Piston Pin

[Hendrik]

Does somebody knows what are the right piston pins for a 99 motor (1500ccm)? I found 2 different types of pins in my motor. 2 of them weighing 94 grams and having a thickness of material of 3,2mm and the other 2 weighing 74gr and having a material thickness of 2,5mm. All of them have an outer diameter of 22,22mm. I think it is crucial to have the right pins with the right weights built in corresponding to the the crank? The pistons are still very good, no wearing, clearance to the cylinders is ok. The pistons are stamped 75mm, probably first oversize.

Yours Hendrik

[simonandjuliet]

Out of interest, are the pistons equal weight ?

What is the length of the pin ? I have new S1 pins and can measure them to see if they are the same (or v close)

[davidwheeler]

My car has a bitza engine, a 1300 bored out to take series II high compression pistons and with Harry Manning shell big ends.   I took it to vibrationfree.co.uk who afterwards told me how it almost leapt off the rig when they started turning the crank.  Smooth as silk now but engine balance is extremely important in narrow V4 engines.

[Hendrik]

Hi together, thanks for your replies. As I wrote the weights are different. 2have 74gr, 2 have 95gr. That is the reason why I would like to assemble 4 identical piston pin. The length is 62mm (because of the bigger pistons than in the 1300 motor. In my old 1300 motor the thickness of the material was 3,2 or 3,15mm, right? 2,5mm seems too weak to me. The crankshaft itself seems to be well balanced. I assume that the crank is still balanced to the original piston weights. Therefore I would like to know the pin weight or the thickness of the material. And maybe the weight of there 1500 pistons because my pistons seems to be an oversize (75mm).

[simonandjuliet]

I have measured the new pins that I have - original Lancia boxes, marked 38-2170

They are also 62mm long, but lighter at 55g approx each. The wall thickness is 1,5mm.

[Hendrik]

Hi Simon,
thank you very much for your help! Unfortunately the thickness ist not enough and the balancing of the crankshaft is problaby made according to the original thickness. There I prefer to know the original the thickness which is propably 3,2mm?
Yours Hendrik

[GG]

Hi Simon,
thank you very much for your help! Unfortunately the thickness ist not enough and the balancing of the crankshaft is problaby made according to the original thickness. There I prefer to know the original the thickness which is propably 3,2mm?
Yours Hendrik

Well, yes and no. Balancing of the crankshafts by Lancia was done in two different ways: from the Lambda up to the Aprilia/Ardea of 1948, Lancia balanced the shafts using only rotating weight (not including any % of reciprocating weight, such as piston, wristpin, or the oscillating upper portion of the connecting rod). De Virgilio developed a balancing formula for their V4 engines in late 1947, and this was adopted as a change into Aprilias in early 1948. This balancing formula included some 32.5% of the reciprocating weight, but only on the t.99 and after 1948.

What is more important is that all the oscillating parts are of equal weight - including the pins, pistons and connecting rods. So getting four of the same pins is key!

Details can be found in: http://www.lanciaaurelia.info/store/p2/Balancing_the_Lancia_V4.html.

[Hendrik]

Thanks Geoffrey for this information. My crankshaft is stamped 1947. As you said the most important thing is the equal weight of all 4 pistons and pins. It's just that the thickness of the wall of Simon's pin is quite little. I could get pins with a length of 70mm, but it won't be easy to short them to 62mm?
Gregor Stampa, our best German Lancia expert, already told me something about a book...now I understand! Good thing that Christmas is coming soon :-)  Thank you for your advice!
PS: I have seen your statements in the film Birth of Modern Motoring... I translated it into German by using an AI software. I'm talking with Josh and Alison at the moment how they can make use of the German version. Great film!

[GG]

Aprilia crankshafts are notoriously tricky to figure out. I found 5 different crankshaft drawings, and was looking at them with Luigi De Virgilio (Franceso's son, and a fine engineer.... sadly no longer with us). Luigi turned the drawing to me, and pointed at a note (no. 14) with a small smile - the note was dated Feb 1948, when the shafts were amended to pick up additional colletti weight per his father's analysis. This is all explained in the booklet.

Of course, I was talking with Mike Kristick here in the US about those five different crankshafts, and he pulls out an Aprilia crankshaft that didn't match any of the drawings! So... care is necessary.

The difference in colletti weight before and after Feb 1948 is about 140g. And yes, that raises its own set of questions....

[Hendrik]

Hi Geoffrey,
amazing how you care about my troubles. Thank you so much. I'm going to order your book "Balancing...", good Christmas literature! I hope I will find 4 equal pins with a wall thickness of 3,2mm. It's better than to have two different types an 3,2 is the thickness of my 97 motor, so it should be the original thickness.
Yours
Hendrik

[simonandjuliet]

Out of interest, how much heavier is an oversize piston ? Would that make a difference, or is it just where the weight is - ie in the centre of the bore/piston ?

[Hendrik]

Good question. But I can't imagine that a plus of 0,xy mm diameter makes much difference. It's partly less of 1%. That makes less than 1% of about 300gr, what makes less than 3gr.

[GG]

Does a change in weight matter? The answer is yes, but also no.... Here's what I learned from years of working on balancing with both John Cundy, a great engineer, and Luigi De Virgilio, who knew Lancia so so well from his father and family.

The most important thing is that the weights across all the cylinders are the same. That's key. And along with that, the weights of each component (piston, pin, con rod) should also be identical. That's good practice.

So do changes in weights matter? Backing up to basic understandings in balancing, lets remember the separation between rotating and reciprocating masses - with the piston, pin, etc. and the upper part of the connecting rod as reciprocating, and the lower part of the connecting rod and bearing as rotating. This is generally assumed through the industry.

But approximations are used, with the general sense that all the reciprocating parts oscillate as they go up and down (and remember the conrod moves around too) as a single "mass" in space - and they are not. So if you change one component (say  different pistons, shorter skirts, etc), and keep the weights all the same, it's possible that the overall center of the reciprocating mass changes. How much does that matter?

The driving part of the balancing equation involves only a percentage of the reciprocating weight for the Lancia narrow Vs, between say roughly 15-25%, (compared to 100% of the rotating weight)  so changes in overall reciprocating mass are not so critical; changes in the location of the center of the mass aren't also that significant for these engines (under 5000 rpm typically, especially for older engines.

So yes, changes in the masses matter - the simplest answer is keeping the same total mass as was original, and making sure each component is the same mass for each of the cylinders. Hope this helps!

[Hendrik]

At least, I got now 2 new pins manufactured for 65 euros. I think this is a fair price for for customized manufacturing. So I have now 4 equal pistons pins.