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Lost compression after replacing a ring

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Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
Ok, I am stumped! Here is the situation. Broke a ring on the #2 piston. Pulled the head, dropped the pan, knocked off the crust at the top of number 2 cylinder, pulled the rod cap, and pushed number #2 piston out the top. Re-ringed it, and honed #2. Oiled it up, and put #2 piston back in. Buttoned up the bottom end. Cleaned the head and block and replaced the copper gasket. Re-fit everything. Fully expected the motor to light off, it didnt. A touch of hard start did not help. Pulled a plug, had spark. Grabbed the compression gauge - there is the problem.

Before the work started, I confirmed the #2 had a ring problem by taking compression readings.

Dry:
1 -151
2 - 90
3 - 150
4 - 149

After reassembly, and no start (wet or dry made no difference):
1 - 120
2 - 100
3 - 65
2 - 42

Thought I screwed up the head gasket - grabbed the torch and a bucket of water, and heated the original up, and quenched it. Pulled head again - put in the old gasket. Same compression readings - exactly!. Permatex both sides - same readings. The head held gasoline over night in each cylinder (with spark plugs re-installed. Heads been off 3 times, and still no change. So I regged up a way to pump each cylinder with compressed air, and measure the pressure. All 4 held 120 psi for several minutes. Number 4 (the worst compression) leaked down to 110 psi after 10 minutes. Definitely not the catastrophic loss of a seal that would cause 42psi. So, the cylinders are tight - which has me thinking valve timing/geometry. The rocker assembly is so simple, I cant see how I could have messed it up - but someone PLEASE tell me that I did!

Not sure where to go from here - thoughts?



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



Edited 3 time(s). Last edit at 2018-03-23 09:54 AM by Born Loser.

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
How's your valve lash?



Randall
56 TR3 TS13571L Once and future daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518780 by TR3driver How's your valve lash?

Originally set it out of the book (for the TR2) at .010 intake and .012 exhaust. Then saw the addendum for the TR3, and reset all to .010. No better.



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

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
Might be time to try pressuring a cylinder with compressed air, and listening to where it is escaping.



Randall
56 TR3 TS13571L Once and future daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518786 by TR3driver Might be time to try pressuring a cylinder with compressed air, and listening to where it is escaping.

Did that - its holding well - 10 psi in 10 minutes, won't hear that. Not sure what's normal, but that cant be why its down to 41 psi.



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

Jacad Avatar
Jacad Gold Member Barry Shefner
Montreal, QC, Canada   CAN
1959 Triumph TR3A "Loose Wheels"
1976 Triumph TR6 "The Tweetster"
If you did not touch the timing chain then it should not be a timing issue although if you did remove the distributor gear and shaft you may not have reinserted it correctly and thrown off timing



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)

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518790 by Jacad If you did not touch the timing chain then it should not be a timing issue although if you did remove the distributor gear and shaft you may not have reinserted it correctly and thrown off timing
I didnt tough the front, engine is still sitting in the car. Never pulled the dizzy either. Only suspect possible cam timing, because it’s the only thing left that makes sense. With the headers off, if I put my hand over the exhaust port, and turn over the motor on the starter, I can feel the exhaust port suck right before it blows (on each cyclender). Is this normal, or is the valve opening too soon?



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

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
Sure doesn't make any sense to me. It's not leaking, but it's not building pressure either. That has to mean either the valves aren't moving as they should; or the pistons aren't.

BTW, distributor problems won't cause those compression readings. You should be able to get good compression even with the distributor off the engine entirely. And for that matter, it should have run with only #2 down to 90 psi. I've run engines with much worse!

Bad valve timing (chain slipped somehow) would certainly cause poor compression, but I would expect it to be more or less equal across all cylinders.



Randall
56 TR3 TS13571L Once and future daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518798 by TR3driver Sure doesn't make any sense to me. It's not leaking, but it's not building pressure either. That has to mean either the valves aren't moving as they should; or the pistons aren't.

Exactly where I am at. Pulled the head, and turned the motor over. The pistons are running exactly as they should. So, that's why this post - the valves have to be doing something improperly - just cant figure out what.



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

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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"
Well if you did not touch the timing chain or timing gears and you did not unmount the dizzy then the timing should be just as it was originally before you removed the piston. I wonder if running with a broken ring may have caused something to skip although I don't see why that should occur



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)

tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Matthew,
"Wet or dry - makes no difference" That result is why you do the test! If it 'makes no difference' then the cause is a valve. The oil will assist rings to seal, and will always make a difference.

Doesn't tell you why the valve(s) doesn't seal, but atleast removes half the possibilities.
JOhn

Jacad Avatar
Jacad Gold Member Barry Shefner
Montreal, QC, Canada   CAN
1959 Triumph TR3A "Loose Wheels"
1976 Triumph TR6 "The Tweetster"
Only other thing i can think of is perhaps a peice of the broken ring found it’s way to the valve and dammaged the seat



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)

ArtL Avatar
ArtL Art Liefke
Kings Park, NY, USA   USA
Pull off the rocker assembly and take compression readings. All the valves should be closed, so that might shed more light on where the problem is.



Art


Beer is proof that God loves us and wants us to be happy. - Benjamin Franklin

CJD john durant
Southlake, TX, USA   USA
In reply to # 1518788 by Born Loser
In reply to # 1518786 by TR3driver Might be time to try pressuring a cylinder with compressed air, and listening to where it is escaping.

Did that - its holding well - 10 psi in 10 minutes, won't hear that. Not sure what's normal, but that cant be why its down to 41 psi.

Could you please explain this? I have never seen an engine hold a pressure more than a few seconds, let alone 10 minutes. How are you doing this test, and what is 10psi in 10 minutes referring to?



John
Southlake, TX

'55 TR2

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1518810 by tapkaJohnD Matthew,
"Wet or dry - makes no difference" That result is why you do the test! If it 'makes no difference' then the cause is a valve. The oil will assist rings to seal, and will always make a difference.

Doesn't tell you why the valve(s) doesn't seal, but atleast removes half the possibilities.
JOhn

Yup, thats why I put that result - same reading wet or dry - so the failure to build compression is NOT rings.

In reply to # 1518823 by ArtL Pull off the rocker assembly and take compression readings. All the valves should be closed, so that might shed more light on where the problem is.

Did that too. Set the piston to the bottom of the cylinder, then screwed in the compression gauge. Only got to about 25psi. Not sure what that even ment. But that lead to me pumping the cylinders full of air to check if they could hold pressure.



In reply to # 1518831 by CJD
In reply to # 1518788 by Born Loser
In reply to # 1518786 by TR3driver Might be time to try pressuring a cylinder with compressed air, and listening to where it is escaping.

Did that - its holding well - 10 psi in 10 minutes, won't hear that. Not sure what's normal, but that cant be why its down to 41 psi.

Could you please explain this? I have never seen an engine hold a pressure more than a few seconds, let alone 10 minutes. How are you doing this test, and what is 10psi in 10 minutes referring to?

First time I have tried this as well - so I really don't know what "normal" is. What I expected was a catastrophic loss in pressure. When that didnt happen, I decided to make this rig, and time how fast they leaked down. The best was the lowest compression cyclender, about 10 psi in 10 minutes of loss. The worst was this one (see Youtube video) - about 10 psi of loss in about 45 seconds
Number 4 leak down. Neither one I would consider bad enough to cause my compression to be so low.



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

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