1438 rebuild

[70spider]

I was looking over some old posts on this subject and I came across this information by fiatfactory

The 1438 uses the same conrod length (128.5mm) and journal sizes as a 1500 sohc engine, changing the conrod (which is also lighter and still a very strong forged item) would allow use of a full floating gudgeon pin and then the use of a 1608 full floating pin piston. Aftermarket conrods are also available for the 1500 sohc and these will fit the 1438 dohc. 1608 pistons are available with a higher compression height and a taller and wider dome so the static compression could easily be raised. Some 1608 pistons also come with larger valve flycuts, so you could fit larger valves and not have to enlarge the valve pockets for clearance, as it's already done... this also yields some small benefits to low lift flow as the larger valve pocket won't shroud the valve. Some later model valves are also a far better shape, which can provide additional flow over the early style valves found in the 1438.

What makes this interesting is I had a 1608 head rebuilt with oversize valves, thus according to the statement my Borgo 1438 high comp. pistons will have to have the valve reliefs cut to accommodate the bigger valves. Also, an interesting point about the 1500 SOHC con rods being a direct swap item for the 1438, is this true? Also, it says one could then use 1608 pistons, is this all possible without any modification to the block? Any advice on this would be great.

[kmead]

Looking forward to the answers to these questions.

[djape1977]

piston pin diameter and conrod bearing diameter are the same in early dohc and sohc
dunno about length though

[djape1977]

what's the bore in 1438?

[70spider]

what's the bore in 1438?

80mm

[djape1977]

please measure conrod length, from center of one hole to center of other, and exact diameter of bottom hole, one that goes on crank. upper hole is 22mm probably.
i can check that against fiat SOHC conrods.

[fiatfactory]

.

[70spider]

I took some picks of the pistons.


Piston with oversize valve.



Rudimental measurement.


From the pics it looks like it would be a tight clearance.

[djape1977]

you can always get the valve pockets enlarged