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MG Midget and Sprite Technical - Head repair

Can alloy heads be repaired ?
The gasket mating surface has erroded over a localised 10mm patch. Could a specialist build this up with TIG weld and then grind it flat ?

Head cannot be skimmed.
Guy

putting that much heat into an alloy head I would worry about two things...

1. Distorting it due to high heat input into a localised area.

2. Altering the metalurgy of the alloy (softening the metal in the weld area) which might cause other problems. The extent of this is dependent on what alloy the head is (I guess unkown).

This said, I have no practical experience of welding or repairing alloy heads. Just in welding of other aluminium structures, it's a PITA!

Cheers,
Malcolm
Malcolm Le Chevalier

Guy
Talk to your local engine reco place, it's a fairly common problem
Our local reco man does it all the time, spark plug holes and corosion around coolant holes where the corrosion has crept in under sealing rings on the gasket are the most common ones he fixes up
He uses gas and a low melting point Eutectic aluminium filler rod with great results
Cheers Willy
William Revit

It depends on the alloy the Head is made from.

I have quite often had Climax race heads welded (indeed my 'Man' adds weld to the inlet ports before re-cutting them at a better downdraught angle).

However, modern alloys such as LM25, as used in the K-Series engine, can not be reliably welded owing to the fact that the alloy is quench hardened on casting; welding it merely causes it to anneal, soften, and loose structural rigidity.
Deborah Evans

Thanks for the comments.
I was posting from a smart phone before and couldn't upload the photo. Here it is now.
The head is a "modern" (2002) of Italian origin so who knows what the alloy is.
Definitely a specialist job, but I knew that at least Malcolm was a metallurgist of some description and might know!


Guy

Me? A metallurgist? Wow, I'm flattered!

Not technically, just wasted a lot of time at university researching the post-weld heat treatment of high strength alu alloys. It doesn't actually mean I know what I'm on about (and it was over 2 years ago now!)

That said, the space frame we built out of the stuff didn't break so I suppose I must have done something right!

The problem with TIG (as it is a fusion welding process) is you are melting the parent metal. therefore temperatures reach about 600+ ish degrees and all the alloy elements go into solution and as they cool and solidify again they move about into a different microstructure to the heat treated casting.

Using a soldering/brazing process as I think Willy eluded to might be more effective but if I remember rightly anything abouve around 250 - 300 degrees and you start to knacker things.

The welding of high strength quenched and soloution heat treated alloys causes much more damage than just 'annealing' the metal. The strength decrease to about 1/3 of full strength and it loses all its ductility. (i.e. the metal nolonger stretches/deforms before breaking it just breaks like snapping a bread stick, albeit a wee bit stronger).

Anyway, I'm waffling, I have no actual experience of welding cylinder heads or blocks, a specialist would be able to give you a deffinative yes/no either way.

Cheers,
Malcolm
Malcolm Le Chevalier

P.S. sorry for poor punctuation and rambling nature of the previous post. It got so long I couldn't really be bothered editing it properly!

Malcolm
Malcolm Le Chevalier

Without arguing with any of the above points, the wonder of TIG is that it is extremely localized and fast, and this does not appear to be a stressed area, and likely has plenty of solid metal beneath and around. It is a very good idea to put some work into finding the alloy and what the best filler is, since welding fillers are made to recover as much of the material properties as possible.

Biggest problem is getting all the corrosion products out of the weld. Commonly necessary to grind it out, weld, then grind the weld out as it boils all the crap to the surface. Then weld again on clean metal. I've done things where I had to repeat this several times; thought I was just incompetent, but later found that it is routine on such parts.

Finishing would be done with a file, since you can't cut the head surface, and it would be near impossible to set up to cut it flat.

There are people who do this all the time, and for the price of Maser heads, I'd go find one. Then again, it's probably just cast out of old frying pans and Fiat brake drums.

