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Lost compression after replacing a ring

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SASSAMON Avatar
SASSAMON Silver Member Roger Colson
Ashland, MA, USA   USA
1957 Triumph TR3 "Bettie"
Mathew,

Could the broken ring have caused a score on the cylinder wall? This could cause the low compression numbers when the motor is turning but shows better pressure during a static test.



Roger Colson
SASSAMON
1957TR3 TS21383L "Bettie"

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Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
That mystery is solved. I am a moron. My cylinder pressurization rig was faulty - it had a Schrader valve in the spark plug adapter that I didn't see. The leak down test was only testing my rig - no air was going into the cylinder, and that's why I couldnt hear a leak. Removed the Schrader valve, and could hear the air blowing right past the rings, into (and out of) every opening in the block. All 4 cylinders. All I can think, when I cleaned up the top of the block before the head went back on, maybe some fine dust went down the cylinder walls, and now all 4 are blowing by. Short of pulling the pan, and pulling all 4, re-ringing them, and honing the cylinders (keep in mind, they were all fine before the ring broke), any idea how to get the rings to seat again?!?



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace

Aridgerunner Avatar
Aridgerunner Silver Member Bill Bussler
Montoursville, PA, USA   USA
1956 MG MGA 1500 "The A"
1959 Triumph TR3A "The Mistress"
When you are doing the leak down test are you making sure the piston in the cylinder being tested is at top dead center, on the compression stroke, and staying there while you apply the pressure? This is a critical part of the test.

Bill

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Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518867 by Aridgerunner When you are doing the leak down test are you making sure the piston in the cylinder being tested is at top dead center, on the compression stroke, and staying there while you apply the pressure? This is a critical part of the test.

Bill

Mute point now. Read one post up. Zero pressure in any cylinder.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace

CJD john durant
Southlake, TX, USA   USA
Yep, a cylinder holding pressure for 10 minutes is unheard of. I figured it was something like your test rig.

Also, it is not really moot to have the pistons at TDC for a leak down test. If you test the leakdown at the bottom you usually get 2-3 times the amount of leakdown as at the top.

My question is how the #2 ring broke to begin with. I fear you have more than just the number 2 broken all along, the others were just not positioned to show it. Broken rings are normally caused by severe detonation or over-Reving an old motor that has a wear ridge at the top of the cylinders. The rods stretch enough for the top rings to slam the ridge and shatter them. The point is that it is rare to only break one ring in an engine. If one is broken there is more than likely damage to more.

Also, annealed or not, it is best to get another new head gasket. These are internally composite, so they are not meant to re-use like solid copper race gaskets are. Reusing old gaskets will complicate your diagnoses.



John
Southlake, TX

'55 TR2



Edited 1 time(s). Last edit at 2018-03-13 09:10 PM by CJD.

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
Good info John. Mute because the blow by is so bad, there is no point in worrying about anything else. Changing piston position and getting 2 to 3 times less blow by will mean I still have a ridiculous amount of blow by.

Big question for me is why did I have 150 psi before the head pull, and crap after.

It is extremely likely I hit the revs hard, and that's what broke the top ring on number 2. I drive it spiritedly every time it leave the garage - and have for nearly 17 years I have had it. I drive it at least 2 times a week, sometime more - so it gets a lots of exercise. I broke a ring on number 3 in 2012 as well. Never did figure out what caused that either. Thought it was just a few years back, but found the invoice, 6 years ago.

I have pulled the head before, and re-used the copper gasket, running it through the same annealing process - but this is the only car I have ever seen with a copper gasket. And back then, could find next to nothing about it, so thats what I tried. Clearly it worked once. No idea if it will work again. But I did find a new one this time from TRF that was about $25 bucks, so thats why I tried the new one. It probably sealed, but I doubted it, and pulled the head again, mistakenly thinking that was the problem.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace

CJD john durant
Southlake, TX, USA   USA
If you rev it regularly, I doubt that was the cause. My father kept his Chevy pick-up on the property for 15 years...it never saw the highway in that time. When he finally took it on the highway it shelled all the top rings! It had not seen high rpm for 15 years. He drove it here to Texas and had to add 10 quarts of oil per tank of gas! Amazing thing is it still ran fine with almost no compression. That doesn’t sound like your case.

Most likely you are getting detonation at higher speeds, which is often hard to hear over the exhaust. You might want to try one carb needle size larger once you get it going again. Edit...actually one size smaller,i.e. richer!

