what are allowed cylinder-measurement tolerance?

This is a hypothetical example, if say your cylinder bore is ideally 70.5mm -- and you hone it -- and after honing it reads:

EXAMPLE #1: 70.58mm

EXAMPLE #2: 70.42mm


What I'm *really* asking here is, what is the 'working range' of tolerance in the bore measurement, if the current bore, IDEALLY, is supposed to be 70.5mm?

Ie. for an in-service engine, what is the range of measurement around a base of 70.5mm that a mechanic would say, "hmm, 70.42mm, close enough" or "well, it's 70.58mm, that's close enough" ?`

I believe the rest of the question is what are the sizes of EACH piston that is fitted to each cylinder ???
If a given piston is exactly 70.5 mm what is the spec for clearence between the piston and the bore ??
My point is you need to have each piston matched to a bore.
I bought MTC pistons from Joe Hooper at Pit Stop awhile back. Each piston varies in size so Joe Bores or hones each one for the proper fit which also can vary based on how a motor will be used.
Just my .02
Dave

Street Fighter LTD wrote: I believe the rest of the question is what are the sizes of EACH piston that is fitted to each cylinder ???
If a given piston is exactly 70.5 mm what is the spec for clearence between the piston and the bore ??
My point is you need to have each piston matched to a bore.
I bought MTC pistons from Joe Hooper at Pit Stop awhile back. Each piston varies in size so Joe Bores or hones each one for the proper fit which also can vary based on how a motor will be used.
Just my .02
Dave

Oh 100% agree on that. Last time I had a bore job done, this was back in 1981 on the very first kz1000 I owned, I bought the new pistons and handed them to the machinist and he matched them up, by that I mean he did the boring to match my new pistons.


But my question is a bit different. This is strictly about honing only, and wanting to keep using the same original piston -- after a honing job on a "supposedly" 70.5mm cylinder bore -- if the cylinder originally measured "exactly" 70.5mm and then you honed it and it now measures 70.58 -- I realize that might be an 'aggressive hone' but THIS IS HYPOTHETICAL --


what I'm asking is, what is the after-honing tolerance? If you keep your original piston and the pre-hone read 70.5mm, what is the *maximum* after-honing bore measurement a mechanic will say "close enough" to?

Your original piston worked fine in the 70.5mm bore, now you hone that cylinder, what is the max new *after-hone* measurement? Is 70.58mm okay? Is 70.6mm okay? Or is the maximum tolerance in this hypothetical example 70.53mm? What?

The answer is the same. The service manual for my kz650 shows the maximum piston to cylinder wall clearance - this is the number that matters as the pistons will vary slightly. From this you can determine what the maximum bore for *your* pistons will be.

DoubleDub wrote: The answer is the same. The service manual for my kz650 shows the maximum piston to cylinder wall clearance - this is the number that matters as the pistons will vary slightly. From this you can determine what the maximum bore for *your* pistons will be.

Is the maximum piston to cylinder wall clearance different for, say, a kz1000 and your kz650? My expectation was it would be about the same number since these are the same company?

cylinder wall to piston clearance varies by bore size,piston material,application.

a kz 1000 with .003 thsnths cyl to wall clearance is okay.

.007 thsnths cyl to wall clearance you can prolly hear the skirts slap.

.010 thsnths cyl to wall clearance is worn out.

ring end gap is critical.

those are the rules i use for my thumb .
leon

531blackbanshee wrote: cylinder wall to piston clearance varies by bore size,piston material,application.

a kz 1000 with .003 thsnths cyl to wall clearance is okay.

.007 thsnths cyl to wall clearance you can prolly hear the skirts slap.

.010 thsnths cyl to wall clearance is worn out.

ring end gap is critical.

those are the rules i use for my thumb .
leon

Good deal man, excellent. Since my digital caliper reads in mm, I used an online inches-to-mm converter and found this:

'Okay clearance' of 0.003in = 0.076200mm piston-to-cylinder-wall

'Can hear the piston skirts slapping' of 0.007in = 0.17780mm

'Worn-out clearance' of 0.01in = 0.25400mm


This is good stuff, one other question -- if you do a GOOD hone, ie. not too much off, you just do a great job, how much metal are you taking off -- how much will your cylinder bore measure grow?

I'm asking this *independent* of the old piston, I don't care if I have to get a new piston, I'm asking if you have say a 70.5mm bore then you hone it, what is the new reading if all you needed to do was break the glaze? Could it go up to 70.6mm? Is that possible?

a "good hone" will remove right around .001 thsnth.

a "glaze breaking" hone will remove less than .0005 thsnth.

leon

531blackbanshee wrote: a "good hone" will remove right around .001 thsnth.

a "glaze breaking" hone will remove less than .0005 thsnth.

leon

Thanks there 531, I have no 'working knowledge' of this stuff, the honing instructions I could find said 'hone it for 5 to 20 seconds' and I'm like 'wtf', surely there's a before/after measurement 'wisdom' or 'benchmark' you can go by -- I don't want to just drop my honing tool into the bore and look at the clock. I wanted to measure the before/after to know where I am -- thanks man.

no problem.
i hope the info helps you.

i have a mitutoyo bore gage that i use.

that way you can measure egg,taper etc.

leon

When I had my 1075 done the machine shop didnt want my cylinder till new pistons came in.....

He then measured each piston to get the Outer Dia. He then bored the cyclinder to get close to recommened max piston dia...what ever the application called for.

He then honed the cyclinder to set the proper clearance and aid in piston ring seating.

You will need to state what the recommended piston/bore clearance and wear limits are at 70.5 mm to get the answer you want.
If you have these figures and piston measurement for that cylinder then you will have answered your own question.
The clearance figure is to allow for expansion depending on what use the engine is to be put too.
If running a race engine or turbo for example you will need a larger clearance to account for the increased heat generated, this clearance may be on the wide side for normally aspirated but perfectly fine for the turbo application.