FRM
FR Millmore

Had my Golf head welded (then skimmed true) where it had erroded at 120k and when the cheap and nasty gasket (my local garage!) went at 160k it was still fine. The place that did it for me had about half a dozen a week from various manufacturers.
John Payne

Thanks all.
Malcolm you say you are not a metallurgist and then say that you researched "post-weld heat treatment of high strength alu alloys". Sounds like metallurgy to me - and appropriately relevant as well!

I can see both the point about the localised nature of heat with TIG, and the alternative of use of low melting point aluminium fillers. Anyway seems there is hope there that a specialist might be able to sort. Will report back for those interested in this non Spridget stuff!

Guy
Guy

This has prompted me to dig out my third year project!

I wasn't interested (I didn't/couldn't understand) the metallurgy. I was more interested in how the mechanical properties changed and how to re gain the lost strength.

I was a bit pesemistic in the previous posts maybe. I just get the heebie-jebbies when anyone mentions welding aluminium! I would probably actually agree with FRM, small area, plenty of metal around it, not structural. You don't really have anything to lose! And as John says it seems a common procedure.

If you ever end up bored and decide you want to build something structural by welding a few aluminium tubes together then see the attached graph. This was a 6082-T6 alloy. For none engineering folk x-axis is 'stretchyness' and y-axis is 'strength' for three samples before and three samples after welding. Basically you can see you lose half its strength and 2/3rds its stretchyness.

Cheers,
Malcolm



Malcolm Le Chevalier

I have had similar experiences to John however going on from what Deb says I have been told in the past that the K series engine head goes "soft" on the exhaust side. So maybe that is due to the material used, I personally have no idea!
Robert (Bob) Midget Turbo

I'd be interested to know what symptoms you experienced which caused you to remove the head in the first place i. e. - how big a problem is it?
Before proceeding down the "weld repair" route which as has been pointed out above, is fraught with danger,why not try sealing the fault with temperature resistant material such as Gun Gum ? After all, you don't really need the mechanical stength of metal in that area, you just need to keep the hot exhaust gas in
M J Chapman

I've watched a colleague of mine at work on an alloy head. He's a marine certifed alloy welder, swears by TIG for the job for the reasons FRM outlines but then follows up the welding process by peining the weld, which he says improves the structure of the weld area and gives a more reliable result.

And yes, the head doesn't heat much or distort, you could put your hand on it easily immediately after the weld, other than in the immediate vicinity of the weld itself.
Paul Walbran

MJ,
Car recently purchased with known HGF. It started and ran fine without apparently overheating. No fault shown on OBD2. Appeared to be running fine on a fairly short 10 mile test drive. But loosing water and showing white exhaust smoke on start up and for the first few minutes of running.

However, looking back through the very detailed service record there is some evidence of coolant losses being ignored over several thousand miles. Did a variety of tests and narrowed problem to water loss into this cylinder which was verified when the head was removed.

Given the work involved in removing the cylinder head (engine out job, and not easy!) I am looking for a reasonably reliable repair rather than a "try this and see what happens" solution.

But I do like a challenge!
Guy

Guy - given that it's a hard struggle engine-out job,
well, I'll get my coat then !
M J Chapman

In the photo on my phone it dosnt look that bad,

can you just have the head resurfaced and if need be a decompression plate added

Prop
Prop

Unfortunately I don't think so Prop. Apparently you cannot skim these heads. You can also see in the photo that the valve chamber in the head is very shallow.

The head is now away to the specialist to assess if it can be repaired. I am also puzzled that the pitting seems to have initiated away from the water jacket - pretty well mid way between two of the water channels. Not obvious from that photo but there is a similar, though much smaller area of erosion in a similar location next to the adjacent cylinder although that one hasn't progressed through to the combustion chamber. As that one doesn't appear to connect to anything I cannot work out where the eroded material has gone to!
Guy

Could it have been a fault in the casting, and that there wasn't much material to disappear to anywhere?

