did my machine shop overshoot these bore sizes?

[CDNTX650]

Stock bores originally. Got a deal on second over pistons and rings. So I went with it. My ring end gaps when I checked were at .014 for the top ring and the second second ring was a little tighter. Never checked oils.

Thought thought that was odd as last engines rings seemed tighter. So put piston into bore and I can get a .004 feeler guage about half way down on the thrust side of the piston from the top.

I had the proper piston to bore clearance for them...they did my last bores...never did the feeler guage thing on my last ones though...but all seems well and has good compression. Anyways.

.0020 to .0022. Is correct is it not....

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[TwoManyXS1Bs]

Make sure everything is super clean, light oil on piston and cyl walls. Lay a 0.002" gauge along the side, hanging down from the top. Insert piston, upside down, skirt aligned with gauge. Lower piston until skirt bottoms are flush with cylinder top. Should feel slight drag when withdrawing gauge. Try again with 0.0025", should be tighter drag. Again with 0.003", piston may not fit, very tight gauge withdrawal.

Widest part of piston is about 1/2" from bottom, top is slightly smaller to accommodate thermal expansion...

 

[chizler62]

Not advisable to use a shim between your piston and cylinder wall. Depending on what boring bar they used its often a ledge forward the time edge of the wall.

The best was is to Mic piston 12mms up shirt and t-gauge the cylinder top middle bottom both axis.
If you don't have the tools then I'd suggest paying a visit with the cylinders and ask then to do it in front of you. It takes 5 minutes

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[CDNTX650]

Make sure everything is super clean, light oil on piston and cyl walls. Lay a 0.002" gauge along the side, hanging down from the top. Insert piston, upside down, skirt aligned with gauge. Lower piston until skirt bottoms are flush with cylinder top. Should feel slight drag when withdrawing gauge. Try again with 0.0025", should be tighter drag. Again with 0.003", piston may not fit, very tight gauge withdrawal.

Widest part of piston is about 1/2" from bottom, top is slightly smaller to accommodate thermal expansion...

Thanks. .003 was a no go. Got it together today. Made another silly mistake with my tq wrench.....set it to 40 for head bolts....luckily caught myself way before i got carried away and tried to the them that far. All acorns set to 30.

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[chizler62]

Sticking a shim in your cylinder to check clearance is REALLY poor advice!
amazed at some of the stuff on here.

 

[figure8]

Let me go grab my popcorn......

 

[CDNTX650]

Sticking a shim in your cylinder to check clearance is REALLY poor advice!
amazed at some of the stuff on here.

seems good enough to be in the factory service manual straight from yamaha as a rough check. The shop that has done 3 for me and is a very reputable shop in town so I'm not to worried about it.

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[5twins]

Yes, it's a long time practice. Now, greasing float needles on the other hand has me scratching my head, lol - amazed at some of the stuff on here indeed.

 

[chizler62]

If they did such a great job why are you posting on here looking for help?


If you don't believe dabbing grease on the float needle is a long taught practice by professionals then go ask a technician at your local motorcycle dealership.

 

[chizler62]

If someone could show me a Yamaha manual that shows you measuring piston to cylinder clearance will a shim or feeler gauge(not ring end gap), I'll eat crow.

I'll be honest and say I've bored cylinders for well over 20 years and never read a manual in that section in any manual other than just for specs

 

[CDNTX650]

I only asked because I didn't realize either that pistons have a taper for thermal expansion so they are a bit narrower at the top. I have never checked any of my bores I have got after boring till now. Probably won't again either.


It seems to be all over as a rough check. Just because you haven't heard of it doesn't mean it doesn't exist.

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[ippytattoo]

chizler, I can't show you in the factory service manual but I can quote from the Haynes manual, copyright 1997, Page 38 section 19 paragraph 3:

"If an internal micrometer is not available , the amount of wear can be checked by inserting each piston in turn (without rings) into the bore with which it was previously associated. If it is possible to insert a 0.004 inch (0.101mm) feeler gauge between the piston and the cylinder wall on the thrust side , remedial action must be taken."

