Reciprocating Weights

[Neil Cundy]

With my Fanalone engine in bits now, I have started weighing the reciprocating components. This has thrown up a few questions that I hope someone may be able to shed some light on. The weights are:

Grammes
1 2 3 4
Rod 696.5 702 702.5 696
Big End 490.5 494.5 495.5 489.5
Small End 206 207.5 207 206.5
Piston 384.5 383.5 383.5 383
Pin 100.5 118.5 100 119
Rings and clips 37.5 37.5 37.5 37.5

What is puzzling me is the difference in weights of the pins. They are also different designs. The lighter set have a tapered hole (ie the thickness of the pin gradually increases to its maximum at the centre as a taper), the heavier has a step change of section in the centre third of the pin (where maximum bending occurs). The corresponding pistons also have different marks on: the two pistons on the light pins are marked "H" on the top and those on the heavier pins are marked "B" - does this have any relevance ?

My dilemma is if I equalise the weights of the pins (or the reciprocating assembly) do I destroy the balance of the engine. I am aware of the fact the crank is of the "unbalanced" design common to V engines, but I do not know the balance factor applied to the big end pins during the balance process (the Aurelia engine 60^ V6 is 100% rotating + 50% reciprocating weight for example), so cannot calculate the effect of removing the weight and, if I do equalise the weights, should I rebalance the crank.

I assume Lancia did not individually balance the engines, and that they were assembled from components that were matched assuming a nominal balance figure based on achievable manufacturing tolerances. If this is correct, then do I have an out of balance engine or an in balance engine (by which I mean has the engine been assembled incorrectly to start with) ? What have others found when they have weighed these items ?

Any thoughts or advice welcome !

Neil

[Geoff Goldberg]

Neil -

I don't envy you this problem. Sounds like a trip to Italy to visit the various (non-web) gurus that lurk in the workshops of wisdom. Not an easy one to sort out - the variation is pretty big.

Geoff

[Andreas]

I would like to say that someone had repair only 2 Zylinder with parts from on other engine

And the marks on the top of the piston show´s, if i remember well, two toleranc classe of the outer
diameter of the piston ( It should not be " H " it is A & B ) delta of diameter i believe was 0,05 mm

regards Andreas

[Neil Cundy]

Andreas,
Thats a good point, I am aware of the different classes, and in fact last night was checking the dimensions as my block comes back from being cleaned and re-honed this week and I was getting my bore gauge out in readiness. Indeed I checked for the class marks when I took it to bits but ignored those marks as I though it would be stamped on the block as most modern engines are. I will check it out and see what I find with your suggestion in mind. I am sure they were "H" and not "A" though but I will recheck before they go off to be barrelled. Book says delta is 0.01mm ( A = 82 - 82.01, B = 82.01 - 82.021).
Thanks very much
Neil

[neil]

Andreas,
I have measured the pistons and you are indeed correct - the diameters correspond with the class A and Class B as shown in the data book - it does say H on the piston top but must be a mis-stamp ?

This still leaves the two different pin designs:
Huib (or anyone), do you happen to have a standard gudgen pin on your bench that you could confirm is stepped and if possible what it weighs ? It has been suggested via the UK LMC forum that the standard pin is of the "stepped" design, and the lightened version is of the "tappered" design.

I will then know what I have got, just leaving the "what to do about it".

Thanks for the help

Neil