Derrington Four branch copy

[Keith]

Mike, Alan....Leave it to me...taking into account you don't want the exhaust dragging along the ground!...I was going to look at both applications...once the samples are complete, I will test the market before having any made...regards Keith

[jarvo]

Yes please Keith. I would like one of the 4 branch exhaust manifolds. I have a burgess twin SU inlet manifold that I modified to suit my sidevalve engine and the 4 branch + the two HS2 carbs should make the engine less asthmatic! I also have a set of terrys double valve springs. Regards, Jarvo

[mike.perry]

There is about 1.5 in difference in the port heights between the Alta and s/v engines.If you design for the Alta and see how low the silencer hangs on the s/v, then you will know if you have to modify the pipes.
My engine is now away for rebuilding, I am undecided at the moment what carb setup to go for. I have a couple of H1s that I can make into a pair or I have the option on a pair of H2s. I want to stick with H series for the period authenticity. Or do I just go for a single larger carb?

[alanworland]

Mike, It depends on how much work you want to make for yourself? I found with my setup the float chambers are inboard of the carbs - which makes for not a lot of space! I can imagine larger carbs = less space?

[RobThomas]

40 DCOE!!!!

[alanworland]

I sold a brand new one of those about 2 years ago! - wish I had kept it!

[RobThomas]

Keith. The race is on, mate!

I finally got to cutting the 1" ID sections out of the motorbike 4-into-1 system (they make it from a 1" pipe sleeved inside a 1.25" pipe, y'know) and have gutted the engine bay of the lowlight to fit everything in place. Tomorrow I might have much of it in place with the 40DCOE hanging off it.

For anyone who might be interested, the bike was refered to as a 'FUZZER' by the bikeheads in the scrapyard and it seems to have come from a bike with 4 cylinders that point forwards and have 4 pipes that drop down the front of the block and then go underneath. the pipes appear to have been mandrel bent rather than compression bent, thus keeping the cross section equal round the curve rather than getting crushed down on the inside of the curve.

[RobThomas]

[frame][/frame][frame][/frame][frame][/frame]

I'm still not able to get the inlet done because I've not been able to make a suitable file on my PC to operate the CAD laser cutting device down the road. I've got a file in .skp format but I can't convert it on this computer. Bu66er! I've hung my SU inlets on it as a temporary measure.

The bottom end of the exhaust will have to be put back to tomorrow due to the MIG welder affecting the TV reception (and the BOSS is watching Eastenders on the BBC)

[RobThomas]

[frame][/frame][frame][/frame]

The Derrington-esque SU carb conversion that I made up 10 years ago for a Morris * engined MG seems to still fit without fouling the float bowls on the exhaust or fouling the shock with the air filter of the rear carb. Nice to know that I have SUs to fall back on if the DCOE doesn't work out. I've painted the downpipe with VHT to make it more visible and have found some old bits of motorbike exhaust to make upi the next section back towards the silencer can.
I'm going to have another go at CAD drawing the intake flanges. I've done the DCOE flange but might want another set of SU flanges and some inlet ends where they will sandwich the exhaust to the engine block.
If I get some done, does anyone else want to add to the order?

[mike.perry]

That looks an interesting system, do you get any gas flow obstruction with 4 into 1 as opposed to 4 into 2 into 1?
I have already got my order in with Keith for the exhaust but I have not decided on the inlets yet. I have my eye on a pair of H2s on an A Series manifold. I am not sure if I can separate the inlets and adjust them to a s/v. Otherwise I am after a separate twin carb 1.25 inlet manifold
The twin carbs on my 1275 LCB system clear the damper with pancake filters.

[RobThomas]

The percentage loss from not having the pairs sychronised is small and on a car with 27bhp there is no way on earth that you'd ever notice it. Effectively it is a 4-2-1 but the 4, the 2 and the one all meet at the exact same place (if you see what I mean). Youd have to go an awful long way to make a manifold that was NOT better than the standard offering from BMC.
I'd guess that the A-series (Midget) manifold is not only the wrong size and shape at the manifold face but also is too short to clear the exhaust pipes on this one. The A-series is also quite narrow so that the SV is already closer to the shock arm before you start modifying but by using mid 1950s carb with the angled float chamber you might be able to angle the intakes up to clear the shock and still not hit the bonnet.
The exhaust ports are 1 inch across and square with rounded edges so I've gone for a 1.25 inch tube and formed the edges to suit the manifold face. These have to be slit and widened slightly where they meet the DCOE due to the slightly larger bore (40mm).
Making the manifolds from scratch has to be easier than adapting a standard part, IMHO.

Who was it who made those beautiful inlets to fit twin H1s? I'm sure I saved the pictures somewhere. Have you got anything to add?

