Date: Sun, 15 Dec 2002 23:24:44 -0600
Reply-To: John Rodgers <j_rodgers@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <j_rodgers@CHARTER.NET>
Subject: Re: Top Overhauls
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Stan Wilder wrote:
> When dealing with a 4000$ crank I've seen them chrome plated to bring
> them back into specs.
Can't say I've seen that done on a crank, although it may well be a
process used. I have seen them ground, re-nitrided, and oversized
bearings used.
> Some aircraft came with chrome cylinders and that was a standard process.
> Although I think the chrome cylinders tended to run a little hotter.
I always thought they ran a little cooler, once the rings are broken in.
The matter of chrome barrels vs. steel barrels are an interesting one.
You prol'ly know that the steel barrels are expected to take the wear
more so than the rings. In the chrome barrels, gray iron rings are used
-soft- so the rings wear more than the barrel. There has been more than
one engine on which the repairman improperly matched the rings to the
cylinder type, and seized the engine shortly after startup. Chrome to
chrome or steel to steel doesn't work well. I had an old Cessna 195
(Actually a military LC-126) with a 7 cylinder 300 HP Jacobs engine in
it with chrome cylinders when I went through aircraft mechanic school
many, many years ago. Bought it for a song because of a cracked case.
The case was magnesium and everybody said it couldn't be welded. Well I
found a spare case for $200, and got my instructor to allow a rebuild of
the engine in the school program. I really got my education going
through than engine and airframe in the school.
Anyway, the barrels were sent out, bored to oversize then re-chromed
back to spec. I though that was a really slick thing to be able to do.
While they were out , new valve seats were installed, and when they got
back, in the school shop I was able to install new guides and ream them
to spec. Strangely the valve stem wear was all within spec except one. I
got a new one to replace it with. Did an aircraft grind on the valves
and seat faces, lapped them in, and put it together. Pistons were fine.
Put in new rings and bearings, Everything down inside the case was ok,
just had to be reassembled. New seals and all.
It was a strange beast. The engine had a magneto on one side and
automotive distributor on the other. The first time it was fired up
after then engine was installed, it belched once and caught fire.
Snuffed it instantly by killing the mixture and opening the throttle
while still cranking. Sucked the flame right up. It was exciting for a
few moments. The manual was unclear as to how to set the distributor
timing and we (me and the instructor) set exactly 180 degrees out, so it
fired when the intake valve was opens. really caused some excitement for
a few moments. Reset the timing, fired her up and it ran like a charm.
Went through the ground break-in then wen out and flew the thing. Never
had a minutes problem as long as I had it. Good airplane, good engine.
> In VW engines the #2 main bearing can be worn more than the #1 or #3 and
> your crank can be in near perfect alignment. Its just the way the bearing
> is loaded at high RPMs that causes excess wear at this point.
> You couldn't measure this wobble on a cold crank ........... it only
> deforms / bends under heat and stress.
> When crankshafts are set up on a grinding machine they are measured for
> straightness before the grinding process is started. In effect a bent
> crank could be machined back to tolerances if it is out only 2/3
> thousandths.
> In short; there really isn't a good way to evaluate your main bearings /
> crank without splitting the case and spinning the crank between fixed
> centering arbors.
> In any event that your engine lost oil pressure immediately, I'd split
> the case. If the oil pressure edged down slightly over several thousand
> miles I'd investigate the rod bearings for abnormal wear on the #2/#3 and
> be wary of the mains.
I wonder if counter balancing and dynamic balancing of the complete
rotating assemblies would help this problem, i.e., counterbalanced
crank, balanced with rods, pistons, flywheel.
I asked Bob Donalds about using different rods on the 2.1L to get around
some of the stretching problems in the lower end of the rod. If the rod
gives, and gets out of round because of the bolts or whatever, then I
would think a substitute would be in order. I have heard that with a
little work chevy rods could be used, but I'm not up on that hot rodding
stuff so don't have a clue.
Anyway, I like my flat four, and don't intend to do a conversion. I
would rather modify what I have. It fits the hole, and is matched to the
van. Just a little more "oomph" would be nice, and I see no reason it
cannot be gotten, without everything going to hell in a hand basket. I
have a basket case engine I want to rebuild in 2003 and would like to
have some mods done before I start. It would be fun.
John Rodgers
88 GL Driver