HG/cracked head/something worse - help!

[benjj]

Right chaps, I need some advice on my problem please.

My very early 2.5 8v has been suffering a little coolant use (around a pint per 100 miles), a lumpy idle, white/very pale blue smoke on start up and heavy throttle and a few other little eccentricities.

Today my mechanic and I set about addressing the problem.

We whipped off the cam cover and had a peer down each cylinder top. Cyl 4 was full of coolant. Not good. The car hasn't turned a wheel in a couple of weeks so it is obviously failing when cold rather than hot.

We drained it and then pressurised the system with compressed air and sure enough Cyl 4 slowly filled up with coolant. Not good.

So off came the head. A bit of swearing here and there but away it came.

Then... Da da daaaah, mystery.

The head gasket looked perfect to both of us. No nicks or cracks.

The cylinder walls look in excellent condition and the liners in good shape.

So, it is going off for stress/pressure testing tomorrow and will be skimmed, gas ported and new valve stem seals if it is good.

In a way I'm hoping for a cracked head as it would pinpoint the problem. If it comes back fine it would mean one of two things: an invisible failure of the head gasket or a problem with the bottom end. It would need a leap of faith to get the head back on without having an obvious point of failure.

I had a good look at the cylinder liners, they look like they're specced for an Abrahams main battle tank - I just can't imagine a failure there.

Am I missing anything obvious?

This evening my specialist is testing the bottom end by brimming the coolant and seeing if we get any seep through overnight.

For what its worth the HG that came off had a very Porsche looking code on it, 944 104 37410 which a search online indicates is a Victor Reinz part, presumably after market gasket rather than the factory fitted article.

So, a bit of a head scratcher.

Has anyone had a HG fail with no obvious signs?

Any help or advice much appreciated.

 

[924nutter]

Water will leak into the bores when the engine is idle. The pressure in the cylinder at combustion far exceeds the 7psi normal system pressure, but when you switch off the system pressure is still at 7psi because it is still hot, and with no opposing pressure the water will leak in as demonstrated by your leak test. Are you having the head crack tested, it is not clear in your post where you mention stress/pressure test. A proper crack test with dye and developer will hilight any cracks. When you have all the info back then choose a course of action. I am of the opinion that some of the OPC headgaskets I have bought over the years are branded Reinz so possibly OEM though not necessarily OPC supplied as,I haven't been able to match that exact part number from current PET files. The ony gasket I could find starting with a 944 is 944 104 033.... Interstingly there is a separate part number quoting "gasket for reconditioned cylinder head" so when you refit the head make sure you get the right one.

 

[benjj]

Thanks John.

To confirm:yes, the head will e properly crack tested so we'll find that out for sure. I'm dropping it in this morning so should have news on that early next week.

I suppose the crux of my problem is that is it possible for the HG to let go without any visible signs? We cleaned it up and it looked absolutely spankingly perfect!

 

[benjj]

A few photos:

This is the cam cover off. You can clearly see that the port on Cyl 4 has been steam cleaned compared to the others.

This is the head off. A little steam cleaning of the piston face but not too bad.

This is the cylinder head and gasket. Nothing jumping out at me here. The gasket looks perfect after a clean up. 'Rot' doesn't seem possible either seeing as though it is metal!

 

[TTM]

Have you checked that the head is not bent/warped? Did the engine ever overheat since you have had it?

I had a HG "fail" with no apparent sign on it but that was because I had not tightened the head correctly.

PS : what year is your car? Seems to be a very early one considering the bleeding plug on the hose coming out at the front of the head.

 

[benjj]

The head is going off for testing this morning so I'll ask them to check for any warping.

I've had the car for about 10,000 miles and it has overheated just once - the day I bought it! That was tracked immediately back to a faulty rad switch and replaced instantly. Since then all is well, no overheating ever. Who knows before me though, quite possibly if the rad switch was borked for a long time.

At the moment I'm making a list in my head of possible reasons. So far I've got:

Invisibly failed head gasket
Cracked head
Warped head
Incorrectly torqued head
Head refitted by previous owner while dirty/contaminated
Bottom end issues

Once I have news on the head from the engineers I'll be able to write some of those off I guess.

Aaaaargh!

 

[benjj]

Just saw your edit. The car is a very early 1982, possibly late 1981 manufacture. I'm in contact with Porsche UK to get some kind of confirmation on a precise date.

