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Discussion Starter #1
Hi all,

During a recent borescope of my engine, I came across this rather alarming view... on number 3 cylinder, the intake valves are totally different colours.

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The left valve looks normal with a typical amount of carbon buildup, while the right looks... hot?

As a comparison, the picture below shows the exhaust valves in the same cylinder, which look normal to me, and the next two pictures show the intake valves from two other cylinders.

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I’m wondering if the off-colour intake valve isn’t opening at all...? This would leave it closed the whole time and the hot gasses from combustion would burn off all the carbon. Maybe a blocked oil passage in the multiair unit?

Anyone have any ideas?

Ben
 

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Hi Ben,

I don't think there is anything to worry about here. If in doubt, take a compression check. If one valve isn't opening, which I think is highly unlikely, compression will be low on that cylinder. Intake valves often vary in how they are gunked up.

Greg
 

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Discussion Starter #3
Hi Greg!

Thanks for the response. I’m wondering though... if the valve wasn’t opening, would that have any effect on the compression? My thinking is that a non-functional valve would fail closed and seal just as well against its seat, and you would see a normal compression value for the cylinder.

In a perfect world, I would find a Fiat engineer to talk to and see if there are any known failures of intake valve actuation. But that might be wishful thinking.

Ben
 

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Can you crank the engine with all spark plugs removed and observe valve action with boroscope? Theoretically, if one valve is not opening then the cylinder would ingest less air, thereby lowering compression.
 

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Discussion Starter #5
Ah... I see now how that would lower compression. I can try doing a compression check... but I doubt there’s room in the cylinder at top-dead-center for my borescope to be there during cranking.
 

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It's a bit hard to compare the pics, I thought the off-colour valve might just be because the borescope light is shining more directly on it? That cylinder seems to have more carbon build up than the other two, especially the last one where the head looks almost carbon-free, yet the valves look to have more carbon than the others? Have you tried any "cylinder/valve cleaning" stuff (RedEx? etc.)?

But my favourite observation is that you have spelt "colour" correctly! ;) :p
 

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If airflow is reduced somehow (on this car that's typically from multiair not opening the intake valves enough) then compression when cranking will read low. If everything is OK, on a warm engine at normal cranking speed you should see about 170psi on each cylinder plus or minus about 10psi.

Greg
 

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I would think the difference in compression reading would be negligible and not noticeable. If both intake valves failed to open you would have a better chance.
 

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I would think the difference in compression reading would be negligible and not noticeable. If both intake valves failed to open you would have a better chance.
If both intake valves fail to open, the compression reading will be essentially zero. If the valves do not open fully, the reading will be lower.

Regarding the comments about putting a borescope in there while cranking, please don't try and do that. The violence going on in there during cranking will make it impossible to see anything, and risk of damage to the borescope or worse, the engine, is very high.

Greg
 
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