Can i replace the pistons on my Mk I Uno Turbo 1.3 with ones used on Uno 1.4 70ie?
I am trying to get my engine rebuilt and it seems to need new pistons. Are the pistons exactly the same? Or are there any recent Fiat ones i can use straight from the shelf? And what about the valves?

e_cag said:

Can i replace the pistons on my Mk I Uno Turbo 1.3 with ones used on Uno 1.4 70ie?
I am trying to get my engine rebuilt and it seems to need new pistons. Are the pistons exactly the same? Or are there any recent Fiat ones i can use straight from the shelf? And what about the valves?

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I very much doubt if the pistons from a 1.4 70 i.e. will be suitable for a turbo. The turbo uses low compression pistons whereas the 70 uses normal compression pistons.

Not only that, but the 1.3 is 1299/ 1301cc, and the 1.4 is 1372cc. Chances are the bores will be incompatible though you may be able to rebore the 1.3 block to take the 70 pistons. But you'll still have the problem of incorrect compression ratio.

The valves I don't know. They could be bigger on the turbo head compared with the 70, but I'm not sure without looking up the specs.

Perhaps your best bet is to find a good used 1.3 turbo head and pistons?

Best of luck,

Chas

Are you certain that the pistons need replacing (generally unusual) - although thinking about it for a moment, I suppose they melted under some tremendous boost pressure.

Go to an engine shop with the 80.5mm bore in mind, and see what pistons exist for other engines. You may be surprised at what is possible - I have heard of pistons from different manufacturers used with success. But I don't know of anything specific for the Uno Turbo.

-Alex

Yes you could actually. They would fit and the engine would run. However the pistons are not suited to turbocharging and the compression ratio would be lower quite a bit lower. The engine would have less power and be less reliable.

Best (only?) idea is to use 1400 turbo pistons, Uno or Punto. These fit allong with a 1400 (or 1600) crank. You need to grind a little off inside the crancase to make it fit (easy job). This gives you 1.4L. With a 1.3T head it will have more compression than standard, you could try some tricks to get it down or just use it as is. A 1400 head would give standard compression. At the end of the day its probably easier to get a 1400T longblock and use that.

SteveNZ said:

Yes you could actually. They would fit and the engine would run. However the pistons are not suited to turbocharging and the compression ratio would be lower quite a bit lower. The engine would have less power and be less reliable..

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Are you sure 1.4 pistons will fit a 1.3 block (without reboring)? Just checked the Haynes manual, and the bore for the 1299/1301cc pistons is 86.4mm. The bore for the 1372 engine is 80.5mm. That's quite a difference!

Plus, don't you mean the compression ratio would be HIGHER when fitting 1.4 non turbo pistons to a turbo block? The turbo pistons give 7.7:1 (1.3), and 9.2:1 on the normally aspirated 1.4.

Higher compression pistons in a turbo engine I would have thought would give more power, but would be more likely to make the engine go 'BANG!' if the power was used! I'd expect blown headgaskets and melted pistons

SteveNZ said:

Best (only?) idea is to use 1400 turbo pistons, Uno or Punto. These fit allong with a 1400 (or 1600) crank. You need to grind a little off inside the crancase to make it fit (easy job). This gives you 1.4L. With a 1.3T head it will have more compression than standard, you could try some tricks to get it down or just use it as is. A 1400 head would give standard compression. At the end of the day its probably easier to get a 1400T longblock and use that.

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Hmm, a 1.6 turbo? That sounds fun

Thing is, aren't the crankshafts also different between turbo and non turbo? I'm sure I read somewhere that the 1.3 turbo had a forged crank (very strong), whereas the 1.4 turbo had a fairly standard crank. Not sure if there were many differences between the 1.6 and 1.4 cranks.

I do agree though that the best option is to find a 1.3/ 1.4 turbo long block and use that instead. Or maybe even a Punto GT engine.

But then again, the 1.3 turbo is a super engine and a bit more revvy than the 1.4 as it has a shorter stroke and is more 'oversquare' in its bore/ stroke ratio.

