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MG Midget and Sprite Technical - HIF44

Hi,
I am fitting a HIF44 on a Mini spares manifold to my 1275. I have been told that an HS6 dashpot damper fits the HIF44 dashpot and it will then not hit the bonnet. Can anyone confirm this? I ask because I have spoken to Burlen and they claim that the threads are different. This has been backed up by me buying a damper and trying to fit it, the threads on the one I have are much smalled than the HIF dashpot.
Can anyone tell me where I have gone wrong?
Thanks.
Dave
Dave Brown

Yes I've been round this loop and the damper threads on the HFs are much smaller than the HIFs.

Clearance is subject to many factors, choice of manifold, engine mount condition and the variability of Spridget chassis.

When I had my Toyota 5 speed fitted I had no clearance problems but when I swapped to the Datsun 5 speed I did. I got round this my filing a flat on the top of the damper at about 30 degrees to the plane of the top of the damper with it's lowest side to the outside of course. Ther's actually a surprising amount of material in that damper cap. I'll try to remember to post pics later.

Oh and the other big factor of course is how near the edge of the engine bay the carb is because the bonnet line falls away towards the wings. I used to have two of the 3/8"ish thick spacers between manifold and carb, I now only have one therefore moving the carb into the 'taller' part of the engine bay.
Jeremy Cogman

I spoke to John at David Manners who sell the Minispares manifold. He said the new manifold has been designed to fit both the Mini and midget. Have you tried it yet?
Rob Newt has a friend who is also in the process. Should be completed in a couple of weeks.
Regarding the damper, there are flat top ones that will fit, but they are rigid as apposed to the pivoting one on the HIF44, not sure if they will work ok.
Cheers John
HALL JOHN

I angled my HIF44 downwards slightly, by cutting the spacer between the manifold and carb with a hacksaw, and then polished it with wet and dry for an air tight seal.

I don't know if this would reduce performance, but wouldn't think so unless you are race tuned and mine seems to be ok.
Lawrence Slater

Well I fitted a flat cap which I thought was HS6. Had to cut down the damper and the "tube" that holds the dashpot oil. Works great.


Geoff Mears

Geoff,
Yes, I saw yours at the Ace Cafe last time. I was not 100% sure it was the same dash pot as mine but it certainly looks like it.
Question is Where can I get one from?
Dave
Dave Brown

I'm sorry Dave, I completely forgot that you saw it. Now then, thanks to Bill jogging my memory as to where I got mine from, it was Andrew Turner (T) 01572 767665 email : www.su-carbs.co.uk
Geoff Mears

So much in the asrchives, but who would ever bother to look there?

This fits:

http://www.sucarb.co.uk/ProductSearchResults.aspx?SearchTerm=LZX%201389
Tom Coulthard

Geoff
I had investigated fitting a flat cap and gave it away when I found that the damper tube protrudes up past the top of the housing. Never thought of trimming the tube, obvious!! After you had trimmed the tube did you check that the piston could still lift fully with the plunger in place?

Jeremy - filing a flat - another good idea, could gain a critical few mm clearance easily.

I got real twitchy about this having inherited an involuntary "power bulge" by not having enough clearance and after making it worse myself needing a panel and paint on the bonnet as a result.

I fixed it in the end by cutting a wedge out of the manifold and welding it up again.

After 3 bonnet repaints between 2 cars (yes, I'm a slow learner, thought we had made enough clearnace but apparently not) we have also taken a belts-and-braces approach by installing a restraint bracket on the LH engine mount (see photo). The bracket is bolted to the chassis bracket and had a 5/16" bolt secured to the engine front plate which protrudes through a 1/2" hole in the bracket. The 2mm gap all round allows the normal range of engine movement but limits it when the engine tries to jump out of bed during autotest flick turns or when on a bumpy field. It has been very successful.


Paul Walbran

I have fitted the carb this afternoon. There are a few minor jobs to finish - choke cable, old heat shield stays and the petrol over flow. But the big problem is that the bonnet does not shut at all! I really need that flat top damper and the dashpot reduced in height.
The car started and ran ok if I held the choke open/on.

Dave
Dave Brown

As I said, I cut the plastic spacer between the manifold and carb to an angle to make the carb sit lower. If your car is standard tune I doubt that you will notice any performance hit. You cut it at an angle, and file the inside to smooth edge. (When you cut it you create a step from the carb to the spacer, and file it away).

I would estimate I have at least an inch of clearance under my bonnet, and I have the raised damper cap.

