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What causes burnt valve/valve seats and high combustion chamber temperature.


Minaj

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 Minaj said:
How lean are we talking ? if it was running lean are we also going to be looking at piston to bore contact ?

Depends on the running conditions.

And if you're running E85, then petrol AFRs go out the window.

Piston to bore contact would be an issue if the piston was getting really hot, yes.

Really, really hot.

And ran tight tolerances.

And was tuned by someone who was a bit of a potato, tbh.

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Isn't just odd if the valves fail before a piston ? Being Alloy if running lean it would have melted the piston or picked up on the side of the bore, which in my scenario I haven't. Don't think Glen Suckling is a potato tuner..

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Were the valves just terrible?

It depends on a bunch of factors... cams would play into it a little bit as well as the valves are only really cooling when they're seated, more duration on the cam = less cooling.

So what's the question.... do you have burnt valves WITH scored bore or just burnt valves?

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 boon said:
Were the valves just terrible?

It depends on a bunch of factors... cams would play into it a little bit as well as the valves are only really cooling when they're seated, more duration on the cam = less cooling.

So what's the question.... do you have burnt valves WITH scored bore or just burnt valves?

Yup valves were cheap ones from STA. Burnt valves and seats, and bores are perfect and pistons.

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The piston and cylinder will be cooler due to the E85. EGT though, dunno if that will be vastly cooler. I expect its high EGT rather than cylinder temp that will burn seats as theyre obviously protected during the actual power stroke... Just thinking out loud here

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 Ninja8) said:
Cheap valves...thats a good place to start

Mind you i hope the replaced valves in my heads werent "cheap"

Yeah that's the place where I would start too, but the person who overlooked the motor keeps on telling me high combustion chamber temps which resulted in burnt valves and seats. I find it so hard to believe to start off with, E85 is a much cooler fuel. Arghhh this whole situation is frustrating.

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What do the plugs look like? They will tell you straight away if it's lean or not.

And of course the engine builder is going to say that, he's probably up for $15k+ liability if it was his fault that it failed.

So where are you going with this? It sounds like what you need is an independent engineering report from someone that will determine the likeliest cause of failure.

If the whole thing is angling towards a civil action (court) then remember that it only has to be "on the balance of probabilities" so if the crap valves were probably the cause of failure then you're set.

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 boon said:
What do the plugs look like? They will tell you straight away if it's lean or not.

And of course the engine builder is going to say that, he's probably up for $15k+ liability if it was his fault that it failed.

So where are you going with this? It sounds like what you need is an independent engineering report from someone that will determine the likeliest cause of failure.

If the whole thing is angling towards a civil action (court) then remember that it only has to be "on the balance of probabilities" so if the crap valves were probably the cause of failure then you're set.

Spark Plugs were fine, no signs of running lean.

Yes, couldn't agree with you more on that one.

I've got a few done, I don't want to disclose everything online for other reasons.

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How many valves? One or all of them?

If a valve isnt seated properly it can burn. Basically happens when the valve sees a flame front which it doesn't normally do without combustion occurring around the valve - antilag, launch control, leaking etc

E85 makes for a cooler charge temp but combustion temp can be just as hot.

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I have also forgot to mention, some of the pistons also has showed signs of some of the valves kissing the piston. Engine builder reason was it was due to valves getting to hot which deformed. I was told there was 4mm clearance piston to valve clearance at TDC.

Could it be the case where the cheap valves have stretched ???

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 Optical said:
How many valves? One or all of them?

If a valve isnt seated properly it can burn. Basically happens when the valve sees a flame front which it doesn't normally do without combustion occurring around the valve - antilag, launch control, leaking etc

E85 makes for a cooler charge temp but combustion temp can be just as hot.

1 exhaust valve on each cylinder, except for cylinder 1

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No way could the valves stretch 4mm. Valve clearances are at 0.2mm intake and 0.25mm exhaust, so if the valves stretched 4mm you would loose all compression and the engine wouldn't run at all. With the exhaust valves at closed position, the valve would be 3.75mm open and the intake valves open 3.8mm.

At top dead centre there might be 4mm clearance piston to valve. But with high duration cams the valve needs to be almost completely closed well before TDC. I think the exhaust cams have been dialled in poorly, piston to valve clearance measured incorrectly or a mix of both.

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 Rosssub said:
No way could the valves stretch 4mm. Valve clearances are at 0.2mm intake and 0.25mm exhaust, so if the valves stretched 4mm you would loose all compression and the engine wouldn't run at all. With the exhaust valves at closed position, the valve would be 3.75mm open and the intake valves open 3.8mm.

At top dead centre there might be 4mm clearance piston to valve. But with high duration cams the valve needs to be almost completely closed well before TDC. I think the exhaust cams have been dialled in poorly, piston to valve clearance measured incorrectly or a mix of both.

I also looked at the exhaust cam gears on both side, one of them was dialed in at another degree and same with the other, they were not dialed in the same. Would this be an issue also ?

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You can't tell if the cam centerlines are dialed in by looking at what the adjustment on the cam pulley's is set to. Half the need for adjustable pulleys on Subaru's is due to any machining of the block or heads changes the distance between the two heads and therefore changes the cam timing because the cambelt is a fixed length. So the timing can only be checked by physically checking the timing, not by looking at what the marks on the pulleys are set to.

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Yeah they'll be close but it depends if he's got adjustable gears or now looking at it again, is he just saying that the marks on the pulleys don't line up perfectly (cause they never do).

Could have jumped a tooth at some point?

P.s. The cams rotate once per two crank revolutions so it's over 720°. So 3.75° per tooth.​

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Another possibility is the valve clearance has been set too tight, when full hot its just slightly holding the valve open, will burn them all day long. Had heavy springs been used? In some cases the high seat pressure can stretch the stem, leading to reduced seat pressure and burn valves.

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