If pistons could be found cheaply then a 1.3 turbo engine could still be rebuilt!

Chas

1986Uno45S said:

Are you sure 1.4 pistons will fit a 1.3 block (without reboring)? Just checked the Haynes manual, and the bore for the 1299/1301cc pistons is 86.4mm. The bore for the 1372 engine is 80.5mm. That's quite a difference!
Chas

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Yes Im sure, Uno turbo 1.3 has 80.5mm bore

1986Uno45S said:

Plus, don't you mean the compression ratio would be HIGHER when fitting 1.4 non turbo pistons to a turbo block? The turbo pistons give 7.7:1 (1.3), and 9.2:1 on the normally aspirated 1.4.
Chas

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The CR would be higher if fitting them to a 1.4 block. However the compression height (wrist pin to piston top) of the 1.4 pistons is about 1.6mm shorter so they will sit below the deck in a 1.3 block. The CR will be lower than an NA engine for sure, it could be around the same as a turbo or lower, it depens on the head you use. Either way its probably not a good option

1986Uno45S said:

Higher compression pistons in a turbo engine I would have thought would give more power, but would be more likely to make the engine go 'BANG!' if the power was used! I'd expect blown headgaskets and melted pistons
Chas

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Not if its tuned well. Fiat kept increasing the CR as time (tuning ability) went by. Punto GT series 3 has 9:1 with a turbo

1986Uno45S said:

Hmm, a 1.6 turbo? That sounds fun

Thing is, aren't the crankshafts also different between turbo and non turbo? I'm sure I read somewhere that the 1.3 turbo had a forged crank (very strong), whereas the 1.4 turbo had a fairly standard crank. Not sure if there were many differences between the 1.6 and 1.4 cranks.

Chas

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1.6 would require an 86mm bore block. Not the best block for a turbo.

1.4, 1.6 and 1.4 turbo have the same crank

1.3 turbo has the same crank as a 1500. These are different to the above

1.3 and 1.1 na have the same crank but different to the others as well.

Unfortunately (for Chas) the Haynes manual is a bit skimpy on clear info, I know the supplement specs. page he was looking at! The 1301cc Turbo engine has different bore and stroke to the 1301cc non-Turbo engine. As Steve says, it's 80.5 bore. The old 1116cc engine was 80mm, just not quite big enough therefore.

Also, the compression ratio depends on the ratio between the swept volume and the volume of the cylinder head combustion chamber, so I see no reason why pistons from one engine wouldn't result in a different CR when placed in a different engine. It depends where they come up to, which also varies with the connecting rod length.

I suggest that Steve will have all the right answers here, since he has built these engines from 'odd' parts before IIRC...

-Alex

Hi All!
To make it short, i am going trial-error way. The engine machining shop sent my bro to a parts shop with the old piston in hand. He came back with pistons from Nüral, a German producer of pistons for Federal Mogul after some measurements in the parts shop.

The new pistons are also 80.5 mm in diameter. Heads of pistons were machined for valve clearance. Besides that, some channels like 0.2 mm in width and maybe 0.1-0.2 mm in depth were opened in the flat between the topmost ring and upper edge of the piston wall. I don't know what this is for. The explanation from the shop is that the channels are for removing the soot that are formed due to combustion, from the cylinder walls. The other explanation, -i am afraid- is that just to resemble the old pistons.

Being an optimistic person i am, (well, actually things went out of my control to my bro, he is so impatient,) i believe knock due to different CR won't be a serious problem. But i have no idea if new ones are of good material to resist heat as the old ones. This weekend, the engine will be re-assembled hopefully. The original head, crank and rods will be used. Since we haven't get the old pistons back, i don't know if the compression height changed as SteveNZ pre-warned me. I wish i had the skills to calculate the volume of combustion chambers and the resulting CR.

I hope to take some photos of the old and new pistons this week and share the practical results of the uncautious movement i did. Thanks Chas, AlexGS en SteveNZ for all info.

Cheers,

Emin