How to check if rings are wore?

[Ken13559]

Without use of compression gauge, how can I tell if my pistion rings are wore? I do see some/little, but not much, white smoke from exhaust but not bluish. Engine don't seem to be consumming luboil or burns very little.
My initial thought that I might have wore out the rings after a 700 miles motoring trip because I found less than 1/2 litre oil in engine when I changed oil and filter. Engine is 10 years old (1280 running hours) Yanmar 2GM20F.

 

[Mark Maulden]

In the ol gas days, you can take a compression test. Then squirt some oil down the hole and repeat compression test. If significantly higher, then rings are part of the equation. If not higher, and if usig oil, then most likely valves. Oh that's right. No comp gauge. Well you can start from a dead stop and adv the throttle to full position and what and how much smoke you get. That's an indication of ring issues.

 

[Johnb]

You do the same compression test as described above through the injector hole instead of the spark plug hole.

 

[Tim R.]

How did you lose so much oil? Or was it never filled after a drain?

 

[juslookin]

Not as bad as you think

If when you changed the oil, you sucked it out through the dipstick tube, you didn't get it all out, so there was probably more in there than that. If there was only a half liter in it, your warning buzzer probably doesn't work. How much you get out when you change oil, depends on angle of engine mounting, but you won't get it all. Maybe used some oil, but 700 miles is at least 100 hours, so a little oil usage would not be a major problem. Change the oil, and watch it closely. See how much you actually burn between changes.

 

[Jake N Eggs]

In general, blue smoke is oil and white smoke is fuel. If an injector is not spraying correctly the fuel will not completely burn thus the white smoke. Un-burned fuel can wash the cylinder wall causing increased oil consumption. On the GM engine you can activate the decompression leavers one at a time. If one injector is not misting correctly the engine could run better on one cylinder than the other. Only do this at idle and the engine will run bad with the decompression engaged.

Check your valve tappet clearance.

 

[kloudie1]

The engine only holds 2 liters, so an oil consumption of 1.5 liters in 175 hours (4 kts for 700 miles) does not sound like a lot of oil consumption. Probably would not make blue smoke at that rate, and is more likely due to worn valve seals as well as a little ring wear.. If the engine starts well from cold, it is probably fine.. but .. It is a good idea to check the oil once a day when motoring like that, and correct the level as necessary. If the engine is not banging a lot under load, the bearings are still OK.. If the buzzer comes on and the oil pressure light shines when you turn the key on, it is OK.. That buzzer is not supposed to operate until the pressure falls to 1.4-4.2 PSI.. and with a half liter or so of oil, the pressure probably didn't get that low.

 

[Bill Roosa]

You SHOULD NOT need to add oil between changes, just like an auto. I with justlookin, you have to have the tube positioned correctly at the bottom of the oil pan where the oil would pool and not at the forward end or have it go in and bend around and up so it is not actually sucking from the bottom.
Did the oil immediatly turn very black after the oil change? A sure sign that there was old oil in there.

 

[FastOlson]

Black Oil......

You SHOULD NOT need to add oil between changes, just like an auto. I with justlookin, you have to have the tube positioned correctly at the bottom of the oil pan where the oil would pool and not at the forward end or have it go in and bend around and up so it is not actually sucking from the bottom.
Did the oil immediatly turn very black after the oil change? A sure sign that there was old oil in there.

Hi Bill,
Not (!) provoking any argument, but our oil has always turned black again almost immediately after a change - oil and filter. Been doing this since we bought the boat in '94.

Our Universal has the oil-change hose to the banjo fitting on the bottom of the pan, and we seem to get all the oil out with the vacuum changer (one gallon even).

I really wish it would stay "clear" after a change.
Engine runs fine and burns too little oil between changes, once a year, to ever need to add any.

About 2000 hours on it.

It would be nice to have clean oil again, but it just doesn't seem to work that way.

Best,
LB

 

[kloudie1]

Bill, I agree that ya shouldn't have to add oil between changes, but as an engine ages it will get to the point that it does need a little between changes. Depending on use and care, engines will age at different rates. A quart of oil every 75 hours or so costs a lot less than a ring and head job, so as long as the engine starts well and makes enough power, it is OK to run it that way until either ya can't stand the smoke or it gets too hard to start..ya just have to check the oil level frequently and replenish as necessary....like many of the cars I've had in my life.