 

[GPF]

I don't understand the references to the bottom end being a possible cause??

Am I missing something?

 

[TTM]

I would tend to think the engine overheated enough at some point to damage the HG on the 4th cylinder, since this is the cylinder cooling the least (it's a design fault). It may look fine but could still have been damaged.

You say you've had the car for 10k miles, but when did you notice the problem appear?

 

[TTM]

ORIGINAL: GPF
I don't understand the references to the bottom end being a possible cause??

Bent cylinder or the top of the block not perfectly flat?
I strongly doubt either possibilites anyway.

 

[benjj]

ORIGINAL: TTM

ORIGINAL: GPF
I don't understand the references to the bottom end being a possible cause??

Bent cylinder or the top of the block not perfectly flat?
I strongly doubt either possibilites anyway.

Pretty much that, I was considering a cracked cylinder wall/liner etc.

The engineers have just called, taking it over now and they'll crack test it and if good will be skimming and gas porting plus valve work. Will look nice at least when it comes back!

The problem has very gradually developed over time culminating, quite luckily, with it going into the workshop. The very slight hydrolocking cyl 4 has coincided with a lumpy idle on start which is cleared by a bit of throttle.

I am now feeling a little more confident. Given a new gasket set and a profiled head I reckon it could be sorted.

Then onto the small job of belts, pulleys, tensioners, new water pump, on and on and on!

Righty ho, off to the engineers we go...

 

[Mike_Pollock]

ORIGINAL: TTM

I would tend to think the engine overheated enough at some point to damage the HG on the 4th cylinder, since this is the cylinder cooling the least (it's a design fault). It may look fine but could still have been damaged.

You say you've had the car for 10k miles, but when did you notice the problem appear?

Gasket looks too good to be original - my '83 was corroded through in 4 or 5 places - so +1 for TTM

I have an early head if you do find its cracked.

 

[ChasR]

Are the inlet manifolds water cooled/heated on the 944 at all? I am surprised the inlet has been steam cleaned, unless I am missing something .

 

[TTM]

ORIGINAL: ChasR
Are the inlet manifolds water cooled/heated on the 944 at all? I am surprised the inlet has been steam cleaned, unless I am missing something .

Coolant sipping through a supposedly failed HG may have been steaming up through the inlet valve during the time it's open.

Only the 944 S2 and 968 have coolant circulating in the throttle body in order to warm up inlet air.

 

[benjj]

Thanks for the replies gents.

I dropped the head in to the engineer yesterday and he gave it a once over while I was there.

He said that the head doesn't appear to have ever been worked on, certainly never profiled.

His opinion was a HG failure on Cyl 4 on the side facing Cyl 3. Not a big failure but enough to count.

He noted just how well ported the chambers were already, really top drawer work by Porsche.

I'll know for sure on Tuesday and will update here.

Off to Carfest now with the kids, can't wait

 

[TTM]

ORIGINAL: benjj
He noted just how well ported the chambers were already, really top drawer work by Porsche.

He didn't comment on the shape of combustion chambers then? Doesn't surprise me ....[8|]

 

[benjj]

Mine will be getting gas flowed so I guess he was keeping his professional opinion to himself!

 

[944 man]

Id be surprised if he can improve on them Ben, but I decided not to comment until after theyd had a chance to look at it. Porsche cylinder heads are superb and the restrictions have been designed in, as opposed to being the result of poor chamber and port design/finish.

I was also surprised to read that the head will be skimmed as a matter of course, rather than only if needed, which I would prefer. Unneccessary head skimming leads to poor cam timing and I think that it is very poor engineering practice to skim every cylinder head.

 

[benjj]

I agree with that, Simon.

I spent a great deal of time (and money) doing the head on the DS but then we had gone for a bit more power

The engineer doesn't skim head as unless they need them but mine certainly does. He as worked on a lot of 70's and 80's Porsches of all models and instantly recognised the factory finish.

This will be the first Porsche head I've ever had done and my instructions have been that I want it as good as it can be. If that means he doesn't need to gas flow it (or at least not aggressively) then he won't. I've told him I'm not changing the chip in it so I don't want a lairy head that requires changes to the fuelling and other tweaks.

Anyway, so far I'm a happy bunny.

Oh, there was a nice champagne coloured 1984 944 in the Silverstone Auctions lot today at Carfest, looked very nice.

 

[944 man]

Ive just read about +/- .30mm on TIPEC...