Gear manufacturing

[Dan Boy]

This might not be the right site to post this but of all the forums I am a member of this seems the best place to start.

I am building a motorbike with a merc super charger bolted on.

I need to use a geared driving system an I am having trouble finding a company that produce gears like companies who produce timing belt gears. You see I want a direct geared system rather than a belt driven.

Can anyone help?

Thanks,Dan

[Hopefuldave]

I can try to help... direct geared is a Bad Idea for a supercharger, particularly on something that goes through gear changes or can stall suddenly, the belt that's normally used acts as a shock and vibration absorber and plays a big part in preserving the supercharger's internal gearing (which synchronises the rotors), bearings and ultimately the rotors themselves.
A centrifugal compressor isn't as picky, but even they SHOULD have some sort of shock absorbtion or a slipping clutch to allow for sudden engine speed changes - WW2 aircraft used 2-stage, multi-speed centrifugal superchargers and the early development (e.g. the Supermarine racers pre-war) was full of disintegrating rotors when engines seized under test and the compressor tried to do a siudden stop!

If you go for a belt drive and still need gears, google for HPC gears, they do a range in both Metric Module and Imperial DP, materials from Delrin to heat-treated steel, priced accordingly! Bear in mind that you need to size the gears, bearings, shafts etc. according to the blower's pumping load - at high boost and high RPM this could be several tens of BHP! Work from the required BHP and gear RPM to get the torque load and be sure to check the torque limit the gears can take RELIABLY.

The superchargers used on the Mercs are Eaton screw compressors and have limits re RPM etc., Eaton's website is quite handy with lots of speed/pressure curves etc. but be warned that you may (if goiing for "adequate" boost pressure) need a bigger blower than you think to make the pressure you want at the RPM you want, a 12,000 RPM bike engine may need a blower running SLOWER than crank RPM if you want it to last more than a few miles :(

[PixMan]

I do agree with Dave. I've never seen a direct drive and what he's written sounds like a plausible reason why.

If intent upon using direct drive gears, how will you determine the widths and pitches based upon what loads? I can cite a couple of websites where you can buy standard stock spur gears, even some helical cut gears but what materials to use is a huge consideration. I'd be excited to make you some custom gears with my rarely used Walter HU-80 dividing head. I charge exorbitant amounts of good will doing projects like that though.

[Dan Boy]

Well thanks for the replies. Seems I was wrong in going for a direct drive. How will I switch direction of drive if the engine turns the opposite direction to the blower?

Thanks , Dan

[TomG]

You can either mount the blower 180º rotated (maybe not practical), or make a simple gear train (two gears) to reverse the rotation and use that to drive the belt. Not sure what rpm they'll be running at, but if it's high, they'll need to be helical to keep the noise down. Suitable gears, bearings and seals should be available from places like McMaster Carr, or Boston Gear. You'll also need to design a suitable enclosure so they can be run in an oil bath.

Tom

[Roadracer_Al]

Great to see another bike builder on here.

You can also include an override clutch in the gear train.

Basically, they can be set to slip at a given torque load. This would protect the blower from sudden starts and stops.

They're not indestructible, so don't use it to set the operational ceiling.

This may not be a good solution, I have no idea about the package size.

[Hopefuldave]

Hi Dan, reversing the blower *can* be done by removing the front casting and turning it (and the rotors I think) through 180 degrees, it's been done on the Eatons, but Some Precision is required as the bolt pattern isn't symmetrical and you'll probably need to drill and tap fresh threads in the main casting, a couple or three dowels in reamed holes would probably be a good idea too!
Rotor tip clearance needs to be maintained or it'll not survive long, I think they're set up with plastigage between rotors and casing, that's then measured and the front casting's adjusted - sounds fiddly!

The Eaton blowers fitted to Mercs (and Cooper S's?) also have a bypass valve to allow 'em to run normally aspirated when the ECU disengages the magnetic clutch (like an aircon clutch) at very low loads, e.g. idling, over-run etc. to reduce friction and pumping losses when the boost isn't required - more complication!

Definitely go look on the Eaton site and check out what size of blower you need running at what max RPM - I'm planning something similar and am intending to base it around a blower from a car making the same max BHP as I hope to get from the bike, which puts it out of the Merc CLK range... Unless I run it well above the manufacturer's designed RPM :(