How to find an elusive cylinder head crack?

I'm not quite sure I follow what the status of the head is...

This indicates that the head is installed, and the engine is fully assembled.

This indicates that the head is off the engine --- or was at some point for the valves to be removed....correct?

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When you had the valves out for the dye (penetrant test, I assume?), did you also remove the valve seats?

If you are SURE that it is NOT the head gasket, and you are SURE that it is leaking coolant (NOT oil), your test results point to one possible scenario ---- the crack is hiding in the recess behind a valve seat. This would explain why the dye test did not find it --- if you did not have the seats removed when you performed the test. It would also explain why the pressure test did not induce the leak --- perhaps the valve in the affected seat was fully closed during the static test, and the pressure exerted by the valve was enough to effectively seal the seat against the crack. And, it also explains why the crack leaks while cranking the engine with the starter as the valve would then be open periodically and releasing the pressure against the seat enough to allow the leak.

I've seen a lot of cylinder heads with cracks in the valve seat recesses, but never one where the crack was completely hidden by the seat --- part of the crack was always visible beyond the seat margins. However, I suppose it is possible that you could have a crack which is completely covered by the seat. Or, there could be a small casting defect, such as a hole or a porosity, in that location.

The way I see it is that you have to remove the head to fix the problem anyway --- regardless of where the leak is. So, I wouldn't waste time doing any further "tests" or inspection (with or without a borescope) with the head on the car. I'd pull the head, take out the valves AND the seats, then repeat the dye penetrant test being sure to include the valve seat recesses. If nothing shows, heat up the head ---- toss it in an oven for an hour or so at about 350 F ---- this will help to open up any cracks. Then repeat the dye test --- hopefully it will pick up the "enhanced" crack(s).

 

Ooops, I just now noticed the photos So, my questions about your dye test are moot then

The test was done with the valve seats IN ---- take them OUT, and re-do the test

 

FTR, ultrasonic testing methods are not really applicable for this type of part --- too heavy and too much material thickness. Ultrasound is used effectively on lighter, thinner cross section pieces or laminated materials to detect "air spaces" such as voids (bond line) or porosities.

And, you are correct in what you have heard about X-ray exam of bulky Aluminum pieces --- standard X-ray equipment and methods are not effective. In the Aerospace world, we use CT scanners to exam such parts. Although the frequency is still in the X-ray region, the intensity level is higher, and the ability to take "slices" makes it possible to penetrate bulky pieces.

 

Thank You. Unfortunately I have already
had the engine built up with the new cylinder head. However, I wish I had known about this type of test before disassembly. Whatever tests I do have do be done on the cylinder head by itself.

 

The engine has been built up with the brand new cylinder head and has not used any coolant in 1500 miles. Based on the last 3 failures I would be expecting to see coolant use increase soon (if the cylinder head was not the problem).

The original head was used in the last 3 repairs but was NOT used this time and I have it off the engine.

 

Well, if you are bored and curious......have a look underneath the valve seats sometime. It would be very interesting to determine the failure just for the sake of posterity

Inquiring minds want to know

And, if it turns out to be a casting flaw (I am highly suspicious of that), maybe you can squeeze a little "lemon" juice out of the folks in Alfa's warranty department ?

 

This was exactly the question I asked the mechanics and engineer. But they said it was not possible that the pressure could be contained in the valve chamber (if that's the right expression) when pressure tested with the valves in the closed position. The engineer and the pressure tester agreed there was no point in testing with the valves out but there was no talk about removing the valve seats.

I didn't want to lead anybody into saying this so I am glad to see it being said. I am going to re pressure test it at a different place. I have the valves out of cylinder 1 which is the suspected cylinder anyway. I will find out how to get the valve seats out. Thank You.

 

You posted as I was writing my reply to you. I want to get to the bottom of this for more than the sake of posterity. I am really angry with Alfa UK. They basically told us to get lost when it is obvious that a car bought new has a serious recurring problem. And I really want to prove the Alfa dealer to be the ................. I think he is.

