Discussion and technical advice the SW20 MR2. 3S-GTE, 3S-GE, 3S-FE etc
Anything and everything to do with maintenance, modifications and electrical is in here for the Mk2.
kev8611 wrote:Keep in mind, when ordering, if you were to get standard 86mm (if you can) you may run the risk of them being too tight/loose in your bores due to wear. I was advised not to buy pistons and expect them to fit perfect in the standard bore due to wear.
Engine builder should be measuring the bores for wear and ovality before ordering pistons.
Yeah sorry missed that bit out. but self explanitory.
Whats the chances of an 86mm fitting as it should in the standard bores?
I was told my bores were fine but got it bored to correct spec for 86.25's using a torque plate just to be sure. Little bit extra power aswell? without pushing the wall thickness of block past safe limits
If the bores are dimensionally perfect in all respects, then the chances of STD size pistons fitting is 100%.
IMO you cannot get the cylinders re-bored until you have the pistons in your hands, the machine shop will generally measure the pistons for you, and then rebore to the clearance that you specify (CP supply guidance on clearances). If you haven't had the cylinders rebored to 86.25 already then I would wait...
And as for power...0.25 is not going to make any real world difference! If you can stick at 86.0 then do it to retain as much material in the cylinder walls as possible.
IMO.
ashley wrote:IMO you cannot get the cylinders re-bored until you have the pistons in your hands, the machine shop will generally measure the pistons for you, and then rebore to the clearance that you specify (CP supply guidance on clearances). If you haven't had the cylinders rebored to 86.25 already then I would wait...
And as for power...0.25 is not going to make any real world difference! If you can stick at 86.0 then do it to retain as much material in the cylinder walls as possible.
IMO.
Bang on.
My machine shop will not repore without the pistons.
Lots of good info, thank you all very much. The block I am using is on a standard bore so if I can I would obviously not want to have to rebore to 86.25 as we all know there is a chance of cracking, even on a standard bore.
kev8611 wrote:regarding block cracking. iirc its due to wall thickness in some areas when running big power. not sure if heat cycles or mileage play a part?
My thoughts were if it has done a lot of miles if it was going to crack it would have by then, obviously running big power is tempting fate.
kev8611 wrote:imo 9 out of 10 blocks especially now with higher miles etc wont meet required clearances for 86mm cp's
kev8611 wrote:purely my opinion based on my own experience with my engine.
Sounds like you are extrapolating a 90% failure rate based on a single data point with one engine...interesting statistical method
Based on my experiences with my own engines (4 x 3SGE's) I would say 75% are still within original manufacturing dimensions (3 out of the 4).
But then I could have been lucky or unlucky with such a small sample size
ok i get the point. il keep my opinion to myself.
mr2rich. sorry to have caused any confusion to you. after all. peter and co are the specialists on here so anyone elses points are invalid
MR2 Rich wrote:Is a higher mileage block less likely to crack due to having done more heat cycles though (is that the word?)?
The cracking of the bores happens because the maximum cylinder pressure is taking place down in the bores and not in the cylinder head where it should be.
This is because too many engines are being built with too high a compression ratio for the fuel or boost being used. This results in the timing having to be retarded to stop detonation. This then gives the max pressure too far down the cylinder wall where there is lack of support.
Designer for turbo set ups on F1 cars, and Nitrous Oxide Systems of the USA in the 80s
kev8611 wrote:ok i get the point. il keep my opinion to myself.
mr2rich. sorry to have caused any confusion to you. after all. peter and co are the specialists on here so anyone elses points are invalid
opinions are fine, but you have to be open to challenge when throwing around statistics like that mate...all meant in good humour, apologies if I offended
MR2 Rich wrote:Is a higher mileage block less likely to crack due to having done more heat cycles though (is that the word?)?
The cracking of the bores happens because the maximum cylinder pressure is taking place down in the bores and not in the cylinder head where it should be.
This is because too many engines are being built with too high a compression ratio for the fuel or boost being used. This results in the timing having to be retarded to stop detonation. This then gives the max pressure too far down the cylinder wall where there is lack of support.
Except in cases like two we've had over the years where the engines were totally and utterly standard - no boost controllers to be seen. One had stock airbox.
One had hairline crack from around an inch down number 3 bore, the other cracked the deck between nos. 2 & 3 bores.
kev8611 wrote:ok i get the point. il keep my opinion to myself.
mr2rich. sorry to have caused any confusion to you. after all. peter and co are the specialists on here so anyone elses points are invalid
opinions are fine, but you have to be open to challenge when throwing around statistics like that mate...all meant in good humour, apologies if I offended
ok so in other words. whats the chances of going and buying a set of 86mm CP's and a standard blocks measurments being bang on for required clearances on the spec sheet down to the last ten thou?
