Semi-helical gears...how noisy?

[stevefoster]

A friend has just upgraded to a T9 semi-helical box. First impressions were... mmm pretty noisy.

Any body else got one and care to comment?

 

Will the noise get less as the box runs in OR?

SPC's web pitch is "WILL NOT WHINE LIKE A SC BOX".

 

I was thinking about swapping out my ali CR/SC box for a CR semi job for less 5th gear whine. Now I am not so sure.

 

The excuse for my swap is that I plan to use the car even more on the road and with the wife in it (like on the haggis run).

 

SPC can do SC 1st, 2nd 3rd, 4th is straight through anyway and a fully helical 5th. Maybe for track / cruising this is a better option. More dosh again of course!

 

Brian Hill was working on a CR fully helical solution. I must check this with him...

[Tony Martyr]

gear train noise is an interesting subject. The general principles are that any mesh design that smoothly transfers torque from mesh to mesh, as happens in a helical mesh tends to be quieter than a spur mesh where the transfer is more intermittant. But single helical meshes create axial loads (double helical meshes do not and tend to be the quietest) which have to be absorbed by thrust bearings that allow movement and create noise. We use gear box noise as an analytic tool since you can pick up tooth contact frequences and all sorts of interesting stuff like torsional resonance (you should not get them in any available gear box!)

Of course the noise from automotive boxes goes up in direct proportion to the number of meshes engaged which is why 4th gear in the Caterham 6 speed box has a distinctive sound. Then there is the running clearance (backlash) between the gears and the exact shape of the gear teeth. It takes a lot of care and soecific detailed design features to make the quietest gear boxes and the features may not be the priority of race track boxes that are designed for quick ratio changes and shorter working lives. You pays your money and makes your choice.