Bore question!!

[98mitsubishigst]

Okay so i need .20 bored pistons...

Now i found a set of pistons.. and it says THESE PISTONS ARE AVALABLE IN STD (85MM BORE), 85.5mm, AND 86mm.


Now... What does this mean. im so confused!

 

[1992awdlaser]

You need .02" over, not .20" over. Stock bore is 85MM. 85.5MM is .02" over. There are 25.4 mm in an inch.

.02" X 25.4MM = .50MM Over +85MM stock bore= 85.5MM final bore.

 

[98mitsubishigst]

i ment to put .02 . thank you very much tho =) love the help on this siteee

 

[Boomdeeze]

Sorry for bringing up an old thread but isn't the stock bore on the block 85.5 mm and the stock pistons 85mm? I read on a website that after a .02 bore that the head gasket you need is the 86mm Cometic head gasket. Is this correct? I just got my block bored .02 and am about to buy the head gasket and don't want to buy the wrong one.

 

[95blackGsTurbo]

The stock bore on the block is 85.5mm. The stock pistons are 85mm so if you get a .02 bore the block will now be 86mm but you will buy 85.5mm pistons and the piston rings fill the rest. The way its described on here make it sound like the bore on the block is 85.5mm when thats the pistons after a .02 bore. So with the .02 bore the head gasket you will need will be 86mm but the pistons will be 85.5 as stated above.

No. As was already clearly stated the stock bore is 85mm. .020" over is 85.5mm not 86mm. The piston is almost exactly the size of the bore. That is why piston to wall clearance is so thin. Typical clearance between the piston and wall on a motor build is .0045". So essentially the piston is the same size as the bore. Please check your facts before posting. We don't need to confuse anyone.

 

[95blackGsTurbo]

Sorry for bringing up an old thread but isn't the stock bore on the block 85.5 mm and the stock pistons 85mm? I read on a website that after a .02 bore that the head gasket you need is the 86mm Cometic head gasket. Is this correct? I just got my block bored .02 and am about to buy the head gasket and don't want to buy the wrong one.

Now after that post I can clarify. Whatever you bore the block to is the pistons you get. They can't bore the block anyways until they have the pistons to measure piston to wall clearance. Even going .020" over you can use a Cometic 86mm head gasket even though your bored is 85.5mm. This is a very common thing to do.

 

[Boomdeeze]

Ok thanks sorry for that confusion but it is mentioned in another forum wrong so thank u for clearing that up.

 

[Rob10_99]

I'm running an 85mm HG with .020 over with no issues so far =) But I have 3 extras and one MLS sitting there waiting for their shot.