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700 twin with 3/32" sleeves


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#1 oldsnomo

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Posted 02 June 2017 - 08:08 PM

Hey all, looking for some help on a bore decision in my sleeved 700 twin. Some background, bore is currently at 79mm which is 1mm os. Lost my crank this spring when the pto rod bearing let go. (High hour crank-15000km). I bought a new crank and seals and now I'm working on a top end plan. Choices are limited for pistons since 670ho and 700 pistons only come in .5 and 1.0mm os. I suffered damage in the pto jug and need to further oversize to achieve a score free surface. Since 2.0mm pistons aren't available, my only option is to with a set of very pricy custom 80mm pistons or bore to 82mm and run 800ho pistons. Problem is I don't know if my sleeves can handle this size overbore. They are LA sleeves. Does anyone know if they can handle a 4mm oversize? Thanks everyone.

#2 krm

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Posted 03 June 2017 - 06:57 AM

Your biggest problem will be the squish on the head as it's not 4 mm over .Just get a new cylinder from some place like Hilderbrant 517 238 5955 :wink_old:



#3 613rev

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Posted 03 June 2017 - 07:15 AM

^^^ x2. Or just send the damaged jug to LA sleeve for a new sleeve, and use the pistons you have been using.

#4 Daag44

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Posted 03 June 2017 - 02:03 PM

It's funny that at this time of the year some owners realize the benefit to post on the General Sled Forum to get different advice. It's how it works in the off season.

 

oldsnomo, now you have Hilderbrand and Kelsey @ RK Tech. You call the pros who deal with these types of questions and ask. It really is that simple. If you can measure/post the piston clearance, pin to crown, and crown angle measurements, then that will be a bonus.



#5 oldsnomo

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Posted 03 June 2017 - 06:02 PM

Yeah Daag, it's all about the connections, that's the best part of this community! I really like getting all the different perspectives, helps me in my time of head scratching! Lol. Thanks again everyone for the direction and contacts.

Edited by oldsnomo, 03 June 2017 - 06:04 PM.


#6 RotaxFlyer

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Posted 16 June 2017 - 03:02 AM

Hey all, looking for some help on a bore decision in my sleeved 700 twin. Some background, bore is currently at 79mm which is 1mm os. Lost my crank this spring when the pto rod bearing let go. (High hour crank-15000km). I bought a new crank and seals and now I'm working on a top end plan. Choices are limited for pistons since 670ho and 700 pistons only come in .5 and 1.0mm os. I suffered damage in the pto jug and need to further oversize to achieve a score free surface. Since 2.0mm pistons aren't available, my only option is to with a set of very pricy custom 80mm pistons or bore to 82mm and run 800ho pistons. Problem is I don't know if my sleeves can handle this size overbore. They are LA sleeves. Does anyone know if they can handle a 4mm oversize? Thanks everyone.

 

Stock Cylinder Sleeves can usually only be overbored, 2mm Max. Per Dave from LA Sleeve, you need a minimum Cylinder Wall of 2mm. So measure Sleeve OD and subtract 4mm, that is how much you can overbore it. Till you overbore them to clean them up, you don't know what Size Piston you really need, 78mm to 80mm.

 

These 700 Twins are (78mm x 73mm) 697.9cc aren't they?

 

Cheapest Option, find some good used std 78/79mm bore cylinders. Next Option, find an off the shelve Piston that meets your oversize you came up with. 3rd option re-sleeve with new std bore Sleeves avg $75 to 117ea on eBay, 4th option is there is probably a 700 Big Bore Option. You can save money on a re-sleeve if you Buy Blank Sleeves Avg $40-$60 and cut in the Ports yourself. Make templates from your old Sleeves.

 

There is some 82mm 700 Big Bore Sleeves on eBay $99.99ea. (82mm x 73mm) 771.3cc. Your Head would need to be opened up for the bigger 82mm Bore.

 

eBay item number:
142129493683


#7 oldsnomo

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Posted 18 June 2017 - 09:25 AM

Thanks rotax flyer. I think my best option right now is to go with option #2 , as I have been advised (by another dootalk member) that with some minor skirt work, a Kawasaki pwc. piston will work. it also comes from an engine with cast bore so oversizes are available in a much better variety than 670ho model units. pin size is the same and pin to crown, crown profile is very similar. my local machine shop can bore and measure until damage is removed and then when I buy the piston they can finish bore to actual size. hopefully no head work is required at 80mm? do you know? Thanks!



#8 RotaxFlyer

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Posted 18 June 2017 - 09:49 AM

Thanks rotax flyer. I think my best option right now is to go with option #2 , as I have been advised (by another dootalk member) that with some minor skirt work, a Kawasaki pwc. piston will work. it also comes from an engine with cast bore so oversizes are available in a much better variety than 670ho model units. pin size is the same and pin to crown, crown profile is very similar. my local machine shop can bore and measure until damage is removed and then when I buy the piston they can finish bore to actual size. hopefully no head work is required at 80mm? do you know? Thanks!

 

Most Heads Combustion Chambers I have measured are 1mm bigger than Std Bore, so if std bore is 78mm, I would guess yours are 79mm. Always Measure! Heads are Aluminum, if you have a Small Hobby Mill or even a Drill Press and a Vice for them, you can buy a cheap Fly Cutter Tool off ebay to Open the Chamber or just take it to a machine shop.

 

This one eBay $16.76 for example.

Attached Images

  • FLY CUTTER TOOL 2.jpg


#9 RotaxFlyer

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Posted 18 June 2017 - 10:01 AM

Or go fancy with a boring head $80 on ebay. Can use them to open a Case for Bigger Cylinder Sleeves also.

Attached Images

  • BORING HEAD 1.jpg

Edited by RotaxFlyer, 18 June 2017 - 10:03 AM.





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