cylinder, piston replacement choices, Poll!

Which way are you likely to (done it) go?

  • cruzin image 2nd over, local bore +-$200

    Votes: 6 25.0%
  • cruzing image 706cc kit, local bore +- $250

    Votes: 7 29.2%
  • 750 kit from YamahaXS650 +- $500 when they're gone they're gone

    Votes: 10 41.7%
  • 750 kit from MikesXS +- $650

    Votes: 1 4.2%
  • Hoos- JE or Wisco pistons, cylinder service, head rework +-$1500?

    Votes: 6 25.0%
  • Hone the cylinder, sand the pistons put in new rings +-$100

    Votes: 4 16.7%

  • Total voters
    24
Yamaha manufactured the barrels at a light interference fit. The different thermal expansion rate between steel and aluminum is enough to make it a slip fit at 200F.
Hmm. So what is the operating temperature for a cylinder? Water often seems to boil off, at least on other bikes. I just tend to think that with such a moderate interference fit, the heat transfer from liner to cylinder would be compromised. When installing larger liners for 750 cc or larger engines, is the same "loose" fit used?
 
I was thinking, since the source of the heat in operation hits the liners first if the fit loosened up the liner would heat up more than the cylinders. This would then tighten the fit and improve the heat transfer. So it would seem to be self adjusting to some degree.
 
The barrel has a flange at the top, it's captured between the head gasket and cylinder by the head studs when assembled. It can't go anywhere.
Yes heat transfer an interesting question. But it doesn't seem to be an issue on these motors. I guess one factor is that in operation the heat is traveling out from the inside so the liner will be at a higher temp than the aluminum cylinder, keeping the fit tight during operation?
A maintenance heads up; there are (4) air passages front to rear between the cylinder and cam tunnel, but they are small and easily obstructed, should be checked/blown clean as part of your oil change? a thin metal blade can be passed through the openings from the front. One of those muddaubber sized larvae deposit areas? Or easily plugged with oil dirt mix if your top leaks a bit.
Bunch O pics in a bit.
 
Just for reference, are any of the options piston weights lighter or equal to stock?
All weighed in grams with supplied wrist pin and rings
Ask and ye shall receive.

Stock bore used
KIMG2983.JPG

Cruizing image +.5mm
KIMG2987.JPG

JE +2mm used
KIMG2984_01_BURST1002984_COVER.JPG
Mikes, XS650Yamaha 80mm big bore
KIMG2986.JPG

Wiseco 80mm big bore (with 22mm wrist pin)
KIMG2988.JPG
 
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When I was racing Formula Vee, a lifetime ago, I built my own engines. We had to run the 40h.p. 1200, stock pistons (77mm) except for lightening. I'd sit there for hours with a die grinder and a triple beam scale getting them down to the minimum legal weight which was 330g. Funny, can't remember where I put my coffee cup, but I remember obscure specs from 40 years ago. Thanks for the clarification.
 
I got my cylinders back today bored for the 706 pistons. I had the piston clearance set to 0.0025 which was a little interesting because there was a 0.001 difference in the pistons.

The other thing noteworthy is that the ring end gaps are pretty wide, about 0.016 on the bigger cylinder... not happy with that. On my other engine that has stock bore I used 1st over rings and set the gaps to 0.008 to 0.009. Does anyone know where I can get rings that are a little bigger for the 706 pistons so I can do the same thing to them?
 
Like photoshop but with welding? ;^)
they had a frontside pic that matched the one you show @GLJ
Cruzinimage
interesting When last had Mr bore do a bunch of jugs for Cruzin pistons he said "I got tired of measuring pistons that were all EXACTLY the same size".
 
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