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MG Midget and Sprite Technical - Oil leak from front of cylinder head joint.

Seems that I ought to relocate this thread as it is becoming ever more technical.
OK, I have a 1275 with a 12G940 head that started leaking oil, slightly at first.
It is I think leaking from the front of the head gasket, which I have replaced twice. First time a copper / stainless(?) type, then a payen Metro Turbo type.
The problem became apparent soon after an overheating problem where the radiator lost it's top pipe dumping most of the coolant in one go. Luckily the engine was fairly cool having driven only 2 winter miles.
Today's findings:-

I decided to look at the engine while it was running to see if I could see exactly where the leak is coming from. At high-ish revs - about 3-4000rpm at a guess - you can suddenly see oil trickle out from the front, at the cylinder head joint underneath the brass plug that Guy so kindly mentioned. The slipstream from the fan blows it immediately up and round the front of the cylinder head where it drops again a few inches back to the joint.
My questions are:
1)Is it likely that the head, or block worse still could be cracked there?
2) If not, is there any sealant / metal filler that could be used to bulk up any low spot in either casting? It's far enough away from the actual cylinder bores to not have the heat and pressures acting against it.
(I do have a granite datum block which suggested that the C/H was pretty well flat, with no obvious low spots, so would be able to dress any metal fillers down to surface by hand.)
3) If the block needs skimming is it necessary to completely strip it of all it's parts?
Any further comments would be most gratefully received!

Dominic Excell

Dominic,

Before I saw you started this thread, I commented on the General one. To what I said there, I would add that if you started with a cool engine, it might be better to remove the fan to observe the leak.

I don't quite understand you use the granite block. It seems to me that if you put the head on a block, you can only see the very edges of it. Normally, you use a known straight metal bar, something like a framing square if you don't have the proper tool, and you check all over the head surface with that. Use light to see if there is any warp, and use feeler gauges if you want to measure the warp.

Charley
C R Huff

Charley, using a granite (or cast iron) block is simple - one uses a sticky blue substance "engineer's blue" spread extremely thinly over the granite block. Carefully setting the C/H down and moving it around picks up blue on any high spots. It also adheres well to one's nose when that sudden itch develops. Of course one only notices the blue nose after having spent a few hours around the town bumping into everyone one's ever known.
And how the hell does one remove the fan with radiator in place? There's only about a 1/2" clearance between the 2...
Dominic Excell

did you use Engineer's blue on the head on the granite block to check for high spots.
mark heyworth

you must type quicker than me
mark heyworth

I did Mark, a very slight (1/2 thou) area between sparkplugs 3 & 4 but that side seems to be completely sealed.
Dominic Excell

have you no way of blueing the block and checking it
mark heyworth

Dominic,

Thanks for the lesson on the granite block. I had not thought of that. Funny how no one will tell you that you have a blue nose. I mean, do they think you did it on purpose?

I was speaking in generalities about the fan. It's been years since I had to deal with that on my Sprite. You could take the belt off if you limited your run time with respect to the water pump being idle.

Charley
C R Huff

I guess people are too polite to mention the blue nose.... maybe they think you've been at the antifreeze again?
Dominic Excell

Being a Brummie quite a few of the people I see around town are Bluenoses

Maybe the people you met felt sad and sympathetic towards you and didn't like to rub it in

;-)

The oil leak is probably from the metal ring area at the front of the gasket

I usually add a ring of RTV round the copper ring area on both faces of the gasket, just in case this happens

As you can guess I have had that happen to me once

But not since I started doing this

Just a smidgen close to the oil ring
Bill1

Thanks Bill, please enlighten me as to what is RTV?
We have loads of blue-noses here in Blackpool too... and I bet they haven't been flattening cylinder heads with a scraper, using engineers blue....
Dominic Excell

he he

RTV =- Room Temperature Vulcanising silicone sealant

I have used Hylomar too but since the head temperatures are awf'y high I started using RTV a few years ago as a precaution

In all honesty I never had trouble with Hylomar either
Bill1

RTV is a type of sealant - 'room temperature vulcanisation' IIRC.
D O'Neill

I was going to say that I must type faster, but really I must read faster, as I was reading through the whole thread! ;o)
D O'Neill

That's alright Dave. I never knew what RTV meant so I probably needed to be told twice.

Bill, are you using a particular hi-temp RTV or does all of it take heat well? Not that it is scientific, but I never thought it looked like it would hold up well to high temps.

