Topic: serious white smoke after big bore

[DMcD]

Hondaman, just out of curiosity can you clarify for me, if 0.001 clearance means the bore is 0.001 bigger than the piston, or is the bore 0.002 larger than the piston, to allow 0.001 clearance all around?

Thanks DMcD

[TurboD]

.001 clearance means the bore would be .001 bigger than the piston.

[Retro Rocket]

Hondaman, just out of curiosity can you clarify for me, if 0.001 clearance means the bore is 0.001 bigger than the piston, or is the bore 0.002 larger than the piston, to allow 0.001 clearance all around?

Thanks DMcD

Thats correct, the .001 gap is all round the piston, so if you were to push the piston hard up against one side of the bore{without rings on} there would be a .002 gap on the other side, this is what you meant isn't it..?

[madmtnmotors]

.001 clearance means the bore would be .001 bigger than the piston.

Hondaman, just out of curiosity can you clarify for me, if 0.001 clearance means the bore is 0.001 bigger than the piston, or is the bore 0.002 larger than the piston, to allow 0.001 clearance all around?

Thanks DMcD

Thats correct, the .001 gap is all round the piston, so if you were to push the piston hard up against one side of the bore{without rings on} there would be a .002 gap on the other side, this is what you meant isn't it..?

Excuse my previous grammar, they weren't so much arguing about how to measure, but whether (for example) a 4" piston specced to have 0.002" clearance would mean a 4.002" bore to have 0.002" at one side, or a 4.004" bore to allow 0.002" all around.

Both argued they were right, and had been building engines for many years, and teaching others to do so.

Even engine builder's can't agree!

[DMcD]

Even engine builder's can't agree!

 

If you want an opinion, the internet is the place to get it!

[johno]

Their may be opinions on what is an optimum clearance, but any qualified automotive engineer in the universe will know there is only one way to determine piston clearance.    If the method was debatable there would be total confusion all over the world at machine shops , car and bike factories etc alike..........as far as I'm aware there is no world confusion so there must only be one way 

[NickO]

Their may be opinions on what is an optimum clearance, but any qualified automotive engineer in the universe will know there is only one way to determine piston clearance.    If the method was debatable there would be total confusion all over the world at machine shops , car and bike factories etc alike..........as far as I'm aware there is no world confusion so there must only be one way 

I assume by the above, you mean ØBore - ØPiston = Clearance (i.e. 0.001")?

[Jim F]

.001 total clearance or .0005 per side

[TurboD]

There is no opinion to this... A .001 clearance means that you have a cylinder that is .001 larger than the piston. Any and every machine shop or race engine builder that I have ever talked with in my 40 years of building race engines has always measured this way.

[joe p]

Jim F and TurboD are perfectly correct.

[madmtnmotors]

.001 total clearance or .0005 per side

There is no opinion to this... A .001 clearance means that you have a cylinder that is .001 larger than the piston. Any and every machine shop or race engine builder that I have ever talked with in my 40 years of building race engines has always measured this way.

Jim F and TurboD are perfectly correct.

That has always been my understanding. 

[Jim F]

There is no opinion to this... A .001 clearance means that you have a cylinder that is .001 larger than the piston. Any and every machine shop or race engine builder that I have ever talked with in my 40 years of building race engines has always measured this way.

yes yes yes and another yes
if they are worth there salt, they should know what this is
Jim

[PeWe]

Good to clearify the piston vs bore clearance. One confusing part for me is the inch vs mm. The clearance has small numbers so .001 total clearance or .0005 per side
--> will be the numbers in " x 25.4mm
--> .0254mm total clearance or .0127mm per side.
Some additional hone will make it too wide rather quick, right? 

I did not meaure the bores at my last rebuild. Found NOS  65mm cast pistons to replace my old working 65mm. Honed with flex hone 240 grit and done! No smoke or oil smoke nor smell when driving, acceleration or heavy deceleration.
I reused the old pistons 3 piece oil rings when the NOS ring was 1 piece...

[Jim F]

another thing you have to be careful of is that, The tighter the clearance you have,
the better the honing needs to be as far as keeping the bores dead straight.
just another 2 cents to think about.

\Jim

[DMcD]

Cheers everyone for clearing that up for me, makes more sense now, so my 0.002 clearance will actually mean there is only 0.001 between the piston and bore during operation.

Looking forward to work tomorrow, to bore my colleagues with my new-found knowledge.

[HondaMan]

There is no opinion to this... A .001 clearance means that you have a cylinder that is .001 larger than the piston. Any and every machine shop or race engine builder that I have ever talked with in my 40 years of building race engines has always measured this way.

Sadly, I can name one in Denver who doesn't think this way...


...some people's kids...

[Big Jay]

.001" total clearance on an ART style cast piston is fine. Have done hundreds of them. I think the OP had an oil ring expander overlapped.