his cogs that contributed to their demise (affecting the heat treatment/hardness).

[Daox]

I showed the pictures to the warranty guy at work (gearing company). The cause of failure was excess loading on one side of the gear. When you get these machined out, you better make darn sure that the gear bore and hub OD are true. The gears we make at work are a higher quality than automotive gearing, but its still a high precision part.

[taredog]

Sorry...can't control it...gotta ask...

Daox, do work for Cogswell Cogs or Spacely Sprockets