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MG Midget and Sprite Technical - 1275 Carb heat shield shape

The heat shield which came with my 1275 engine was bent in places so I straightened it out as best I could before painting. After fitting together with carbs I noticed that the centre top where the cable "ferrule" is was too far towards the carbs such that the cable would catch the inter-carb fuel pipe. So I've bent it back a bit. I've now noticed, looking closely at engine bay pictures (as we rebuilders do) that the upper central part for the cable guide should fold back towards the engine such that the inner cable exits very close to the heat shield.

So I'm wondering how critical this is to stop the cable binding. Or am I making too much of it and should just see how smooth it is with cable connected and bend more if needed?



Bill Bretherton

Bill, I think ideally it needs to bend towards the engine a little to move the locating bush for the ferrule in line with the plane of the shield. Otherwise over time the action of the throttle will be to lever it forwards and tend to bend the shield towards the carbs.

Nice clean carbs!
GuyW

Thanks Guy, I'll bend it in a bit more then. ideally I suppose the heat shield should be removed and modified but I don't really want to do that unless I have to.

The carbs cleaned up quite well. I'll do a fuel test soon to check for leaks. Battery to be ordered next week I think (oil pump was primed and pressure achieved via jump leads).
Bill Bretherton

looks good Bill. have you got the 2 lower stays to stop the bottom of the shield flapping about?
Bob Beaumont

Thanks Bob. Yes, I fitted the stays yesterday. I had a lot of trouble with the rear stay as it wouldn't reach initially (bolted to the correct bell housing bolt). I had to bend the lower right corner of the shield inwards and elongate both stay attachment holes. Yet something else that didn't fit first time!
Bill Bretherton

You learn something every day on this forum - well, I do anyway!

I never realised, until I read this thread, that the heat shield was supposed to have stays! Even though I've looked at the carburettor parts pages of various suppliers loads of times, I've never actually noticed the stays!

I've always known that my heat shield is a bit odd as it has been cut and bashed about a bit, presumably to accommodate the original LCB exhaust. For some reason it has been welded across the middle, maybe a PO tried a cut-down variation. Also, there are no bolt holes for stays and the cut-out in the top left corner is isn't there.


Are the stays really necessary or would they foul the Maniflow three branch exhaust manifold?

I'd like to put a stainless heat shield on but wouldn't want to have to butcher it, would one fit without modification?

It was only when I read a different thread some time ago that I discovered that Sprites have breather tubes from the fuel pump to the boot. Mine has never had such a thing. It's run fine for 8 years so I guess they can't be too essential.

Colin



C Mee

Colin
I think your shield is an earlier 1098 one which lacks holes for the stays - I have one similar in the garage that came with a 1098CG engine. So it looks like those engines didn't have stays. Someone else might clarify this.
Bill Bretherton

Thanks Bill.

As I said in another thread, my Sprite is held together with a random set of nuts and bolts - but it clearly doesn't stop there!

C Mee

Bill,
as you well know I'm no engineer but I'd guess the quite intricate bends and positioning at the cable ferrule would be to give correct alignment of accelerator cable to fitting throttle cam and to strengthen the ferrule fitting so quite important.

Whilst my shield was out of the car I used three thin wire rods to check vertical alignment of, the ends of linkages, the off-centre of the cable and the trunnion fixing side of throttle lever. Which side the cable fixing of the trunnion goes makes a difference to cable alignment too (goes r/h/s).

Hope these two photos, from a previous thread you may remember, help.

I found with mine at least it was a matter of bending the rear stay rather than the shield even then it was a tight fit.







Nigel Atkins

Colin,
IIRC in my 1974 Haynes (which doesn't have all the stuff for my 1973 car and has errors) it has a photo of placing a strengthening rod to the bottom of the heatshield without stays.

My 1275 with LCB has standard heat shield with stays no issues with fitting. The heat shield you put up looks a right mess to me. The only advantage of stainless steel (other than bling) is to me as far as the s/s exhaust goes anyway is that it heats up and cools down quicker.

For the fuel pump it depends what you have fitted, if you have one of those old SU hit-it-with-a-stick points (points!) pumps then they have tubes running to the inside of the boot so that water and crud doesn't get in or block.

If you have an later fit 'n' forget Hardi (electronic) type they're not required.






Nigel Atkins

Bill,
the braided fuel hose, I hope it's not the type with piss-poor rubber hose inside that deteriorates, unseen, because it is piss-poor and sometimes very quickly.

Nothing to do with ethanol or use or lack of use of the vehicle but all to do with piss-poor rubber that (?)used to be(?) (stil is?) about.
Nigel Atkins

I agree, Nigel, my heat shield is a mess. As long as it's been doing its job it's just not been on the priority list for changing, though it's getting nearer to the top now that my engine's been re-built and is looking a bit smarter with its new coat of paint!

After a quick rummage in the garage, I can confirm that the original pump was the older style SU, complete with breather connections; they just weren't connected to anything. I fitted a Facet years ago and that has coped without any additional breathers.

Thanks for the info.
C Mee

My car bits boxes didn't include a carb heatshield so I bought an Ashley Hinton one. I went for a plated rather than SS one as I didn't want a bling version. I didn't realise when I ordered it but it came with the two stays as well. Nicely made and I thought it good value.
GuyW

Colin,
the older style SU is just that, older style, it needed the vent pipes, the Facet (noisy little buggers generally I've found) don't.

Neither does the Hardi type (mine is a QH).

The two cut strips on your heat shield I'd have thought would let exhaust heat through and the angle it's bent might have put different pull/slack to the springs.

