Login Register

low compression in cylinder #2 - should I attempt a ring job?

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, including 850 R, 850 T-5R, 850 T-5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

Post Reply
dudlo
Posts: 12
Joined: 16 Oct 2006, 09:01
Year and Model:
Location: Dallas, TX
Has thanked: 2 times
Been thanked: 4 times

low compression in cylinder #2 - should I attempt a ring job?

Post by dudlo »

Friends, I have a '96 NA 850 with some 237,000 miles. Cylinder #2 had low compression, some 110-150 psi while other cylinders had consistent 200psi. I am now rebuilding the head. To my dismay, the valves looked fine - I could see no difference in valves from #2.

I will go ahead and complete the valve job (remove valves, lap, new seals). But I am debating if I should attempt to do a ring job. There are plenty of tutorials on how to remove the oil pan, and even how to do the rebuild (this site is a great resource!). But I feel queasy cutting ("reaming") the cylinder and do all the ring work. At the same time, I'd hate to put the head back up only to find I still have low compression.

A few facts about the engine:
- in 2010 I had a burnt exhaust valves on #2. The compression was 0 and the valves were clearly burnt. I removed the head, had it machined (cleaned, new valves in #2, resurfaced) at a machine shop. But the guy had since retired
- recently I checked the compression after getting misfire codes
- the engine was leaking oil like a sieve. At least 2 cam seals were pushed out. I suspect the oil pump and front main were leaking as well.
- the oil separator, flame trap were all dirty (leaking oil). This has been a problem for a few years
- there was no coolant leak (or super slow). There was no sign of burning oil
- when I removed the head, I flipped it and poured Marvel mystery oil into the depression the head top created (to help dissolve the carbon). All valves held fine for 3 days
- the head and the cylinders look fine - carbon where expected but no gauges/scratches or any visible problems
- I have never opened the oil pan, so most likely I have all problems of sump pump seals. When I removed the oil pump, there was a piece of dried mangled o-ring sticking from the bottom hole (pic below)
- oil pressure was never a problem; the engine was not starved of oil
- I am in no hurry. This is a labor of love to last a few weekends. I can expand it but only if it is makes sense or looks like useful/necessary/achievable

I guess I am asking:

- am I jumping the gun? Should I just calm down, finish the head job, and the compression would come back (or perhaps it was not so bad to begin with)
- how much more work is it to do the ring job, compared to the head job, and oil pan/sump o-rings? That cylinder reamer looks nasty, and I do not even know if the parts stores rent it these days
- if I were to do it, I only wanted to touch #2 - I have no desire to do all 5 cylinders. Would that work?
- are the piston rings simply cleaned up and put back? I do not even see where to buy just the rings - FCP sells the whole piston kit (30750664) but not rings

Thank you for your advice,
dudlo
20220131_183149.jpg

User avatar
abscate
MVS Moderator
Posts: 28786
Joined: 17 Feb 2013, 17:54
Year and Model: 99: V70s S70s,05 V70
Location: NYC, ALBANY NY
Has thanked: 785 times
Been thanked: 2142 times

Post by abscate »

It’s possible to have bad rings on one cylinder but pretty rare. The time to check is with a leak down test while the engine is still together. Since you have to drop the pan to do the oil pump o rings, I would inspect the cylinder for hone marks and go from there. If those look good, bite the bullet and put it back together.
Empty Nester
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 BMW
Link to Maintenance record thread

User avatar
befarrer
Posts: 183
Joined: 11 Nov 2019, 07:41
Year and Model: 1998 V70 AWD
Location: Edmonton, Alberta
Has thanked: 1 time
Been thanked: 19 times

Post by befarrer »

I've got lower compression in one cylinder, I'm wanting to do new rings, I think the rings in my cylinder are stuck, causing the low compression. I have no oil consumption. My car sat around for awhile, and if it was driven like an old person, the engine could carbon up. I'm also getting above average blowby with a new pcv system. I would drop the pan and put new rings in it, can check condition of rod bearings then too.
98 V70 GLT AWD
05 VW Golf TDI
93 Mazda B2200 with 13B rotary engine swap

dudlo
Posts: 12
Joined: 16 Oct 2006, 09:01
Year and Model:
Location: Dallas, TX
Has thanked: 2 times
Been thanked: 4 times

Post by dudlo »

Guys, thank you for your response. It turns out I failed to disclose some damning evidence:
20220205_172116.jpg
The vertical line in the middle is a gash/nick. I have noticed it today when going over cylinders (last time I just removed the head and call it the end of a long weekend).

The nick goes from the bottom to about half way up of the piston travel. I can feel it but I cannot measure how deep it is. I guess it is deep enough to cause pressure of only 110-150psi.

I suspect it's been there all these years (given the oil mess in/around oil separator , flame trap, and pushed out seals). Call me sloppy: I do not recall doing a compression test back in 2010 after I put the engine back together with new valves - I was happy it ran better.

At this point I believe my options are:
A. putting it all back together and live with less-than-perfect engine and an occasional check engine light (for misfire), or
B. pull the engine out, take the block apart, bring it to a shop to re-bore, and install all new stuff (I assume it would need new pistons, not just rings).
C. get some magic remedy/tool/potion to fix this in-the-car

As much as I love this car, B is way too much work - I just looked up write-ups on engine removal; it is a ton of work, and I am not even sure I have enough clearance in my garage for a lift. That job is too much for my skills and patience.