One other possibility is that the piston ring grooves are either worn or machined with too much clearance, so the rings are loose enough to flutter and break at speed. That is easily checked with a feeler gage when you replace the (likely) bad rings in 3 and 4.



John
Southlake, TX

'55 TR2



Edited 2 time(s). Last edit at 2018-03-14 08:00 AM by CJD.

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tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
You've been trying to do a 'leak-down' test, but that must be down with the piston at TDC on the firing stroke else the valves will be open, even a tad, and you'll get no presure in there.
See: https://mobiloil.com/en/article/car-maintenance/car-maintenance-archive/how-to-do-a-leakdown-test

But a leak-down is a static test. The valves have plenty of time to cliose completely.
When you do a compression tet, it's dynamic. Could it be that you have sticking valves, that close a tiny bit slower than the cam descends? Or a broken spring?

But TWO bores, and adjacent. Seems unlikely two valves at once. Gasket seem most likely from that, which I'd expect on a six-cylinder, as they are so close together, but you have a massive gap between the bores, all filled with gasket!
Stumped.

John

PS The assembled gurus of North America seem stumped too! Care for a second opinion? Try the TR Register in the UK, and the specific model forum: http://www.tr-register.co.uk/forums/index.php?/forum/4-tr233a3b-forum/ J.



Edited 1 time(s). Last edit at 2018-03-14 05:42 AM by tapkaJohnD.

charleyf Silver Member Charley Fitch
Redding, CA, USA   USA
1962 Triumph TR4
1963 Triumph TR4 "MR.T"
I am not likely to solve the problem -- but if you have bad compression for two adjacent cylinders it might well be a bad head gasket.
There has been a discussion about which way the head gasket should be fitted to the engine. Our TR engine gaskets can fit two ways. I have found that placing the gasket with the seams facing up is the better approach. Otherwise the seams are prone to getting attacked by the water in the block side of the gasket.
Charley

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Jacad Avatar
Jacad Gold Member Barry Shefner
Montreal, QC, Canada   CAN
1959 Triumph TR3A "Loose Wheels"
1976 Triumph TR6 "The Tweetster"
I am wondering if Matthew may have disturbed one of the sleeves removing the piston or honing the sleeve and it is not re-seating correctly giving the required .003 to .005" protrusion above the top of the block. If the top of the sleeves are not all the same that could perhaps affect the gaskets ability to compress and result in compression loss. Would be easy to check if the head were off the engine. Anyone think that this might have merit?



Barry
59 TR3A 0TS57675LO - "Loose Wheels"
76 TR6 CF54266U - "The Tweetster"
Website: Triumph TR2-TR3-TR4 www.trtriumph.com/ (sorry for not keeping it current for the past couple of years)



Edited 1 time(s). Last edit at 2018-03-15 01:38 PM by Jacad.

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1519234 by Jacad I am wondering if Matthew may have disturbed one of the sleeves removing the piston or honing the sleeve and it is not re-seating correctly giving the required .003 to .005" protrusion above the top of the block. If the top of the sleeves are not all the same that could perhaps affect the gaskets ability to compress and result in compression loss. Would be easy to check if the head were off the engine. Anyone think that this might have merit?

I did run a straight edge from number 1 to 4 and did not see any daylight at any place the straight edge touched the liner tips. Good point, thanks.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
Update: so I pulled the head again, broke loose the oil pan, knocked the ridge off of the other 3 cylenders, and pushed the pistons up. Somehow, with the piston all in their cylenders, I managed to break the top ring on all 3. The only thing I touched, I cleaned the carbon off the piston tops with an air die with a soft pad. Must of been too much for them, never would have guessed it. But, the were cast iron rings.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace



Edited 1 time(s). Last edit at 2018-03-15 02:42 PM by Born Loser.

offsideundo Keith Anderson
Brandon, MS, USA   USA
Matthew:
The compression tester gauge is holds the pressure until you press the release valve.
So even if you disconnect the air line, the pressure gauge holds the same reading.
That is why it "appears" that the cylinder is holding pressure.

CJD john durant
Southlake, TX, USA   USA
Well, at least you found the issue and are on the way to getting it running again. When you mention the “ridge”, that implies the cylinders have worn with at least some taper.
Highly tapered cylinders are another cause of broken rings. They get flexed as they go up and down the bores.



John
Southlake, TX

'55 TR2

davek46 Avatar
davek46 David Kulak
Bristol, CT, USA   USA
1958 Triumph TR3A "Blue TR"
Matthew, Check for broken valve springs.

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