Piston ring gap tolerance?

[Yohns Kustom Fabrikation]

Im putting together a 701 and need to know the ring gap tolerance. Also should both the upper and lower rings have the same gap?

 

[#ZERO]

They should both be the same around 0.014" to 0.024" depending on your piston type.

Also most engine builders will add some extra piston clearance for added heat from more compression, porting, race pipes, more timing, etc.

 

[Yohns Kustom Fabrikation]

Mine looks to be around .030 on the bottom ring and .060 on the top. I just honed the cylinders and they are in good shape. I guess my next question is where can I get some good reasonably priced std. rings?

 

[#ZERO]

If your ring gap is 0.060" on the top you're going to need more than just rings.

 

[Yohns Kustom Fabrikation]

Well I put the rings in the same spot in the bore to check them so i know ther is no varience there. Am I missing something or maybe going about checking improperly? i put the ring in the bore lined it all up evenly and checked the gap. Is this correct?

 

[crammit442]

Well I put the rings in the same spot in the bore to check them so i know ther is no varience there. Am I missing something or maybe going about checking improperly? i put the ring in the bore lined it all up evenly and checked the gap. Is this correct?

The easiest way is to use a piston to push the ring down into the bore so you can be sure it's square.

 

[Kaveman]

While you have it down go ahead and use a bore guage to measure cylinder bore and out of round. As 0 stated you probably need to have the cylinder bored.

 

[Yohns Kustom Fabrikation]

I checked the bore tonight and it is within factory limits. My bore however measures 81.54924mm rather than 81mm so this means my motor is .5 mm over stock, right?

 

[#ZERO]

I checked the bore tonight and it is within factory limits. My bore however measures 81.54924mm rather than 81mm so this means my motor is .5 mm over stock, right?

Whose factory limits??? :scratchchin:

It's time to get some new pistons and bore that cylinder. :twak:

How did you come up with 81.54924mm most digital cylinder bore gauges only go do to thousands of a millimeter? :thinking:

 

[Matt_E]

Heckuva gauge, that's how. :biggrin:

 

[DangerBoy]

I call BS on the measurement

I have "a heck of a gauge" and there is no way you are measuring down to less than a millionth of an inch

Db

 

[#ZERO]

Actually most digital bore gauges go down to 0.00005" or 0.00002" increments in inches but only .001 millimeters.

It must be one heckuva metric gauge. :Eyecrazy:

 

[DangerBoy]

Actually most digital bore gauges go down to 0.00005" or 0.00002" increments in inches but only .001 millimeters.

It must be one heckuva metric gauge. :Eyecrazy:

I took his mm measurements 5th digit being a 4 and assumed the counter moved by half that , has to move and count to display right ?,
so .00002mm would be .oooooo7 in inches or less than a millionth of an inch

Resolution of a gauge is always different than the accuracy, last didget us usually dropped
so a bore guage with a resolution of .00005 only has a accuracy of plus or minus .0001

lets see the linear temp movement of alum is .000013 per inch per degree F

he must have a temp controlled shop as well


But to answer his question before we thread jaked it
On a 701 mtr I like to run .016 in ring gap

 

[Matt_E]

I call BS on the measurement

I have "a heck of a gauge" and there is no way you are measuring down to less than a millionth of an inch

Db

Hence the > :biggrin: <

As in, a joke.

 

[Yohns Kustom Fabrikation]

Im using a standard non metric gauge and running it on a metric conversion chart. 3.2106" = 81.54924mm. And as far as spec im going by a factory Yamaha SJ Service Manual. I put some rings from another old 701 in the bore also and they had the proper gap. Is it possible I have std bore rings in a .5 mm over engine giving me such a large gap?

 

[SUPERTUNE]

I call BS on the measurement

I have "a heck of a gauge" and there is no way you are measuring down to less than a millionth of an inch

Db

Actually most digital bore gauges go down to 0.00005" or 0.00002" increments in inches but only .001 millimeters.

It must be one heckuva metric gauge. :Eyecrazy:

I think you guys should say your sorry about the comments you made on here on how he came up with his measurements!
HE DID IT THE ONLY WAY HE KNEW HOW, without having metric measuring equipment...

I would suggest in the future you guys, HELP him with his question and not take jabs at him for asking a question about the problem he was concerned with!

O.K. With that said, It's possible someone could have put std. rings in if they didn't measure and assumed the bore was std. size.
And yes they could have worn that badly over time. I have seen that before from mild rust build up on the cylinder wall between running/riding and every time you fire up after sitting, they wear quickly from scuffing the rust. Fogging engine, proper storage and running ski time to time in between rides with be a great help against this kind of ring wear.

 

[#ZERO]

Check the number on top of the piston and see if it's a definite .5mm oversize.

Also you can measure your piston at the mid skirt area and check it with your bore size to find the actual clearance.

I don't see anything wrong with the comments. oke:

 

[DangerBoy]

Ok, My bad
Instead of calling BS on the measurement, I should have asked him How he achieved his measurement, too often people are using a tape measure
he did state that the bore was honed and measured "within factory limits"
factory limit is 3.193 or 81.1mm so I questioned the accuracy

We both answered the original question

I have seen standard rings on oversize pistons far too many times also so that is a real possibility

classic speed , I apoligise if I offended you.

Db

 

[Yohns Kustom Fabrikation]

Its cool guys im just new to skis and trying to figure some stuff out thank you for your help. Ill try to get a metric gauge this weekend to make things a little easier.

 

[DangerBoy]

No need for a Metric guage .
take your inch measurement and devide by.03937
than Drop everything past the significant digit of the devises acuracy limit (not resolution)

:beerchug: