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Bravo Exhaust Valve Failure - Root Cause


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IIRC, Savvy supposedly scans for a saw tooth pattern in the EGTs which is the telltale sign of pending valve failure. I would send a note to Mike Busch, they might be interested in looking at your data, personally I don’t see anything wrong till you pull the power back before EGT goes wild.

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On 3/30/2020 at 4:11 AM, Phil EF said:

Valves don’t know whose name is on the data plate. 

Indeed, but all valves are not the same.  IIRC Lycoming exhaust valves use the sodium pellet to get more heat away from the head, whereas Conti use a straight solid (friction welded?) assembly

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On 4/17/2020 at 10:17 AM, ArtVandelay said:

IIRC, Savvy supposedly scans for a saw tooth pattern in the EGTs which is the telltale sign of pending valve failure. I would send a note to Mike Busch, they might be interested in looking at your data, personally I don’t see anything wrong till you pull the power back before EGT goes wild.

They could not find any signs of failure in my data...

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The failure is always the same. yours is classic. A hot spot because ...................

On one hand, it is incredible that the internal combustion engine even works

On the other hand, why just the #5 cylinder and not any others? They all were exposed to the same operating conditions. Let's rule out operator error.

The most likely reason is the slow wear of the valve guide combined with poor manufacturing. The valve must fit in the guide and the angled surface must seat evenly all the way around. 

When the valve guide begins to wear (why?) it allows side loading on the valve stem from the rocker arm to push the valve a little to the side as it is opening. This side load put more pressure at a point somewhere on the seat and less pressure elsewhere. At some point the valve stops rotating. The lack of contact in the seat because of this mismatch reduces the transfer of heat from the valve face to the seat at that point. At 2500 RPM this is happening a whole bunch of times (you can do the math)

Repeated cycles of less and less heat transfer from the valve face to the valve seat results in the what happened to #5 in the picture above. 

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Just now, Cruiser said:

On the other hand, why just the #5 cylinder and not any others? They all were exposed to the same operating conditions. Let's rule out operator error.

Since purchasing it he has replaced all of the other cylinders except #5. Since he's also had to do a lot of exhaust work, and I think a turbo, let's rule back in previous operator running it way too hot.

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