Technical Head gasket?

[Semm345]

Hello all,

i have a mk2b sportsound, in wich lays a 1.2 16v engine. the 188A5000. had it overheat on me wich (i thought) blew the head gasket. after replacing the head gasket and having it skimmed, cleaned an put new valve seals in i put it back together only to find out there is somehow still exhaust gasses coming in to the coolant. plus there is a knocking sound from the valvetrain (im thinking something to do withy the hydraulic lifters) wich is new. i am also thinking maybe there is a crack in the engine block somewhere. anyone have any suggestions on how to check for this?

 

[bugsymike]

Hello all,

i have a mk2b sportsound, in wich lays a 1.2 16v engine. the 188A5000. had it overheat on me wich (i thought) blew the head gasket. after replacing the head gasket and having it skimmed, cleaned an put new valve seals in i put it back together only to find out there is somehow still exhaust gasses coming in to the coolant. plus there is a knocking sound from the valvetrain (im thinking something to do withy the hydraulic lifters) wich is new. i am also thinking maybe there is a crack in the engine block somewhere. anyone have any suggestions on how to check for this?

Leak test.
Sounds simple and is if you have a garage air compressor and an adaptor to fit the spark plug holes.
Basically you put the engine on TDC on firing stroke on the cylinder you are testing and lock it up so engine doesn't turn, (Jam flywheel is best) then plug in air pressure with rad cap off, if air bubbles out you know which cylinder is faulty. Repeat on rest of cylinders.
Note this works for checking inlet and exhaust valves and piston wear as well.
The test is meant to be at 90psi but I always use 150 psi.
If engine seriously overheated the block could have warped as well, I always check the cylinder block with a straight edge and feeler gauges when doing a head gasket job as well as having head skimmed.
Re hydraulic tappets/cam followers I leave the new ones soaking in engine oil overnight to "prime " them. If reusing the old ones I do the same for them but also make sure to replace in original positions.

 

[GrandePunto PL]

Who did the "repair" (skim etc.) and how much was trimmed?
Skimmed without checking for cracks?

 

[bugsymike]

So many things can be a problem even if not a cracked block.
Were the threads in block cleaned so bolts torque down correctly etc.
Was the original cause of overheating fixed.
Was air bled fully from system.
Not accusing you of anything, it is just so many things can cause an issue.
I have even had duff quality head gaskets that didn't compress correctly to seal, the machine shop I used wanted to supply the gaskets to increase their profit margin, this was 25 years ago and to this day I will never use Ultra Parts make of gaskets one was a Ford Fiesta and the other a Triumph TR7!

 

[Semm345]

Hi all, thanks for your replies!!

so update: i had the cylinder head checked for cracks and that seems to be good. the guy who did the checks did know what the knocking sound from the valvetrain was. i spimply made the classic mistake of putting the head gasket on the wrong way round so the oil feed to the cylinder head was blocked.... so if you ever plan on changing a head gasket on a FIRE engine, be weary of this.

as for the exhaust gasses in the coolant, there must be something wrong with the engine block itself. are they known for cracking or warping?

 

[bugsymike]

Hi all, thanks for your replies!!

so update: i had the cylinder head checked for cracks and that seems to be good. the guy who did the checks did know what the knocking sound from the valvetrain was. i spimply made the classic mistake of putting the head gasket on the wrong way round so the oil feed to the cylinder head was blocked.... so if you ever plan on changing a head gasket on a FIRE engine, be weary of this.

as for the exhaust gasses in the coolant, there must be something wrong with the engine block itself. are they known for cracking or warping?

No more than any other cast iron block , unless it has been frozen through lack of antifreeze , or boiled to a stand still and refilled with cold water, that can do it .
First though I would check the cylinder block for flatness as I mentioned before using a steel straight edge and a feeler gauge, if a 002. thousands of an inch slides out then to me the block is not flat and will blow head gaskets unless machined flat again.

 

[Pugglt Auld Jock]

Leak test.
Sounds simple and is if you have a garage air compressor and an adaptor to fit the spark plug holes.
Basically you put the engine on TDC on firing stroke on the cylinder you are testing and lock it up so engine doesn't turn, (Jam flywheel is best) then plug in air pressure with rad cap off, if air bubbles out you know which cylinder is faulty. Repeat on rest of cylinders.
Note this works for checking inlet and exhaust valves and piston wear as well.
The test is meant to be at 90psi but I always use 150 psi.
If engine seriously overheated the block could have warped as well, I always check the cylinder block with a straight edge and feeler gauges when doing a head gasket job as well as having head skimmed.
Re hydraulic tappets/cam followers I leave the new ones soaking in engine oil overnight to "prime " them. If reusing the old ones I do the same for them but also make sure to replace in original positions.

Sorry to be so late to this thread but thought it worth mentioning about leak testing. In the workshop we had an actual leak down tester which had gauges etc and a pressure regulator so you could vary the air pressure/flow being fed to the cylinder. However the really useful thing is being able to admit compressed air to the cylinder - which you've set up to TDC on it's compression stroke, so both inlet and exhaust valves will be closed - and then listen and watch for where the air is escaping.

As you'll obviously know Mike, there should be no leaks from inlet or exhaust so, stick your "listening tube" in one ear and the other end into the inlet - remove air filter of course and you may need to open the throttle butterfly - Now do the same at the exhaust pipe, you shouldn't hear any "hissing" at either of these locations, but there will always be some from the engine oil filler orifice if you remove the filler cap and listen because the piston rings can't be a total seal. How much hissing is acceptable only comes with experience or by observing the gauges - which I don't have at home. Of course if there's a crack in the head or top of a bore you'll see air bubbles in the radiator/expansion tank. stick your "listening tube" in one ear and have a listen to the spark plug holes on the cylinder/cylinders either side of the cylinder being tested. A hiss here means the gasket is blown between the cylinders.

So, for those without experience of leak down testing, you'll understand you can diagnose a lot simply from being able to introduce compressed air to the cylinder and for that - for very simple testing - you don't need the pressure regulator or gauges, just a way of introducing the compressed air into the cylinder. I accomplished this by smashing out the central ceramic core of a spark plug and brazing in a male air hose connector to which I can connect my air line. Screw the modified plug into the engine plug hole, connect your air line and you have a way to introduce compressed air to that cylinder. I think, if you don't have access to brazing gear then you could JB Weld it in just fine. Most small compressors run around 90 to 110 psi so you're not going to do any damage to a good gasket with that when you consider the sorts of pressure is generated on a power stroke.

One final word of warning. setting the piston to TDC compression - on the cylinder you're testing of course - and then applying the compressed air will result in the piston being forced down the bore (unless you've got the piston very precisely positioned at TDC which is difficult) and thus the crankshaft turning, with some force, through half a turn. Lots of damage to fingers etc can be so caused! Putting the handbrake on and engaging a gear (top gear) is unlikely to stop this happening so blocking the flywheel at the ring gear is advised.

Of course you need a compressed air source, but, if you've got even quite a small compressor then making this simple adaptor gives you a very useful diagnostic piece of kit.