Certainly, I would like to get the cost of the repair back. Also I would like to sell the car, but I am not prepared to sell it to someone who might have struggled to save up only to find this happen to them. So I would like to know for that reason to. If I was able to prove it, I wouldn't play nice with Alfa UK. I would send a letter, a final demand and issue a court action. I am quite pee'd off.

 

Thanks for that. I made some calls but none of the engineering business offer it around here. The only thing available is X Ray and not a sophisticated method which is not suitable for the reasons you described.

They did say it would be good evidence if I could locate the crack to have an X ray taken as proof.

 

I agree with them that it would be highly unlikely......but, stranger things have happened.

To quote an old college buddy of mine who is now a Pathologist / Medical Examiner, "I've never seen that before, but it doesn't surprise me." ---- he says that often, by the way .

 

Yes,I have been suspicious throughout of the Alfa dealers insistence that the external cooling system (which was checked and rechecked) kept coming up with numerous new faults and it was nothing to do with the engine.

I should have kept the engine apart on the 4th failure and had the block and the head tested at the same time. It would have been much more expensive and that did lead to my decision to build it up with the new head. First time I have had to deal with a problem like this.

 

If you haven't already tried, and you have an airport nearby, call some of the aviation maintenance shops and ask where they get their NDT done and will do non aviation work. I would recommend looking for a shop that can do Zyglo inspections (http://www.magnaflux.com/ProductOverview/Penetrant/tabid/96/Default.aspx).

Zyglo can detect finer flaws that are sometimes missed with Dyecheck (Spotcheck). And as has been previously mentioned, knocking the valve seats out will allow a thorough inspection in that area as well.

I was in aviation maintenance for quit a while and Zyglo was preferred over Dyecheck for non-ferrous assemblies.

Hope this helps.

 

you may need to etch the surface first to open the crack as well. Especially if you do something like pull a valve seat. Aluminum smears fairly easily and that can hide a crack from the dye penetrant.

In the aerospace world, we frequently have to etch before penetrant inspection especially if we are removing a crack and want to be sure we got it all.

Etching only removes .0015/.002" from the surface but that is enough to expose the crack.

sand or grind, then etch, then dye penetrant inspect.

Typical etchant for aluminum is sodium hydroxide or sodium nitrate mixed with water, you can also add corn starch to thicken it so that it wont run.

Use it luke warm, let it sit for a minute or two and then rinse it with a bunch of water to neutralize it. If you get a big reaction (lots of foaming), its too strong and just rinse it off right away with water.

Normal mix for aerospace etching use is about 6 oz of sodium hydroxide per gallon of water and will etch about 5-15 mils/hour at 100-120 degrees F (.005/.015" deep etch in a hour).

Enough to brighten up the surface a bit is usually enough to allow good penetrant inspection.

Sodium hydroxide is more commonly known as lye. Crystal drano used to be soidum hydoxide as well.

If you do go to an aircraft joint they will know how to do the etching and will have fancy controlled solutions. The above is the garage version.

btw, a dilute solution of lye and water is a good way to remove stains from bare aluminum... it will also wreck any anodizing so dont use it for any aluminum thats colored or clear coated.

 

Davidoloan, that's a nasty story you got there. I can totally sympathise with you and I understand you would like Alfa to st*ff it.

But wouldn't you rather just chuck the old cylinder head down the bin (or through the showroom window of the Alfa dealer ;-), and be done with it? This story proves again that the experience of a car is very much dependent not just on its reliability but so much on the dealer. This is also why I do all car maintenance myself, I just had too many bad experiences. It's extremely difficult to find a good garage that gives you your money's worth.

