Has my piston ring gone?

[PaulB]

Hi All
I need a bit of advice. I was driving my spit along the moterway when I noticed the noise of the engine changed and she started to loose power on accelerating.
The engine noise only change when accelerating/ i.e. going down hill and the car sounded normal.
It sounded almost like the exhaust was blowing. I pulled over but the exhaust was fine. In fact she now sounds a bit like a volkswagon beetle!  
I'm not sure if she's misfiring or whether the piston ring has gone on one of the cylinders.
Any help is much appreciated.

[Ridgetone Triumph]

Hi PaulB,

I would be inclined to do a compression test first  

[sparky_spit]

Hi Paul - first check would be to pull each plug lead off, in turn, whilst the engine is running and see if the engine slows the same amount for each lead you pull off. Then do a dry and then wet compression test, looking especially at any cylinder that showed less difference in engine speed when you pulled its plug lead off.

Low compression when dry could be rings or a burnt valve, if it gets better with a teaspoon of oil down the bore for a wet test, then it would indicate rings at fault.

[BrendanD]

Sure the manifold-downpipe gasket is OK?

[PaulB]

sparky_spit wrote:

Hi Paul - first check would be to pull each plug lead off, in turn, whilst the engine is running and see if the engine slows the same amount for each lead you pull off. Then do a dry and then wet compression test, looking especially at any cylinder that showed less difference in engine speed when you pulled its plug lead off.

Low compression when dry could be rings or a burnt valve, if it gets better with a teaspoon of oil down the bore for a wet test, then it would indicate rings at fault.

Hi Mike,
I've tried pulling each lead off one at a time and all seemed the same.
Now this is where I show ignorance here. How do I do a compression test?
Thanks, Paul

[sparky_spit]

Well, that could be good news. You need a compression tester to do the test, instructions are included with it. I've got one here, but that's not much use. I'll put it in the car and if you don't have things sorted by tomorrow, I can drop it off on my way back from the CSMA autosolo - would be about 5pm - 6pm I guess. I'll PM you my phone number now, so you can text me if you want it.

[PaulB]

BrendanD wrote:

Sure the manifold-downpipe gasket is OK?

Hi Brendan,

I checked the downpipe that's fine. Thanks

Mike,
Thanks for the offer, I've PM'd you and will text you in the morning.
Cheers,
Paul

[JohnD]

If you had such a sudden failure of a piston ring that performance is worse and noise was greater, then all you need do is remove the oil filler cap with the engine running.   There will be a blast of oily fumes, as that piston suffers severe blow-by.
A compression test would be superfluous in those circumstances.

Has the thrust bearing moved?   Take a lever, a large screwdriver or just a length of wood, stick one end between the crank pulley and the block and try to lever the crank forwards.  If it moves more than a few thou, the bearing is either worn or fallen out.  If you can see the crank move when someone steps on the clutch pedal, same thing.

If it sounds as you say, I fear it's not simple or cheap.
Is there smoke, more than before, from the exhaust?  Perforated piston? (Running too weak can do this)
Are all the valves moving as they should?  Take off the rocker cover & see.   A stuck exhaust valve could do this.
And so on.

Hope it's not too bad.
John

[mikeyb]

accurate diagnosis impossible via the pc - but I'd put my money on a burnt valve

rgds

Mike!

[Steve Cureton]

Cracked or broken manifold?

[Velocita Rosso]

You can get the same symptoms with somethng as simple as a spark plug malfunction, running on three etc

[PaulB]

I've just done a compression test and they read 11 to 12 psi except number 3 cyclinder  which read 1 psi!

I will now take the rocker cover off but I think it is the piston ring ratherthan the valves.

[BrendanD]

I think its the valve. If it was the ring it would be billowing smoke...... (been there...)

[PaulB]

JohnD wrote:

If you had such a sudden failure of a piston ring that performance is worse and noise was greater, then all you need do is remove the oil filler cap with the engine running.   There will be a blast of oily fumes, as that piston suffers severe blow-by.
A compression test would be superfluous in those circumstances.

Has the thrust bearing moved?   Take a lever, a large screwdriver or just a length of wood, stick one end between the crank pulley and the block and try to lever the crank forwards.  If it moves more than a few thou, the bearing is either worn or fallen out.  If you can see the crank move when someone steps on the clutch pedal, same thing.

