Beetle stalls on long drives and hot weather.

Well ... yes and no. You just knew I was going to say that, right? ;-)

Cylinders are just tubes with cooling fins on the outside.

Here are a couple:

http://63.230.74.177/ghia/MVC-369F.JPG On the left is an old 85.5mm cylinder. On the right is a 90.5mm.

There are several important dimensions to think about. The first in the outside edge of the cooling fins. This can't change or the tin won't fit over the outside.

The inside of the bore is of course where the piston lives, 85.5mm on a

1600.

The space between the outer edge of the fin and the inside of the bore is taken up by the cylinder wall and the fin width. If one gets bigger (cylinder wall) the other must be smaller.

The slip-in 88s are made by taking a stock 85.5 cylinder and just boring it out. All the outside dimensions remain the same. But you get a very thin cylinder wall that distorts easily if overheated.

Machine-in 88s have the same 88mm bore, but a thicker wall. So the outside dimension of the "tube" is larger and the case must be machined to accept it. Also, the fin area is slightly reduced. This is true of basically all the larger bore cylinders. Except the afore-mentioned slip-ins.

The ability of a cylinder to transfer heat to the passing air is determined by the amount of surface area exposed to that air. Primarily, that is the fin area. Plus the exposed outside of the cylinder at the base of the fins.

The ability of a cylinder to hold it's shape when hot is largely a function of the thickness of the cylinder wall. The thick wall doesn't help it cool.

PS: Better cooling is why the surface of the fins is rough. That increases the surface area. http://63.230.74.177/ghia/MVC-377F.JPG True also of the heads.

Max

"Mark Detro" wrote

I took quick looks at RMMW, CB Performance, Chirco, CIP1, Action Import and AC.net (ok, I'm bored ) .... only Action Import and AC.net had 88s listed at all. AC.net specifically states that they are machine-in. Action Imports says "extra thick for superior strength" ... I guess that means machine-in?

-- Scott

.............I have machine-in 88's in my '77 bug. The PO built the engine with mostly Berg parts so that might be the source for the thick walled

88's. After about 12,000 miles, much of it at 75-85 mph, this engine still has great compression (I can barely turn it over by hand). Some of the bus guys say that a 1679 (machine-in 88's, counterbalanced crank & heavy pulley, single port heads, dual kadrons or ICT's, etc.) is an ideal type1 engine for durability in a bus. Makes sense to me.

1641 - 87mm thin wall, no case work needed

1679 - 88mm VERY thin wall, no case work needed

OPTIONAL: 1679 - 88mm "machine in" type, thick wall, but requires case to be machined

1776 - 90.5 - thick wall, requires case to be machined

1835 - 92mm, thin wall again. Fits in the same size case hole as 90.5

1915 - 94mm, thicker wall and bigger outside diameter again, so the case needs to be bored out even bigger.

For longevity, you should stay away from the first two and the 92mm cylinders. They all have thin walls.

The thin wall means it overheats easier, and overheating means the cylinder loses shape. It goes oval, and barrel shaped. One side of the piston would BIND, causing friction and heat, while the other side would have too much play, causing blowby. Piston rings can't follow the new shape cose enough to seal well. The problem grows exponentially, making itself grow as it gets worse.

The best size for most applications would be 90.5mm. Nice thick wall, and the case hole isn't reamed up too big yet.

The 94's have thick wall too, but they bring other potential problems with them.

Jan

Well, what da ya know. Usenet is indeed educational!!!! LOL.

But back to the 1776cc - if the case is bored out to make way for the bigger cylinders... ahhh... then wouldn't the strength of the crank case be weaken then... not to mention the four long screw things around the crank case holes... um studs? And wouldn't it be better to bore out the cylinders then to tamper with the crank case.

Thank you Max for your thoughtful reply.

Thanks Jan,

I think I am starting to understand. But the other people that I talk with in my VW club say the 1641cc is preferable over the 1776cc due to the fact that the 1641's crank case does not have to be bored out.

