SonexBuilders.net

After having a stuck exhaust valve on one of my old style cylinder heads, I decided to go ahead and replace both cylinder heads with the new heads Sonex sells that are produced by Empi. While I was at it, I decided to replace the entire top end while I had it all apart. Because my Waiex was due for the condition inspection during all this, I needed to make sure everything passed the leak-down test to get signed off. After reassembling everything, I did the leak-down test, which failed on multiple cylinders on both sides of my Aerovee. I assumed I overlooked something or did something wrong while assembling it, so I re-did everything, and it failed again. I got some guidance from Sonex tech support, dismantled everything several more times, followed the manual to the letter, and triple checked everything (even measured things that the manual doesn't call for to ensure things are well within specs (everything within .004"), each time with failures on the leak-down test. One cylinder only holds 22 psi, while another holds 46 on the other side of the engine, one holds 76, and another holds 64. I narrowed it down to some badly leaking exhaust valves, and a single leaking intake valve, as well as something with one of the heads that isn't allowing the head gaskets to seal (I suspect the inside of the head isn't machined perfectly and not sealing properly against the cylinders/head gaskets). I've had multiple automotive sources, including one of the most reputable VW shops in Dayton that I regularly deal with, tell me that Empi heads are no longer ready to bolt on and use, despite coming fully assembled. After I sent video showing severely faulty valves (I'll try to post a link to the video here when I get a chance), Sonex also confirmed that sometimes, the heads may require valve work prior to use. This isn't noted anywhere in the most recent version of the Aerovee manual, but I believe it should be, as brand new and fully assembled parts may not be suitable for use on our aircraft.

Please don't get me wrong, I'm not posting this to blast Sonex, as I think the folks at Sonex are great, but I do think this issue needs to be addressed as this is something that was apparently a known problem, but not disclosed. I highly recommend that if any of you have purchased Empi cylinder heads and you haven't installed them yet, you may want to at least lap the valves or have them checked to ensure they're good for use in your aircraft, and to save you the frustration I've gone through (not to mention $200 worth of head gaskets). I'll be pulling mine for the 5th time and sending them to the VW shop I deal with here to have them go through the heads thoroughly to make them usable and let me know if there is anything the heads require other than disassembly and lapping the valves. I'll keep you all posted.

There is a way to test the heads before installing them. Especially if you are lapping your own valves. Cut a wood plug long enough to sit in the head and stick up a little and make a gasket to seal it. I think I just used a coating of red silicone. Drill a steel plate for four bolts to the head bolt pattern and bolt the plug in the hole. You can run the compression test on the head and only the valves are being tested. It's very easy then to tell where the problem is and you don't have to go through the assembly/disassembly process. I have found that running the engine before the compression test will yield higher readings.

I think the conclusion is that *no* VW Type 1 parts these days can be trusted to just be "bolt on"....

I was actually wondering what the tolerance of the two head gasket surfaces in the head being coplanar was when I was assembling our Aerovee. That's one that's not easy to check. I have in fact heard leakage past the head gasket when the engine is cold. I'm not sure that necessarily implies a leak during operation since the gasket pressure increases considerably once everything's heated up.

I would also not necessarily worry about leakage past rings before the engine is broken in, since breaking in an engine essentially means "getting the rings to seal". I wouldn't want the valves to leak though, that does suck.

I never did a compression test after assembly, but I did spray PB-blaster into the intake and exhaust and verify that none was wicking past the valves. Compression tests are notoriously unreliable indicators of engine state anyway.

Another easy way to check the valves is to install some spark plugs, turn the head over so you can fill the combusion chamber with fuel and none should leak past the valves to the intake or exhaust port.

Just finished putting the new heads on yesterday, luckily leak down was good and no issues so far.

Tom - I’m really sorry to hear of these issues. I’m sure it’s very frustrating to get brand new parts and have this issue. Hopefully the word can get passed around so others know they need to check valves before the heads are ready to use.