If it sounds as you say, I fear it's not simple or cheap.
Is there smoke, more than before, from the exhaust?  Perforated piston? (Running too weak can do this)
Are all the valves moving as they should?  Take off the rocker cover & see.   A stuck exhaust valve could do this.
And so on.

Hope it's not too bad.
John

I've ran the engine with the oil filler cap and no smoke came out. I took the rocker cover off and all the valves seem to be going up and down as normal. I tried moving the crank pulley with a screwdriver and that didn't move.

Could it be the head is worn out? Or is it the piston rings? Smoke does come out the back under hard acceleration.

[PaulB]

BrendanD wrote:

I think its the valve. If it was the ring it would be billowing smoke...... (been there...)

Is there an easy to test to see if its the vavle?

[Jason]

PaulB wrote:

Is there an easy to test to see if its the vavle?

Yes, a wet compression test. You do the same compression test you've already done but you squirt a little heavy oil in to the bore, if it's piston ring failure then the oil should give you a little better compression reading, if it's a valve then you won't see any difference.

My money's on a valve issue, just whip the head off and find out. Order us a gasket set and whilst you're waiting for that get the head off ;-)

[PaulB]

Thanks Jason, that was what Mike was eluding to. I will try that.

[GT6 M]

No one has mentioned head gasket,!!!!

have you checked the  rocker gaps,!!!! cam lobe worn away, :-/

if you want to see the valve, then tek the plug oot, and turn engine over with a spanner,
and you should be able to see the valve end,
and with the aid of a small pen light, see if it is burnt worn away,.

will only be the exhaust, that will be giving trouble,

but my loot is on heed gasket,or worn cam.

regards  Marcus

[Jason]

Head gasket could be gone but that usually fails between two cylinders so you get reduced compression reading on two cylinders. Again, whip that head off :-)

[BrendanD]

Yes... Off with the head......! ;)

[herald948]

I don't know if this is very common on these engines (it's not happened to me in a Triumph), but it could be a burned piston. I had it happen on a Volvo 144; unfortunately, it burned at the top edge of the piston and scored the cylinder wall badly.   :o

[PaulB]

Ok, so I did a wet test and no improvement in compression, so I think (I hope) its just the valves. I've ordered a head gasket today and will start to take the head off tomorrow night.

Now, I've never taken a head of a car before. I have my Haynes manual and lots of enthusiasm, but are there any tips when tackling such a job?

[Rich_s]

I did the head on my 1500 a few months back, just in the nick of time as found one of the exhaust valves was not sealing and had started burning the valve and seat away, luckily after 1 hour of lapping it all went back to being round and seating properly.

A few years back i was not so lucky and burnt the valve away and knackered the head on my mini, just hope your head has not gone this way.

As for changing them, its really quite simple, just drain the water and start unbolting, keep track of where things go and what bolts go where, keep the pushrods in order aswell so end up back in same place. Get a torque wrench as well for re-fitting the head.

good luck
rich

[Deleted User]

PaulB wrote:

I've just done a compression test and they read 11 to 12 psi except number 3 cyclinder  which read 1 psi!

I will now take the rocker cover off but I think it is the piston ring ratherthan the valves.

Has no one else picked up on the fact that the engine would not run at all with compression readings as low as this.

First one has to question the way the compression was tested.
Paul has already indicated that he doesn't know much about mechanics and as a result he may have made a mistake in the way that the compression has been measured.

1. Remove all the sparkplugs
2. Fit the gauge to 1st cylinder
3. Fully open the throttle
4. Crank the engine for 10-15 seconds to get a maximum reading
5. Repeat for the next cylinder

Good readings should be in the order of 140-180 PSI

Repeat as a wet test, with a small amount of oil in the cylinder being tested.
But beware when doing cylinders 2, 3 & 4 - when cranking the oil in the previous cylinders will be expelled via the sparkplug holes and will make a mess of nearby objects.

[PaulB]

932 wrote:

I did the head on my 1500 a few months back, just in the nick of time as found one of the exhaust valves was not sealing and had started burning the valve and seat away, luckily after 1 hour of lapping it all went back to being round and seating properly.

rich

Hi Rich,

What is lapping? Or is that a typo?

Luckily I have a torque wrench, it was a Xmas present.

I will make a note of the push rod order.

Cheers,
Paul