PM 'Power Valve' thingy

[sugarlump]

Ebay Link

What's this bit of magic kit that obviously didn't work then...

Not a power valve in the yamaha sense, description leans towards a turbo of sorts...

[RICSPEED]

just about every street racer in scootering had these around 88/89 ,in hind sight i think they were just bling as no one i have spoke to had any thing good to say about them

[tony]

A boost bottle in reverse. Did they work...well... not really. But then again we didnt understand enough to make them work or rather design one to work.
Re powervalves that cezeta posted... well this is similar. Not as effective imo or working in the same way but an attempt to broaden the band.

[gnasher]

I had one of these fitted to a mikeck on a 210 reed valve, taffspeed fitted it while I waited. It worked great by reducing the flat spot before the power band. Worked fine until the diaphragm operating the valve split...then split again and again....then it fell apart in the middle

[jonny snatchsniffer]

i had a pm on a p2 and my mate had the same with the valve, so we swapped over pipes to go 2up to hih and mine was transformed, lots more torque and pulled 2up into wind uphill, lost a bit of power with shite dutch fuel, but then my brother had one on his ts1 and it was a load of wank

[drunkmunkey6969]

Not seen one of those for Lammy before.

Where does it fit, and how does it operate?

[sugarlump]

I also started this thread in the chit chat of the lcgb and got a great explanation from 'a-teamlambretta'...

Hope he doesn't mind me cut'n'pasting his reply

i have been using one on a mikeck exhaust. it does work but takes some looking after and setting up. have a read at this. also look in the tuning section for mikeck rubber mounts and brackets .


Mine lasted 2000Mls, from new, through lacl of info/knowledge/advice. I hope I can save you a bit of grief at least based on my mistakes.

Firstly pull the thing apart Being VERY VERY careful with the outermost lid. This contains the diaghphram that actuates the valve under exhaust pressure. Be very careful here as the diaghphrem is a thin viton type material that tears easily.

The outer circumferance is coated some sort of asbestos type gasket material to seal the two surfaces: this sticks to the two mating surfaces of the chamber and can cause it to easily rip if not handled with utmost care.

There is a threaded nut/collet on the shaft that secures the diapragm to the shaft through a metal eylet in the diaphragm center: go gently here too!

Draw an accurate pattern of the diaphragm: It will eventually fail and spares are not available from 'Athena' the manufacturer. I've got a decent supply of diaphragm material (supplied against a sample) in petrol + heat resistant material + stronger spec. Replacement diaphragms will have to be DIY.

De-coke the unit (they coke up fast).

Re-assemble replacing the stupid nylock nuts originally fitted (do that really think that will not melt at ehaust temperature :-/ ). Securely 'double-nut' all fastenings + your best Loctite: They fall apart so easily under vibration. As much thread to bear as you can!

Adjustment: When re-assembled unscrew the brass top cap (looks like a large falve cap). The end of the actuating shaft is threaded to accept a little 'indicator rod' that comes with the new valve. As designed this screws in-to the top of the shaft and pokes out of the hole allowing you to visualy monitor and adjust the operation of the valve as the engine runs and is revved. Either make-up an equivelant when you stripped the unit (or as I did) 'make-do' and glue somthing in there: strong enough to withstand the vibration but weak enough to be separated after...and not leave too much mess either.

Now you need to know when your pipe 'kicks-in' the power band. EG mine was (per Dyno) 5400rpm. You want the valve to be open below power-band and to close at 'kick-in' letting the spanny do it's work. Knowing the 'kick-in' point (seat of pants/GPS/Gear Ratio/exhaust reports/dyno) choose the point you want it to close. Strap-up a rev-counter (I borrowed a digital one). Rev-up the engine and monitor when the diaphragm (valve) closes. Adjust the opening pressure via the spring tensionner. When set loctite this too (I found it had to be fairly 'out/slack'.

Check/re-inforce the flange to down-pipe weld if it looks frail as the weight and vibration stress that too. (`I beefed mine-up but then a spiral crack happened in the down-pipe anyhow....)

Aside all that, when it was working the power delivery was fantastic: transforming a peaky pipe on an average tune into somthing that boxed well above it's weight

Hope this helps: U cannot beat the sound of a Mikeck in my oppinion .

PS I have (currently) a chrome standard (44mm) Mikeck down-pipe on the shelf if it all goes titz-up on you

My next venture with mine (DIY MK2 version) includes a vacuum breather from the inlet to the breather on the diaphragm top to give it 'double-action' and be more responsive still. Perhaps a bit OTT as they are mega fun when they work as intended....just follow the maintainance precautions as they are irreplacable.

[Adspeed]

Where does it fit?

[jonny snatchsniffer]

its welded to the downpipe by a flange after a hole is cut into it, how the f@@k it operates i dont know, all i do know behind the theory is its supposed to increase the volume of the downpipe at low revs to give more bottom end.

[drunkmunkey6969]

Where does it fit?

Yes?