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MG Midget and Sprite Technical - head gasket gone ?

car is running on wot appears to be three or sometimes two cylinders, checked for spark and all seems good with sparking at the plugs, im guessing that the head is main culprit so going to do a compression test, anybody have any other suggestions. dan
d a hadaway

I had a 1275 head fail and leak water into the inlet passage. That didn't help the running any but wouldn't have shown any issues with compression.
David Billington

I once saw someone identify a misfiring cylinder with one of those remote infra-red thermometer guns. It was on a V8 and difficult to be sure which cylinder was the culprit, but the infra red gun showed that one cylinder was running cooler than the others. It gave an instant diagnosis when two other "specialist" garages had failed to spot the problem.

Maybe this is common place but I thought it a cute way of dealing with it. Some may know the garage as they have a strong MG connection. It was the smart and rather cute daughter of the owner of Dreadnought in Calendar who quickly put the other experts to shame!

Lesser mortals just pull the plug leads off in turn to see which one doesn't worsen the misfire!
Guy

thanks for those comments , just been looking at prices for head gaskets at moss etc. also looked at ebay, they have complete gasket sets for the head inc gaskets for manifold etc for about six quid, they must be crap??? the moss ones are about 25 quid just for the head, that was wot i was expecting, any body any recommendations. dan
d a hadaway

Ah, Dreadnought Garage. The Caledonian Centre of the MGCC have a strong link to them and we have technical sessions there from time to time. Claire Luti is definitely NOT the usual image of a mechanic. As you say, she is trim, cute and generally nice, but also is a prodigiously expert motor technician. Her brother Paul is a demon MG TF racer. The TF is generally not quite as fast as the best ZRs on track, unless Paul is driving it! I've seen him in action at Silverstone - gripping stuff.
Mike Howlett

As far as head gasket going some signs that you sometimes get are

missing whilst running
loss of power
coolant in the oil (white mayonase but this can also be from short journies only)
gases in the coolant
can runs hot
lost of coolant

these things are not always all present or noticable at the beginning at least

You can buy a Frost block test kit if you think it really might be HGF - http://www.frost.co.uk/automotive-engine-and-mechanical-tools/block-tester.html
also see, this page, ignore title and very top of this web page - http://www.frost.co.uk/how-do-i-flush-and-refill-my-cooling-system
Nigel Atkins

Go to your local Partco and buy from them a payen head gasket set with a composite (black) headgasket

Not sure how much that will be but a headgasket BK 450 on its own is about 15 quid and you then need a manifold gasket say a couple of quid and a rocker gasket another quid total must be less than 20 quid.

When you have this take a couple of hours and remove the head to see what is wrong.
Robert (Bob) Midget Turbo

Agree with Bob - Try your local first, e-bay as a last resort! local parts companies are often much cheaper than the specialists and as it's standard a series stuff often will have what you want in stock. I have bought head gaskets and wheel cylinders for example. You can take it back if there is any problem and no postage or waiting also!
John Collinson


Hi Dan,

I did my head gasket the weekend before last, was running OK but weeping coolant from the back of the block and no other noticeable symptoms. But, having done it, the engine definitely feels 'stronger'.

I bought my head gasket kit from Minispares, came to just about £20 for the set. I've always found minispares to be reasonable (ie cheaper than the MG suppliers) and good service. Think the BK450 was £12.

First time I've done a midget head gasket, albeit having done a Mini in the past, it took me a (longish) morning to do the job...half way through the job I decided I should have jacked the front up high to make it easier on my back.

Go for it,
Mark
MarkH1

if you're going to do the head gasket

(I'm not sure this has been established as the cause of your problems but I might have missed something or forgotten)

as well as replacing oil and filter

then if you've not already done so in the last few years you could also clean the cooling/heating system and replace the coolant

rad, heater matrix and engine block (block has drain plug) - flush, back flush, flush, clean, flush, back flush and flush til clear

course that could lead on to replacing hoses and other stuff

Good time to do this sort of work, better weather, ready for summer use and your not doing the extra work as a distress job
Nigel Atkins

just had another look to try and convince myself its not the head gasket, im sure it is, as i said there are sparks at plugs but front two cyclinders[nearest rad] not doing there job. thought maybe its the carbs but dont see how really even though they are a little worn. if it was carbs i would imagine the promlems would be a little more gradule. oh well weekend job to do. just thought nigel, i have the mot soon, might fail this time lol
d a hadaway

sorry about my spelling
d a hadaway

Don't worry Dan it probably wouldn't fail on HGF :)

Check the Archives there's been a couple of long threads fairly recently about similar problems

It's the full diagnostic path required bit - perhaps Bob and Guy have tired of the process and battling all the scattered suggestions

Unless you really want to take the head off for the experience why not send off for the £40 Frost kit - you could get your money back by testing for others
Nigel Atkins

I was waiting to hear the results of the compression test that Dan said he was going to do. Surely that is the first step - it should confirm the problem if it is a HGF sufficient to be the cause of the misfire.
Guy

Dan,

Anticipation is what's worrying you... Changing the head gasket really is not a drama. If it is the H/G that has failed (Compression test should show this easily), don't use the car.... If it's blown between cylinders it will burn the head and possibly the block. Attend to it sooner than later.

