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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
Comments: To: VChimento@AOL.COM
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


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