 

[Bill Roosa]

I agree kloudie1
My point was that it is more likely that he did not get all the old oil out. I was not trying to suggest he had a ring problem.
The first time I change a "marine" engine's oil through the dipstick I had this problem. I have sense developed a "mechanics sense" and can "feel" the end of the tube hit the bottom port corner (my case, yours will be different no doubt) of the oil pan. I have sense had nice clean oil for around 50 hours after an oil change. FWIW, technique is EVERYTHING.

 

[kloudie1]

Ahhh Haaa I see that interpretation.. I thought he meant that he pulled all the old oil out and only found that much.. He could indeed have not gotten to all the old oil.. Bill, I know exactly what you are talking about.. my 3 GMF oil dipstick points right at the oil pick-up screen .. on the 2 gmf the pick-up screen housing is even bigger and flat on top .. easy to stop the suction pump tube there..

 

[Ralph Johnstone]

Lazy Man's Compression Test .......................

My 2GM always has always had a touch of reluctance to start when it's not been used for a couple of weeks. This is due to a lack of oil on the rings. The oil seals the rings and promotes high and hot compression on the first revolution. I find I need about half a dozen revolutions on start-up if the engine has lain unused for a several weeks.

However, the following day with the engine stone cold, it starts within half a revolution. This is due to the oil which is still stuck in the rings. With worn rings, you'll always have a tough time starting.

An easy test and may give you a better idea of what's going on in there.

My personal opinion is that the 2GM is the toughest, meanest, little chunk of cast iron going and I wouldn't give the rings a second thought until you see one of them spat out and lying on the cabin sole. These engines seem to last forever if cared for (clean air, oil, and fuel) and yet I've read a few reports where they've been brutalized and still seem to go on forever.

Enjoy and go sailing.

 

[robertsapp]

OK, check my math here and see if this makes sense. The OP wanted to know if there was a quick way to check his rings. If the rings are worn or not seating well (not necessarily the same thing, as carbon buildup can cause the latter) then you'll be getting some blowby into the crankcase, which will pressurize it a little or a lot depending on the degree of blowby. With the engine running, carefully pull out your dipstick. If an oil geyser erupts, you have a big problem. If not, put your finger over the dipstick hole. Does it get sprayed with a bit of oil? You have some wear, but not dramatic. No oil spray, but you can feel a little pressure? Probably nothing to worry about.

Now do the same thing with the oil filler cap on the valve cover. This should give you a rough idea of whether your valves and valve seals are basically OK or crap.

Does this make sense to you diesel gurus out there? Tell me if I'm full of it.

And remember, white smoke that dissapates quickly can also be a cooling problem and not necessarily fuel related. Poor cooling can cause steam in your exhaust. It never hurts to check your exhaust elbow and make sure your heat exchanger is clear.

 

[Charles Erwin]

If the rings are quite worn, the bores polished or glazed (these are not the same thing) the crankcase will become pressurized - overly so - by combustion pressures going past the rings and into the crankcase, called "blowby". Oil may be pushed out the dipstick and this overpressure may be evident when removing the oil fill cap, but these symptoms will be relatively minor at idle RPM. In any case, the same symptoms can also be present if the crankcase ventilation system is blocked. So first make sure crankcase ventilation is operative. If the vent system is blocked by debris you will notice elevated oil consumption. The ventilation system iinvolves a tube - usually between the valve cover and the cumbustions air intake called the "intake manifold." The idea is that intake vacuum draws crankcase vapors (there is always some "blowby") from the crankcase via the tube to the intake mixes these vapors with air drawn from the atmophere and re-burns the vapors during cumbustion. The vent system may also have an oil separator, metering block or valve, any of which might be fouled to the point of blocking this ventilation system. Anyway - check the crankcase ventilation system to be sure it is clean and get back to us with results. Then we can talk about valve stem seals and other oil consuming possibilities which - also - have nothing to do with piston ring condition.

