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So while working on repairing the spark plug threads, I noticed what appear to be cracks between the valve seats:


They don't seem to be just surface features, but they don't seem to be deep enough to go full through to the intake/exhaust ports either. At least at the surface, they are clearly not fresh, but that could just mean they've been progressing a long time. The heads have something like 130h on them and the valves have been redone at least once in that time.

Has anyone noticed anything similar? I don't know whether it would be acceptable do operate the engine in this condition. My gut feeling is that as long as the cracks don't propagate all the way through, it would be OK, but it also seems that once fatigue cracks like these get going, they can progress to a complete crack through in very short time so might not be noticed between inspections? On the other hand, it seems that the design of the AeroVee head, with the studs going through the entire head, would prevent complete head separations like you see on Lycomings, so maybe the worst case of a crack would not be a complete cylinder shutdown?

Opinions appreciated.

/Patrik

Extremely common probblem with these VW engines, just search one of the VW car forums like thesamba.
Most say you can continue to drive a million miles with cracks between the valve seats,
However, we're not driving are we, I would ask Sonex for advise...

I would guess that 90% of all VWs have that crack....or at least that's what the local VW shop told me. I flew mine like that for hundreds of hours.

Thanks for the input guys. Kelly Fores at Sonex agrees with you all: extremely common and as long as the integrity of the valve seat isn't compromised, no problem to continue using.

Just keep an eye on the exhaust valve clearances. If it keeps getting tight and you have to back off the rocker arm adjustment screw at each 25 hour interval it is a sign that the valve seat has started to loosen up and you need to address the crack.

Keith
#554

I’ve just received my freshly rebuilt heads back after 110 h TT and they are identical to the photo. Replaced 4 exhaust valves and despite never exceeding 1250F EGT was told I’ve been running much too lean.

Egt value is not relevant, what chts where you running?

Bruce593SX wrote:Egt value is not relevant, what chts where you running?

320-380F in cruise at 3200 RPM on 100LL fuel. Nice grey exhausts.
400F occasionally on climb in summer.

Roger, your temps are certainly normal for an Aerovee. Why did they think you were too lean?

radfordc wrote:Roger, your temps are certainly normal for an Aerovee. Why did they think you were too lean?

Possibly because after 110 h I had burnt out 4 exhaust valves. The photo above is how they appeared before overhaul.

I have another theory and it relates to my Nikasil barrels that were “mushrooming” under the heads causing the valve clearances to disappear and creating their own brand of havoc. But that’s another topic.