Mayonnaise

[Tootall]

The sun's out and the salad days of summer are here, so naturally thoughts turn to dragging the convertible out of hiding.

Or, more accurately, trying to work out why the poor old dear wouldn't start a couple of months ago, when I first tried to stir her from her slumbers.

Then, she spluttered onto two cylinders, very occasionally three, and simply wouldn't idle.

The breather cap and rockers were liberally coated with mayonnaise, as was the dip stick.

Since returning to the road about 18 months ago, she's had little use and - to be honest - I'm not quite sure when she last had oil / water / filter changed. Not recently, I admit.

She's got a well-built, balanced 1275, with a properly-worked Cooper S head and fast road cam, so it should be a sweet little engine. And normally it is. Last summer she started no problem and charged about the place, seemingly happily, on the race occasion when I got to drive her.

However, suspecting a head gasket problem, I took her apart last week.

Warning: Please turn away if you're faint-hearted...

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Looks like the head and gasket are OK. I have just re-fitted the head, with a brand new Cooper-Payen gasket and everything is back together, with new plugs and all new leads.

She fired up pretty much immediately this morning but refuses to idle. With a lot of throttle, she'll hold a lumpy 1000rpm but the moment you let off the gas, she stalls.

All four seem to be running, so I'm looking accusingly at my carb - a single 1 3/4 SU (HF6?)

Any bright ideas what might have gone wrong with it over the winter?

Is there something I can do, before unbolting it and posting it to Burlen Fuel Systems?

[mogbob]

Before you write out the label for Burlen.
You don't say if you worked on the carb before or it's condition. If it was working before I'd try a blast of carb cleaner. Remove the air cleaner and inspect the cleanliness of that. There may be dirt in the fuel bowl / grit in the needle valve .Remove the lid carefully , so as not to break the gasket. Squirt the needle valve and gently move the float to check operation. Squirt the carb cleaner down the air inlet opening to get the needle , piston area clean. Check that there is oil in the dashpot and that the piston drops freely onto the bridge with a clonk.

See what impact that makes on performance. You can buy overhaul kits for the carb from Burlen , increasing in complexity , depending on the issues on the carb. A full gasket set as a minimum if you're going to take it apart yourself.
Bob

[simmitc]

Regardless of the carb, all that mayo looks like a mix of oil and water. Did you check compression before you removed the head? What's the radiator level and content like?

[oliver90owner]

Does it have a working thermostat?

Re starting and running - is the fuel stale?

[philthehill]

I would disagree with the statement that the head gasket is good - the head gasket surface between No:2 and No: 3 cylinder is not good.
Compare the gasket between the other cylinders and you will see what I mean. They are nice and shiny.
Water could have been seeping between head and block and causing the oil to mayonnaise.
The gasket shown as fitted would not be my gasket of choice - the copper faced head gasket is the best.

http://www.minispares.com/product/Class ... assic/head gasket.aspx|Back to search

[les]

If the S head is the original type, rather than the 940 casting, cracks are quite common.

[philthehill]

940 head fitted with larger valves at the top and 12G185 original Cooper S head below.
The 12G185 head had the valves closer together so less metal below and around the valve seats to allow the transfer of heat and the head was very prone to cracking between valve seats.
The one good thing about the 12G185 head is that it can be fitted to a small bore engine without having to worry about sinking the valves or clearances. Non sintered rockers also fall correctly and centrally over the top of the valve stems.
The 12G185 head pictured was removed from a 948cc engine.
Note the combustion chamber shape - virtually the same as the 948cc/1098cc combustion chamber. Also the lack of brass water flow restrictors at the front and rear of head.
It was supplied in 9 stud and 10 stud/1 bolt variants.
The later 1275cc Cooper S head was stamped 12G1805 at the front of the head on the flat face next to the thermostat housing.
Again in 9 stud and 10 stud/1 bolt variants.
The later Cooper S head had the valves further apart with a revised internal casting/water jacket which resulted in a more reliable and less prone to cracking head.

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[Tootall]

Today's (lack of) progress...