Charles

 

[Bill Roosa]

You guys don't do much diagnosis with customers do you?
As someone who did this with autos for a bunch of years you have to understand that the customer is usually wrong. He does this amazing thing like change his oil and only gets 1.5 qt of oil out.... well clearly his rings are shot. Not the first thing I would think. I believe ( and have no end of examples to illustrate) it is MUCH more likely that he simply did not get all the oil out cause that is pretty difficult without some practice or knowledge of the internal layout of the oil pan. AND the engine is apparently running fine. Now if it ran like crap, smoked like yours truly AND had only 1.5 qt of oil in it he might have a leg to stand on blaming the rings.
I believe this is Occums razor stuff. the simplest solution is usually the correct one

 

[Charles Erwin]

Bill
One must be extraordinarily gifted in order to be able to conclude an owner is never reliable - but many of us are not so gifted. This is not a case of relaible. It is more a case where too many things are missing. All we know is he "got 1/2 out." We do not know oil consumption (dipstick level) at any time from last oil change to - maybe - 100 or more hours. We do not know whether 700 nm was 100 hours or 200 hours. We do not know whether there is evidence of oil leaks - you know 1 drop/20 feet is 1 quart /100mi.
It is possible that you are right of course -- but it seems to me that if he did not get "it all out" then when he refilled with 2 qts he would have been way over dipstick full. Lilkely he would have recongnized he didn't "get it all out" and -- so --- he would never have asked the question in the first place.
In answering questions - perhaps we should ask questions to rule out whether the owner is right. As it is - excepting certain obvious maintanence tasks which should be done anyway -- there is not enough fact here to support any definite diagnosis.

Charles

 

[robertsapp]

Nope. Nuclear reactors and computers are my thing, diesel engines are just a hobby. I was just trying to give the OP some kind of answer to his original question, which was "how can I tell if my piston rings are worn." Regardless of how much oil was or wasn't there or he may or may not have removed/added, were my helpfully offered suggestions out to lunch or not? Cause I'm trying to confirm my own possibly imperfect understanding of what's going on inside the beast.

 

[Bill Roosa]

Which is exactly my point guys. If you listen to the customer you are doomed to be mislead. My rationally being if he knew the answer, or how to get the answer, he would not even be asking the question.
SOoooooo
When someone comes to me with a problem my first assumption (and it is just that an assumption) is the they don't know beans about the particular problem they are having.

He a nice little old lady who recently lost her husband show up at the station one afternoon complaining about her heater not working. The engine was not that hot (and it was cold out) so I cracked the radiator cap, released the pressure and checked the water level. the most common reason the heat does not work. The level was OK, so I put the cap back on and told her that I'd have to check under the dash to make sure that none of the vacuum control lines had come loose (the second most common reason). Well while I'm under there I notice that the (GM car) mode control was on OFF. So I put it over to HEAT and guess what the heater vent starts blowing out hot air. I gave her a quick course in how the three controls (mode, temp, fan speed) work and that was too much so I set it on HEAT and middle fan speed and explained that when you want it to be warmer push the temp slider to warmer and ....... You get the idea.
Well about 4 months later she pulls in the first warm day and guess what she complained about. Yep! the car was too hot. We both had more time then so I gave her a crash course in "dash controls"
It leaves one to wonder how she handled rain.
She was a very nice lady and we got a lot of word of mouth business out of her.
So when Ken says "it does not appear to be using lub oil" and "I only got a quart out of her" and begins the conversation with "how do I check if my rings are good or not" I make the following assessment:
Oil consumption is OK
Engine runs OK or he would have mentioned it
Only got a 1/2 qt of oil out during oil change and does not know how to check for piston ring problems so he may not know how to correctly change the oil. there is that much in the oil filter which he says he changed.
Ran the motor for 700 miles and it only had a 1/2 qt of oil so if it runs at all beyond idle, he clearly didn't run it out of oil. also does not mention a low oil pressure alarm going off.
Highly suspect the oil rings are ok
probably did not understand the complexity, heck I didn't the first time I did it, of changing the oil through the dipstick, talked to a friend who gave him the oil ring idea........came to the BB for advice.

 

[Bill Roosa]

Oh yea, I almost forgot, diesels absolutely do not run well with bad compression. If the rings are going you will know, smoke, smell, bad performance, probably knocking noises cause rings don't "just let go" with out loss of oil which would show up first in the crank journals and probably stop the engine.........
Ken I know you are get WAY more than you asked for. Please do not thing I think little of you or that your are dump. Ask me about setting clock on the VCR and I'll still give you the RCA dog look.