nicholas Posted May 6, 2009 Share Posted May 6, 2009 My pathfinder's been diagnosed with worn piston rings, well just one cylinder has the worn rings. Anyways I got the news today and was wondering wether it was worth getting into replacing the rings myself. There's no way I'm gonna pay the mechanic to do it, and I can't/won't pay for a new engine. Could you all please tell me how involved replacing worn rings is. Do I have to pull the whole engine, or can I just pull the head and get the piston and connecting rod out that way? Also if I do get into it what else should I do while I've got the whole thing in pieces? Timing belt? Valves? I'm a rookie at this sort of heavy duty engine repair, the most I've ever done is a head gasket. This totally sucks though, if I don't do the repair I've basically got to call it quits for the pathy. It's a 91 SE-V6 and I've owned it for barely 4 months. Brutal luck. Link to comment Share on other sites More sharing options...
unccpathfinder Posted May 7, 2009 Share Posted May 7, 2009 yea...you need to pull the engine strip it down take it to a shop and probably get it taken to .030 over get new pistons/rings and replace all the bearings...pretty much rebuild the entire bottom end... Just out of curiosity is it burning oil (blowing blue smoke) or did it fail some other test like a compression or draw down test? Link to comment Share on other sites More sharing options...
Precise1 Posted May 7, 2009 Share Posted May 7, 2009 Yep, like he asked. How many miles on the truck?? and I can't/won't pay for a new engine. Look around in your area for any sort of donor vehicle also. You may be able to find a running motor to swap in. B Link to comment Share on other sites More sharing options...
GrimGreg Posted May 7, 2009 Share Posted May 7, 2009 Yeah, to do a ring job, might as well do a complete rebuild, or complete motor swap. Link to comment Share on other sites More sharing options...
Ramon Posted May 7, 2009 Share Posted May 7, 2009 In Mexico worn piston rings is equal to "cancer" in your case is detected on time I believe is better to swap the engine cos now you fix one cylinder tomorrow the next or something else and the battle will continue and never end until you have done the whole engine rebuild better if you do it at once Link to comment Share on other sites More sharing options...
88pathoffroad Posted May 7, 2009 Share Posted May 7, 2009 You might ask for a second opinion. Mechanics have been known to tell people they need more work than they actually do sometimes. Best way to test for bad rings is an initial compression test dry, then add several tablespoons of oil to the cylinder through the spark plug hole and do the test again. Increased compression with the addition of oil indicates poor ring sealing. Link to comment Share on other sites More sharing options...
nicholas Posted May 7, 2009 Author Share Posted May 7, 2009 Thanks all for your responses. It was quite weird how the rings went, one day after work I started her up and it was belching blue smoke down the street. Fogged the whole area! Anyways, my mechanic is a pretty solid dude so I trust him on the ring diagnosis. An engine rebuild is daunting, might go back to the Toyotas and drop enough coin to pick myself up a reliable 4runner. Anyone want a pathfinder with a perfect body but a flawed engine? In Edmonton? Oh Precise1 the trucks only got 180,000 kms. It seems a little early for rings to be going it thought but still, I guess they've gone. Cheers Link to comment Share on other sites More sharing options...
Precise1 Posted May 8, 2009 Share Posted May 8, 2009 might go back to the Toyotas and drop enough coin to pick myself up a reliable 4runner. For 2x the cost of a reliable Pathy. Yes, that is early for motor trouble for a Pathfinder. Perhaps it was abused by the PO?? How does the mechanic know it's the piston rings and not the valves? If the rest of the truck is in perfect condition, fix or swap the motor. I have a motor that runs perfectly, I'll sell it to you for $500... B Link to comment Share on other sites More sharing options...
Tungsten Posted May 8, 2009 Share Posted May 8, 2009 yep had that happen to mine but luckily i did not pay for it the engine on my 91 was just replaced with a 94 engine, good as new Link to comment Share on other sites More sharing options...
unccpathfinder Posted May 8, 2009 Share Posted May 8, 2009 ususally dont rings start billowing smoke slowly...a blown head gasket to me sounds more reasonable but I could be wrong...eveyr car i've seen with bad rings was slow to start smoking and then started clouds but head gaskets were just clouds in an instant... Link to comment Share on other sites More sharing options...
Kingman Posted May 8, 2009 Share Posted May 8, 2009 (edited) Mine blows a little blue when I rev it up to like 5k+. Other than that, nothing. A common problem on the 3.0L Mitsubishi engines in the Chrysler minivans. I see them pull away from a stop and it's a total bat screen. Edited May 8, 2009 by Kingman Link to comment Share on other sites More sharing options...
88pathoffroad Posted May 12, 2009 Share Posted May 12, 2009 LOL, old Chryslers are the worst. Link to comment Share on other sites More sharing options...
