Author Topic: pilot piston/ bore clearance.  (Read 8390 times)

lee1969gb

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pilot piston/ bore clearance.
« on: February 20, 2007, 10:52:29 AM »
Can anyone please tell me what is the best piston to bore clearance to have on a pilot, I am getting bad scuffs on the front and rear of the piston and jaming the piston rings in the grooves.
When I used to do 250 gearbox karting and running a kawasaki kx engine we used to drill two small holes in the front of the piston to help lubricate the bore in a problem area, has anyone done this on a pilot or any other ideas, its costing me a fortune in pistons.

odypilots

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pilot piston/ bore clearance.
« Reply #1 on: February 20, 2007, 02:47:15 PM »
It depends on if you're running a Honda piston or Wiesco. I like to set them up a little loose, .006 for Wiesco. Wiesco says .004. I havent run a Honda piston for so long, I forget what they recommend. If your rings are sticking, it sounds as if your jetting is too lean, overheating the piston, and smearing it into the ring grooves. I'm no engine guru, so take this as just my 2 cents.

The Pilot doesn't have an exhaust bridge, so I've never heard of any cooling holes in it's piston.
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Odyknuck

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Bore clearence
« Reply #2 on: February 21, 2007, 11:04:47 AM »
.006" is nice and safe however short lived. .004" is better for top end life. The key is of course jetting. I can tell you that a piston seize between a 4 or 6 thousands bore is about 3 minutes. So why not take advantage of the extra 2 thousands. On a larger bore the cylinder port openings will tend to ware quicker and force you into a larger bore versus a simple piston change and cylinder honing.

Odyknuck

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Plug chops
« Reply #3 on: February 21, 2007, 11:10:37 AM »
Lee have you done WOT and midrange plug chops to check your jetting. This is so imporant on a 2 stroke motor. Also have you done a leak down test on the motor. If your going thru that many pistons than there is something wrong in one or both of these areas.

odypilots

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pilot piston/ bore clearance.
« Reply #4 on: February 21, 2007, 02:36:22 PM »
Are you talking about a Wiesco, Steve? I've tried .004 with them, and it didn't work for me. It would always scrape itself out to around .006, anyways. I'm not the most careful jetter around, though. My latest top end is on it's 3rd set of rings with the same size piston, so it has lasted good for me.
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Weed

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pilot piston/ bore clearance.
« Reply #5 on: February 21, 2007, 03:13:04 PM »
What is the life span of your set of rings(in hours).  The number of sets really doesn't describe the longevity.

lee1969gb

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pilot piston/ bore clearance.
« Reply #6 on: February 21, 2007, 04:09:57 PM »
Does any one "high spot" there pistons. What you do is fit the piston run it in then strip the motor and clean up the piston, with wet and dry paper remove any high spots or areas that show signs of picking up then rebuild and thrash.

odypilots

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pilot piston/ bore clearance.
« Reply #7 on: February 21, 2007, 05:16:26 PM »
I don't log hours, but I have 2 seasons (icluding ice racing) on the last set. A few Silver Lake rides, mostly short motos, but always at maximum throttle.

My post was more to Steve's assertation that a looser bore will lead to needing to go to the next size piston sooner than a tight set up. I realize that is affected by the number of hours on an engine, as well. The rings weren't always worn out, just changed as long as it was apart. The amount of hours on this size piston has been as long as any bore in my Pilot history, where , when I set them up tight, the damage caused sticking the piston required going to the next larger bore right away.

Lee, I have never done what you describe. If you set them up tight, that might be a good idea.
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Odyknuck

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bore
« Reply #8 on: February 22, 2007, 06:17:19 PM »
Dave, Yes I was refering to a weisco piston. I have allways set mine up at .004" to .0045".  Jetting is the key. Also the port champhering is as equaly important especially the horizont edges of the ports. If the edges are sharp they increase ware and can and will catch a ring. When the bore gets loose it allows the piston to slap and it wares the top and bottom of the intake and exhaust ports more than the rest of the cylinder.  That in its self without a seizer will cause you to have to go to the next bore size.  Thats why its good to cahnge the piston at least once a season.  Just replacing the rings only gets your compresson back and does nothing to tighten the bore.

odypilots

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pilot piston/ bore clearance.
« Reply #9 on: February 23, 2007, 09:16:53 AM »
Thanks for your thoughts on this, Steve, and I hope Lee got the info he was looking for.

Hey, Lee, I never asked what clearance you had been using and which make of piston when you had your problems. Would you mind posting that?
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lee1969gb

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pilot piston/ bore clearance.
« Reply #10 on: February 25, 2007, 12:57:02 PM »
I was using a wiesco piston both times this happened. I am mixing my 2 stroke oil 25 to 1.

lee1969gb

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pilot piston/ bore clearance.
« Reply #11 on: March 02, 2007, 03:05:09 PM »
I stripped my pilot engine today and found out why there is no compression. the piston rings are very badly worn near the exhaust port. These rings have only done about 20 hours. not sure what has caused this, possibly blocked exhaust?

PILOTBOB

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compression test
« Reply #12 on: April 27, 2008, 06:33:14 AM »
Hi  guys,  I'm  new  here,  just  picked  up  a  89  pilot,  took  a
comp.  test  and  I  have  123lbs,  runs  and  starts  fine,  just
wondering  if  that  compression  number  is  still  ok  to  run  it,  and  if
not,  can  I  still  get  a  stock  piston  and  rings  from  Honda  shop?
Thanks  if  someone  can  help  me  out.

Adnoh

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pilot piston/ bore clearance.
« Reply #13 on: April 27, 2008, 09:35:16 AM »
May I add fuel to thought process related to piston clearence.

Odyknuck

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pilot piston/ bore clearance.
« Reply #14 on: July 16, 2008, 01:34:50 PM »
Sure go ahead