As reccomended above, if it's a 1275, use the BK450 gasket.

Mark.
M T Boldry

Guy, I reckon I might know one or two people who might have or know someone with a compression tester but I'd have thought most people just looking after their car wouldn't have such kit to hand

but I see where you're coming from

I know a mate with plenty of the Frost kit left, if Dan lived nearer he'd happily test it for him
Nigel Atkins

I have a compression tester and run a test on my car at regular intervals - every few months. The test itself, and more importantly the record of tests carried out over a period of time are a useful check on the overall engine condition. Compression testers are cheap enough and I think are a useful addition to the toolbox. One of the top 5 anyway.
Guy

Sorry no it would just give me another (or two, or three, or four) thing to worry about

Anyway I wouldn't have a clue what to do with or about the information I gained from this, oh, no
Nigel Atkins

http://cgi.ebay.co.uk/AUTOMOTIVE-COMPRESSION-TESTER-GAUGE-KIT-PETROL-ENGINE-/250689979901?pt=UK_Diagnostic_Tools_Equipment&hash=item3a5e4985fd

- Although at that price I must admit I would wonder about the quality! For general testing accuracy isn't actually that important, although one would want something that was consistent.
Guy

A compression tester is an invaluable diagnostic tool. Definitely worth checking compression before pulling the head.

Might also be worth checking that your throttle linkage hasn't worked loose. I once bought a 1500 Midget which was running a bit rough and needed choke just to get it moving. My mate drove it back from Bristol for me,,,rather slowly!

When I took a look at it to try and find the cause of the problem, I noticed that the throttle linkage had come loose and the front carb wasn't opening at all.
Dave O'Neill 2

I just had the exhaust gas test done on the radiator, which came up positive - so definitely head gasket? Or, should I still get a compression test done?
gusangora

just got my compression readings they are as follows starting from front near rad. 1=150 2=135 3=155 4=160 i had to do when the engine was cold, looking at no two cylinder [which i double checked] i guess this means head gasket?
d a hadaway

The readings aren't *that* bad. OK, no 2 is a bit lower than you would like and would need investigating.

I checked my brother's recently acquired MGB a couple of weeks ago and that was 160, 130, 160, 160, but it runs fine with no missing, smoking or anything.
Dave O'Neill 2

David,
I agree with Dave - those figures aren't conclusive of a blown head gasket. Often a blown head gasket will give two adjacent cylinders markedly lower than the others. Yours doesn't look like that to me, and the low one is only 15-20 down on the others which might suggest the valves could do with lapping but nothing serious. I doubt if it is anything to do with your misfire.

Did you do the tests on each cylinder exactly the same? i.e. all 4 plugs out, tester screwed in properly to the cylinder being tested, foot right down on the throttle pedal and then count the same number of engine revolutions for each. I usually count to 10, take a reading and then repeat. It also then helps to redo the process, adding a small amount of oil before each test. This will help to identify between bore leakage and valve leakage.
Guy

im a little puzzled by it now, just been out and started the car it ran on all cylinders for about two minutes, it sounded fine but then got rough and went back to two cylinders, as if the front two cylinders were been flooded by the front carb, wierd
d a hadaway

And when it begins to sound rough, what does the tachometer needle do? If it flickers, then it is an electrical fault, not a fuel fault.

Although if it is on the HT side then it may not make the needle flicker either. Could be a spark plug or HT lead failing as it warms up.
Guy

i think i may have to buyv new plugs and leads although i think there ok. do you think its possible that the coil is at fault, just clutching at straws now
d a hadaway

If it had been my car I would have done a simple headgasket change because by doing that you could have been sure it was fine and you could have been able to check all the valves. These things can be assertained by other means without removing the head admittedly but it is not a difficult job to do, unlike it is perhaps on a Ferrari V12.

Secondly it does sound like you carbs may be the problem so setting these up would be a good idea before you commit the major sin of changing everything that does not require changing.
Robert (Bob) Midget Turbo

Bob is right, you really need to try and diagnose the fault before you just start changing items at random.

That may work for a mechanic for a modern car with the backing of a store-room full of parts that can be tried and then returned to their boxes (or charged to the customer anyway, even though there was nothing wrong with the original!) But it is not the way to deal with a problem on a classic car! The only exception is possibly swapping plugs around to see if the fault follows the component or stays with the same cylinders.