If owners got together more with vehicles that can be be driven and passenger seat rides, or even drives, swapped more would be learnt about the cars by those that took part.

Looking at a shiny static car can tell you a lot (if it's correct of course) but a moving car that you can see, hear, smell and feel could tell you more again.
Nigel Atkins

Nigel
The most important alignment, as I see it, is from the cable seating at the top of the heatshield to the quadrant. I think I'll align it in situ after the throttle cable is installed.

The braided hose is from M**s which may bother you! I'll give it a go and call you if I break down near Northampton. Make sure you have quality hose in stock!
Bill Bretherton

My '71 car uses an SU, and like Colin's, it doesn't have the breather pipes to the boot connected up. I just never got round to fitting them and it doesn't appear to have caused any problems.

For the other car it should have a mechanical pump but I wanted electric and I have a choice of a Hardi like that one of Nigel's or an SU. I've fitted the SU. The Hardi will sit on the shelf as a spare.
GuyW

Bill, just make sure that the cable seating position is aligned with the plane of the heat shield so that the pull of the cable doesnt bow the heatshield forward.
GuyW

Guy, thanks, that makes sense. I presume that the ideal is a dead straight pull when the lever/ quadrant is either half way through its travel or quarter/ three quarters as the latter case is midway in a front to back orientation.
Bill Bretherton

Bill,
the triangular rearward bends, as per orange outline below, I think might add to alignment angle with the operation of the throttle cam bar link and strengthen to ferrule.

Under the red arrows I think should be strengthening indents too.

I'd hope that the big suppliers would have a large and fast turn over of stock of stuff like that and got through the real sh*te stuff by now, if only by sending more of it out as replacement, and responded a bit by getting in (really cheap made) better versions.

I think I've got some various 6mm named stuff, or even some short bits of 1/4", in the shed, or about 20m of 30 year old 15mm garden hose. You could have all for free if you were to breakdown in the fair county - of course me driving it out to you could cause a cost to your emotional and mental health.

I also have wire, tape, cable-ties and larger off-cuts of hoses to administer a proper classic car breakdown hero repair to give the proper intrepid, further stops for further repairs journey home to communally regale at meetings of the similarly inclined.



Nigel Atkins

Nigel

As you say, let's hope the current hose is of a good enough standard. I think the triangular indents probably add strength.
Bill Bretherton

The triangular indents will stiffen it, but their purpose is to position the ferrule in line with the main part of the shield so there's no leverage.
GuyW

I removed the heat shield whilst waiting for the boiler guy. It's bent the wrong way at the top. I'll have a go at bending it back but I'll never get that original shape - I don't have appropriate steel blocks/ dies to press it back in the vice. Might get a new one - tenner or so from AH Spares.
Bill Bretherton

Bill,
don't forget the two supporting brackets of you don't already have them.

For just heat shield, if you're in MASC you might get discount at A Head 4 Healeys, and a few pence cheaper before that anyway. - https://www.ahead4healeys.co.uk/HEATSHIELD-id12696.aspx
Nigel Atkins

I believe they are all supplied by Ashley Hinton. He does the plain steel and stainless variety
Bob Beaumont

Thanks Nigel - AH spares similar price so depends n carriage.
Bill Bretherton

Bob is right. £14.50 for shield, brackets and 6 gaskets, plus £4.95 P&P on his ebay shop. - https://www.ebay.co.uk/itm/254824799612?
Nigel Atkins

That's the kit I got (and recommended earlier) Its plated, not just plain steel. Excellent quality.
GuyW

I modified one as I have maniflow inlet manifold and twin HS4's. Worked a treat! I personally have always been happy with Ashley's products.
Bob Beaumont

Bob, Nigel, Guy
Thanks, sounds like Ashley Hinton is the supplier then. I now wish I hadn't bothered preparing and painting my original, but wasn't thining how significant the cable position is. I had a go at re-shaping mine but it's not easy without the right resources.
Bill Bretherton

Bill,
you must have missed my impressively long thread on my butterflies not fully opening as it included cable position, by association at least.

If you have factory original parts that correspond to the relevant carbs then keep with them. I still wonder if the original insulator spacer blocks being (IIRC) 21mm instead of replacement black ones at (IIRC) 23mm might make a slight difference but you work with what you've got (or is available).

Fitting the shield the brackets can be a bit awkward and out of line so best to fit the brackets loose until the heat shield and carbs are fully seated and then fully tighten brackets.

When you put the carbs back in and adjust them do check every time (that's where I went wrong by not every time) that the jets, cables and linkages are exactly where they're meant to be and with free movement and slack where required.

For setting the mixture (not that I ever successfully did) I'd recommend the proper small short handled spanner to make things easier on your fingers.
Nigel Atkins

Nigel
I did read the butterfly thread but it was before my attention turned to carbs! I battled a bit with the existing brackets but the Ashley Hinton heatshield includes them so I'll put those on. I think they're meant to be "tight" so as to hold the heatshield firmly. I don't have a jet spanner - always did it by hand in the past but it's a good idea. Yes, I can see you have to be careful with the choke mechanism to make sure the jets seat back properly.
Bill Bretherton

Or that one of the jets doesn't intermittently stick after you *thought* you'd solved that problem.

I ended up slightly bending the rear bracket to get it to line up so I could get the setscrew through the holes as I couldn't easily get to loosen the bellhousing bolt - an engineering modification!

Nigel Atkins

This thread was discussed between 31/12/2020 and 05/01/2021

MG Midget and Sprite Technical index

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