1438 rebuild

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70spider
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Your car is a: 1970 Fiat spider
Location: N.E. New Mexico

1438 rebuild

Postby 70spider » Fri Mar 03, 2017 11:23 pm

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.
1970 Fiat Spider 124 Sport aka "Pesto"
2002 Mazda Protege5
2013 Buddy 170i

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kmead
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Your car is a: 1969 850 SC 1970 124 SC 85 X19
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Re: 1438 rebuild

Postby kmead » Mon Mar 13, 2017 7:39 pm

Looking forward to the answers to these questions.
Karl

1969 Fiat 850 Sports Coupe
1970 Fiat 124 Sports Coupe
1985 Bertone X1/9

djape1977
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Location: Belgrade, Serbia, eastern Europe

Re: 1438 rebuild

Postby djape1977 » Mon Mar 13, 2017 9:58 pm

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

djape1977
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Your car is a: 1970 fiat 124bc
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Re: 1438 rebuild

Postby djape1977 » Wed Mar 15, 2017 6:32 am

what's the bore in 1438?

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70spider
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Your car is a: 1970 Fiat spider
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Re: 1438 rebuild

Postby 70spider » Wed Mar 15, 2017 9:44 am

what's the bore in 1438?

80mm
1970 Fiat Spider 124 Sport aka "Pesto"
2002 Mazda Protege5
2013 Buddy 170i

djape1977
Posts: 985
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: 1438 rebuild

Postby djape1977 » Wed Mar 15, 2017 1:01 pm

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
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Re: 1438 rebuild

Postby fiatfactory » Wed Mar 15, 2017 11:57 pm

.
Last edited by fiatfactory on Tue Jul 02, 2019 12:02 am, edited 1 time in total.
nothing to see here... move along.

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70spider
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Your car is a: 1970 Fiat spider
Location: N.E. New Mexico

Re: 1438 rebuild

Postby 70spider » Thu Mar 16, 2017 9:15 am

I took some picks of the pistons.
Image

Piston with oversize valve.
Image
Image

Rudimental measurement.
Image

From the pics it looks like it would be a tight clearance.
1970 Fiat Spider 124 Sport aka "Pesto"
2002 Mazda Protege5
2013 Buddy 170i

djape1977
Posts: 985
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: 1438 rebuild

Postby djape1977 » Fri Mar 17, 2017 6:05 am

you can always get the valve pockets enlarged


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