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4G63 Valve Breakage??????


20G TSi

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A friend of mine with a 1G TSi just called with a puzzleing question. "What would make a valve break?"

 

I've heard of people burning valves, but he says this one looks like a chipmunk bit part of it off. He's bringing it to me so I can see.

 

So, what would cause ONE valve to break? He says everything else is fine, the roller was still on the tappet and the cam.

 

Any comments would be appreciated.

 

Jason

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Your friend is almost guaranteed to have other porblems with his engine. You can check the turbo by pulling the intak pipe off, and wiggling the compressor shaft. If it moves any more than a millimeter or two, it may need a rebuild. I doubt the turbo will be damaged, so if it doesn't wobble a lot when you move it don't worry about that just yet. He could have cylinder wall scarring, a marred piston, broken ring lans etc.etc. The important thing is to figure out why the valve broke, if it was from extreme changes in temperature (detonation as previously stated) then he need to find out why. Usually valves break at one of two places, right where the stem meets the head or where the keeper grooves are machined in the end of the valve. Let us know what you find out. Later.
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Whats odd is that its broke off 1/3 of the valve head, not the stem. His chipmunk description was right on.

 

weird....

 

This is a head from a junkyard, unk. miles. The old head was a TB victom.

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Oh, to add, its been running great with this head for about 4 months.....

 

His only mods are the aircan cut/maf silencer removal. He doesnt even have a manual boost controller, so he's running stock boost.

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Originally posted by The TSi U Fear:

Though to have just one make contact is nearly impossible..or highly unlikely rather.

How is his timing belt/tensioner assembly?

Its a possibility that there was a damaged valve guide and it cause the valve to hang enough to hit the piston. how was everything else on the head? was the valvetrain ok? how about the shortblock? (besides obvious damage)
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I agree with the possibility of a bad valve guide.However I don't think the valve was hitting the piston (that would be more likely to bend a valve). Check the spark plugs for signs of detonation to hopefully eliminate that as a cause. Check the valve seat and surrounding area for damage(if the one edge of the valve seat looks signficantly more worn than other sides) from a misaligned guide. What happens is when the valve seating is off square, the valve flexes everytime it seats,causing it to eventually break. This is more than likely what happened, but without pictures it is hard to say.
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Originally posted by slow4now:

I agree with the possibility of a bad valve guide.However I don't think the valve was hitting the piston (that would be more likely to bend a valve). Check the spark plugs for signs of detonation to hopefully eliminate that as a cause. Check the valve seat and surrounding area for damage(if the one edge of the valve seat looks signficantly more worn than other sides) from a misaligned guide. What happens is when the valve seating is off square, the valve flexes everytime it seats,causing it to eventually break. This is more than likely what happened, but without pictures it is hard to say.

That sounds like it is probably the case. I'll have to have a look at the head.

 

Thanks all who replied! We just want to be sure of the cause before we go and put the head back on and have a repeat occurance.

 

Thanks again,

 

Jason

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Originally posted by slow4now:

I agree with the possibility of a bad valve guide.However I don't think the valve was hitting the piston (that would be more likely to bend a valve). Check the spark plugs for signs of detonation to hopefully eliminate that as a cause. Check the valve seat and surrounding area for damage(if the one edge of the valve seat looks signficantly more worn than other sides) from a misaligned guide. What happens is when the valve seating is off square, the valve flexes everytime it seats,causing it to eventually break. This is more than likely what happened, but without pictures it is hard to say.

I have seen P/V contact snap valves like twigs on more than one occasion. they bend the first hit, and break on the second.

 

wait a minute..the shortblock was fine? it didnt hurt the pistons at all? if thats the case it wasnt PV contact...where there any peices of the valve in the cylinder/ if not I would bet it was detonation 'eating' away at the valve

 

[ 15 May 2002, 12:58 AM: Message edited by: rl ]

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