Date: Thu, 14 Jun 2007 14:18:29 -0700
Reply-To: David Kao <dtkao0205@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Kao <dtkao0205@YAHOO.COM>
Subject: Re: Is this the cause of my engine compression problem?
In-Reply-To: <BAY125-F2679D2A5755F5F76F49BA7A01F0@phx.gbl>
Content-Type: text/plain; charset=iso-8859-1
Dennis, you are absolutely right about it. The cause of misalignment of my
front exhaust header is not by the cylinder heads being ground. My
rear header is in perfect alignment. I should have realized it myself.
I think I have confirmed that my compression problem is caused by this front
header. I removed it from the engine this morning. Re-torgued all head nuts.
All were correctly torgued previously. I had to remove the intake system
in order to re-torgue. Double checked and double checked just like what
I did previously.
After reassembling of everything, except the front header I did a compression
test immediately cold. I read 160-155-150-155 PSI out of 4 cylinders.
This is the first time I ever had good pressure reading out of #1 and #3
concurrently. #2 and #4 always had good pressure concurrently. Yesterday
I had only 60 PSI from #1 but it had 150 before the weekend trip. The #3 had
100-110 last week and became 150 yesterday and now it is still 150.
The liner I put in was new Cofap. Not likely to have a problem in it. The
front header is out of alignment. I noticed it in my previous failed rebuild
already. I was able to install it with some struggle I ignored it totally.
I noticed the same alignment problem this time and I still ignored it.
I know I can't bend it to bring it into proper alignment. It has to be bent
correctly and it is nearly impossible. So I am going to drill the holes
of the mating flanges. The holes will become slightly oval. I only need
to shift the holes by 1mm from each side (2 holes on each side though).
That will shorten it by 2mm. Hope I will be able to install it back without
dropping the engine.
I believe I under estimated how difficult it is to rebuild a wasserboxer.
I successfully tore apart my 84's engine to reseal the heads once. I removed
all cylinders and pistons. I thought if I ever went that far I can replace
the liner in this rebuild.
This is going to be a good lesson from a misaligned header, if this proves
to be the real cause of the problem. I will report back tomorrow. I can't
get it done today.
Thanks a lot for your professional advices. They do help correcting some
of my incorrect understanding of many things.
Also, many thanks to whoever pmailed me to help, especially to Bob from
Boston for his article about wasserboxer lifters.
David
--- Dennis Haynes <d23haynes57@hotmail.com> wrote:
> I think your really grasping at straws here. The flat surface of the head
> where the rubber gasket meet has absolutely nothing to with where the head
> is positioned when tightened down. If ground, milled, altered or whatever,
> it will only affect the amount the rubber gasket is compressed. When the
> heads are tightened down, it is the top of the cylinders hitting the crush
> or metal gaskets pushed into the cylinder recesses that determine where the
> head sits. This is also the critical interface relying on both cylinders
> being perfectly parallel and level and the recesses in the heads being
> properly machined to seal the top of the cylinders to keep the coolant in
> the jacket and combustion gasses in the cylinders.
>
> If the heads are properly torqued, it is unlikely the exhaust mis alignment
> will cause a head to lift. If it does, you will have coolant system
> troubles.
>
> Compression tests alone are often un reliable and as you found out, do
> little to tell you where the problem is. You need to do a leak down test to
> quantify the leak and then full air pressure to determine where the leak is.
>
> As for the exhaust mis alignment, it is probably the result of an
> aftermarket exhaust. This is a common problem. You can;t just bend the pipes
> as then the flanges will be at an angle causing the gaskets to leak. best
> choice is to drill out the mounting holes.
>
> If you only replaced one liner, it is possible the liner is a slightly
> different height than the other. This will keep the head from properly
> sealing. This problem again can show up as a cooling system problem due to
> combustion gasses getting into the cooling system.
>
> The most important part of any solution is proper diagnoses. This requires
> some knowlwdge and the proper tools. A leak down tester and small compressor
> is relatively low cost. if you plan doing your own work, the compressor is
> almost mandatory anyway. A low cost Milton leak down test gauge is around
> $75.
>
> Dennis
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