Fiat Dino Forum (FDF)

Hi all,
My engine (chassis 665) has the 8mm shim under bucket adjustment.
Is it possible to “just” change these for the 25mm style buckets.
M

Looking at the Spare parts Catalogues you will notice that not only the valve tappets were replaced when the valve shim system was
changed, but also the actual valves.
The valves outer diameter were slightly changed, but more important, the valves total length were shortened. I have found my
old measurement notes over this:

Early type exhaust valve = 106,35 mm
Early type intake valve = 95,55 mm

Late type exhaust valve = 104,65 mm
Late type intake valve = 94,50 mm

This was made to compensate for the differences in "actual thickness" between the early and late type of the valve tappet.

You can re-use your old valves by cutting off the valve stems, but then you also have to make changes in the valve springs
locking cones positioning, which make it much more complicated. The best alternative today with new correct valves easy
availible, would be changing all the valves and valve tappets together.


Dinoswede

I would never change it, and if, only the other way around.
The early style is much better. It is much lighter, easier on the cams, easier on the valves, harder surface than the shims, able to rev higher. Beside that it will take you 2 extra hours setting the valve clearance (which you never have to do, mines only changed 0.01mm in 15.000km) it only has advantages and no disadvantages.

Thanks Stephan didn’t realize the cam wear would be greater. So many engines I’ve owned had the shim on top arrangement.
I guess you saved me another project .
Anybody have a stack of 8mm shims they’d like to trade for my 25’s?
Michael

Hi Stefan. I’m curious, why did Fiat change it if the prior system was better?

Mainly for maintenance reasons as you can let the camshafts in to adjust the valve clearance. With that you also not have to adjust the timing new when it’s correct. The Dino was at that time quite complex for Fiat workshops and the later version was a bit easier to maintain and don’t overwhelm Fiat mechanics not being used at all to these kind of complex engines.

And yes, the later version wheighs more/is heavier what influences the free revving of the engine. I will also keep the earlier system on my Spider as its originally was/is.

I cannot see any other reason as the reason described above, and beside that also the assembly time at the factory. I would assume that assembling a 2.4 head in the factory only takes half the amount of time compared to a 2.0 head.

I would anyhow assume that many of the changes were done mainly to improve efficiency and price. I mean machining a cast iron block only involves drilling 6 somewhat halfway precise holes and hone them afterwards and your done.
Where with the aluminium engine you need to spindle the bores for the liners very precise, than you need to machine the liners very precise, press them in, make sure they are also sealed watertight, machine the top of the deck and separately machine the top of the liners, hone the liners after they are pressed in, make sure they stay in place while honing etc. etc.
With the above in mind, i guess that making a 2.4 liter engine only takes a fraction of the time compared to making a 2.0 engine.

If you then, on the end of the line also end up with something that is almost as good, and in this case for the majority of the customers probably even better for only a fraction of the price, tooling an labor, you did a very good job as an engineer.

Greetings from a process engineer;-)