Kingman Posted May 12, 2009 Share Posted May 12, 2009 Sudden bellowing of blue smoke+"worn" rings... Doesn't compute. Link to comment Share on other sites More sharing options...
k9sar Posted May 12, 2009 Share Posted May 12, 2009 agreed. the symptom of bad rings is loss of power. Excess of oil in the cylinder is due to valve seals. The lubrication to the cylinder walls is done from the main bearings squirting oil against the walls through an opening in the conencting rods. Most of it runs back down the inner wall and drips back into the pan. There is NO PRESSURE to force oil into the cylinder past the rings. They are not designed to seal the oil, they are designed to seal the compression. There is also no way to SUCK oil into the cylinder past the rings as the area below the piston is not oil filled. If you are blowing blue smoke, you have lost your valce seals. Pull your plugs to determine which one(s) are bad. The plug will most likely be wet with oil. You can get at the seals from the top without pulling the heads. Just make sure you get each piston in the up position (use a feeler through the spark plug hole) before you remove the springs on the corresponding valves. Alternatively, you can pressurize each cylinder that youa re working on with a compressor and a spark plug hole adapter. (I found that removign the rocker arm assemblies and the spark plugs makes it easy to turn by hand (disconnect your coil) and keep your valves from falling into the block when you pull the keeps. If you do the seals, post. There are lots of helpful hints that we can all share to keep you from running into terrible problems (like stuff rags ir similar into your oil drain holes before moving the valve keepers. you don't want to drop them down the hole) Link to comment Share on other sites More sharing options...
nicholas Posted May 13, 2009 Author Share Posted May 13, 2009 Well, I talked to the mechanic and he said that he didn't even need to check it out to thoroughly. From the sound of it, a look at the tailpipe (it's seriously blackened), and from pulling the plugs (one was seriously oil fouled) he concluded that it was a worn ring. I asked him straight out if he was confident that it was the rings and he said he was absolutely certain. So I don't know. The idea of worn valves does give me hope though, I'll have to check it out myself more thoroughly. If you don't mind I'll go through the symptoms once again and let me know if it still sounds like worn valves. The vehicle get very poor gas mileage (~300 kms a tank). It's idle speed is excessively high and fluctuates from stop to stop, sometime at 2000rpm and sometimes at 1000. It sounds like it misses every once in a while and there is a small popping backfire in the exhaust. I pulled some codes and I got the o2 sensor and crankshaft angle sensor. Replaced o2 sensor and no real difference, though it was seriously fouled when I pulled the old one out. Oh and when you shut the engine off you only then realize how unhealthy sounding the thing is . . . you shut it off and the engine shudders and shakes to a stop. Grim . . . but if fixing a valve were to help with this HOEWWEE I'd be pleased. Link to comment Share on other sites More sharing options...
GrimGreg Posted May 13, 2009 Share Posted May 13, 2009 (edited) Still looking at a partial top end rebuild, once you pull the heads you can find the leaks. If it is a bad ring, you will probably see some scoring in the cylinder wall. If it is a leaking valve seal, you should be able to see a build up on and around the valve. Edited May 13, 2009 by GrimGreg Link to comment Share on other sites More sharing options...
k9sar Posted May 13, 2009 Share Posted May 13, 2009 If you are burning oil, the O2 sensor is probably having a cow. The ECU is having a fit due to the O2 sensor and is probably adjusting your mixture which will make it run like crap. From your description (fouled plug, dark tailpipe, etc), I have no doubt that you are burning oil. The only question is where it is coming from. Check the easy first. If compression is good, it's valve seals (probably the intake one). in a 4 stroke engine... 1. compression: valves closed, piston coming up, any leak would be out of the cylinder 2. power: valves closed, piston driven down by ignition of mixture. again, any leakage would be out 3. exhaust: intake closed, exhaust open, piston coming up driving gasses out. 4. intake: intake open, exhaust closed, piston moving down SUCKING in air and whatever else from the intake valve The intake stroke is the only one where the cylinder is not pressurized. Step one... pull all plugs, look at them to determine which cylinder is having issues and do a compression test. Link to comment Share on other sites More sharing options...
k9sar Posted May 13, 2009 Share Posted May 13, 2009 Still looking at a partial top end rebuild, once you pull the heads you can find the leaks. If it is a bad ring, you will probably see some scoring in the cylinder wall. If it is a leaking valve seal, you should be able to see a build up on and around the valve. if it's the valve seals, you do not need to pull the heads, just the rocker assembly. It is MUCH easier than pulling the heads. Why tear into it more than you need to unless you are looking to do it yourself and are going to regrind the valves, etc while you are in there Link to comment Share on other sites More sharing options...
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