Assessment of My Cylinder Bore/Piston Measurements

[YL82]

Original Measurements

1976 XS650C, ~14,000 miles.

Stock Bore: 75.004 mm (2.95290"). "004" scribed into both cylinders near bottom.

Pistons: 74.953 mm (2.9509") "953" printed atop both Piston Crowns.

Original Piston Clearance: 0.051 mm or 0.002"


Current Measurements

Left & Right (Measurements were identical on Left & Right)

TOP (1st measurement taken parallel to crankshaft, 2nd taken perpendicular...)
2.9544"
2.9544"

MIDDLE:
2.9539"
2.9544"

BOTTOM:
2.9530"
2.9530"

OD PISTON Measurements @ Piston Skirt: Taken 10mm up from bottom edges of the pistons.

PISTONS: 74.955 mm or 2.951" for both L & R.

Crunching The Numbers

I calculate the Piston to Bore Clearance to be:

2.9530" (Min. Bore) - 2.9510" (Max. Piston). = 0.002"

Cylinder Bore Taper: 0.0014"

I'm thinking that I just need to hone the cylinders to remove glaze, use my Pistons (have em' cleaned up real shiny) and go with new 1st OS Rings and grind them down to proper ring gap.

No, I've not used a feeler gauge. Was planning to wait until I get in new rings.

Comments?

 

[XSLeo]

You listed the bore measurements, how about the piston measurments? You can't calulate the clearance without both the bore AND piston measurements.
The markings on the pistons and sleeves were what they were when new. They have nothing to do with now. Measure the pistons on the skirts perpendicular to the pins up about 1/2 inch from the bottom. That's were the wear the most.
Leo

 

[YL82]

Piston measurements added to above data.

Thanks kindly for catching that omission, XSLeo. My bad.

 

[XSLeo]

I just reread your first post. Your worn parts are bigger than they were new. I might suggest you remeasure. Worn parts don't grow, they shrink.
Leo

 

[YL82]

I'll double check my nos. it's a bit tedious and easy to make errors showing both inches and millimeters...

I think my numbers are ok. I just presented the numbers and especially the Units very poorly. For the original piston specs, I listed inches first and then mm whereas for the current specs I listed mm first, then inches. Confusion may have come from 74.953 mm and 2.951 inches being shown for before and after measurements giving the false impression of a growing piston.

Bottom line is that the pistons have worn by .002 mm. Or: .0001 inches.

My sincere apologies for the piss poor presentation of the numbers....

 

[5twins]

The bores will grow, the pistons will get smaller. Yes, I think you can get by with a hone and new rings this time. Next time you will want (and probably need) to bore it.

 

[YL82]

Thanks kindly, 5twins. I lack one of those nifty ring grinders that I've seen on other posts of yours. Are these cost prohibitive or otherwise hard to find?

What are other alternatives to grinding rings down? A Dremel?

 

[5twins]

I don't think they're cost prohibitive. I think you can find them for about $35. I got mine years ago, before the internet, and bought it locally from a tool store. I think it cost me near $50 but I use it all the time so it's paid for itself many times over. Filing rings by hand totally sucks and it's easy to break one.

Wait, I think I spoke too soon. It seems they are still about $50. Don't lose hope though, shop eBay .....

http://www.ebay.com/itm/K-D-Tools-8...Car-Automotive-Hand-Tools-Parts-/281118117528

http://www.ebay.com/itm/K-D-Tools-8...e-USA-Car-Automotive-Hand-Tools-/121122371901

This is the exact same one I have.

 

[YL82]

Hey, I can both afford and justify spending more $$ on nifty tools since I'll be saving $150 or so by not having to buy new Pistons from Mikesxs.

Can I assume that one can buy replacement discs?

I hate to totally go off topic, but do you recommend going with SST Valves from MikesXS over buying OEM (new OLD STOCK) ones from EBay?

Thanks for the links!!

 

[5twins]

Yes, you can get replacement discs, probably right at one of the local auto parts stores because this is a K-D brand tool. They make a ton of automotive specialty tools and most auto parts stores have some. They would probably need to order it from the K-D catalog for you but I'm sure they could.

I've heard some bad things about Mike's stainless valves (like they're junk). You're probably better off with originals. But why are you replacing them? I've only replaced one Yamaha valve in my life and that's because it was bent. And I replaced it with a good used one to boot, lol.

 

[YL82]

Bent Left Intake Valve. I've already picked up a pair of OEM Intake Valves from Ebay for $50 from a seller named jgroom888. I've bought some "hard to find" OEM parts there.

Actually, I checked my Exhaust Valves in a drill and the seem to run true. Plus, I've cleaned them up pretty good and will likely reuse them to save $$.... So I can buy more tools, I guess..