Charley
C R Huff

Hi Charley I usually use the RTV that comes in big tubes for automotive use, usually clear type

I have always wondered about its heatproofedness but it seems fairly intact when the head is taken off it

Bill1

RTV....I never new what the acronym stood for ither

That said... a couple of important notes

There are variations of RTV, some handle oily issues better, some handle heat better, some are more mositure resistant

But ALL WILL CLOG YOUR OIL GALLERIES and blow up your engine...be very carful, this stuff never breaks its basically rubber in a tube, so use every percaustion when using this around the oil hole ... cause if it gets loose, its going somewhere to find a new home, and it wont be outside the engine block...just be very carfule with where you apply this stuff

Nigel probably has a hand book for the stuff, and denny probably got a case of the stuff for free...haha

Prop
Prop and the Blackhole Midget

RTV....I never new what the acronym stood for ither

That said... a couple of important notes

There are variations of RTV, some handle oily issues better, some handle heat better, some are more mositure resistant

But ALL WILL CLOG YOUR OIL GALLERIES and blow up your engine...

be very carful, this stuff never breaks down its basically rubber in a tube, so use every percaustion when using this around the oil hole ... cause if it gets loose, its going somewhere to find a new home, and it wont be outside the engine block...just be very carfule with where you apply this stuff

Nigel probably has a hand book for the stuff, and denny probably got a case of the stuff for free...haha

I also posted on the general side... and I to mentioned that the crush washer has gone bad... rtv probably wont help being you will need a new HG

Proap
Prop and the Blackhole Midget

Hi all, the cylinder head is now back from being skimmed and I've just cleaned up the holes putting a very fine chamfer on each one (not far from invisible) so that there is nothing to get between the 2 surfaces.
I find that I can just get a .05mm (.0019) feeler in at the very front where the oil was escaping from, very much an interference fit. Is this gap within acceptable limits or do I still need to do some work on the face of the engine block?
By the way the new Payen gasket has a much better crush washer around the oil hole than the others I fitted, it looks like a rubberised layer to it which should help.
Any comments would be gratefully received as always!
Dominic Excell

Your .0019" is within most machining tolerances and the head gasket should, easily, take care of that fact. Racers have been known to lap the block and cylinder head together for an almost perfect fit. Certain assemblies on machine tools are fitted closer than .001", by a process called "scrapping". Either process is quite labor intensive and, in my opinion, not necessary on any relatively standard automobile engine. You should be fine as is.

Les
Les Bengtson

Thanks Les! Sounds good to me!
Dominic Excell

Does anyone think it would be a good idea to pre-tighten that corner just a bit before swinging into the torque sequence? I was thinking maybe 15 ft lbs and then go to the normal sequence. I've never done this, but it does occur to me.

Charley
C R Huff

I'll use the cylinder head as my "surface or datum" plate, and try and match the top of the block to that (within reason!) Hopefully will be fairly close now. Engineers blue on the cyl head face, and then see what high spots still remain on the block.
Dominic Excell

Dominic. When machine tool rebuilders match up the ways on milling machines and lathes, they do not use "Engineer's blue" (Dykem) because it is, itself, about .001" thick. Having had some friends in the machine tool rebuilding business, and having done some similar things in the firearms area, I would suggest that you simply install the Payen head gasket and get on with driving. Nothing more need be done.

Les
Les Bengtson

Les,

Are you thinking of the right Dykem product as they do one for picking up high spots such as Dominic is using , engineers blue, and a layout dye which is also blue and much thicker such as the 0,001" you mention. The former can be used to tell much finer detail.
David Billington

This engineers blue is nowhere near .001" as it is smeared on as sparingly as possible, leaving just the thinnest trace left to transfer to the high spots. I doubt if it's as much as .0001" when properly applied Les. I know the stuff you mean though, and as David says is a layout blue. Hopefully will be driving again tomorrow!
Dominic Excell

I suppose you could use copper dye to check for marks.

At my old works if I needed some very delicate scribing I used to pop round to the testing lab attached to the toolroom where the scientific types would prepare us an amazingly fine dye by adding copper sulphate to dilute sulphuric acid. (I THINK!)

Wipe over clean steel and you could mark the finest of scribed lines to work to.

No discernible thickness to it either just a chemical copper pink coloured steel.





AND back to the head

With such a small gap I would just trust the Payen gasket.

There's a reason we put lots of trust in Payen's products after all.
bill l

HGF. Third attempt of yours truly the novice. Payen and fixed.

Say no more.
Dave Squire

Head back in place now, ready for tightening down tomorrow. New Payen gasket, high-spots removed.
Someone on here mentioned a possible blockage or an undrilled rocker pedestal as a possible cause of excess oil pressure. It looks as if the rocker shaft may not have been in alignment so the holes weren't matching up. They do now so it's wait-and-see time tomorrow!
Dominic Excell

I was being stupid. (or maybe just tired after a long day at work and a long evening in the garage). Of course the oil holes match up, thanks to the grub screw with the squared off end and the locking washer keeping it captive.
Dominic Excell

So is it working...

Prop
Prop and the Blackhole Midget

It is indeed Prop, started 1st turn of the key. Kept it running for 15 mins to set the exhaust paste (all this dismantling and rebuilding took it's toll on the exhaust / manifold joint) and will be taking it out for a run tomorrow. Re-torque time next weekend. No signs of oil yet but I won't worry too much until after it's 500ish mile re-torque.
Dominic Excell

Thats great news dom ... congrats and good luck

Prop
Prop and the Blackhole Midget

Thanks matey!
Dominic Excell

This thread was discussed between 26/05/2014 and 07/06/2014

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