I'll take a picture and post it on here. Actually thinking back, I think I also cut some of the top of the carb too. I checked that the piston still rose fully and it does.

Like I said I will post a picture.
Lawrence Slater

Dave - I see the link I posted above does not hit the right page - the flat-top damper is SU Part No. LZX 1389, available from Burlen Fuel Systems as per the link.
Tom Coulthard

Tom,

Thats a very useful link you supplied. I have just read the technical on the HIF type, and didn't realise the carb could be mounted fully horizontal. According to the technical, it can be mounted 0 degrees to 40 degrees downdraught. I had always assumed that you needed to maintain a degree of downdraught. But it seems not. If I had known that, I would have angled my spacer even more and not cut the top of the dash pot.

I'm not a carb expert, can someone explain the advantage of downdraught for me?
Lawrence Slater

Here's a pic showing my angled spacer.

(I'm not point out the spacer by the way, just moving the vacuum gauge tube out of the way for a clearer shot).




Lawrence Slater

Someone please correct me if I am wrong, but it has been my understanding that, updraft, sidedraft, downdraft, in the case of an SU, the key point was the angle of the fuel float bowl, and with the HS carbs, that was controlled by rotating them accordingly. In the case of the HIF, it is built in to have the 40 degree range without negatively affecting their operation.

Other than the float bowl, the carb was happiest operating at a 0 degree angle, but was able to be rotated either 30 deg (HS, if the float bowl is kept at 0 deg) or 40 deg (HIF) without trouble.


Norm
Norm Kerr

It's on and the bonnet shuts. I filed the top of the damper down quite a bit and took 5mm off the dashpot and piston and now have a couple of mm clearance. I will be getting the flat top damper in the week, thanks for the part number Tom. So I should have plenty of room.
I think I will also take your advice Lawrence and wedge the spacer a little to make sure I have loads.
I just need to get the correct needle now and get it running smoothly. I'm off to hunt through the archives.
Thanks for the help.
I will post a picture and list of the parts I used for anyone else who wants to do the same thing later.
Thanks once again.
Dave
Dave Brown

The needle I use is a Peter Burgess 'special' adaptation of the original BDL MG Metro needle

I'd start with BDL because even before Peter performed his magic on it the car was running very well

Geoff hasn't answered you Paul, I understand he's off to foreign climes for a while but as I was with him when we decided to whip a few mm of the length of the damper rod I can confirm that after the cropping the piston has been able to rise to its full extent in the dashpot with no restriction. You do need to ensure that the rod is seated firmly back in the hole in the cap, as the original end is ball shaped to allow the moulded grip section to act we stuck Geoff's rod in with stuporglue instead

I know he took a few mms of the threaded end of the dashpot but I don't think he touched the actual damper tube and we only took a similar amount off the piston's rod as came off the threaded end of the dashpot casting

I seem to recall the flat top piston that Geoff had from Andrew Turner has a slightly different threadform but a little judicial easing of the start thread soon has this screwing as usual

Dave it sounds to me as if you have been sold a piston off a 1¼" SU rather than the larger threaded HS6, is money back an option?

Hope this additional info helps
Bill 1

I'm sure you dont need reminding about the engine twisting, so until you are certain you have plenty of clearnce it might be worth cushioning the bonnet above the dashpot. I stuck a plummers solder pad (thinn-ish flame proof padded cloth) just above the carb until I was sure. I put a blob of greaseon the top of the dashpot cap and went for a vigorous drive to try and twist the engine, then pulled the bonnet to check if there was grease on the cloth.

I have also remembered that I slotted the engine mounting braket bolt holes, and allowed the engine to drop a little on the carb side, lifted on the distributor side. Not much, just enough.

I wish I had taken pics of all this at the time.

Others have said that spridgets are all different so you have to be careful. My rubber engine mounts seem to sit the engine quite low anyway. Maybe if I changed them for new ones the engine could sit higher.
Lawrence Slater

Norm, that stuff about the float bowl angle makes sense to me.

In which case, instead of just discarding the remains of the plastic spacer as I did, I could have theorectically inverted it and put it on with my existing spacer and gained almost horizontal, and that would have given a massive clearnace under the bonnet.

An even better way might be to have two new plastic spacers, and wedge them both for maximum angle, and then fit them in the way I described.

Much easier to cut the plastic spacer than the manifold and probably better than altering the dashpot/tube/cap, although doing so doesn't seem to cause any problem to the carb at all.
Lawrence Slater

This thread was discussed between 07/07/2011 and 11/07/2011

MG Midget and Sprite Technical index

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