Date: Sun, 5 Dec 1999 14:26:04 -0500
Reply-To: Bob Donalds <bostneng@FCL-US.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bob Donalds <bostneng@FCL-US.NET>
Organization: Boston Engine Exchange
Subject: head temps gauges and seats falling out
Content-Type: text/plain; charset=us-ascii
Samuel Chimento wrote:
>
> Question??
>
> Since the valve seats drop out by over heating the air cooled engines in the
> Vanagons then
> what heat gauge is the best to install so that you can keep a close eye on it
> and prevent the
> problem.
>
> Thanks
>
> Sam
Sam and the list
valve seats do fall out of the air cooled type two/four engines this
includes vanagons this common to both the intake and exhaust seats. I
have been told by a fellow in the rockies that after climbing up over
the long passes and after starting down the other side the intake seats
falls out. also when the type 2/4 engine was used in the scca road
racing formula super vees back in the 70s they had problems with the
intake seats falling out after going threw puddles the carb intake was
right at the rear wheels. both of these scenarios suggest that the
intake seat can cool down faster than the cylinder head and shrinks due
to cooler incoming air, fuel and in the case of the race car I mentioned
water.
So with this in mind the cure for intake seat failure would be to
install the seat at a higher press fit. the oem seat is installed at
aprox .005ths to .007ths as are most valve seats. its now common that
type 2/4 heads have both intake and exhaust seats installed at .012ths
press fit.
The exhaust seats on the other hand get hot and stay hot. to take the
extra heat the oem exhaust valve seats are heat treated but when the
temp of the heat treatment is exceded they become soft and pound out the
seat surface taking the valve guide with it. this is also very common
problem with air cooled type 1 propane fueled engines used to power
older zambonis ice resufacing machines
Air cooled combustion chamber temps and exhaust seat temps are
affected by several things but at the top of the list is load,
compression ratios, cooling system efficiency this is loosly defind as
incoming air temps, timing, exhaust leaks and abnormal combustion also
known as ping, dieseling or preignition. the inability of the newer
fuels to resist abnornal combustion combined with the air cooled engines
hotter combustion chamber temps means trouble for the hard working air
cooled van engine.
Is the air cooled engine no longer usable to power the vans? thats not
the case yet but to make it last the cooling system most be working well
scoops are a big helps in the summer months.
the engine also needs to be tuned correctly and have the compression
ratio lowered to keep the heads temps within reason. the proper exhaust
valve seat material is needed one that is not heat treated works best
but it is 4 times the cost.
new aftermarket heads dont have the higher press fit or the proper seat
material
I have seen more than 1 pair show up at my shop with aprox 6000 miles
on them and a seat falling out
I have heard the all the storys of external oil coolers lowering oil
temps BUT THEY DONT LOWER HEAD TEMPS ! the hotter the heads the less
power the engine makes and the shorter the life of the engine. the
cooler head temps the more power the engine makes. let me restate it in
a clearer manner
Lowered compression ratio air cooled engines will last longer make more
power run cooler!!!!!and then you dont need an external oil cooler
his is a fact I will back up and publish at a latter date when all my
reseach and writing is complete
this post will also be expanded on and posted on my web site in the near
future
the only gauge you need for the air cooled van is a oil temp gauge and
a clear understanding is also needed as to the limits of the aircooled
engine
I hope this helps
I know I feel better
Bob Donalds
http;//www.bostonengine.com