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G10 Valve burning/failure progression; Are there various failure mechanisms for valves in these engines?
Topic Started: Nov 6 2012, 12:31 AM (655 Views)
cwatkin


I have a question about how the valves typically fail in these engines and if how they fail tells something about why they fail.

I am on my third used engine in my car. The first one had a burned valve from the previous owner never changing the oils and the second one had a blowby issue with the rings. This third engine seems to run very nicely and I am not seeing any appreciable blowby. The oil is staying very clean and I am not seeing any consumption. My only complaint is that the compression is uniformly low on this engine across all three cylinders. I am getting 125-130 psi. I did a wet test and the numbers were no different than the dry test so this tells me the weak link is the valves but is it normal for all to be uniformly weak?

I was wondering if the previous owner might have used too thick oil in this engine or might have had the timing too retarded. I am not sure about the oil viscosity as I changed it but the insides of the engine were clean, the PCV system wasn't nasty, etc. so I think this engine had decent care. Again, I am not seeing blowby and the oil is staying very clean so I think the rings are good.

My questions are.
1. Is it normal for valves to uniformly loose effectiveness in these engines?
2. Does this indicate the cause of failure? Retarded timing? Too thick oil?
3. If valves are not sealing well, does this indicate they will fail soon and this engine shouldn't be trusted on long trips, even if I run the correct oil and timing? I figure leaking valves mean hot gasses will continue to erode them.
4. If you had two extra spare engines sitting around needing a rebuild, would you pull a head and rebuild it, then swap it onto my current engine?
5. If I redo the head and new valves are lapped in, do you feel that I will then stress my rings with this increased compression?

All in all, the engine seems like it wasn't neglected like my others. I think they either had the timing wrong or used oil that was too thick. Do my symptoms sound diagnostic of anything?

Conor
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JellyBeanDriver


Mileage? All engines wear out eventually. I do believe regular oil changes goes a long ways to keep our engines running. I've been using 10W30 since I bought mine used with 108K on the odometer, but I live in So. Calif so this weight may not be appropriate for your area.

Everything I've read here, if you do the valves, do the rings too as you'll just wish you did if you don't.

BTW, my engine is probably an anomaly. Maybe nearly all freeway mileage has a lot to do with longevity too.
Edited by JellyBeanDriver, Nov 6 2012, 01:00 AM.
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idmetro
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cwatkin
Nov 6 2012, 12:31 AM
I have a question about how the valves typically fail in these engines and if how they fail tells something about why they fail.

I am on my third used engine in my car. The first one had a burned valve from the previous owner never changing the oils and the second one had a blowby issue with the rings. This third engine seems to run very nicely and I am not seeing any appreciable blowby. The oil is staying very clean and I am not seeing any consumption. My only complaint is that the compression is uniformly low on this engine across all three cylinders. I am getting 125-130 psi. I did a wet test and the numbers were no different than the dry test so this tells me the weak link is the valves but is it normal for all to be uniformly weak?

I was wondering if the previous owner might have used too thick oil in this engine or might have had the timing too retarded. I am not sure about the oil viscosity as I changed it but the insides of the engine were clean, the PCV system wasn't nasty, etc. so I think this engine had decent care. Again, I am not seeing blowby and the oil is staying very clean so I think the rings are good.

My questions are.
1. Is it normal for valves to uniformly loose effectiveness in these engines?
2. Does this indicate the cause of failure? Retarded timing? Too thick oil?
3. If valves are not sealing well, does this indicate they will fail soon and this engine shouldn't be trusted on long trips, even if I run the correct oil and timing? I figure leaking valves mean hot gasses will continue to erode them.
4. If you had two extra spare engines sitting around needing a rebuild, would you pull a head and rebuild it, then swap it onto my current engine?
5. If I redo the head and new valves are lapped in, do you feel that I will then stress my rings with this increased compression?

All in all, the engine seems like it wasn't neglected like my others. I think they either had the timing wrong or used oil that was too thick. Do my symptoms sound diagnostic of anything?

Conor
Did you do your compression test on a warm engine with the throttle wide open? http://geometroforum.com/topic/2574993/1/ It is not common for the valves to all fade away at once, I suspect you may have other issues contributing to your low compression numbers.

Maintenance (or lack of) plays a HUGE role in the longevity of these engines. With a used engine which appears to be in good shape I have had good success with pulling the plugs and putting 3-6ozs of Seafoam in each cylinder and letting it soak overnight, then spinning the engine to remove as much liquid as you can (remember to put some rags or paper towels over the top of the open spark plug holes to soak up the liquid), re-install the plugs and go.

Run a good quality oil and change it regularly, I've been quite happy with Mobil 1 5-30W lot of oil discussion here: http://geometroforum.com/topic/4141719/1/

As for long trips - if the car is running well then I say go for it! I would not expect any issues.

Redoing just the head seems to have very mixed results on any G10 engine with more than 100K on it. As for me I would hone the cylinders and put in new rings as well. I have no desire to wind up fogging for mosquitos...
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cwatkin


Ok, here is my plan. I am going to take a head from another engine (have two here) and rebuild it. I will use the one with a completely dead/burned valve since other smoker I had was running decently when pulled. This will allow me to keep driving the car.

When the head it off, I will give the cylinders a look and measure them. If there is any doubt, I will re-hone and re-ring at the very minimum. If boring is needed, I will look into rebuilding one of my other engines and keep driving this one. I will likely use one of the cheap $10 head gaskets everyone hates if I put the existing head right back on this engine to keep driving it for the short while while I get another engine together. I would use one of the suggested Mark's gaskets for a permanent repair.

As for my compression tests, they were conducted according to the instructions here. Another thing is that I have my timing almost ALL THE WAY advanced and have no pinging! The engine runs better, smoother, has more power, etc. with the timing set this way. The slot to rotate the distributor is not showing at all and there is only a small bit more room to play with. I ran it this way for a bit and started hearing slight pinging so I backed it off a little and that is where it is staying for now. Several people told me that engines with compression issues often run best near full advance so I thought that was diagnostic of my situation. Anything non-engine related that might be causing this such as a vacuum leak? I would see that as causing more issues with pinging due to lean burning.

A wet test made no difference in my compression numbers. I also do not seem to be seeing any evidence of excessive blowby in the oil and there is no oil consumption from this engine.

I am running a Dexos1 approved synthetic 5w30 in my engine right now and plan to switch to European formula as soon as I get all engine issues ironed out. I am not sure what they were running before but the inside of this engine was very clean. I did a 30 mile flush with some cheap oil and MMO just in case and it came out really clean. I have put 500 or more miles on this oil and it looks as clean as the day I changed it so I don't feel the rings are too bad on this one.

The timing on this engine was extremely retarded when I got it. Could this have uniformly slightly weakened/burned the exhaust valves on this engine?

Conor

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wizard 03


"slaps head" The reason for your low preassure sound more like a timeing issue, not a bad valve problem. If the timeing is way too far advanced, or retarded, the cylinders won't fill up compleatly. Instead it will push back out, or not fill the combustion chamber compleatly. In this case, its probably pushing back out.
As for valves burning out, It usually happens to one cylinder at a time, not all at once.

However, the rings could still be shot, dunno till you reset the timeing.
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