Technical Cinq running weak. Help.

[jonjg]

Hi. Having taken the cylinder head off the cinq 1.1 sporting as I think the head gasket has gone, I've noticed the plugs are running weak.

Any idea what would cause the engine to run weak?

I've included a pic for help.

Head bolts weren't very tight to undo.
It's got an 866 cam in, 38mm TB, aftermarket air filter. No splits or cracks in pipes, fuel filter changed recently.

When I undo the fuel filler cap, it hisses which my other 2 don't do.

 

[bugsymike]

Hi. Having taken the cylinder head off the cinq 1.1 sporting as I think the head gasket has gone, I've noticed the plugs are running weak.

Any idea what would cause the engine to run weak?

I've included a pic for help.

Head bolts weren't very tight to undo.
It's got an 866 cam in, 38mm TB, aftermarket air filter. No splits or cracks in pipes, fuel filter changed recently.

When I undo the fuel filler cap, it hisses which my other 2 don't do.

What were the symptoms of head gasket issue?
Plugs, valves and combustion chamber area don't look excessively weak in my opinion, I assume you don't potter around town as if that was the case it would look more sooty than white.
I have seen many engines with head off look similar after 50-60 k plus miles.
Engines can run weak due to air leaks at inlet manifold or throttle body, also vacuum servo pipes or leak at servo it's self.
After market air filters often being less restrictive can be a cause of weaker mixture especially if no other fueling has been increased to match the new air flow.
Most modern fuel systems when removing filler cap do the hiss, in the old days it could be caused by a blocked fuel tank vent.
By the way re head gasket issue, if engine was just running a bit hot, but no massive water leak, looking at the water ways in cylinder head , they look a little rusty, so if radiator internal core tubes are similar it could account for any raised temp especially during fast driving when a blocked rad has more problem getting rid of the heat.
With head off now would be a good time to lap the valves in and recheck valve clearances where applicable.
Assume a new set of plugs also. I can't see the electrodes of the spark plugs clearly, but if you suspect signs of them running too hot then possibly you could change to a different heat range plug to match the normal driving the car gets.

 

[jonjg]

What were the symptoms of head gasket issue?
Plugs, valves and combustion chamber area don't look excessively weak in my opinion, I assume you don't potter around town as if that was the case it would look more sooty than white.
I have seen many engines with head off look similar after 50-60 k plus miles.
Engines can run weak due to air leaks at inlet manifold or throttle body, also vacuum servo pipes or leak at servo it's self.
After market air filters often being less restrictive can be a cause of weaker mixture especially if no other fueling has been increased to match the new air flow.
Most modern fuel systems when removing filler cap do the hiss, in the old days it could be caused by a blocked fuel tank vent.
By the way re head gasket issue, if engine was just running a bit hot, but no massive water leak, looking at the water ways in cylinder head , they look a little rusty, so if radiator internal core tubes are similar it could account for any raised temp especially during fast driving when a blocked rad has more problem getting rid of the heat.
With head off now would be a good time to lap the valves in and recheck valve clearances where applicable.
Assume a new set of plugs also. I can't see the electrodes of the spark plugs clearly, but if you suspect signs of them running too hot then possibly you could change to a different heat range plug to match the normal driving the car gets.

Thanks for the reply. That's good news about it not looking too bad. I have had to bleed the car repeatedly maybe once a month maybe more for a few months as blowing cold through the air vents. It would blow through warm but then go cold if it had gone on a longish run. It would go cold over 90 but maybe go warm once it cooled down to 70ish sometimes. Changed thermostat and it got worse.

Checked with air compressor on water expansion tank and it held pressure. Checked with smoke detector, same no issues. Compression was down on 1 cylinder, can't remember the reading but it wasn't massive. Think it was cylinder 3 from memory.

No mayonnaise in the oil but expansion tank always smelled a little fuely I think. My guess is it has been leaking across maybe a few cylinders.

The expansion tank would have built up pressure in whenever I took the cap off even with engine cold.

Recently it would just overheat massively and turning the rad fan on (aftermarket switch) wouldn't make any difference. I might have a combination of blown head gasket and blocked radiator perhaps?

 

[jonjg]

Wife uses it mainly 16 miles a day up and down dual carriageway to work and back.

 

[bugsymike]

Re the heater bleeding, it does sound like a slow headgasket seepage.
Are you going to have head skimmed or at least test it with a steel straight edge and 2 thou feeler gauge.
Those tests are good , but I prefer a leak test using compressed air as it is more conclusive although takes longer.
You could may try back flushing the rad and see if any brown muck comes out.
So wife gives it the hard driving.

 

[jonjg]

I have a few cylinder heads spare in the garage so I'm no sure yet. I will have a look at it. I have a feeling this cylinder heads been skimmed before.
That's a good idea about the back flushing the rad I'll give that a go
Haha yes she drives like a lunatic. Takes corners much faster than I would

 

[bugsymike]

I have a few cylinder heads spare in the garage so I'm no sure yet. I will have a look at it. I have a feeling this cylinder heads been skimmed before.
That's a good idea about the back flushing the rad I'll give that a go
Haha yes she drives like a lunatic. Takes corners much faster than I would

I don't know what is the max that can be skimmed given the quality of fuel these days. If head is warped a light skim should be OK.
One thing I always do is clean the threads in the cylinder block and run the bolts all the way to check so I know when torqued they are pulling the head tight onto gasket and block.
Also if new bolts I grind flutes on an old one to act like a tap and use that to clean the threads.

 

[jonjg]

I don't know what is the max that can be skimmed given the quality of fuel these days. If head is warped a light skim should be OK.
One thing I always do is clean the threads in the cylinder block and run the bolts all the way to check so I know when torqued they are pulling the head tight onto gasket and block.
Also if new bolts I grind flutes on an old one to act like a tap and use that to clean the threads.

How do you clean the threads in the block? When you say flutes do you mean cut some sections out like a thread tap?

 

[bugsymike]

How do you clean the threads in the block? When you say flutes do you mean cut some sections out like a thread tap?

If you have an old cylinder head bolt I run it against my bench grinder length ways so it looks like a thread tap, then give it a wire brush up to clean it, when you run it to the end of the cylinder block bolt holes it picks up any dirt etc. and you know the threads in the block are clean so when you torque the head down the torque wrench doesn't click off at a setting that isn't actually pinching the gasket, just dragging on the bolt threads.
I use a speed brace to run the bolt down the threads when cleaning, nothing powered.
I am also able to blast them with an airline to finish. Some head bolt sets come with a fine grease to put on the threads which also helps, just not to excess or it will block the threads and hydraulic lock.