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Intake Valve Boroscope IO-390

LR60

Active Member
Ok all you gear heads, What is causing the "burnt edge' appearance on these Intake Valves. All four cylinders have the same unique appearance. I can only speculate that oil is running down the valve stem while sitting and then burns off?

130 hours TSN
Compression all above 76 and exhaust valves look great.

Thanks
 

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Intake valve is not rotating. Need to drop the valve, clean the guide, clean the stem, and lap the valve. Springs and keepers likely have excessive deposits on them. Some exhaust flows thru the intake due to valve overlap. This is by design.
 
Intake valve is not rotating. Need to drop the valve, clean the guide, clean the stem, and lap the valve. Springs and keepers likely have excessive deposits on them. ...

Seems surprising this would happen on such a low time engine.
 
All four are not rotating ?

Bob, Oh man not what I wanted to hear.

Valves not rotating was my first assumption when I looked in the first cylinder. but it’s happening to all four valves and it’s “burn pattern” is in the same clock location on all four valves. That lead me to believe it could be something more benign such as the oil leak.

VA-980. It’s ok, better than the VA-400 pic quality wise but No focus or way to adjust the light. Flex cable makes it little more difficult to position in the cylinder vs the solid shaft.

Thanks
 
Bob, Oh man not what I wanted to hear.

Valves not rotating was my first assumption when I looked in the first cylinder. but it’s happening to all four valves and it’s “burn pattern” is in the same clock location on all four valves. That lead me to believe it could be something more benign such as the oil leak.

VA-980. It’s ok, better than the VA-400 pic quality wise but No focus or way to adjust the light. Flex cable makes it little more difficult to position in the cylinder vs the solid shaft.

Thanks

While it is a heat signature, it is not necessarily burning, as when this pattern is seen on the exh valve. Intake valves tend to get different deposits that can only form on that valve because it is cooled so well by the relatively cold intake air passing by it. The areas where it is not forming is too hot to create those build ups, but not necessarily too hot to create damage or "burning." Notice how that area looks just like the exh valve. Definitely not from oil. Something is not right and I would follow Bob's advice on remediation, but I wouldn't worry yet about damage. A leak down will tell you if the seating area is compromised and I doubt it is. Heat damaged intake valves are pretty rare.

Larry
 
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Intake valve is not rotating. Need to drop the valve, clean the guide, clean the stem, and lap the valve. Springs and keepers likely have excessive deposits on them. Some exhaust flows thru the intake due to valve overlap. This is by design.

Very good advice, but I would argue that the overlap promotes flow from intake to exhaust during the overlap period. The Exh tends to have a lower pressure due to the velocity than the intake and the overlap is designed in to create a positive flow from In to Ex in order to expel more exhaust before the downstroke to avoid exhaust dilution of the intake charge. This is why lumpy cams with excessive overlap produce an exhaust where you can smell the raw gas. They go to the extreme to get every bit of exhaust out and accept losing raw gas out the exh pipe in the process.

There is a very slight period where gas can flow into the intake at initial opening, but it reverses so quickly due to the pressure differential that it is considered inconsequential.

Larry
 
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Injectors?

What’s the possibility that this is from the injectors spraying and causing one side of the valves to have a cooler side, which in turn dictates how deposits build up on the valve face.

BWDIK

Thanks.
 
Ok all you gear heads, What is causing the "burnt edge' appearance on these Intake Valves. All four cylinders have the same unique appearance. I can only speculate that oil is running down the valve stem while sitting and then burns off?

130 hours TSN
Compression all above 76 and exhaust valves look great.

Thanks

Any follow up information on this issue?
What did you do?
Did you get any additional information on the burnt edge appearance?
 
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