It doesn't really look like erosion/corrosion. It looks like a raw cast mark.
Lawrence Slater

Lawrence, You may well be right. The engine is wet linered. Whilst it appears to be a head with large clamping surfaces the corresponding top of the block is all empty spaces (well, water jacket actually!) Where the "eroded" areas are, is in contact with the gasket but with no corresponding block to provide a sandwiching effect. However the patch in the photo against #6 cylinder has penetrated through across the top of the liner and into the cylinder. So the bit needing repair is really just this narrow neck, not the whole depression. It is very minor, but still critical!

Attached is another photo (not this car) of the top of the block of the same model engine.

Guy

as lawrence says, perphaps a casting defect. Perhaps some porosity?

There is a fairly well known article about K-series head gasket failure where it mentions this as one of the issues with the K.

This is the picture from that article. Looks similar to my untrained eye. no?

2002 vintage italian V8, must be a 3200 then? Does it have the bomerang rear lights?

Cheers,
Malcolm

Malcolm Le Chevalier

What do we think is the failure mechanism here ? I'm thinking this could be an example of "wire drawing" - normally associated with high pressure steam and partially closed valves, but here it could be that there was a pin-hole in the edge of the chamber(or a surface irregularity in the gasket) which has allowed high pressure hot exhaust gas to enter and subsequently over time, a narrow channel has been eroded in the head. When this channel breached the "sandwiched" area, it could then push the gasket away allowing the gas to expand and form the spoon-like larger eroded area which may then have allowed coolant to be blown to atmosphere ??
M J Chapman

Now that is a crazy looking engine deck, ive never seen anything like that before....its so exposed .... What keeps the cly linners from moving around

Wet cly. Linners ..... I got to remember that

Prop
Prop

"What keeps the cly liners from moving around?"

Prop, they are basically press fitted into a collar cast in to the base of the block. The interference fit between the liners also helps prevent shuffle.

Wet liners are what I use on all my racing Climax engines (along with Wills Rings instead of a head gasket).


Guy, any chance you could fit Wills Rings to that motor?
Deborah Evans

Prop,

That type of design has been around for a long time, IIRC Renault were using it on engines back in the 1960s if not earlier. The normal problem is that the engine mustn't be turned when the head is off as it can cause the liners to move and result in coolant leaking between the liners and block into the sump. A common safety is to add liner clamps when the head is off to prevent that issue and allow the crank to be rotated if required. When the head is on and torqued down the liners are securely clamped in place.

Deborah,

Wills rings had occurred to me but I've never looked into the details of their use in a cylinder head. Could they be fitted into grooves in the alloy head.
David Billington

Well I have had a message to say that they can fix the head, but I know no more detail than that.

Sorry about all this non Spridget content. I posted it because I was looking for a discussion with the knowledgeable folk on here and value your comments. I also thought that a bit of "exotica" might be of interest. But genuine apologies to any others who maybe see this as an irrelevant topic for the BBS.

Guy
Guy

Guy. Without wishing to appear sycophantic, I don't remember you ever writing anything irrelevant to the BBS. It's always nice to see some Italian exotica and to read what more knowledgable people than I have to say about things. There are so many people on here with amazing amounts of skill and knowledge that it makes it just about the best forum on the net,IMHO. And of course we've also got our own secret weapon. Prop!

Bernie.
b higginson

It's called "crevice corrosion" and is very common in places where fluid flow is restricted in narrow gaps. In this case, where the gasket is held very close to the head but not clamped. All sorts of electrolytic cells are set up, depending on all the elements present, the flow, temperature etc. Something as minor as a very small inclusion in the head, or a speck of something on the surface when the engine was assembled could start this off.

There are related phenomena, as "filiform corrosion" (which this is) and "pitting corrosion" (ditto).

Even mechanical things are involved, as high frequency vibrations, which cause cavitation. Cylinder liners on heavy diesels are a prime example, where vibration of the liners from combustion pressures will eat worm holes through the liner walls. Very peculiar, since there are lines of pits in specific areas, depending on the characteristics of the engine; primary are on the thrust side, secondary on the non thrust side, and tertiary on the longitudinal axis of the engine. Mechanical vibration could be a factor here, as the combustion chamber (liner) edge moves every time it fires, since it is not well supported laterally by the design.

