Author Topic: Re-Sleeve Back to OEM bore -OR- B i G - B o R e ??? Pro's / Cons ?  (Read 1253 times)

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Offline cfowler

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Hey everyone,

I've had an 88.0mm Wiseco piston in this bike for ages and it finally checked out when the intake boot cracked and breached, allowing atmospheric air into the combustion cycle (poor maintenance on my part). They have 1 sleeve readily available in stock at my machine shop, they also have 1 piston available as well- meaning no waiting on parts which is weeks of added time otherwise. Then I found Wossner's big bore pistons 90mm & 91mm available. What I didn't initially realize was that the head will likely need modification, as well as the power valve and who knows what else. I initially thought i'd be saving money by not having to re-sleeve but it doesn't appear that way in the slightest (I'm still waiting on the actual quote as they're swamped right now). Does anyone have experience or input on this topic? I'd be willing to spend a little more now to make this big accept the bigger pistons but not if it means a bunch of revert work when the time does come to re-sleeve and go back to OEM bore and specs. I'm ultimately after durability and longevity. Sure the extra CC's and power is enticing, but not if it increases the probability of issues. If the mods are done to accept the 90/91mm pistons will this work then have to be reverted when I re-sleeve & go back to OEM bore or will this work be compatible with all piston sizes? (86-91mm). What have you guys experienced and what would you recommend? I do know i'm going to be sending the head out for the decompression mod by Larry Wiechman. Any thoughts on the matter would be appreciated! Thanks. Chris-
« Last Edit: April 23, 2021, 04:53:13 PM by cfowler »

Offline sandblaster

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Yep, the bigger the bore the more you will need to trim back the center exhaust valve.
Going beyond 90mm gains very little HP and only a little torque increase.
It also requires that you modify your cases to keep the piston from hitting.
The bigger you go the more you will have to relieve the cases.
In order to take advantage of the bigger bores you need to stroke the engine as you quickly run out of crankcase volume.
I really like the 88mm and would consider plating the sleeve so that I could continue using the 88mm Bore.
Yes, Millennium Tech can plate your sleeve.
The four stroke engine: That's one stroke for producing power and three for wearing the engine out.

Offline cfowler

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Re: Re-Sleeve Back to OEM bore -OR- B i G - B o R e ??? Pro's / Cons ?
« Reply #2 on: April 26, 2021, 02:39:05 PM »
Thanks very much for that. I'm told they can't warranty or guarantee anything past 89.5mm so I guess a re-sleeve it is.

Offline motorman455

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Re: Re-Sleeve Back to OEM bore -OR- B i G - B o R e ??? Pro's / Cons ?
« Reply #3 on: April 27, 2021, 07:55:51 AM »
Are they able to just replate your 88mm bore or is it too far gone?