As to my question, I think I had seen some comments somewhere that played up Mikesxs valves being stainless steel and a must have...Refer to "Valve Lapping question for a Fresh Build!" thread

I have noticed that OEM exhaust valves are around $50 EACH on Ebay for what some call new old stock. This is a rhetorical question I suppose, but why can I get a pair of OEM Intake Valves off EBay for $50 total?

 

[5twins]

For some reason, intake valves are cheap, exhaust valves cost more. I don't know why, they're smaller, lol. Check the prices on new O.E.M. ones, you'll see. That one I replaced was in a Virago. It was an intake and we could have gotten a new one for like $35. The exhausts were over $50 each.

 

[YL82]

I don't think they're cost prohibitive. I think you can find them for about $35. I got mine years ago, before the internet, and bought it locally from a tool store. I think it cost me near $50 but I use it all the time so it's paid for itself many times over. Filing rings by hand totally sucks and it's easy to break one.

Wait, I think I spoke too soon. It seems they are still about $50. Don't lose hope though, shop eBay .....

http://www.ebay.com/itm/K-D-Tools-8...Car-Automotive-Hand-Tools-Parts-/281118117528

http://www.ebay.com/itm/K-D-Tools-8...e-USA-Car-Automotive-Hand-Tools-/121122371901

This is the exact same one I have.

5twins, I ended up winning a K-D Tools Piston Ring Filer from the 2nd eBay auction you listed. Thanks kindly for the eBay links!! Won bid for $39 + $8.99 Shipping. Not bad. As always, there was a flurry of bidding at the end by another bidder, but my single max bid held up by $2 before time ran out. Probably another Forum member that also saw your listings on here. LOL.

I'm looking for a source that has replacement cutters (PN #872). Per your suggestion, I'll check with local auto parts stores....

I also found that AdvanceAuto sells this same tool new for $83.00. They also offer a comparable ProForm model for $56.00.

http://shop.advanceautoparts.com/we...-tools_22981182-p?searchTerm=piston+ring+tool

 

[5twins]

Here's a nice little PDF from Wiseco on ring end gap and installation you can download. I use a few tips from it but don't subscribe to all they say .....

http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

The way they show the hand grinder being used is not how the included instructions tell you to do it. The instructions tell you to place the ring on the other side of those 2 "buttons" like so .....

Also, their install diagram for the end gap spacings appears to be for a car motor. They place some end gaps over the piston pin which I've always read is a no-no. They also show the "Engine Front" arrow pointing in line with the piston pin. That doesn't happen on many bikes. I took their diagram and "modded" it to suit our needs .....

They also recommend filing only one side of the ring. I file both. They say that filing one side allows you to use the other as a reference to help keep the ends square to each other. If you sight down over the blade and make sure the ring ends align with each other, you will get them square.

A couple of their tips I do follow are setting the oil rail gaps at .010" (Yamaha says .012") and making the middle ring gap slightly larger than the top. Yamaha specs .008" minimum for the top 2 rings. I set mine, from the top down, at about .008", .009", and .010".

 

[YL82]

Awesome information, 5twins!

Update: I ordered a couple of replacement cutters from one of the websites (actually, I think both sites the very same parent company out of Seattle, WA).

Got a call from where I ordered and guy said the item had been Discontinued, so they cancelled my order. I'm gong to Edit my previous post and remove those sites....

Not sure what condition my eBay filer and cutter will be in, but I'm back on the hunt for a replacement cutter.

Thanks again for the assistance.

 

[5twins]

I looked at the auction pics and yours looks in pretty good shape. The grinding disc is pretty long lasting. I've done probably close to 50 rings with mine and it still works fine. You can clean the disc if the area that contacts the rings appears to be getting "clogged" with one of those little detail wire brushes.

 

[xjwmx]

For some reason, intake valves are cheap, exhaust valves cost more. I don't know why, they're smaller, lol. Check the prices on new O.E.M. ones, you'll see.

It's because exhaust valves are the ones that burn up. The intake ones get constant cooling. Likewise left side covers on Specials are more expensive than righties, I assume because they get taken off more frequently because of the connectors under them and so are more likely to get the little post broken off. GoldToothGarage has a good fix for a broken post btw.

 

[YL82]

Agreed. I'll just check it out upon arrival. I've only got 1 bike, so I'm likely good to go for the foreseeable future.

My inclination is to go with OEM RINGS (1st OS).

A good choice or should I go with MikesXS (05-0018)?

 

[YL82]

Interesting, xjwmx.

Along those lines, is it accurate to state that Intake Valves tend to get bent more so than Exhaust valves? That may be my incorrect perception based upon very little data and experience and biased due to my bent Left Intake Valve and others that I've read about being bent Intakes.

 

[xjwmx]

^Probably not. But if you saw enough of it to be significant then it might be because the intake valve is less likely to get changed and so gets more time to accumulate a good bend...