All this stuff can be controlled to some extent by coolant chemistry, a very involved subject. Worth checking to see if this is an isolated failure, or a systemic thing with this engine. Then pay careful attention to the Mfr recommendations on coolant.

A pic of the gasket would be interesting. The best way to eliminate this is to eliminate stagnant liquid pockets in narrow spaces, so it might make sense to cut grooves in the non-load bearing faces or drill holes in the gaskets etc.

FRM
FR Millmore

What ??? You mean we are supposed to only talk spridgets here....hahaha

I for one am glad you posted this, i always love to learn about new things and a wet linnered cly is a new one for me...besides its not like we got a velvet rope outside the forum keeping people out, today is one of the most active days ive seen in a while for the bbs

Prop
Prop

Its nasty when you get crevice corrosion. I would lay off the strong curry! ;-)

Joking aside, it is entirely plausable. It is something that is a problem in my day job. Pipes connected with flanges can suffer rather rapid corrosion in the crack between the two surfaces. It's exactly the same situation at a block/cylinder head interface.

This is however a story for other day perhaps. Or I can stand on the other side of the velvet rope and shout in to you guys!

Malcolm
Malcolm Le Chevalier

Putting together the various comments and observations, I think the scenario is this:
Casting blemishes at those points don't seem to be critical as it isn't a part of the head that applies any clamping action as it matches against the water jacket in the block. But the gasket isn't revealed between the ports in the head (design fault?) so small isolated cavities are created where the coolant either never penetrates, or if it does it is isolated from the circulation. High localised temperatures, possibly wrong coolant mix and crevice corrosion starts. Works its way outwards until it penetrates the head across the wet liner contact ring. At this point it starts to loose water into the cylinder and become an apparent problem.

Here's a picture of the (correct, Maserati) gasket. The combination of casting blemishes in the head and a continuous gasket not clamped at those points seems to me to be the problem. Poor design!


Guy

So perhaps a manufacturing/design fault that simply took time to show up.

Do you have any way to find out if other engines the same as this in other maserati, have had the same problem? Maybe there's a web forum for the same engine, and you might find out there.

Also, (toungue in cheek) have you seen this stuff? hardly a professional approach, but ?? --- http://www.jbweldadhesives.co.uk/auto%20weld.html (you have to cut and paste).

They claim it fixes cylinder heads and casting defects

Does anyone know why some links work and some don't?

Lawrence Slater

Does anyone know why some links work and some don't?


I think it tries to sanitise URL's with special characters (%, in this case) and therefore breaks them.

URLs with no "special" characters should therefore work, if my theory is correct.

http://www.google.com should work

but

http://www.jbweldadhesives.co.uk/auto%20weld.html doesn't

OrangeSpyderMan

There is a lot to be said here about using the correct coolant to suit alloy and changing it regularly. The problem you have there looks to me like the coolant has gone off and become corrosive.--
Willy
William Revit

Some years ago I used to work at a Skoda main dealer garage and the engine that had been in the back of the "Rapid" models in a North/South configuration behind the gearbox, driving the rear wheels, was put into the then new "Favorit" models in an East/West layout in the front of the car driving the front wheels. In the Rapids there had been very little trouble, but in the Favorits they were experiencing HGF at about 25000 miles, with the associated alloy head corrosion Guy mentions. As you can imagine, the warranty claims were horrendous. I left before the problem was solved and then VW took over, eventually dumped the engine and the rest is history, but what FRM says above about high frequency vibration (possibly caused by the engine being in a different location and configuration) and a different coolant mix, may have had something to do with it.

Bernie.
b higginson

As for that link not working, any link path containing a space may be problematic, as the space is interpreted by some servers as a "%20", as seen in the above URL. I build web stuff all the time, and I always use underscores vs. spaces to avoid such issues.

By the way, this is an interesting discussion!