 

[hard_y_rd]

chizler, I can't show you in the factory service manual but I can quote from the Haynes manual, copyright 1997, Page 38 section 19 paragraph 3:

"If an internal micrometer is not available , the amount of wear can be checked by inserting each piston in turn (without rings) into the bore with which it was previously associated. If it is possible to insert a 0.004 inch (0.101mm) feeler gauge between the piston and the cylinder wall on the thrust side , remedial action must be taken."

Yummm, crow tastes good. LOl

 

[TwoManyXS1Bs]

The use of feeler gauges for bore checking is mostly old-school practice, primarily used on freshly bored cylinders. The service manuals are geared towards the mechanic service procedures, and will reference the use of micrometers and bore gauges to allow the mechanic to determine the wear/taper/egg-shape of cylinders to assess the need for cylinder boring. The service manuals don't enter the arena of cylinder boring processes as that is in the realm of the machine shop. Just like Ford and Chevy manuals don't cover repairs to Delco radios, not a mechanic thing.

CDNTX650 has a freshly bored cylinder. So, (unless the machine shop has poor condition boring tools), the need to measure taper/egg/out-of-round/ring-ridge & etc isn't necessary, and a quick/confirming check with ribbon-type feeler gauges was a standard practice.

So, in essense, these are two different worlds.
The mechanic assessing a fresh teardown for the need for machine shop work.
Machine shop practices, post machining inspections.

Nowadays, with the availability of 'previously cost prohibitive' measuring equipment, I can see how commonly accepted old-school practices can be challenged.

http://www.xs650.com/forum/showthread.php?t=27476

But, these are old technology bikes that don't use or require new technology stringent standards. Kinda like the continued practice of repacking old/vintage steam engine sealing surfaces with packing rope.

 

[chizler62]

Yummm, crow tastes good. LOl

Huge difference from "Yamaha manual" and a Haynes copy and paste for 86 different models manual.

Even with a kwik way boring bar you need to use snap gauges and a mic. post boring and honing. Especially on two strokes that you have to relieve ports and chamfer.
1. Honing process can easily taper the cylinder.
2. heat and bit deflection during boring will actually machine a taper to begin with.
3. Speeds are only set for one speed and don't vary during the cut. You can not compensate for the skirt that has "no heat sink" behind it. That's one reason you bore the cylinder upside down.
4. You can cut .060" a pass. which is a ton.

If an average machine shop does boring their Bridgeport typically only has a 5" down feed and can't do it. So they do it on an engine lathe. Using the lathe references the lining and not the gasket surfaces. Accuracy is diminished. I've seen where machine shops, that do auto boring, will not remember the wall thickness while honing and over heat the bottom of the skirt and it'll taper the cylinder slightly.

In short. I know that old school car guys would use shims to check clearances. The piston radius is typically much larger than a motorcycle. You can increase the accuracy if you cut the width of the feeler gauge. But, you could spend less than $100 and buy the tools to check it properly.

Kid that works for me just said he bought snap gauges $15, Bore gauge $65 and a 3pc 1-3" mic set for $39.95

 

[TwoManyXS1Bs]

...If an average machine shop does boring their Bridgeport typically only has a 5" down feed and can't do it. So they do it on an engine lathe. Using the lathe references the lining and not the gasket surfaces. Accuracy is diminished. I've seen where machine shops, that do auto boring, will not remember the wall thickness while honing and over heat the bottom of the skirt and it'll taper the cylinder slightly...

Oh, gawd! Even THAT was not an accepted practice back then. Shops like that should be blacklisted...

 

[G_YamTech_314]

Not advisable to use a shim between your piston and cylinder wall. Depending on what boring bar they used its often a ledge forward the time edge of the wall.

The best was is to Mic piston 12mms up shirt and t-gauge the cylinder top middle bottom both axis.
If you don't have the tools then I'd suggest paying a visit with the cylinders and ask then to do it in front of you. It takes 5 minutes

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This will save a cylinders life. X and Y axis measurements, top middle bottom. This was a lot of fun to learn in school. Pain in the butt at first to set the tools up, but by far the best way to get accurate piston cylinder clearance. I cringe at the thought of using a feeler gauge between pistons lol.

Here’s a pic of a measurement template we used when I was in school. Hope this helps someone