Photos below are of the heads and piston tops/cyls of my VW 2180cc engine at approx 250 hours. I'm soliciting comments from those knowledgeable in such things.
Background:
During my annual condition inspection, a borescope inspection found a crack between the intake and exhaust valves of my right rear cylinder head. Also, the left rear cylinder had previously had poor compression (55/80, all other cylinders were in the low 70s), the leak was through the exhaust valve. I took the heads off today to learn more. I burn 100LL exclusively, normally I fly fairly rich (1150F - 1200 EGT) to keep CHTs below 350 deg F (175 deg C) in cruise. Previously, the plugs have looked good with no significant lead buildup. The engine has always run fine.
Right head below. Rear cylinder (with known exhaust valve leak) is on left
Right piston tops and cyls below (the left side looks the same)
Left Head below. Note hairline cracks between valves in both cylinders
Questions:
1) Comments on the degree and cause of the buildup in the head and piston crown? Is this normal? It's not what I expected to see. Suggestions for removing it?
2) Replace one or both heads? Cracks between the valve seats is apparently fairly common in these large-valve heads (there's just not much meat there), and I was surprised that many VW engines in airplanes are knowingly flown this way for hundreds of hours. The same is done in cars/Combis. Doesn't seem prudent to me, I'm worried the exhaust seat will become loose and things will go downhill fast. Anyway, it turns out that both of the heads on the left side have this crack. So, I'm planning to replace it. Now I'm trying to decide if I should replace the other side as well (the one with bad compression on the rear jug). I haven't determined the exact place where the leak on that exhaust valve is, and what can be done about it. Finding a place that knows Type 1 VWs well and can be trusted to do a good three-angle valve job isn't easy, and by time you've paid for their time it seems a better use of the $$ is to just spend $300 on a new head and have new valves, springs, seats, guides as well in the same price. I guess that's the beauty of these engines.
Comments and observations welcome.
Background:
During my annual condition inspection, a borescope inspection found a crack between the intake and exhaust valves of my right rear cylinder head. Also, the left rear cylinder had previously had poor compression (55/80, all other cylinders were in the low 70s), the leak was through the exhaust valve. I took the heads off today to learn more. I burn 100LL exclusively, normally I fly fairly rich (1150F - 1200 EGT) to keep CHTs below 350 deg F (175 deg C) in cruise. Previously, the plugs have looked good with no significant lead buildup. The engine has always run fine.
Right head below. Rear cylinder (with known exhaust valve leak) is on left
Right piston tops and cyls below (the left side looks the same)
Left Head below. Note hairline cracks between valves in both cylinders
Questions:
1) Comments on the degree and cause of the buildup in the head and piston crown? Is this normal? It's not what I expected to see. Suggestions for removing it?
2) Replace one or both heads? Cracks between the valve seats is apparently fairly common in these large-valve heads (there's just not much meat there), and I was surprised that many VW engines in airplanes are knowingly flown this way for hundreds of hours. The same is done in cars/Combis. Doesn't seem prudent to me, I'm worried the exhaust seat will become loose and things will go downhill fast. Anyway, it turns out that both of the heads on the left side have this crack. So, I'm planning to replace it. Now I'm trying to decide if I should replace the other side as well (the one with bad compression on the rear jug). I haven't determined the exact place where the leak on that exhaust valve is, and what can be done about it. Finding a place that knows Type 1 VWs well and can be trusted to do a good three-angle valve job isn't easy, and by time you've paid for their time it seems a better use of the $$ is to just spend $300 on a new head and have new valves, springs, seats, guides as well in the same price. I guess that's the beauty of these engines.
Comments and observations welcome.