Stripped and thoroughly cleaned carb. Refitted and rebuilt it all. No change, chuffing along at 1000rpm on full throttle and stalling immediately throttle released.

Suspected coil. Replaced coil with brand new unused one. No change.

Eyed distributor suspiciously (Aldon Automotive electronic dizzy.) Removed cap, all clean, not sign or arcing. Squirted lubricant under plate, just in case. No change.

EXCEPT, on the second time of trying, the engine revs gradually built up to 3000 and I was able to gently rev it. When I released the throttle, however, she stalled and I have not been able to replicate this since.

Squirted more lubricant in dizzy to hopefully do more penetration overnight.

This is the head: not a big-valve Cooper S but it is a 10-stud S head...

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I agree that the fuel is likely not the freshest, after 6 months in the lock-up... but it should run OK, if a little fluffy.

If the head had cracked or the gasket had blown, how would that produce the non-revving symptoms I have? Granted, it'd be a cause for the mayonnaise but what's perplexing me is how a car that drove perfectly well when it was reversed into the garage now won't even idle...

Haven't got a compression-tester but may have to look for one in Halfords tomorrow...

Still looking for ideas on the fuel / sparks / timing front, to see if I can cure this...

[Tootall]

I would disagree with the statement that the head gasket is good - the head gasket surface between No:2 and No: 3 cylinder is not good.
Compare the gasket between the other cylinders and you will see what I mean. They are nice and shiny.
Water could have been seeping between head and block and causing the oil to mayonnaise.
The gasket shown as fitted would not be my gasket of choice - the copper faced head gasket is the best.

http://www.minispares.com/product/Class ... assic/head gasket.aspx|Back to search

The gasket is the one recommended by the engine builder and as supplied by Mini Spares. Between 2 and 3 some of the black material has gone, which is why I fitted a new one...

If the gasket was blowing, I'd expect mayonnaise and a loss of power, perhaps - but I'd still expect the thing to idle and rev, neither of which it currently does.

I'm happy to fit a copper faced gasket but I still feel I have some sort of timing / electrics issue...

However, it has been AGES since I've tried to diagnose any problems with the car, so very happy to follow all leads.

My only basis for judging is that when I first had the car, I had a warped head for quite a while. Living in Bucks and working in Leics, I used to fit a new head gasket midway through my journey every single day, for about three weeks, before I had a day when I could drive to a machine shop, whip the head off and have it planed. At all times, however, the car started and drove... which it currently doesn't...

[Tootall]

Before you write out the label for Burlen.
You don't say if you worked on the carb before or it's condition. If it was working before I'd try a blast of carb cleaner. Remove the air cleaner and inspect the cleanliness of that. There may be dirt in the fuel bowl / grit in the needle valve .Remove the lid carefully , so as not to break the gasket. Squirt the needle valve and gently move the float to check operation. Squirt the carb cleaner down the air inlet opening to get the needle , piston area clean. Check that there is oil in the dashpot and that the piston drops freely onto the bridge with a clonk.

See what impact that makes on performance. You can buy overhaul kits for the carb from Burlen , increasing in complexity , depending on the issues on the carb. A full gasket set as a minimum if you're going to take it apart yourself.
Bob

Hi Bob,

I stripped it all this afternoon, cleaned it and reassembled, with fresh oil in the dashpot. Absolutely no difference. Will try a few blasts of carb cleaner as well, for belt-and-braces...

[Tootall]

Regardless of the carb, all that mayo looks like a mix of oil and water. Did you check compression before you removed the head? What's the radiator level and content like?

Radiator needed occasional top-ups last year... I suspect I have a porous pipe or two... Haven't had a change to compression test... Rad is now full of clean water after removing the hoses to remove the head. Hasn't lost any yet but then has barely run at all...

Would overheating cause the non running symptoms, though? That's what's perplexing me...

[Tootall]

Does it have a working thermostat?

Re starting and running - is the fuel stale?

Thermostat DID work last year.

Fuel very likely stale... but would it cause my non-idling, non-revving symptoms?