[alanworland]

Might have been me





Looks like your project is coming on well! Nice radius to exhausts, will this join up with the existing exhaust at the first joint? (in front of the silencer)

[mike.perry]

I should have mentioned that the H2s I have my eyes on are are semi downdraft on an LCB system so there might be a long enough inlet tract to play around with, just a case of shaping the square ports.
When I get the engine back I shall probably run the standard setup until I have put some miles on the engine ,then fit the twin system and mess around getting it balanced.

[RobThomas]

Alan. I don't suppose you have a .dwg file for those end pieces to get them laser cut? It would be handy not to have to draw them up on the CAD program again since it took me a whole day to do the weber mounting plate.

Your bodyshell looks like a later A-series one or did they change MM shells to fit the A-series before they stopped sidevalve production? I guess that they have a bit less room aft of the rear carb for the float chamber to sit in or maybe the engine mount holes are further back? I can lose the heat shield off the damper to make room for a heatproof spacer on the manifold-carb joint if I ever use the H1s but the DCOE will fit by sitting above the level of the damper.

Cheers

Rob
tessa dot thomas at tesco dot net[frame][/frame]

[RobThomas]

Progress! I took on the idea from Mike about Midget/Sprite carbs and manifolds. Lacking a frogeye manifold, I cut a Midget one in half and spaced the sides out and drilled the mounting flanges for the crankcase studs. The ports were much too large but I lathed down a sleeve to fit inside the port and make the manifold the same inner dimension as the block. The inlet hole in the block is square so I ground out a bit of the manifold near the block face and battered the sleeve into the right shape. The other end is way too large and another sleeve has been lathed up to narrow it down to 1 1/8 to match the carbs. The stud holes for the carb end will be doweled and new ones drilled to take the 1 1/8 sized studs on their smaller PCD.
The manifold needs a small (1/3 inch?) spacer to allow for the larger distance between the ports in the block plus I'll need to chack the length of linkages etc. The standard-ish 1 1/8 carbs I've got have a zero degree cant on the float chambers but the Midget seems to be either 20 or 30 degrees so I'll need to rummage round for some other float chambers in the shaeds. I'm sure there are a few! I'll still get the Derrington air filters on or I can run up some fancy long rampipes for it to make it even racier. I might have to ground some material out of the manifold to allow me to get the nuts on that secure the manifold to the block. I'm going to be using the inlet to sandwich the exhaust onto the block rather than having the manifolds assembled all in one, as per the original manifolds.
Looks like it will all work out quite nicely.
I've made the exhaust manifold just long enough the it will come out without the use of a hammer. The end is now about one inch beyond the hole in the rear of the engine bay. From that point back to the silencer I will have to fabricate something once I've worked out which silencer to use. There are some lovely stainless motorbike cans available for a very good price.

I also have enough bits left over for anothe kit of parts. If anyone wants more details of how to do this job, I'd be happy to coach them along.

Cheers

Rob

PS Away tomorrow morning. Cardiff to Exeter in a 767. Should take about 10 minutes. Exeter back to Cardiff will, however, take about 4 hours by car.

[mike.perry]

Graham is using an Alexander pancake air filter with a flat on one side on his H1 carb. With the flat side towards the back it might solve the clearance problems.
I take it that you will need some large flat washers under the manifold nuts to clamp the inlet and exhaust parts securely. Will there be enough length on the studs? Are you keeping the bakalite spacers between the carbs and the inlet pipes and a heat shield over the exhaust pipes?

[RobThomas]

None of the options I have tried so far have had any clearance problems.

The Midget intake manifold has enough meat on it that I won't need big washers to spread the load. Moving the bolt spacing inwards gives me quite a lot of overhang past the studs, ensuring that the whole thing is quite tight and steady. I can use standard 1098 phenolic spacers to keep the heat out but I've not got much space to keep a heat shield in place. It migh be necessary to wrap the float chambers in a special heat-resistant aluminised matting that I've used on aero engines. Works well.
Hopefully I'll have had another crack at it tomorrow PM upon my return from work.

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

[alanworland]

Looks like you are romping on with the construction - most rewarding eh!
Sorry Rob the only drawings I had was on a cigarette box! (not that I smoke!)
Mine is a 52 body but I believe the bulkhead section in particular was changed (curved upwards in the middle) to accomodate the 803 engines as well as the sidevalve.
The H1's I fitted have inclined float chambers (not sure now of the angle) which involved making angled inlets so the carbs are inclined up at this angle.
The air intake I constructed so I can use the original air silencer - which has ended up in virtually its original position.



and another showing inlet to carbs

[mike.perry]

The more pictures the better but I am not running the website.
Alan, your photo has appeared twice so you can delete the original. I like the air silencer pipes, presumably they are the same height as the original setup. The advantage is that you can get to the dash pots without having to take the air silencer off.
I wish they would move the postings info so that we can see the whole photo.

[Keith]

Rob, I think this company can supply you an off the shelf manifold set....give them a ring on Kingston 5621... [frame][/frame]