Derrington Four branch copy

[alanworland]

Phones out, try their website!!

[Keith]

Better start saving....they also sell those just released Alta heads....but no one is interested in those, now the new BMC 803cc engine is available [frame][/frame]

[mike.perry]

The Alta head is three weeks wages!!

[Kevin]

Mods. Is it OK to keep pasting pictures here or is it frowned upon for taking up too much cyberspace?

Not at all Rob especially when it comes to items that are not run of the mill, as the saying goes a picture is worth a 1,000 words.
Alan I have combined your 2 postings into one so it makes more sense.

[RobThomas]

I've got the Derrington head here. Identical to the MM Qualcast one but the chamber shape is different and smaller.[frame][/frame]

Keith. Do you have any other 'period' adverts or info from which to steal ideas?

[mike.perry]

[frame][/frame]
Comparison of the combustion chambers

[Keith]

Rob, I do, although I can go one better I have an Derrington twin carb manifold for the MM, its an aluminium casting so probably not practical for small batch runs...I have the carbs also if you are interested in the type used originally...

The Derrington exhaust carb mounting are tubular and looked very similar to the one's you and Alan have made. I have the dimensions somewhere, if that would help...

Re progress of the copy...the pipes have been copied as per my original, I have the mounting plates cut, I now have to supply my friend a car so he can do the final assemby on the car...again time isn't on my side...I just need to strip down the front of a low light I have, so he can get good access...and take it up to him...maybe Easter...

regards Keith

[RobThomas]

Had a rummage in the shed for some angles float chambers for the H1 carbs and found some H2s from an early MG Magnette saloon. They fit nicely and have the bigger float chambers at the correct angle. Not convinced that they aren't too big for the MM.[frame][/frame]

The engine end of the manifolds is now tapered out to match the engine block. The sleeves are held neatly in place by the carb and the engine.[frame][/frame]

The Midget manifold is perfect for the job (Thanks, Mike) if you sleeve one end and slice it apart for spacing. The levers for the choke can come off the H1 set. I'll need to open out the cross-pipe from 12mm ID to about 14mm so that I can slide and seal a piece of copper water pipe in there to bridge the gap. The option of using a rubber flexi between the manifold sides has gone due to the proximity of the hot manifold for Nos. 2 and 3 cylinders.[frame][/frame]

[Keith]

The Derrington inlet manifolds were a very simple design, two tubes, square shaped welded to the engine manifold mounting plate, cirular at the other with a carb mounting plate welded at the end. About 100mm long, set at approx 15 degress with a balancing pipe between the two.

The carbs had the small cirular filters fitted. If the larger circular filters are used. the right hand one would need modifying as it would hit the shock absorber.

regards Keith

[mike.perry]

It looks as though we are going to have a facinating collection of tuned engines. I wonder how they will compare.
Is everyone going to be using the standard DKYH4A distributor or are there any other tweeks such as 25D4 with vacuum advance or electronic ignition?

[RobThomas]

Bu66er! I spent the day making a tubular steel inlet manifold for 30 degree float chambers, only to discover that I had about a half dozen 30 degree chambers but all left hand. A few minutes of searching the internet and I discovered that they don't do 30* in right hand. I had to slice the manifold apart and reweld it for 20 degrees. Fortunately I have lots of zero and 20* float chambers and some nice 2 inch diameter ones that will fit. The 20* ones will still clear the shock absorber.

I now have lots of twin-carb inlet manifolds and will eventually have some for sale.


Mike. I have used the 23D4 from the Cooper S (part number 40819, my security pass secret authorisation number at work!) but I have some 65DM4 super-dooper electronic ones that don't use ponts or condensers. They come off of Metro and Maestro models. Once I've sorted out a rolling road session I will get a few of them done. I have some 40251 and 40056 versions of the original dissy but they are all mouldy or have slack springs. Frankly they aren't worth keeping.

[mike.perry]

I could be interested in a pair of twin inlets for H2 semi downdraughts. It depends if I can use the inlets off the set I am after, and the angle of the carbs.

[ian.mcdougall]

Hi Keith
How are the exhaust manifold coming along
Just aquired these carbs and manifold off a Midget at a local autojumble on Sunday so looking forward to seeing pictures of the exhaust and the cost , and getting on to adapting carbs to fit I hope.

Ian[frame][/frame]

[Keith]

Ian, The pipes, mounting plate etc have now been copied as per the original. It's now up to me to take a car to the person who's making the manifold, so he can complete the final assembly on the car, he needs to get the clearances correct where the 4 branch exits the engine bay, clearance under the car etc.
So its down to me again I'm affraid, I have a low light which I need remove the wing and front panel before trailering up to him.
I don't have much spare time at the moment, I will try and find some time this month...if not it will be Easter.
Re your carbs, are they 1 1/8 inch SUs or 1 1/4 inch. I won't go into the ins and outs of each, read back through Rob Thomas/Mike Perry posts on the subject.

regards Keith

[RobThomas]

[frame][/frame]

I've put some welded steel inlets on, having got bored with trying to make the Midget manifold fit. Not much room to get the bolts on so I will fabricate some brass special bolts for the engine when I get back from Longhaul next week (assuming I can find a 5/16 BSF tap)
These inlets are set at 20 degrees for MM standard carbs. 30 degree carbs don't come in 'opposite pairs' but I now have manifolds to accept either 1 1/8 or 1 1/4 H-type carbs with either T1 ot T2 float chambers. Since taking this shot I've added a balance pipe between inlets plus a boss for the lambda sensor.

[ian.mcdougall]

Hi Rob
My manifold studs are metric thread are you sure yours aren't as well
What is the reason for a Lambda sensor

[Keith]

My ins and outs comment was directed that maybe twin 1 1/4 inch SUs are overkill on the MM engine, the original Derrington and Alta twin carb kits had twin 1 1/8 inch SU...I'll leave this discussion to those in the know....

[mike.perry]

These inlets are set at 20 degrees for MM standard carbs.

? Standard MM carbs are horizontal. As for the difference between using H1 or H2/HS2s it is going to be a case of suck it and see, use what is available and compare the results. The 948 Midget used HS2s and there is not a lot of difference in capacities of the two engines or the size of the carbs.
I have just measured my manifold studs and they are definately 1.0mm metric pitch

[RobThomas]

Just got back from Cuba and am going throught the messages etc.

I should've said "20 degrees for standard MG carbs" and not MM. The Lambda sensor boss is for tuning the carbs using a wideband kit that data-logs whilst you are driving. It will plot how the air-fuel ratio is working out whilst you are driving along. I used the same kit to tune the aeroplane engine since there is no other way to work it out with any degree of reliability.

I'm going to pull the studs and see if they have been drilled oversize and maybe BSF put in. I might even get lucky and find they are still metric on the block! It will be easier to get brass metric nuts to go on there and I've already lathed down the original (?) barrel nuts on there for clearance so that they don't foul the pipes when you wind them on. Not a lot of spare room in there! I'm still a bit jet-lagged so will maybe have another snooze at lunchtime and then go on the attack.

[PeteMorrisMinor]

These look great! Depending on price and transport to NZ I'd be interested.