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Engine guides and mods

Piston DV Servicing

Your dump valve has to put up with a harsh environment so every now and then it's a good idea to give it a bath.

Modification Details




The dump valve (DV, BOV, POV) is a much argued subject among smart owners.

Some believe they are silly and make a funny noise, some people think they
make oil spray all over the engine, some people like the noise and some
people think they damage the engine.

I'm not here to help you decide which group you fall in,
its totally up to you to make your own decision.
Everyone seems to have their own ideas based on what they have been told by other people.
Very little of the 'information' given out by others is backed up with any authority or hard facts.

Read what I think about dump valves
here.

If you don't have a remap then its very possible that it won't make a proper DV noise,
the oil spray is a non-starter, it will always be in the pipe, the DV has nothing to do with that.

What I will say is a dump valve will not increase the performance of the car,
no matter how many issues of Max Power you read.

If you have had your dump valve on for a while you may
notice air escaping or that it doesn't dump properly.
There is a good chance that the whole thing is full of crap and needs a good cleaning.

Servicing a Smart Tune or Evil Twin DV

These are standard twin piston DVs with twin seals.

Undo the jubilee clip and the vacuum tube and take the DV from the car.



Clean the outside using hot water and a bit of washing up liquid.
Hold the main body and twist the top anticlockwise.



Once you have retrieved the lid from the next room and marvelled
at the powerful spring inside we can start disassembly.



Push your thumb in the neck of the DV and push the insides out.
In the centre you can see the main piston sitting on a smaller spring



Pull everything into its component parts and wash the lot in the hot soapy water.



Don't forget to remove the rubber seals and get everything as clean as possible.
Dry every part completely preferably on one of your Mum's best towels.
Before putting the main silver piston back in make sure you apply a fresh layer of grease to the seals, the wideway and the chamber.
The grease aids movement of the piston and ensures a good seal.

Here is the grease that I used but almost any light grease will work.



In true Haynes manual style 'Refitting is the reverse of removal'

Bailey Piston DV

This is the standard single piston DV with a single seal design.



Using a 2mm allen key, remove all 5 bolts from the head of the DV.



Take off the top and remove the spring, wipe off any old oil from all the parts.



Push your finger into the neck and push the piston out, again, clean with a rag.
The piston has a single seal that should be removed and cleaned, don't stretch it.



Grease the piston and refit the seal. Grease the piston housing wall and the top seal.



Slide the piston flat side down into the chamber making sure the seal doesn't get caught.
If the seal rucks up, just carefully push it back in with a finger nail.



Replace the top and replace the 5 bolts, don't overtighten. Wipe the DV down with a rag.

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