One way or the other, enjoy the 166, hope it is done being a trouble child. Mine has not been without issues but it's a high mileage example by now and I use it as a car for the bad periods in the year - winter and rain. Apart from the interior heating unit which can leak and the rather weak suspension, they're so much better than you'd expect. Alfa tried to go premium with this model and I think you can feel that in almost every aspect with this car.
Despite Alfa's reputation, people I know with BMWs or Mercs have certainly not had less things wrong with their vehicles. Only the friends with Japanese products seem to have lesser issues... but that's a step I'm not willing to take ;-)

Let us know if you find anything on the cyl head!

 

I stick to my original opinion. Pressurize the coolant passages with air at fairly high pressure and leave it at least overnight in an area with constant temperature. If the pressure is unchanged, I don't believe there is a crack (or a porous casting, which is more likely anyway because cracks aren't this hard to find). I have found areas of porousity in old Alfa heads (which had pretty poor quality castings) using this method. I can't see that the crack (or whatever) is going to close up to the point where there is NO leak over an extended period of time with 50 psi air.

 

Its a good attitude. I took it back to the engineering shop this afternoon to have the seats removed from cylinders 1 and also 4 since the valves are out already. They will retest it by Wednesday if all goes well.

To Gearjammer & NW328GTS : Thanks for your advice. If the upcoming pressure test with the valve seats removed is not successful I will have a go at doing another penetrant test and I will make efforts to have prepare properly for it this time.

If this fails I will have to give up unfortunately.

Of the two options I would rather throw the cylinder head through the showroom window, but seriously I want to attempt to prove the fault if at all possible. The attitude of Alfa UK and especially the dealer is bad. When we took it back using large amounts of coolant again for the last time he said it was coming from the heater system this time and told us to take the car away and that would not deal with it again.

I have got hundreds of thousands of miles on BMW's and I love them, especially the wonderful straight sixes. Other than service items, bushes and suspension parts, I have had to replace a radiator, an air intake pipe and an oil breather pipe + a couple of minor electrical issues. That is all ! They are also drivers cars which the modern Alfa's are not. The only thing that puts me off the latest ones are the Bangle styling and the new concentration on a car for every niche, so called off roader etc and the fact that they are getting a little fat. My ideal everyday car would be an brand new E32 7 series with the later 24 valve straight six. I had the V8 version and it was great. A very elegant car too in a stern German way.

If I had a Ferrari 456 along with an Alfa 166 I would also use the Ferrari daily and the Alfa occasionally. Much Cheaper

 

I believe that is what I did because I had it on test all day long. But you may be right - the head may be faultless. It is going to be done again. Should know by Wednesday. It may be that the block is at fault.

 

Alfa 166 Top Gear http://www.youtube.com/watch?v=jgG1wF7OZn4

 

Of course. And if you can't prove the fault you can still chuck it through the showroom window.

I love BMWs too, but I tend to find the new ones a bit boring inside, unless you really spec them up. I like the Bangle styled E60 5 series, I think that design ages very nicely. With that car, Bangle got it right imho.
As per the Top Gear video, the interior is by far the best thing about the 166, I fell completely in love with it and have been for the past 5 years. You say it's not a driver's car, but I disagree. The twin spark engine is too small for it to make it a driver's car. Try a 3.0 V6 with a Bilstein chassis, and you'll look different at that statement. It's still fwd of course though.
The E32? For the cash you have to fork out these days for a 1 series you can get one of those AND get it completely restored complete with that 24v engine you wish for!
I have a low-mileage E9 as well that I like very much, compared to most modern cars it's even light and small - that was the other way round when it first came out. Would be good to have a 24v in that as well though, come to think of it.

{smirk} haha, well in my experience that's a bit different ! Until now I've enjoyed the 166 very much, even though the two are in a totally different league. I use it only for winter driving, hauling stuff etc. A real workhorse. For me it has proven to be an excellent daily driver with little issues - despite that it's becoming a high mileage car by now. I'll run it until it becomes cumbersome. May not be far off, but I'll see. Hope she'll last a little longer as I just blew my savings on the 456!