Few questions to experts after head gasket leak

[nemoo]

Hoi guys,

I wanted to ask you guys for some advice based on the following story.

A few weeks ago my 1974 Spider wasn’t idling well, holding back at freeway speed and eventually even started to make a ‘clattering’ noise under load.

After taking the head off I found the following (I don't seem to be able to post pictures somehow):
- Head gasket leak between cylinder 1 and 2, but no indication of oil in coolant or coolant in oil
- A small hole on the no. 2 head surface right next to where the head gasket was perforated. It is not on the sealing surface though and no idea whether this was the result of the head gasket leak or whether it even caused the gasket to leak in the first place
- Valves are all still sealing very well. When I pour water in the combustion chambers, the level will stay the same for at least 10 minutes. I didn’t see any water leaking around the valves into the ports
- A little wear on some of the cylinder walls. One slightly deeper scratch in number 2 cylinder, but not quite deep enough to catch my finger nail
- When I pour oil on top of the pistons, hardly any leaks away in hours, so piston to cylinder sealing still seems good

A bit of history:
- 1800 cc engine with no internal engine work done in the 14 years I have had the car. Didn’t smoke and didn’t consume much oil, but various external seals have been leaking for years.
- Pistons look like standard pistons to me
- No idea if any engine work was ever done or when head gasket was installed and by whom
- Cooling system: was in good order as it has an aluminium Mark Allison radiator, electric fan with lower temperature switch, fairly new pump, bright green coolant and a high point vent. Thermostat is a European style Savara. It doesn’t feel to me like I could replace the internal thermostat.
- Fuel system: not that good and initially I suspected that it was the cause of the poor running.
- The electric fuel pump in the boot was rated for 100 l/h, but I measured only 15 L/h at the return line from the 34DMS carburator, so the engine may have been running lean under high load. Both pump and fuel pick up from tank have now been replaced.
- Ignition: for the last 10 years Megasquirt, Ford EDIS4 with Ford coil pack, triggered by a 36-1 toothwheel behind an aluminium pulley and a crank sensor.
- Timing belt was about 40,000 km and 10 years old. It felt a little loose to me and before taking it off, it seemed to me that the TDC mark I put with felt pen on the crank pulley didn’t quite match with the pointers and holes on the cam pulley. Crank may have been advanced.
- In the past I have checked valve clearances by pushing the car backwards and forwards in 5th gear, which apparently could stretch or loosen the belt.
- At the moment I am a little confused as to how I initially set up the ignition, as the ‘missing tooth’ on the sprocket is not lined up with the crank sensor when the engine is at no.1 TDC, so I will have to read up on Megasquirt thing again.
- In the past I put a bunch of FIAT Marelli point and EI ignition curves in an Excel spreadsheet and think I eventually loaded the following curve onto ECU by laptop
500 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 7500
15 12 16 20 24 28 31 34 36 36 36 36


Based on what I have seen, my plan is:
1. Leave valvetrain alone given valves are not leaking and engine was not smoking.
2. Leave engine block alone as there seems to be minimal wear.
3. Just install a new head gasket and timing belt kit.
4. Tempted to go for Mark Allison head studs and nuts in combination with a ‘normal’ head gasket instead of multilayer.
5. With the head already off, I will probably take out engine and gearbox out of the car as well and replace all seals as some of them have been leaking for years.
6. Rebuild 34DMS carburator

Questions:
- I would love to show you the pictures and curious if anyone sees anything ominous, but somehow couldn't. Do I need extra permission?
- Any theories as to why the head gasket leaked?
- Has anyone ever seen a little hole on the head mating surface just next to the head gasket? Will it be a problem, even if it isn't on the actual sealing surface?
- Any views on head bolts vs head studs? Does the head and/or block still require machining for a normal gasket?
- Any view on my ignition curve or the set up with megasquirt?

[18Fiatsandcounting]

You've given us a lot to chew on here, but without a picture of the "hole" in the head surface, it's hard to say whether this is an issue. My guess is that the head gasket failed and the combustion gases going between the #1 and #2 cylinders etched a hole in the aluminum, perhaps at a weak spot.

This site doesn't support pictures directly. You have to load your pictures up to Imgur, smugmug, etc. and then link to those in your post.

Here's what I would do: Take the head to a machine shop, remove the valves, lightly skim the head for a new gasket, and inspect. Don't take too much material off the head. The shop should be able to tell you if the hole is an issue, and they might even be able to weld it. I've had some coolant passageway holes in cylinder head repaired with welds, and they look as good as new.

Put it all back together and see how it runs. I'm thinking the poor idle and power is the bad head gasket, but there could be fuel or ignition issues as well.

And yes, definitely put on a new timing belt and tensioner pulley. By the way, I have not heard that rocking the car back and forth in 5th gear can damage the belt, but if this causes the belt to skip a tooth, that's not good. I have heard to always turn the engine in the normal direction (clockwise when viewed from the front) as turning backwards can cause belt skip.

-Bryan

[nemoo]

Hi Brian,

Thanks very much for the reply.

I suspect there may have been a combination of a few things:
- fuel supply probably was an issue, so the engine may have run lean at high load.
- valve timing may have been off because of the belt being too loose and slipping by me rocking the car against the normal engine direction
- ignition advance may have been too agressive, resulting in detonation, head gasket failure and even the little hole in the head surface

I will probably take your advice and consult a machine shop on the little hole and general flatness of the head.

Apart from that I am leaning to just sticking in a new gasket and seals to stop various oil leaks, because as far as I am concerned the engine only needs to do another 10 years or 50,000 kms until we can all upgrade to plentiful and therefore cheap clean, powerful, quiet and reliable electric motors/batteries ....

