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MG Midget and Sprite Technical - How do I tell where the leak is?

Hi
I have a fairly original 1959 frogeye. There is exhaust smoke under the bonnet.
I assume if the exhaust has no holes, this can only becoming from a leaking manifold gasket or the join between the manifold and the exhaust pipe?
But to get to either, it looks like I have to completely remove the carbs! So I won't be able to tell where the leak is from, unless it's obvious from a visual inspection. Am I missing something? If there is no short cut I guess it makes sense to replace both once the carbs are off?

Many thanks, Graham
g Victors

Most exhaust shops can put it on a rack for a free looksy

Barring a hole...

my bet is on the exhaust donut is whats failed the 2nd location would be the manifold gasket

In the past ive ran the engine up hot.. esp on a hot day ... then kept my body cool and with the engine still idealing hot i just slowly move my hand and fingers over the various areas as close as I can WITHOUT touching anything and you can feel a blast of hot air where its leaking

An idea I just had off the top of my head, mark your carb settings then readjust the carbs to run really rich that would produce some black smoke to escape out the leak and would be simple to see...then just readjust the carbs back to there orginal setting you marked out

Prop

Prop and the Blackhole Midget

A variation on Prop's suggestion is to hold a piece of paper over the places where gas might be escaping. It should remain still but if it shows movement you have located a leak.
Chris Hasluck

Graham,

First check to see that the smoke is not from oil leaking onto the manifold or pipe and getting burned off.

To help locate a leak, have someone take a rag and block the tailpipe with it while you look for the leak. The build up of pressure will make a leak easier to find by sight or sound. The rag holder may need to let the pressure off every now and then.

Charley
C R Huff

Hi
Thanks for those very helpful suggestions. I will try out tomorrow if I can get the time. Only problem is that on my car, everything is tucked well away behind the heat shield.
Has anyone successfully repaired join between manifold and exhaust without removing the carbs? Not sure it is possible
Thanks, Graham
g Victors

Usually if you have an exhaust leak you will hear it before you see smoke.

I'd guess that it's most likely the manifold - downpipe joint. Overtightening the clamp can distort the bell-mouth on the downpipe (sometimes even cause it to fracture) and if this is the case, you will never get it to seal properly without straightening it out. All very much easier to do when the carbs are off. Check also that the strap between the bellhousing and the downpipe is secure (is it even there?) because if it isn't the joint will fail and you could even end up with a broken manifold.

When you put it all back together, give the mating surfaces of the joint a good clean so that the firegum (or whatever sealant you use) has something to stick to.

Simon
SA Wood

Thanks Simon.
I came up with what seems a clever little trick. With the engine cold (and the wife out). I duck taped a hair dryer to the tail pipe. I brushed some soapy water over the manifold,etc, & switched the dryer on. Immediately the tell tale bubbles appeared!
So I now know I have a crack on the the manifold, very near the rear bolt attaching to the head.
Unfortunately the old style manifold is apparently no longer available and the nice man at Frogeye spares explained the area below around the chassis will need some rearrangement to accommodate the new style manifold.
So will have a go with paste. Anyone have any views on what is good or to be avoided? Gun gum? Firegum?
Or alternative manifold that fits maybe?
Thanks
Graham
g Victors

I would consider Brazing the crack. using a grill I would heat the entire manifold as hot as you can then braze the split. continue with the heat on the grill but slowly lower the heat. This should allow the manifold to stabilize.
SANDY

The exhauste manifold is cracked ?

You can braze it shut or have a pro/simi pro do the deed, theres lot of people around with a oxy/aclt set up

Try ebay... im sure there are 12 on there right now

There are after markets and a better choice then factory unless you have to have orginal

Look thur minispares, moss, (mogc??), amazon...google under the shopping header

Theres lots of options

As long as the valves are closed... good trick, 8 points awarded for creativity

Prop
Prop and the Blackhole Midget

J.B.Weld?
Alan
Alan Anstead

I had 3 original manifolds cracked (the lying policeman over here..) Second hand manifolds, on e- bay, were not expensive, they are now! I do have a Maniflow, no cracks anymore.
Flip
Flip Brühl

Oxygen/ Acetylene and metal coat hangers. Low heat and go slow. Did this many years ago on cast iron Chev 350.
K Hawkins

Alan

I wouldnt advice JB weld.... as a hillbilly myself, ive tried JB weld to assemble my exhaust system on my old truck, it lasted about 50 miles... just to much heat, but I do love the stuff

Prop
Prop and the Blackhole Midget

Graham
If it suits. If you contact me at enquiries at midgetandspriteclub dot co dot uk I can put you in touch with someone who has an original exhaust manifold to sell.
Alan
www.masckent.org
Alan Anstead

I've successfully (so far ) mig welded the broken flange back on to the cast iron manifold on my 73 midget. That was completely broken off. So I reckon a crack wouldn't be that hard to fix. Do you have or know someone with a mig welder?
Lawrence Slater

MIG would not be a good choice for cast iron repair unless you had maybe MIG brazing wire. The low heat input of MIG leads to a chilled weld HAZ (Heat Affected Zone) and carbon take up from the cast iron leads to a very brittle weld interface likely to fracture easily. The usual advice for welding CI is preheat and slow cool. You can buy CI repair rods for use with stick welders and they work well if used correctly, they contain a high percentage of nickel so don't suffer from embrittlement due to carbon up take. You can often buy them in small packs for repair work.
David Billington

Hi Alan
That is very kind. I have emailed you
Regards, Graham
g Victors

AFAIK Frogeyes used the A35 exhaust manifold with a plate bolted over the top opening.

I think I have one on a spare engine.
Dave O'Neill 2

Graham,

I had the exact same problem on my old cast iron manifold. I had it welded but it didn't last and I bought a PECO LCB instead which hardly went anywhere near the car - that was a mistake. So I bit the bullet for a second time and bought a Maniflow LCB from Kim Dear at MagicMidget - a perfect fit - nice high quality item. I, (and I think that others here would echo) that unless you are after outright originality, the Maniflow item is a very worthwhile substitute.

Simon
SA Wood

I agree David. Everywhere i read, it said migging CI won't work. But since I had nothing to lose, I did, and it IS working. -- So far.
Lawrence Slater

This thread was discussed between 23/04/2015 and 27/04/2015

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