Another piston clearance question

[Tron]

Hey guys,

I have been doing a lot of searching and can't seem to come across max tolerances for piston clearance..

I de-glazed/honed mine and they are at .004" on each piston. Measured correctly.

I have new rings as well.

Is this too large of a gap? Do i really need to rebore?

The cylinders and pistons are both in good shape

 

[5twins]

I think that's right about at the max. It should work but it won't be the tightest engine around. You probably won't get standard sized rings to fit with the end gaps in spec. Go 1st oversize rings and file the end gaps to the low end of the spec. Next time you're in there, it will be time to bore it.

 

[Tron]

Next time im in there, it'll be 700cc hoos pistons, shell #1 cam, stronger springs, and a rephase.

Addict..

 

[retiredgentleman]

Tron;

Did you read the Yamaha Service Manual...............www.biker.net. The engine specs are there for all to read.

I agree with 5twins..................0.004" is borderline to not being acceptable.

Here is what I understand from the Service manual:

0.002" is good
0.005" is bad
You should not be able to insert a 0.004" feeler gauge on the thrust side.

On my engine re-build I had 0.003" clearance. so I just de-glazed, and used new stock rings. My engine has run just great ever since.

 

[Tron]

Thank you for the reply Retiredgentleman,

I do have the biker.net manual as well as 2-3 other ones in front of me at all times, but I guess am having troubles with conversions..

I not so sure a .0004" feeler guage would go in (cause of the width), as the pistons and cylinders were measured quite precisely with a micrometer.

Was your .003" measurement before or after deglazing?

Im thinking if .002-.003 is stock clearance, I could probably get away with it for a year or two until I get my performance parts together..

Love what happens when you go to simply replace a couple gaskets

 

[XSLeo]

In the Clymers book, page 70, the spec reads .0020 to .0022 inch standard, with a max of .0039. The best way to find these specs is to measure the pistons and cylinders. Slipping a feeler gauge between the piston and cylinder isn't as accurate.
Leo

 

[5twins]

Here's a neat little metric to inch converter I keep bookmarked in my "Favorites". Comes in very handy with these metric bikes .....

http://www.industrial-enclosures.com/html/conversion_mm_inch_2x4b.htm

 

[Tron]

.0039 max...to ride or not to ride...

Shit.

Agreed on the feeler guage Leo.

 

[retiredgentleman]

Thank you for the reply Retiredgentleman,

I do have the biker.net manual as well as 2-3 other ones in front of me at all times, but I guess am having troubles with conversions..

I not so sure a .0004" feeler guage would go in (cause of the width), as the pistons and cylinders were measured quite precisely with a micrometer.

Was your .003" measurement before or after deglazing?

Im thinking if .002-.003 is stock clearance, I could probably get away with it for a year or two until I get my performance parts together..

Love what happens when you go to simply replace a couple gaskets

My 0.003" was after de-glazing, but de-glazing does not remove much material, its just scratching up the surface.

Yeah, these are old engines, so you never know what you will find.

If you're on a budget (and who isn't?) , just go ahead and re-use the cylinders/pistons with new rings (as per 5twins advice), and I think your engine will run just fine. The worst thing might be a little piston slap noise, and maybe a little lower compression, but not enough to be of any concern.

 

[Tron]

thanks a bunch everyone.

I never had any compression issues with this motor before even with a leaky base and head gaskets. So I imagine it will only improve with new rings, valves and gaskets!
I did a light deglaze as well. Since I just got some stock sized rings in the mail I think I'll throw em on the pistons and take some measurements. if they are too far out of spec I'll grab some 1st over as per the above suggestion.

Thanks again everyone for the quick and knowledgable replies. I can't believe that three of the best gurus on the site just answered so quickly.

 

[5twins]

To check the rings, don't put them on the pistons, insert them into the bore and measure the end gap with a feeler gauge .....

Some tips for doing this - inserting a ring into the bore by laying it flat and trying to compress it into the hole is a pain. Instead, hold the ring perpendicular to the bore, gap down, and simply push it down in about 1/2" then rotate it in the bore to the horizontal position. To insure it's positioned squarely in the bore, seat it down in using a clean piston turned upside down. Push the ring down into the bore and align the bottom ring groove (oil ring) with the bore top all the way around. That will place the ring square in the bore about 1/2" to 3/4" down and it'll be ready to measure.

 

[YL82]

5twins,

In reference to your nice image and comments, this same process (end-gap measurement) is done for top ring, middle "wiper" ring and each of the 2 rails, correct?

Is the end gap to be checked at the same level in the bore for each of the above rings?

One suggestion I saw on youtube recently is to have the 2nd (wiper) ring installed on the piston that you will be inverting into the bore until the ring catches ensuring that the ring is evenly pushed down into piston for measurement.

 

[5twins]

Yes, you measure all the rings the same way. I set them all about the same distance down, maybe an inch, where ever that oil ring groove puts them when it's even with the top of the bore. I never heard of having a ring in the piston to act as a stop but that sounds like a good idea. In fact, I may clean up an old piston and old ring and make myself a new "special tool", lol.

 

[YL82]

Hey, you gotta love the concept of a free, homemade tool!

Here is the link to the YouTube video that I was referring to. Also shows use of a piston ring filer tool, a Proform brand, I believe.

 

[YL82]

Question withdrawn. Already answered on other thread....