Do you have any view on:
- type of gasket (old fashioned or multilayer)
- original bolts vs studs/nuts?
- does a block ever have to be machined for a new head gasket?
- and most importantly my ignition curve for a pretty much standard motor? Is it too aggressive in general?

Thanks again,

Kees

[Nut124]

If the head surface under the fire rings is intact, you could just clean the surface up and re-install. Check for straightness.

The studs can leak coolant thru the nut threads. That is what happened to me. Sealant must be used in the threads in the block. I took them out and went with the torx (ribe?) head bolts.

I think your full ignition advance comes in a bit early at 2800. Might be OK due to low CR.

Turning the engine backwards is OK as long as the tensioner is not loose and the belt is not too loose. If loose, it will skip teeth at the intake cam.

[Nut124]

Does the head gasket have any evidence of pinching of the fire rings?

The MLS gaskets are much stronger but require a perfectly smooth, mirror-like finish on the head. Regular gaskets can seal minor scratches.

[18Fiatsandcounting]

Nut answered many of your questions above, and it does sound like you might have had some detonation going on, and that caused the damage. The machine shop could probably advise you on that.

Do you have any view on:
- type of gasket (old fashioned or multilayer)
- original bolts vs studs/nuts?
- does a block ever have to be machined for a new head gasket?
- and most importantly my ignition curve for a pretty much standard motor? Is it too aggressive in general?

I just use regular old fashioned gaskets and they've been fine, but I'm not a racer nor even a particularly aggressive driver. I prefer head bolts, but many prefer studs, and there are advantages/disadvantages to each.

You can check your block with a metal straightedge, but I've never seen one that was warped. I do carefully scrape off all the old gasket material with a razor blade, and go over it with a 3M Scotchbrite pad or the like. Don't use a Brillo pad or anything that will shed metal fibers or soap. It's also a good idea to cover your six oil supply holes and stuff rags in the cylinders, as Scotchbrite will shed some particles and you don't want that in the oil. Vacuum everything thoroughly when you're done.

Your ignition curve doesn't look too aggressive, perhaps just a bit, but maybe in conjunction with a lean mixture, you were getting detonation. Perhaps retard a few degrees in the 2000 to 3000 rpm range. 36 degrees total advance should be fine on a stock engine.

-Bryan

[Nut124]

I misread the ign curve because the columns did not line up. Looks better now. Pretty much what I run.

[nemoo]

Thanks for those answers guys!
A little late, but below I have put some pictures.

I drive fairly leisurely as well, so after scraping off gasket material and checking for straightness I may just go for a normal 'gasket' in combination with the old bolts and a little less ignition advance between 2000-3000 rpm then.

Worst case is that the gasket fails again and I can still come up with another plan then.

Probably will still take out engine and gearbox to fit new seals everywhere.

https://photos.smugmug.com/photos/i-pZ7 ... 3Fd-XL.jpg
https://photos.smugmug.com/photos/i-LdQ ... NZj-XL.jpg
https://photos.smugmug.com/photos/i-Bts ... 6cf-XL.jpg
https://photos.smugmug.com/photos/i-CJs ... Nm9-XL.jpg
https://photos.smugmug.com/photos/i-Fxk ... dKJ-XL.jpg
https://photos.smugmug.com/photos/i-hKp ... C4W-XL.jpg
https://photos.smugmug.com/photos/i-ZvK ... KZQ-XL.jpg

[Nut124]

That is a strange looking failure. How deep is the hole in the chamber?

You will want to carefully examine the head where the failure was for any defects or distortion using a straight edge and thinnest feeler gauges.

[18Fiatsandcounting]

I agree, that is a strange looking failure. And thanks for the pictures. I can't quite put my finger on it, but the head gasket looks "odd". Notice how some of the coolant holes are cut through the fire ring around the cylinder openings. I haven't seen that before. I wonder if this was a replacement gasket and wasn't quite right for this engine, or was just a poor quality aftermarket gasket. And it failed.

The pinhole is rather odd, but it doesn't look catastrophic to me. A shop can advise you on this and likely just weld it up.

Clean up the block surface, get a good quality head gasket, and I'm guessing that you'll be fine. Don't forget the two dowel pins in the block for the oil lines to the head. Torque down the head bolts in the recommended order to around 60 ft lbs (I forget the exact number), put a few hundred miles on the engine and then retorque the head bolts.

-Bryan

[Nut124]

Looking at the pictures, it almost seems like #1 cyl was running hotter, lean, and the narrow land between 1 and 2 just melted. Detonation at #1 perhaps.

I have seen failed head gaskets with other failure modes. One is overheating. The excess pressure in the cooling system literally pushes the fire rings into the bore. The fire rings then get pinched by the piston, which leads to failure.

The other mode I have seen is a minor defect in the head, an inclusion or a scratch at the fire ring, which allows increasing amounts of combustion gas to escape under the fire ring. In this case the head always needs to be resurfaced or scrapped because the flame path has cut it pretty deep.

Is your head intact there at the 1/2 land?

[nemoo]

Thanks again guys!
I stuck a pointy small screw driver in the hole and it went in at least a few mm. It was pretty deep, but luckily outside the sealing area.
No idea where the gasket came from or who installed it.
The previous owner told me that the engine was built by a guy used to be a racer of FIAT cars here. There are hardly any parts here in Australia, so maybe he 'adapted' a head gasket for another car or engine.
This summer it has been stinking hot here in Perth, so I try to stay out of my shed as much as possible. If I wake up early enough tomorrow morning I may remove the gasket material and check exactly whether there is any damage to the head.