Since we’re on the subject, let’s talk about valve jobs on the heads. Out of curiosity, who all on here does their own valve lap job on their heads? I know several people do this every other year or few hundred hours; I’m curious what all tools are required, steps, etc. If it’s a fairly easy procedure but I’ve never tried it, and I’m curious how it’s done.

Initially, it looks like the main tools required is whatever is needed to remove the springs. I think the basic “grinding” by spinning the valve around looks simple enough once everything is disassembled.

Has anyone gone as far as removing and replacing valve seats?

OK. Possibly a rube question. But I see US made performance heads with port and polish and sized to cylinder specs. Sure twice the price - but I'm imagining (possibly wrongly) that worth paying for less hassle?

https://www.mofoco.com/category/Performance_Heads/c52

MichaelFarley56 wrote: Out of curiosity, who all on here does their own valve lap job on their heads? I know several people do this every other year or few hundred hours; I’m curious what all tools are required, steps, etc. If it’s a fairly easy procedure but I’ve never tried it, and I’m curious how it’s done.?

After replacing both of the original heads of my Aerovee during assembly (one had a gap in an intake valve so big I could shine a light through it, the other stripped a spark plug on the first try) I lapped my assembled engine valves on the replaced cylinders and saw immediate compression test improvement on cold/new cylinders (they have held solid/improved over the first few flights.)



Video of my leaky cylinder head that I sent back to Sonex: https://youtu.be/dzyMxkS5LfM
A few details on my lapping results here: http://www.rynoth.com/wordpress/waiex/2 ... ompletion/

I only needed 3 things to do the lapping... spring compressor, lapping tool (suction cup on a stick, found at most auto-parts stores) and lapping compound.

This spring compressor does NOT work: https://www.amazon.com/gp/product/B002GQEZH0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

This style of spring compressor DID work: https://www.autozone.com/loan-a-tools/l ... r/2052_0_0

I used this valve lapping compound: https://www.amazon.com/gp/product/B0002UEOMS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
It was relatively easy to do and the immediate compression results spoke for themselves on valves that were at least partially seating OK already.

Thanks for the info Ryan! It does seem like a rather easy process for a quick valve and valve seat cleanup. I guess this could be done on condition as needed (I wouldn’t want to remove heads unless I really need to!) but I could see this being a benefit on cylinders that have leaking valves.

Were you able to fix the original heads you had (the one with the valve seat issues), or were those to far gone to be repaired?

I find this tool makes removing the valves pretty simple (and especially replacing the valve stem locks).
https://www.amazon.com/Empi-Bench-Mount-Volkswagen-Assembly/dp/B00BJPYAYW

I also have this tool, but I find it much more difficult to use:
https://www.amazon.com/OTC-4572-Large-Spring-Compressor/dp/B000F5ECUY
I've performed a couple valve lap jobs on my heads when I discover leaky valves. I use valve lapping compound and a suction cup to rub the valve into the seat. It's not very fun. Last time, I ended up with at least one valve where the face was concave and pitted to the point that it would require hours of lapping to get a good sealing surface again. I suspect that heavy lapping removes a hardened surface on the valve face and makes the valve more susceptible to pitting and wear, so this might be my fault. I took it to a local shop and they used NEWAY cutters to fix the seats and I replaced the valves with new parts.

While expensive, I think the NEWAY cutters are the way to go and I plan to buy some for next time. I haven't read of any successful/reliable techniques to replace the seats, so when I get to that point I plan on getting new heads. Like GraemeSmith, I'm willing to pay more if I knew the heads/valves required less maintenance.

If I were starting over, I would closely inspect the valves and seats and if needed, get the seats cut with an NEWAY or similar cutter (rather than lapping) before the first flight. You can apply prussian blue or graphite, etc., to the valve seat and lightly rub the valve against it to visibly inspect the size and continuity of the sealing surface.