[RobThomas]

One way to find out...for just the cost of a few wasted gallons. Still cheaper than another head gasket set.

[les]

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The head you have has the valve heads virtually touching, this closeness I had in mind when mentioning cracking, aeg163? However I'm not saying that's your problem, just a possibility, as with these heads it's relatively common. As Phil posted the head was discontinued because of issues. I don't know if cracking is common in a 940 casting with big valves. Anyhow, good luck.

[ianmack]

One way to find out...for just the cost of a few wasted gallons. Still cheaper than another head gasket set.

There’s no need to waste stale petrol, add it in small proportions to your fresh petrol, once it’s running properly.

[philthehill]

What is the casting number of the head which can be found on the top of the head?
You mention 10 studs.
The heads are either 9 stud or 10 stud and 1 bolt.
There is not a factory 10 stud head variant.

Looking at your photo of the head above the gasket seating areas around cylinders 2 & 3 does not look good.
I would suggest that you clean it all up and check the face for trueness. Anything more than 0.003" and the head requires a skim.
The head gasket can weep so causing mayonnasing but not show a discernible loss of power.

Les
I did have a large valve 940 head crack on one of the valve seats but managed to machine below the crack and fit a valve seat insert.
In the main 940 heads do not suffer from cracking unless pushed to the limit as regards valve sizes/seats.
Phil

[Tootall]

Today's (limited) progress...

Before pulling out the distributor, I thought I'd just loosen the clamp and try altering the timing... I advanced it substantially (around 10-15 degrees around from the mark where it was originally...)

Guess what?

Fired immediately, ran (pretty) cleanly, revved past 5000 and - once I'd adjusted the idle screw, idled.

So, somehow, between being parked and having the garage door opened again, the timing had retarded itself to the point where it barely ran at all. The clamp was tight the whole time, by the way, until I loosened it off today.

The plugs - which were jet-black after yesterday's chugging - were soon a whitey-grey.

Sensing this might be a good thing, I closed up the lock-up and started for home.

For the first mile or so, all was good, then it became clear the car didn't really pick up well from low revs, though it ran without fluffing through the rev range quite happily.

One long incline before home, it started to miss, so I changed up early into top... but it just slowly died.

Bonnet up, No1 plug removed, crank over... no spark. Same with no2 plug.

Got a lift back to the lock-up, picked up spare coil. Tried with that, no spark.

Towed the car home, where tomorrow the distributor is coming out.

I'll have a look inside before packing it off, back to Aldon Automotive, where it was rebuilt a couple of thousand miles ago...

I will be interested to learn what they find...

Old cars. Don't you just love 'em?

[Tootall]

What is the casting number of the head which can be found on the top of the head?
You mention 10 studs.
The heads are either 9 stud or 10 stud and 1 bolt.
There is not a factory 10 stud head variant.

Looking at your photo of the head above the gasket seating areas around cylinders 2 & 3 does not look good.
I would suggest that you clean it all up and check the face for trueness. Anything more than 0.003" and the head requires a skim.
The head gasket can weep so causing mayonnasing but not show a discernible loss of power.

Les
I did have a large valve 940 head crack on one of the valve seats but managed to machine below the crack and fit a valve seat insert.
In the main 940 heads do not suffer from cracking unless pushed to the limit as regards valve sizes/seats.
Phil

Looking at that pic of my head, I think there are the studs on the rockers (three?) the studs on the other side (5) and one stud/bolt at either end... honestly, I can't remember exactly... and it's dark outside now...

The head may well need looking at... but the rough/non-running seems to have been down to the timing/distributor...

[johngrigg]

Does your Aldon dizzy have a vacuum advance? It all sounds rather like the advance mechanism ,whatever it is has stopped working . Maybe seized up while at rest in your garage. This would at least explain why advancing it up provided a temporary cure. Cheers John G

[Tootall]

Does your Aldon dizzy have a vacuum advance? It all sounds rather like the advance mechanism ,whatever it is has stopped working . Maybe seized up while at rest in your garage. This would at least explain why advancing it up provided a temporary cure. Cheers John G

No vacuum advance on this dizzy.