I am using Mahle 87.5mm pistons- did Mahle cast and make them specifically as 87.5mm or did they take a 85.5mm and bored it out?

On Wed, 21 Jan 2004 13:25:33 GMT, "CC" ran around screaming and yelling:

how about a big NO....the engine vw designed is very strong...it has been proven since the 60's to do quite well when bored out for larger cylinders, and even when material is removed on the inside at the webbing(cast in for strength) to clear a counterwieghted and longer stroke crank....boring them out to fit the 90.5's is a baby step in material removal compared to what has to be removed to run a long stroke crank and cylinders such as 94's...(which i am in the process of gathering parts for now...building a 82x94(2275cc)) J

Popular is not always right.

It is safer to bore the case for 90.5 than to have a thin walled cylinder. No argument.

I think they make them like that from some raw cylinder castings, doesn't matter much what size they drill them to..

Jan

You got to find a new club.

It sounds like they are mainly concerned with the ease/cost of building the 1641. But when those 88s warp, you'll be doing it all over again. So much for any savings.

Perhaps they are just afraid to split the case and do it right?

Max

Hello there,

My mechanic reckons the reason my VW was stalling on hot days (100F+ 37.77cc temperatures) was due to vapor lock. He didn't want an electrical pump fitted in as it would be pumping in the same amount of petrol when it was idling or doing 80mph.

So he fitted in a Pierberg pump - it is mechanical pump. And hopefully it will fix the job at hand.

Now I need some hot weather!

Cheers,

CC

Hmm... well I don't know much about the engine modifications accept from what people and my various mechanics tell me. I guess I will comment more on the 1641cc at a later date when I get more drivin into it.

BTW, My mechanic reckons the reason my VW was stalling on hot days (100F+

37.77cc temperatures) was due to vapor lock. He didn't want an electrical pump fitted in as it would be pumping in the same amount of petrol when it was idling or doing 80mph. So he fitted in a Pierberg pump - it is mechanical pump. And hopefully it will fix the job at hand.

Cheers,

CC

Cheers,

CC

On Thu, 22 Jan 2004 11:01:04 GMT, "CC" ran around screaming and yelling:

CC, i don't want to sound like an "ass", but it may be time for a new mechanic...even a stock vw pump will pump *more* gas than the carb needs at all speeds, that is why the carb has a needle valve and a float in the bowl...i'm not real sure what his real reasons are, but the one he gave you is a load of shit...(sorry) J

................Electric fuel pumps that are designed to work with carburetors work just fine. Your 'mechanic' is wrong. When the float in your carburetor shuts off or restricts the fuel inlet to the bowl, a facet style electric pump maintains a proper 3 to 5 psi pressure without actually pumping an excessive volume of gasoline until the float drops down enough to allow flow to resume. A facet type pump installed underneath the fuel tank is perfectly OK and has been used that way by many many knowledgeable ACVW mechanics for decades. I'd find a better mechanic. The one that you've got right now is ignorant.

WOW everyone is jumping on that mechanic. 8^) Maybe it was meant to say that the electric fuel pump COULD/WOULD supply a constant flow of fuel no matter what speed the engine was at, and the mechanical would operate in relationship with the speed of the engine. The faster the engine rpm the faster the pump would be pumped. Is this called semantics or something? I think the glass is half full! lol

I prefer the quiet mechanical pump over the electric pumps, unless there is no place to install the mechanic pump like on a T1 FI engine.

Make sure the the fuel line is free of any holes, that the fuel hose is new, that the fuel line over the engine is not touching the metal of the engine and that the engine is getting enough cool air. JMHO later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Hello,

In all due respect to my mechanic - I am only relaying what he told me in between his business work. But like Dave said - that's what he meant.

As for the smartness of my mechie, he is considered a trusted source in the VW community here, I have sent my Beetle to other mechanics but they have been ... not so good.

I don't exactly want to move to another country to get a better mechanic either :)

Anyhow, I took the Beetle and drove it long distance yesterday and it was OK. Didn't give me any problems.