So unless you guys know of some option C, I guess I will live with less-than-perfect cylinder #2. If it were running OK like this since 2010, it may give me a few more years. I am still debating if I want to do the sump o-rings given the engine condition.

Thank you,
dudlo

User avatar
abscate
MVS Moderator
Posts: 28786
Joined: 17 Feb 2013, 17:54
Year and Model: 99: V70s S70s,05 V70
Location: NYC, ALBANY NY
Has thanked: 785 times
Been thanked: 2142 times

Post by abscate »

Is that a scratch or a split in the block cylinder wall? Yikes. Have not seen that before, except on thin walled R motors

Put it back together and drive it with love. I think you are only going to get another 10 years out of it at best

:D
Empty Nester
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 BMW
Link to Maintenance record thread

rguzz
Posts: 526
Joined: 07 Oct 2015, 08:41
Year and Model: 1996 850 turbo
Location: VA
Been thanked: 15 times

Post by rguzz »

Second leaving it alone. Do the oil pan o rings though and avoid being tempted to do more "while you're in there." Did you mention anything about oil consumption, might have missed that. Not sure why compression of 120-150 in one cylinder would cause a misfire? The vertical line does indeed look weird.

dudlo
Posts: 12
Joined: 16 Oct 2006, 09:01
Year and Model:
Location: Dallas, TX
Has thanked: 2 times
Been thanked: 4 times

Post by dudlo »

I hate open-ended (unresolved) problems, so I want to follow up and close this soap opera. I ended up completing the head job (removed all valves, lapped, put it all together). Against better advice here, I did not do the oil pan rings (since they would be as much work later), The motor runs about as well as before. That is, I can hear the imperfection but my daughter that drives the car cannot hear or feel anything wrong. In the past few months since the repair I replaced all mounts and did the zip-tie compressor hack/fix. Everything is happy and running fine. No misfire or other codes.

To answer questions above: it was a nick, not a crack. I assume the burnt valve actually lost a piece of metal (some 12 years ago). I can imagine how the fragment bounced in the cylinder before being blown out.

The engine was losing oil before the repair but it was from leaking seals; 2 camshaft seals were "loose". Crank seal was definitely leaking. After the repair, there is no puddle under the car, and I cannot detect any burning oil - no loss.

Overall, I am happy. Perfection is overrated and this engine is good enough. THANKS for all responses and advice. I hope to pay it back some day.

User avatar
MrAl
Posts: 997
Joined: 08 Apr 2015, 16:45
Year and Model: v70, 1998
Location: New Jersey
Has thanked: 9 times
Been thanked: 15 times

Post by MrAl »

befarrer wrote: 04 Feb 2022, 11:46 I've got lower compression in one cylinder, I'm wanting to do new rings, I think the rings in my cylinder are stuck, causing the low compression. I have no oil consumption. My car sat around for awhile, and if it was driven like an old person, the engine could carbon up. I'm also getting above average blowby with a new pcv system. I would drop the pan and put new rings in it, can check condition of rod bearings then too.
Hi,

That's interesting about what you say about the clearance in the garage for the engine.

Back when i was much younger i pulled the engine on my Pontiac Catalina. It had a 389 cubic inch V8.
I assumed i could get it out by hoisting it then rolling the car backwards then dropping the engine into a wagon so i could roll it out and down into the basement.
What happened was there was not enough clearance between the bottom of the engine (guess the oil pan) and the front of the engine compartment. However, when you have a line (such as a chain) of a certain length that is perfectly vertical and you tilt it, the vertical distance decreases (from trigonometry). That means that when i rolled the car back and the bottom of the engine caught on the front of the engine compartment, the engine moved back with the car slightly and that tilted the chain holding the engine up and so the the vertical distance ceiling to engine compartment front decreased. After a certain point, it was enough to clear the compartment and since the engine was now farther back than when it rested with no tilt, once it cleared the engine it swung back a little and then back and forth slightly. It was a little funny but because of the angle when it caught on the engine compartment it was able to finally clear the front and the car was then clear of the engine and the engine could then be lowered.

It was funny to see a 389 cubic inch V8 engine swing back and forth a little, and i think the whole garage moved a little ha ha. But it worked.
Getting it back into the car was the reverse. Swing the engine back a little, then roll the car under the engine, then swing it back into the vertical position.
You may still have to measure though to make sure even with the tilt you still have enough clearance. I would bet you do, but if it swings too much i would say have two people, one with a rope to stop it from swinging back and forth once it clears.

The other thing is these engines are super heavy. The beam in the ceiling has to be able to support the weight because if it can not, the engine will crash to the floor and that will be the end of it for sure. It's also a little dangerous so nobody can be standing around. They can use a rope though to stabilize the rocking so they dont have to stand close to the engine.

Whatever you decide to do, good luck with it.
I’ve been driving a Volvo long before anyone ever paid me to drive one.
1998 v70 on the road since April 2nd, 2015

Post Reply
  • Similar Topics
    Replies
    Views
    Last post