Plugs bent over and engine running rough and hot.

[xymox]

So junk the head now or what?

A new head from Sonex is about $300, and a valve job and new valves will be less than half that cost. Might be worth a try to recondition the head and see how that holds up before deciding to replace it.

Jeff

Having followed your struggles and builds for quite some time perhaps unbeknownst to you I really do respect your opinion. Would you have the head reconditioned AKA TIG welded along the crack and a valve job done or just order a new assembly?

[sonex1374]

I wouldn't tig weld the crack, but I would do the valve job. If things got worse again, at that point I'd replace the head. The tig welding likely won't really last that long anyway before cracking again, and the presence of the crack isn't as dangerous as it would seem on first look.

I've suspected for some time that the exhaust valves start to burn long before noticing any loss of compression, and that if caught early enough (say with a borescope inspection or just periodically pulling the heads for a visual inspection) that the valve could be re-lapped to the seat to restore sealing and heat transfer. If I'm right, this could save the valve and seat and lengthen the time in service before needing any work.

Jeff

[lutorm]

Yeah, I was told when I asked about the crack between the valve seats in our heads is that it's really common and not a cause for concern unless it's actually compromising the seat. That valve and seat looks pretty bad though.

Did you notice the valve clearance needing a lot of adjustment?

[xymox]

Yeah, I was told when I asked about the crack between the valve seats in our heads is that it's really common and not a cause for concern unless it's actually compromising the seat. That valve and seat looks pretty bad though.

Did you notice the valve clearance needing a lot of adjustment?

yeah they were in need of some .006 pretty bad. I'd say some were about .06. that was causing it to run real bad.

[lutorm]

Yeah, I was told when I asked about the crack between the valve seats in our heads is that it's really common and not a cause for concern unless it's actually compromising the seat. That valve and seat looks pretty bad though.

Did you notice the valve clearance needing a lot of adjustment?

yeah they were in need of some .006 pretty bad. I'd say some were about .06. that was causing it to run real bad.

If the clearances tighten up, that's a sign the valve is dropping into the seat, or the stem is stretching. That's another flag that can be used, if you find yourself having to open up the clearance on a valve repeatedly, that's also sign it's time to pull the head and investigate. If the clearance gets *larger*, I can only think of one think causing that and that would be deposits on the seat causing the valve to remain open, which is also bad.

[mike.smith]

If the clearance gets *larger*, I can only think of one think causing that and that would be deposits on the seat causing the valve to remain open, which is also bad.

I've used TCP fuel additive for lead scavenging for the 300 hour life of my engine. I've never had any issues with lead deposits. Carbon deposits have been controlled with proper fuel mixture, but of course that's a bit of a moving target in the AeroVee since the front and rear cylinders get demonstratively different fuel mixtures.

[xymox]

Yeah thinking fuel injection is the way to go based on the variables with carboration

[lutorm]

Carbon deposits have been controlled with proper fuel mixture, but of course that's a bit of a moving target in the AeroVee since the front and rear cylinders get demonstratively different fuel mixtures.

I've been collecting data on the individual runners and plenum I designed to even out the mixtures, but that was delayed a bit by the need to rebuild the engine. I don't have full data yet but indications are that the GAMI spread at full throttle is something like 15%, while at 2200RPM it seems to be about 7%. (I suspect the mixture distribution is better at partial throttle because the low manifold pressure helps vaporize the fuel, but it could also just be the fact that the fuel comes out at the orifice on the back of the intake so the flow isn't completely symmetric.) I think it's in a state where I would be comfortable taking it on a test flight, which should make it easier to get the data than in ground runs.

In any case it seems to substantially improve the mixture distribution over the stock intake.

[tom0nex74]

If no air escaped through either the exhaust or intake manifolds during your compression check, the crack between the seats has not propagated through. Are your other pistons striking the plugs? Do you have the same number and size of spacers on each cylinder? While you have the piston out, get a standard wrist pin from your local VW shop and check the con-rod bushing for play, there should be none............. The local VW motor heads here get a new head, recondition it and put in upgraded 40 int and 38.5 exh valves before putting in their engines. They run at higher RPM's than we do.
good luck 0nex 74............

[xymox]

just the bottom plugs, you can tell by where they milled the new plug holes in that they are not set into the combustion chamber as far as the primary (top) plug holes. I was using the autolite 4163 on the bottoms but switched over to a slightly shorter ngk. I can chalk that up to bad quality control on the part of mofoco as I would have chosen a slightly better spot more toward the center of the combustion chamber. all in all that was a secondary issue in my opinion. the real issue with the movement of the valve clearnaces across all 4 cyls which was making it run like poo.