-:G:-
Gryf Ketcherside

Guy-
Perzackly correct.
The track of the deterioration across the critical surface can be taken as a cross section through a corroded area, and is effectively what is called the "filiform" variety.
Note that in the guise of "pitting corrosion", this can progress from any corrosion laden pits left in the surface, so they should be ground out clean. That would also "ventilate" those areas.
It is all very like the tunnels in the plexiglas "ant farms" of our youth!

I would consider it a design fault, but there might be a cure in correct coolant. As I said, I would consider grinding grooves in the head, or drilling holes in the gaskets. The gasket may have stainless wire mesh in it or some other structurally important components.

I expect Bernie's Skodas to have had some other change, like increased power output, changed materials, etc.; the position being a red herring. When Cummins and other truck engine builders had the liner problem, they actually tracked truck usage to see if there was a connection between direction of operation and the earth's magnetic field. Trucks running N-S NY to Fla. on the east coast were compared to those running E-W NY to California. No difference. It turned out that it had more to do with increasing power outputs, hence more liner vibration leading to cavitation. The cavitation caused the protective oxide coatings to break up, leading to local pitting, and then pitting corrosion at the bottom of the pits, where oxygen and the anti corrosion additives couldn't penetrate. Improved corrosion inhibitors solved the problem, so long as they were religiously maintained so that no pits developed in the first place.

While Lawrence's JB weld seems a bit off, I have seen it done successfully. A customer had a Spitfire that had been rebuilt before he bought it, and it worked fine for about 15 years. He broke a valve spring, decided to change it himself, and dropped the valve down the bore. Then he called me! So we took the head off, fixed the valves, put it back together - water everywhere! This was the late Spit with the stupid counterbores in the block, and it tuned out that #4 had been linered and machined incorrectly, and they had filled it with JB weld. The JB weld was invisible, since it looks just like dirty cast iron, and we had scraped it off in cleanup. I wound up fixing it with carefully calculated inlaid copper wire around the counterbore.

FRM
FR Millmore

Guy

Are these steel liners pressed into the block, or, alternatively a pure aluminium liner (silumin?) that the piston runs in?

The point of erosion, on the head face, looks to have started along the thrust/anti-thrust axis of the cylinder.

See if you can see any signs of waterside erosion/marking on the liners as it may offer some reason (liner vibration/cavitation) for the erosion on the head face. That is, if you are able to discount a combustion path via poor clamping between head,gasket,block and liner.

Alternatively it could be a load of 'old cobblers',but, as was drummed into me in my formative years 'If you don't nail the root cause it'aint going away!

I bet both Columbo and Lampredi are looking down from above on your deliberations!

Peter
PJ HOBSON

FRM,
Did you ever hang around in Wandsworth South London UK in your youth, and go by the name of Sonny? I ask because I have never since, heard anyone other than my mate Sonny use the word, Perzackly. :)

And I really was joking when I suggested the JB weld.

However since then I googled and discovered that Renault used it in the workshop (it is said) to cure cylinder head corrosion problems. So along with your 15 years use in a spitfire engine, maybe there is some mileage in it.

But it would be sacrilegious to put the stuff in a Masserati engine. Wouldn't it?
Lawrence Slater

Lawrence-
Unfortunately, I've not been to the UK, so it likely wasn't me, though strange things do happen. I may have learned it from my father, also before he ever was in the UK, or is it PG Wodehouse or such?.

JB Weld or similar, as Devcon Liquid Steel, are used industrially for all sorts of things, like building up eroded pump casings, etc. Devcon make it with a lot of different fillers, aluminum, bronze, carbide, as well as steel. I once salvaged a Bristol block; an in car repair of a freeze crack that extended the full length of the engine, using Devcon Plastic Steel. Were I to try it on this, I would probably use Devcon's Plastic Aluminum, since it would be one less extraneous element in the galvanic mess. Only thing I'd worry about here is the critical compressive load at the liner top edge. I expect even (or especially) Eyetalians would rather spend the lira on cheese and vino than another casting!

FRM
FR Millmore

This thread was discussed between 26/09/2011 and 29/09/2011

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