The best start would be to do a proper methodical service (as often recommended by Neil)
Guy

I'm with Neil

I was going to suggest starting from a full and proper service as I'm sure Dan said he'd got a copy
of the owners Handbook

Regular full and proper servicing and maintainence can help to prevent, find or rectify problems like this

. . . I wonder if Neil gets commision on those Handbooks

I discovered a faulty HT lead one Xmas night when I lifted the bonnet to see it sparking in the dark - was it a sign, yes it was, it was a sign iterminent faults can be hidden in components that look in good condition and are not

another intermitent fault that would stop the engine dead was a dissy cap on a V8 that looked fine

these are why I do the 36,000 mile service asap after first buying the car now to save these interminent faults and breakdowns and frustrations and not making destinations or enjoying the drive
Nigel Atkins

well good news i have discovered the prob, after taking those compression readings and hearing your advice i decided to look elsewhere for the solution
i.e the carbs. took the front dashpot off turned on the ignition and hey presto fuel gushed out like a fountain,so it appears the needle valve is faulty and the fuel pump just keeps on forcing the fuel though the jet therfore flooding the two front cylinders. i have had the car running on all cylinders , but as you watch the carb intake you can see a build up of fuel and the car starts to sound spluttery but then a few revs and back to normal. i did dismantle the carbs to some degree but they are very worn on the spindles , so its a rebuild kit or some nice shiney rebuit ones,

so who is going to be first to shoot my theory down in flames lol . dan



















d a hadaway

>>so who is going to be first to shoot my theory down in flames lol . dan<<

Guns loaded and ready :)

which of your theories?

learn from others advice (and in my case mistakes)

Bob & Guy - >>you really need to try and diagnose the fault before you just start changing items at random<<

You could follow advice given in other thread or just change the float adjustment or change needles and seats but note my trouble with float needles and seats as per my post in - http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=thread&access=&subject=97&source=T&thread=201104271654587921

Nigel Atkins

OK Dan, I am not going to "shoot your theory down" far from it - the fuel level should be such that it doesn't actually flow out of the jet in the carb mouth. It gets sucked out by the venturi effect when the car is running. So with the engine off your are quite right - fuel should not be "fountaining" out of the jet, at least certainly not when the choke is pushed fully in.

So the fuel level in the carb is too high. Could be a punctured or wrongly adjusted float, but more likely to be a leaking needle valve. Easy to change, or maybe just remove the needle, flush out the bit of grot that is making the valve stick open, and job done!

Of course - just because you find and fix a problem, don't assume it is the only problem!

Do the methodical service that Nigel (not Neil, sorry!) is always recommending!
Guy

Will the BK450 gasket do the job on a 1098 engine? I'm about to have my head skimmed to increase C.R. and I would like to get a better than standard head gasket to cope with the increased pressure.

Bernie.
b higginson

Bernie,

I would assume the big bore ie 1275 BK450 would work as the big bore gasket is what is used when a 1275 head is fitted to a small bore block though I would be inclined to use a good quality small bore gasket if you have the standard small bore head option even with raised compression. If you did use the larger bore gasket you would want to work out what difference it would make to the compression ratio.
David Billington

Dangerous to assume anything.

The 1098 12G295 head has a large waterway hole in the head, close to number one cylinder. The hole in the head is larger than the corresponding hole in the block.

The fire ring on the 1275 gasket will overlap the hole in the head, but not the hole in the block.

The 1275 head has a smaller hole in it, so the fire ring doesn't overlap the hole.

The small-bore gasket has a hole the same size as the hole in the head.

With me so far?

The small bore block tends to corrode around the waterway, as there is a larger hole in the gasket.

If you fit a 1275 head to a small bore block, you need to make sure there is no corrosion around that hole, or the gasket will blow and a flame will shoot out from the front of the engine!

Don't ask me how I know.

Therefore, the 1275 gasket will not work on the 1098 engine when using the standard 1098 head.

I would try talking to some A-series/Mini tuning specialists to see what they would recommend.
Dave O'Neill 2

Dave,

I'm aware of that issue now as I fitted a 1275 head to a 1098 that had a bit of corrosion on the block surface and the fire ring just slightly overlapped the damage causing some weeping and pressurisation of the cooling system. I wasn't aware of the issue at the time I did the mod but initially corrected the symptom by moving the expansion tank take-off to the downstream header tank then solving the problem by welding up the small corroded section under the fire ring. BTW it did go well with the 1275 head on and a 276 IIRC cam, seemed to pull as normal at low revs then took off above 3.5k IIRC.

Anyway thanks for posting a more full list of potential issues with using the big bore gasket on the small bore engine. I'd go for the quality small bore gasket on the engine as I mentioned before.
David Billington

This thread was discussed between 26/04/2011 and 01/05/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.