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Discussion Starter #1
Hi

I am rebuilding my 2.0 TS engine. The pistons are abit scuffed on the side. So thought id go take out the rods and piston of my spare 155 2.0 TS altho each part have different size, together they should add up to the same as 75?. The 155 pistons also has scuff marks, but the ring grooves are tighter.

Should i put in the 155 rods and pistons?. they are 120grams lighter. worth it?

Would it be bad to mix up these parts?. used pistons in used liners.
 

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Is the 155 engine an 8 or 16 valve? Nothing intrinsically wrong with using used pistons/liners, as long as there are no scores and the rings are good or you replace the rings. If it's an 8 valve they should be the same bore/ stroke as the 75 as far as I know, but you need to do some really accurate measurements to verify this

also you would potentially need to re-balance the crank
 

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Discussion Starter #3
Is the 155 engine an 8 or 16 valve? Nothing intrinsically wrong with using used pistons/liners, as long as there are no scores and the rings are good or you replace the rings. If it's an 8 valve they should be the same bore/ stroke as the 75 as far as I know, but you need to do some really accurate measurements to verify this

also you would potentially need to re-balance the crank
8v ofcourse ;).
No scores to see on the liners. But the pistons.
75 --- 155




Got new rings, bearings, etc.
But pondering about, if i should try the 155 rods/piston, now that i have them. ligther piston means i can rev higher?, but no other benefit?

Already been some talk here, and other places about it. But none who wanted to do quiete what i have in mind. (use both).

some good pics of differance. 164, but its the same.
http://www.alfabb.com/bb/forums/engine-conversions/165414-ts-engine-75-milano-vs-164-big-difference-same-engine.html
 

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it there the same distance from the top of the piston to the centre of the gudgeon pin hole the same? looks very close at least. if so, it looks like they have just removed some mass below the gudgeon pin, which would not affect the combustion chamber geometry at all. Are the rods the same length between 155 and 75?

The lighter pistons would only allow the engine to accellerate up to speed quicker, not rev any higher, the limit of revs is mostly due to the slow brain of the Motronic ECU. Bear in mind this would also lose revs quicker, which affects shifting, but the effect I think would be less than, say, lightening the flywheel
 

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Discussion Starter #5
it there the same distance from the top of the piston to the centre of the gudgeon pin hole the same? looks very close at least. if so, it looks like they have just removed some mass below the gudgeon pin, which would not affect the combustion chamber geometry at all. Are the rods the same length between 155 and 75?

The lighter pistons would only allow the engine to accellerate up to speed quicker, not rev any higher, the limit of revs is mostly due to the slow brain of the Motronic ECU. Bear in mind this would also lose revs quicker, which affects shifting, but the effect I think would be less than, say, lightening the flywheel
I was sure the 155 rods only were 2mm shorter, but after a "crude" measurment, they are 3mm shorter.

So.
155 rods 3 mm shorter than 75. same weight
155 piston. (hard to get measurement with my tools). but just about 2.40mm taller than 75.

better accellaration, i wouldnt mind that.
 

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by your measurements, the total length of 155 rod + piston would be .6mm less than the 75, so it would decrease compression ratio, as the piston would be lower in the cylinder at TDC. Also, the 155 engine has a different stroke to the 75 ( 155 stroke 90mm, 75 strike 88.5mm ), which would explain the difference in sizing. the 155 engine is 1995cc displacement, the 75 is 1962cc

also in reference to the 155 piston being 2.4 mm taller, is that the height from top of piston to gudgeon pin?
 

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what may be interesting, is to see if the 155 piston could be machined back to use with 75 rods as a high-compression piston. I think that without machining, the piston would hit the valves, but if you could mill down the top, it might work, and would be even lighter
 

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Discussion Starter #8 (Edited)
by your measurements, the total length of 155 rod + piston would be .6mm less than the 75, so it would decrease compression ratio, as the piston would be lower in the cylinder at TDC. Also, the 155 engine has a different stroke to the 75 ( 155 stroke 90mm, 75 strike 88.5mm ), which would explain the difference in sizing. the 155 engine is 1995cc displacement, the 75 is 1962cc

also in reference to the 155 piston being 2.4 mm taller, is that the height from top of piston to gudgeon pin?
Yes, that is what i meant. Just had the both 75 and 155 setup installed. 155 is 0.40mm further away from the deck. so all the numbers ads up.

I should proberly stop fooling around and install the original pistons. All who i spoke to about havent exactly said that it sounds like an good idea. :D
 
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