Posted by Bob Grimstead on Wednesday, February 2, 2011 @ 09:28 AM:
Hi Guys,
I think most Fournicators know that Volkswagen cylinders are held in place with special, big, nuts & washers.
Take a look at these.
Now look more closely at the fifth nut from the left.
When I dismantled my new Aeropower engine, I discovered that nut was a normal, undersize one.
I discovered this because it needed a smaller socket to remove it.
Just an annoyance I thought.
This was the second from rear lower nut on the right cylinder head (the one that gets hottest).
But look at this cylinder and head.
Combustion gases have been leaking here, where that smaller nut was.
Bear in mind this engine only ran maybe three hours on the dyno (max) plus 2:30 in flight.
So, either there is a fault in that cylinder or (new) head, or that nut does not do the job even when it is properly torqued, or Mike forgot to go and get a smaller socket to tighten up that nut properly.
I have to say that I didn't notice it being any less tight than all the others.
A new nut wil be on order tomorrow.
Only an annoyance, but if it had bneen like that for long, I would soon have needed a new head -- Yes, some say I already do!
Yours, Bob
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Posted by jb92563 on Wednesday, February 2, 2011 @ 04:14 PM:
Just a note that when you have no gasket between the cylinder and head the head torquing process and sequence is very critical.
Some folks use a copper gasket that being softer will accommodate a less than perfect head and/or torquing sequence and still make a
good seal.
Retro fitting one however will reduce your compression ratio slightly perhaps by 0.5 unless you remove a cylinder shim as well to compensate.
Also if you want the most perfect, smooth running, and powerfull VW you will meticulously match and balance the volume of the cylinders
and their compression ratios with shims and Dremel as explained in the Great Plains Assembly Book. Its easy to do and worth the effort.
I think that if you start messing with VW's Bob, you will find them to be simple to work on yourself and there is a lot of wisdom out there
to help you through. Details you can do yourself that engine builders just do not have the time or desire to fiddle with that can improve the
performance and smoothness of your engine.
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Posted by eugenio on Wednesday, February 2, 2011 @ 04:47 PM:
Your leak problem may be fom the heads not sealing perfectly on the cylinder. The VW type 1 don't use any kind of gasket between the head and the cylinder, only type 4 uses them.
You need to flycut the heads to restore the sealing surface and for perfect tightness you can lap the head sealing surface with the cylinder and some grinding compound (like for the valves and seats). I had a similar problem with a Limbach 2000 last fall, and after the flycut the problem was solved. Flycutting just 1 or 2 tenth (mm) won't change your CR and solve all your problems. Obviously the nut should be changed, but this in another story.
Eugenio
Posted by Jorgen on Wednesday, February 2, 2011 @ 05:07 PM:
Right honorable Fournieteers,
Thanks for sharing. Yes, the VW engine is a mechanical marvel, both simple and sophisticated at the same time. Good points about proper cylinder seating. Your finding doesn't necessarily imply that Mike did a poor job on your engine Bob, but I agree that you might have prevented future problems.
Eugenio, per piecere, flycut- does that mean rotating a loose cylinder against its seat in the engine block with some rubbing compound in between? Do you seal the stud and piston openings, care to share your tricks?
May the 4's be with you/ Jörgen
[Edit by Jorgen on Wednesday, February 2, 2011 @ 05:07 PM]
Posted by eugenio on Thursday, February 3, 2011 @ 02:47 PM:
No tricks, everything is on most VW books and manuals, I just follow the advice of who knows better than me these engines. Flycutting is the operation that you do to remove some materials from the head, to restore the sealing surface or to reduce the CR (compression ratio) or even to use a larger bore cylinder (in this case you flycut also laterally), or, in the case of the engine crankcase, you enlarge the hole for the cylinder base (big bore cyl.).
Rotating a loose cylinder against the head is lapping, and it is done on new parts or flycut parts to have a perfectly tight seal.
Eugenio
