John Bouyea wrote:
> How much did you space your cylinders out from the case to increase
overall
> exhaust flange widths?
> On your efforts to rework the heads, was there any measurable slop in the
> guides? Which brand of valves do you use? Do you use a differential
pressure
> tester as well or just the compression gauge? P&L's too?
My 2180cc VW engine is over a half inch wider because I have .258"
spacers under each cylinder. Why? Because the crank is designed for
Chevy rods, which are a bit longer (5.7" rather than the stock VW ~5.4"
rod center-to-center length), so the pistons protrude from the cylinders
if you don't have spacers. What made me stupid enough to buy that
crankshaft? It's all Marty Roberts had when I called him at
GPASC....desperate for a Force One prepared crank so I could make it to
OSH in 2017. I don't know why he had one, but my guess is he was either
desperate or inattentive when he bought it. They are definitely not
worth the hassle. The problem is that it's not trivial to stretch an
exhaust system a half inch to install it on the heads, and even then,
the pipes are always under that stress (although it's probably relieved
a bit after repeated thermal cycling).
But before I even noticed the exhaust was cracked and leaking badly, I
checked the compression (hot after a flight) and it was down from
something like 158 psi on all four to a range of 116-118
psi.....consistent, at least! Still ran great, just worrisome
compression numbers. Leakdown test showed a lot more disparity (I
suspect the adapter sealed better) showing between 40/80 and 60/80!
The leaks were from both intake and exhaust valves....LOTs of leaking!
I was debating whether or not I wanted to fly the thing to OSH that way.
I KNEW it wouldn't be smart, because if the exhaust valves aren't
sealing well against the seat, they aren't dissipating all their heat to
the head, and they are getting hot, and getting weak, and then you suck
a valve head. Then I found the split collector, broken exhaust pipe,
and metal erosion, which gave me a definitive answer....fix it right now!
So I pulled the exhaust and started looking for a replacement, and
ordered new Mahle forged pistons and cylinders.....while I'm going to so
much trouble, might as well eliminate any concerns with those also.
After a few dead-stick landings, this is how you think. Then I pulled
the heads and ordered some Total Seal second rings and a set of exhaust
valves from Revmaster. Make that TWO sets of exhaust valves....a spare
set for next time. Since these heads have required almost NO valve
adjustment when checked every 25 hours, I'm super impressed with the
design and metallurgy of the Revmaster heads, so I'm not changing to
somebody else's valves!
Then after ordering the pistons and cylinders, I found a brand new set
exactly like them sitting in the hangar....from the same place (Moore's
Performance Parts), so now I'm already set for the next rebuild. Then I
ordered everything required to build a new exhaust system out of 304
stainless steel. The hardest thing to find was the VW exhaust flanges
(to the head) in 304 stainless, but finally found them at
AeroConversions (Sonex), ready to ship. Right after all of that was
ordered, I heard from Doug that he had an exhaust system for me, so
welding up the stainless system will be done when I have more spare
time...and preferably during the winter when flying days are more
sparse. It takes a looooooog time to weld up an exhaust system, so it
can wait.
Inspection of the valve guides found the clearance still quite tight,
with no wear apparent, but three were slightly cracked on the combustion
chamber side, so out they came. I put in new guides, and then reamed
them out a bit to spec minimum. Intakes were fine...no discernible wear
at all, so I left them alone. I recut the seats with a three angle
valve job to the proper contact surface width, and had the intake valves
resurfaced at the local speed shop. He did it while I looked over his
shoulder, and said it was free but I gave him $10 for his time. These
were the same intake valves that came with the Revmaster heads.
I reassembled the heads with the same low pressure springs and keepers
and they are now installed on the engine, along with the exhaust system.
One thing about the engine being a half inch wider....the pushrod
tubes need to get longer! The local dealer was fresh out, so I had to
reuse the old ones. This means stretching the bellowed ends of the
eight tubes out quite a bit to get a good seal, which was one of the
biggest pains of the whole affair! Now it's just baffling, intake
pipes, primer lines, etc.... which isn't exactly trivial on this plane.
I really need to tidy up the baffling, but it may have to wait a
while. I've got a lot going on and would rather just get it back in the
air for now.
For more on what's involved in rebuilding a 2180cc VW engine the right
way, see
http://www.n56ml.com/n891jf/2180/ (the first time the engine was built,
not the recent "refresh" version).
Mark Langford
m...@n56ml.com
http://www.n56ml.com
Huntsville, AL
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