Removing SU dashpots, new Morgan air filter - Help and advice sought

mrtask

mrtask

Well-Known Member
Hello all. Seeking refuge from the searing hot sun I tinkered in my garage yesterday afternoon. I wanted to fit a shiny chrome-plated air filter box (tube?) off a Morgan Plus 8 which I acquired off ebay. The two extensions on the underside are welded on, unlike the bolt-on pieces on the original Rover P6 air filter. They're too short, so don't reach the studs extending up from the intake manifold. Anybody got a cunning suggestion as to how I can raise the studs about 2 cm?
Will it affect the carburettion now that the intake nose between the carbs is about twice as large as the restrictive snout on the original airbox? The paper filters (brand new) are thicker than the ones I have used before as well.
I wanted to polish up the dashpots to complement the shiny air filter. Five of the retaining screws came off no problem, but one is very tight indeed and the 'groove' for the screwdriver head is damaged, opened right up, so I can't get a proper purchase without the screwdriver slipping out. How do I get this pesky screw out? One shiny dashpot and one dull lustreless dashpot just won't do!
 
ooh dear ..... can you use a hacksaw balde to cut a new slot? try heating the aloy carb a bit - the different expasnion rates may release the screw; else you would need to cut the head off and deal with the remainder of the screw; that would entail reming the car off the manifold, drilling the screw and pickout out the remainder of the thread.

When you cut the new slot, use an impact hammer but support the underside somehow (again off the manifold to do this).

Depnding on wchih screw it is you may be able to get at it from the undersiade, drill in the cnetre to weaken its hold and try to unscrew.

Is it the one with the tag? If it is, 1 in 3 chance - you may be able to file that away form the side again releasing its grip.
 
Can you get a small (or large) pair of mole grips on the screwhead. A good clamping & a twist should sort it out without a lot of cutting & drilling hassle.
 
HI, WHAT HAS WORKED VERY WELL FOR ME IN THE PAST, WITH ANY TYPE OF STUBBORN SCREW,STRAIGHT OR PHILLIPS,THAT HAS GOT DAMAGE IN THE UNDO DIRECTION, IS TO GET THE BEST QUALITY AND TIGHTEST FITTING SCREWDRIVER YOU CAN,AND, ATTEMPT TO ""TIGHTEN IT"" A BIT FIRST!! USE AN IMPACT DRIVER AND HEAVY HAMMER TO HELP!! THIS WILL
"HOPEFULLY" ,BREAK OR CRACK THE SEAL AND SHOULD MAKE IT EASIER TO UNDO, BUT OBVIOUSLY, IF IT IS TOTALLY STRIPPED OF ITS SLOT,YOUR IN FOR A FIDDLY JOB. EVEN BOLT HEADS WITH A SIX SIDED SQUARE EDGED SOCKET SET!! CAN BE FREED IF YOU TIGHTEN IT FIRST TO " CRACK IT!!" THE SEAL THAT IS!! APPLYING SOME GENTLE HEAT MAY HELP,BUT AS METAL EXPANDS,IT CAN GET TIGHTER!!
I AM NOW IN THE HABIT OF GIVING ANY UNKNOWN NUT,BOLT,SCREW ETC A LITTLE TIGHTEN FIRST,JUST IN CASE!!!
GOOD LUCK!!!! HAVE FUN :p
 
Thanks for all the suggestions for tackling knackered screws. A larger pair of mole grips than the itsy bitsy ones I tried at first did the trick, now all is sparkly. :)
Anybody reckon that my new airbox with a wider diameter 'snout' and bigger paper filter elements will affect the carburetion?
 
mrtask said:
Thanks for all the suggestions for tackling knackered screws. A larger pair of mole grips than the itsy bitsy ones I tried at first did the trick, now all is sparkly. :)
Anybody reckon that my new airbox with a wider diameter 'snout' and bigger paper filter elements will affect the carburetion?
Click to expand...
Well it may breath a little better if anything, which is no bad thing.
It may be worth checking all the carb settings are still correct when she's up and running though, just to make sure.
 
Hi

I opened up the "snout" on a standard filter box and it definatly helped, a nice radiused end goes a long way too. Since you have gone to the effort why not get some performance filters (K&N ?), Ive always found them much better than "cardbourd" ones especially non OE repro stuff (how does air get through them ?) and they last forever !.

As an aside about dashpots, apparently the covers and the piston inside are matched paires machined to be a exact fit, also don't lose the springs !!.

PS, all my tinkering meant the carbs needed retuning as they were running lean.
 
Glad to hear your errant screw succumbed!

While you've got the dashpots off see if you can find a thread I did a few months back on sorting out SU carbs. In brief summary they can be massively improved by getting the fall rate the same in both dashpots. Remove and put to one side the oil piston thingy from the top, then clean everything up until its perfectly dry. Push the pistons up to the top of the dashpots and time or compare the length of time they take to fall back down. 100 to 1 it will be different for the two carbs. The effect of this is that as the pistons lift under manifold depression you will get a different lift and hence different mixture from each carb. If possible have a selection of pistons and dashpots and mix and match until you have a pair with the same fall rate. Your engine will then run the same mixture from both carbs under all conditions. The transformation in engine behaviour can be quite dramatic. Note this is not the same as "balancing" the carbs - that refers to getting the throttle opening and mixture settings the same at idle and only really affects things as you start to depress the throttle. The other thing to check is that both carbs reach full throttle simultaneously; adjusting the linkage between the two to achieve this.

Chris
 
Rumblin_Ron said:
get some performance filters (K&N ?), Ive always found them much better than "cardbourd" ones especially non OE repro stuff (how does air get through them ?) and they last forever !.
Click to expand...
from when I had my MGB there was lot's of discussion about this. apparently the original filters are best but they clog up quickly so in the long term K*N provide better flow. also K&N are cleanable so saving in £££ there.
 
I'm a little bit confused. When I bought my '73 it sported a pair of conical K&N filters instead of the 'elbows' and tin air filter box. Looked pretty racy, much more intake noise, but wouldn't pass the strict test of historical accuracy for 'H' plates here in Germany, so I took them off.
My shiny new Morgan air filter box has wider (approx 2.5 - 3") paper filters in each end than the fairly slim (approx 1.5") Unipart paper filters in my '73 P6.
Do K&N make replacement flter elements to fit inside each end of the standard air filter box?
Are the dashpots and pistons really matched pairs?
 
If you read web sites from purveyors of SU's today, there is an implication that, yes dashpots and pistons are paired. I bet they weren't when the cars were new though - British Leyland quality control and all that!!!

Irrespective of what the actual production paractice was, the theory of how the SU operates quite clearly drives you to wanting a matched pair. In fact a purist would contend that the needle profile is specifically dependent on the precise piston fall time and therefore there ought to be paired needles and pistons/dashpots as well! I've always taken the view that thats just too difficult and the SU's fuel control (whilst arguably better than a webber) is not accurate enough to make that discussion meaningfull. The fall time discussion does have real "feelable" benefits though!

Chris
 
mrtask said:
Do K&N make replacement flter elements to fit inside each end of the standard air filter box?
Click to expand...
I don't think they do. But Unifilter in Australia do.

http://www.uniflow.com.au/

They are oiled foam filters, that are claimed to have better flow and filtering. Like the K&N's you just periodically wash them out in White Spirit and re-oil them with the 'Filterfix' oil.

I bought a pair for my 3500S a while back and they seem to work well.
Part No. UC140 60S/2 for the original round airbox.
 
You must log in or register to reply here.
Back
Top