Ring, Valve Or Gasket

[gav_mi16 0]

The Mrs' car is a 1.6 GTi (XU5JA engine)

 

It's been down on power and running a bit rough when cold.

 

Cold compression test reveals, No1 from flywheel

No1 5 bar

No2 10 bar

No3 10 bar

No4 10 bar

 

Now if I put a few good squirts of oil down No1 then compression increases to around 7bar.

 

Would I be right in thinking this will be worn / broken piston ring?

 

The car burns / uses no oil. It does 10k+ miles a year and top ups are every 3 to 4 months and that's only 1/2litre or so.

Uses a little water, about 1 litre every 4 weeks or so.

 

I had intended building a fresh head for this, but if it turns out to be the rings then it's a bit pointless and i can't afford to have the car off the road for longer than a weekend.

 

Cheers

[woodsy 0]

Hi mate, it would say try to get a leak test done at a garage that way it would tell whether its rings or valve etc before you start taking it apart.

[gav_mi16 0]

Hi mate, it would say try to get a leak test done at a garage that way it would tell whether its rings or valve etc before you start taking it apart.

 

Yeah that is probably the best way to diagnose this, but she needs the car 8am to 6pm daily, and I don't have the time to take it anyway.

 

Just wanted to know if my thinking of a ring was the most likely from the description above, not an actual diagnoses.

[kyepan 291]

Yeah that is probably the best way to diagnose this, but she needs the car 8am to 6pm daily, and I don't have the time to take it anyway.

 

Just wanted to know if my thinking of a ring was the most likely from the description above, not an actual diagnoses.

 

one would imagine that if the oil control ring is worn you will get blow by of oil vapours into the combustion chamber, and blue smoke out of the exhaust, if a compression ring has gone you may get crank case pressurisation and heavy breathing / lots of extra oil in the breather pipes.

 

seems strange that only one cylinder is down as ring / bore wear should be roughly even across the cylinders.

 

Perhaps you have had some kind of valve train problem, either it's not closing properly, or is bent... or perhaps broken / damaged.

 

so purely based on what i have read, a ring does not seem the most likely, because it's only in one cylinder.. however i could be wrong

 

Check for smoke out of the back when you rev it.. listen to the engine and see if it's firing smoothly across all cylinders.

 

I would say head gasket is more likely, look for oil contamination in the header tank, hold the water hose coming off the thermostat with it running to see if you can feel pulses of gas in the system, buy one of the hydro carbon testers to detect exhaust gasses in the header tank...

 

rule out the head gasket, and then look for other issues.

[dcc 855]

I would hesitate a guess at the rings from your description. The bonus is that if it is the rings, you can do it in a day with little worry, however, if the liners need a hone, then you are going to have to be careful, but I am sure you can still get that done with the block in place in the bay as the liners come out! but you might need to have the liner base and block cleaned to make sure they don't leak

 

I would doubt it is valve related, as a damaged valve usually wouldn't alter the compression when oil was used to line the bore.

 

The starting point for you is head off and have a good look!

[gav_mi16 0]

Thanks for the replies.

 

Just to add, there is no smoke at all from the back. The oil is clean and uses very little, the water is clean and does not over pressurise or pulse.

When cold it does not run smoothly at all and frequently stalls, much better when warmed a little, but it's still down on power.

 

Could one of the compression rings have snapped in two? I've seen this happen on a Mini years ago.

 

Hmmm anyone got an engine? I think i'd like to drop a decent runner straight in and then re-condition this one.

[dcc 855]

I know goliath took a very good 1.6 he bought from Welshpug out of his sorrento to put the v6 in.

 

he might still have it!