dump valve diaphrams
Turbo Mini Forums

hey up just a quicky,
ive been having problems just lately with the car not cruising properly and generaly misbehaving on low boost. i seem to have traced it back to the dump valve leaking boost pressure.
when you hold the throttle it leaks out just a little, ive tried nipping the signal hose to it to stop any vacume and it still does it so im guessing the diaphram or the spring must be at fault but i cant seem to see anything wrong. the diaphram dosn't aprear to have any splits or holes, but i suppose the hole might only show itslef with some pressure pushing past it, and the spring apears in good condition too. plus i cant realy see how it would fail unless it was excesivly old and had compressed a bit.

anyway for the price of it its probibly worth just getting a new kevlar diaphram but i was unsure as to weather they are a universal fit or if i need one specific for it? ive had a quick look on avonbars site and they only seem to sell one kevlar jobby.

anyway any advice or help would be much apreciated.

steve

doh! why did i start messing with it!

hi steve!!! forge motorsport get them there there cheap and they sent me 3 for the price of one lol

Previous Engine: 1040cc Morespeed engine, 1275 turbo head T2 Turbo Mirage Manifolds Megajolt
Previous engine: STD metro turbo, megajolt
Drives: 399bananahp (flywheel) Honda Civic Vtec b18c4 T28 Turbo 1968 Mini

Megajolt maps to download: http://www.jamesfawcett.co.uk/cms/index.ph...&gid=3&Itemid=3

... or get a baileys!

Previous Engine: 1040cc Morespeed engine, 1275 turbo head T2 Turbo Mirage Manifolds Megajolt
Previous engine: STD metro turbo, megajolt
Drives: 399bananahp (flywheel) Honda Civic Vtec b18c4 T28 Turbo 1968 Mini

Megajolt maps to download: http://www.jamesfawcett.co.uk/cms/index.ph...&gid=3&Itemid=3

ive got a bailey one, and the seal swelled, as they react with the petrol

now i cant get another seal, so im currently using a broom handle

Kevlar reinforced diaphram from avonbar

Metro turbo weekend driver,Mini turbo in the making again!

http://www.speedgenie.co.uk/avonbar/mainFrameset.html


A201

Metro turbo weekend driver,Mini turbo in the making again!

i have a piston dump valve and the O ring swelled. i got another O ring from the local car parts place that was way too small. i stretched it over the piston and that was fine. the next problem was fuel sitting in the piston and making it stick. i found the best grease is silicone based and to mount the dump valve with the signal/vacum pipe facing the ground.
have had no problems since.

I have had a kevlar diapram in mine i bought from Avonbar about 8 years ago. The first rubber one split but the kevlar one is fine.

JF.

I have a brand new Blitz one this one here http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...me=STRK:MEWN:IT

Its brand new and in the box won it for £25, the photo of it looks old but its never used.

Previous Engine: 1040cc Morespeed engine, 1275 turbo head T2 Turbo Mirage Manifolds Megajolt
Previous engine: STD metro turbo, megajolt
Drives: 399bananahp (flywheel) Honda Civic Vtec b18c4 T28 Turbo 1968 Mini

Megajolt maps to download: http://www.jamesfawcett.co.uk/cms/index.ph...&gid=3&Itemid=3

lol cheers guys, yeah thats the one i was looking at dangerous cheers, i'll get one ordered. i would have liked to swap it to a nicer one but im sorta stuck with the one i have due to it being welded directly onto the plenum! it was working fine up till now so will have to try the new diaphram and cross my fingers.!

steve

doh! why did i start messing with it!

erm feebs.....have you outgrown your tutu now or gone for a snazzy pink number instead?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...item=9321401690


sorry, couldn't help being a nosey cunt

the secrets out lol

Steve if its a forge one, or one of the similar shaped ones, i think you can reverse the internal bits of it, so like make it so the sping is pushing the other way. Mine was together wrong like that when i bought it for my red mini it was a blue anodised one that sounded like a toilet flush haha! should get you up and running?

Haha i can explain the tutu! ill have to tell you later tho

Previous Engine: 1040cc Morespeed engine, 1275 turbo head T2 Turbo Mirage Manifolds Megajolt
Previous engine: STD metro turbo, megajolt
Drives: 399bananahp (flywheel) Honda Civic Vtec b18c4 T28 Turbo 1968 Mini

Megajolt maps to download: http://www.jamesfawcett.co.uk/cms/index.ph...&gid=3&Itemid=3

hmm well i got the new diaphram and fitted it but no luck :S im still leaking boost somewhere.
the diaphram did need swapping there was a tiney tiney pin hole in the old one, which turned out to be kevlar, the new one sounds and works a lot smoother if that makes sence, but the engines still buggering up and showing 10lb of boost at 3500 rpm. its certainly not making that much pressure. i can hear it blowing air past somewhere but i'll be damned if i can find it :(
the boost guage is taken from the plenum - ragulator feed so im guessing the bad running is because the fuel regulator is getting the message to give full fueling even when its only running 1/4 throttle? on full throttle or crusing on high boost it runs perfectly!

anyway i had the dashpot off the carb tonight to swap the internal spring to a bit stiffer one, but i noticed there was no seal between the dashpot and the carb body itself. which seems a bit strange considering the dashpot piston is sealed and clamped in place! am i missing a gasket or is that normal?

i'll strip the carb off the inlet tomorrow night and replace all those gaskets too since i have a few kicking about. ive made sure the intercooler piping is all clamped very securely too so it shouldnt be leaking anywhere there!

steve

doh! why did i start messing with it!

defo sure its a turbo carb as they didnt have seals under the dash pot. there should be one

you still doing the carb rebuild kits iain? its probibly about time it had a rebuild anyway.
i want to pull the engine and fix a few problems before avon so might as well sort that too while im at it.
thanks
steve

doh! why did i start messing with it!

arghhh! nope its still blowing air out of the bloody dump valve.
just to clear some things up before i start pulling parts off.
would i be right in thinking the valve could be leaking because theres another air leak somewhere on the inlet, causing a slight vacume untill theres enough boost pressure to null out the amount thats being lost? or would that be complete bollocks and im barking up the wrong tree?
the diaphram is brand new and rated up to 30psi, the spring apears to be good and takes a fair bit of effort to compress when putting the valve back togeather and the hose from the inlet to the dumpvalve is perfect with no holes, splits or chunks missing same goes for the dump valve casing etc and the hose goes to a carb spacer with a hose take off on it.... anyone got any other ideas as to why it could still be leaking boost? because im getting stumped.

steve

doh! why did i start messing with it!