I'm about to install the Mahle Euro (flat top) pistons and cylinders. I know that it is critical to have the pistons facing the correct direction relative to the flywheel. I'm used to seeing an arrow on top of the piston that is supposed to be pointed toward the flywheel. These Mahle pistons have no such marking.

This picture shows the top of the piston. Is that funny little symbol supposed to represent a crankshaft & flywheel? Is it critical which side faces the flywheel end or just that all the pistons are the same?

I'm hoping someone answers quick - I'd love to get the heads on tonight!

Look on the backside...one of the pin bosses will have a raised bump that goes towards the fly.

Show me a pic first.

Mark -

Here's the bottom of the piston.

I'm guessing from your description that the left side in this picture is the side that would go toward the flywheel. That is the same side that has the funny symbol on the top.

It took me awhile, but I found this page at Mahle's web site. It indicates that this symbol is for installation direction and that this goes toward the flywheel.

http://www.mahle.com/am_na/am_na.nsf/out/1...cument&,1700114

Yep left side

All mahle pistons have some sort of bump on the pin boss that goes towards the flywheel.

Thanks, Mark! The first P&C is just about ready for checking the deck height. WooHoo!

The funny symbol, in this case, is a crankshaft and a flywheel. Squint a little bit--see it? The flywheel is on the very right-most side of the glyph, which means that the right side of the piston (when viewed from the "top") should be closer to the flywheel.

The reason the symbol is there is because the pistons have very slightly offset wrist-pin holes. This keeps the forces going from piston through connecting rod to crankshaft (and back the other way) lined up a little bit better, which reduces the "piston slap" and the piston rocking in the cylinder bore.

It's not critical, but it's a good thing to do correctly if you can.

--DD

silly rabbit tricks are for kids. the picture of the piston top shows you a picture of the flywheel. If using the piston as it is in the picture the flywheel would be on the right. which would be correct for cylinder #1.

Thanks guys...

Now, about deck height. I assembled the first piston with the thinnest barrel gasket. I measured the deck height using a straight edge and my feeler gauges. As I measure it, the deck height is .022". The only info I have on deck height is from Tom Wilson's book on overhauling air-cooled engines. This indicates a minimum height of .040"

Do I need to increase the deck height by using a thicker gasket or are the specs different because of the non-stock pistons?

You should figure out your proper CR then get custom spacers from Jake or rimco.

here's the math....enjoy

Engine cc formula:

Bore (mm) X bore X stroke (mm) X 0.0031416 = Engine cc

Example: 90.5mm X 90.5mm X 78mm X 0.0031416 = 2006.97cc



Deck volume cc formula:

Bore (mm) X bore X deck height (in.) X 0.01996 = deck volume cc

Example: 90.5mm X 90.5mm X 0.080" X 0.01996 = 13.07cc



Head cc is measured by using a Head cc kit (stock T1 is about 48-50cc, 914 2.0 about 60cc)



The CR formula:

Head cc + deck cc + (engine cc divided by 4) = CR
Head cc + deck cc (+ piston notch cc, if any)

Example:

54 cc + 13.07 cc + (2006.97 divided by 4) = 568.8125 = 8.48
54 cc + 13.07 cc = 67.07

568.8125 divided by 67.07 = 8.48 or 8.48:1 CR

Mark: Your trying to make an engine builder out of him. Kewl!!!
Joe

That's OK Joe. I want to understand why, not just be told what to do.

However, in this case I'm having trouble working through this myself. I'm afraid my poor Algebra skills are coming back to haunt me.

This is a stock engine in every way except using Euro pistons instead of stock pistons. It's my understanding that this gives you slightly higher compression using stock settings in every other way.

The stock CR is 7.6 and the pistons are 94 with a stroke of 71. Using the Engine CC formula it comes out to the expected 1970.9 cc. So, substituting those numbers in the CR formula I get:

60 cc + deck cc + 492.7254 = 7.6

solving for deck cc I get: deck cc = 7.6 - 60 - 492.7254
so that would make deck cc = -597.5254 which obviously makes no sense!

So, assuming you are building a totally stock engine, what should the deck height be?

You have to cc the heads and allow for the dish in the top of the pistons. Somewere here there was a post about how many cc's a stock vs euro piston has.

Then use this calculator:calculator

I was using the value of 60cc that Mark Heery provided for the head cc.

I'm feeling pretty dumb right now - I just went back and reread Marks' forumula and realized I had missed the very last part about dividing the results. Duh! I'll give it another try.

In the meantime I tried that calculator, providing what I know and asking it to calculate the deck height. With a bore and stroke of 94 & 71, and a CR of 7.6, it correctly calculated the engine size, but it says the deck height is .424 inches. Clearly something isn't right about that!

It's time for bed. I'll think about math again tomorrow!

If your combustion chamber is in fact 60cc's and you have .022" deck height and you used a .030 spacer you would have a compression ratio of around 8.1 / 1.

Things like flycutting the head can change figures in a hurry and I state "about 60cc", as this size was never a constant right from the factory...I'd say that size +/- 2 or 3cc (more often +).

I know Dave Hunt made up his own head cc plate, maybe if you asked him nice he would make you one or let you borrow it.
Or most bug shops carry 94mm Type1 plates and the head cc kit is about $20.

You can also use the plate to get your dish cc, it's not very big on a euro, somthing like .5 to 1cc.

i'm doing the same thing (assembling the engine top end)

i cc'ed the heads (made my own plastic disc and borrowed a burette from the chemistry teacher). pretty messy the first time but got about 61 cc/head.

checked and rechecked the deck height. i finally measured .030". i don't see how people can measure to the thousandths as the uncertainty has to be .002-.003". maybe something i'm doing is wrong but i'm using a caliper with a depth "stick" (thing that comes out the end of the caliper) and a ruler. i used a dial indicator to bring piston to TDC. then i measured the width of the steel ruler, then with the caliper on the ruler extended the stick to touch the piston crown. from that measurement, i subtracted the width of the ruler.

unfortunately, the order containing my cylinder spacers is going to the wrong address (UT instead of VA, but that was probably my fault, i thought i changed the delivery address) so progress has ground to a halt.

i did measure the crankshaft end play and have the final solution for that and i cleaned the pushrod tubes and ordered oil pump mounting studs from the porsche dealer. HA, he listed the price as 50 cents per stud! (N014.532.2) 8mm x 32mm