boring out cylinders

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AZRD350LCGUY
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boring out cylinders

#1 Post by AZRD350LCGUY » Mon Oct 31, 2016 8:05 pm

How far can the RD350LC cylinders be bored and still be reliable?
A 66.5 bore brings the cc out to 375.25.
A 67 bore out to 380.92.
And a 67.5 bore out to 386.63.
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

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JonW
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Re: boring out cylinders

#2 Post by JonW » Mon Oct 31, 2016 8:33 pm

huge bores require larger custom gaskets really, but Ive read of people going quite big on these cylinders.... however youre limited by the thickness of the liner, and you never want to be too thin....
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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ghezzi
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Re: boring out cylinders

#3 Post by ghezzi » Tue Nov 01, 2016 12:53 am

So when does anorexia set in?
I'd rather ride a slow bike fast, than a fast bike slow.

evan_calgary
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Re: boring out cylinders

#4 Post by evan_calgary » Tue Nov 01, 2016 1:15 am

Liners look thicker than RZ from what I have seen and they can do 66mm. PV may be limiting factor for RZ? Not an answer but moving in right direction. Don't forget you need to find pistons as well. Can you use banshee overbore pistons? Maybe?

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JonW
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Re: boring out cylinders

#5 Post by JonW » Tue Nov 01, 2016 1:19 am

Ive read you can fit 68mm but not done it. how thin would the liner be at 68 i wonder.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

Re: boring out cylinders

#6 Post by AZRD350LCGUY » Tue Nov 01, 2016 3:51 am

I am looking at 66.5 pistons form a Yamaha DT175. I do not want to buy the pistons unless I know it will work.
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

evan_calgary
Posts: 1368
Joined: Tue Nov 12, 2013 2:34 am

Re: boring out cylinders

#7 Post by evan_calgary » Tue Nov 01, 2016 4:07 am

Probably better looking at banshee cylinders/pistons...this isn't the sort of thing you typically 'know' until you order the parts and try it. Any non-off-the-shelf mods requires some trial and error and inevitably some wasted cash...

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JonW
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Re: boring out cylinders

#8 Post by JonW » Tue Nov 01, 2016 4:30 am

Have an ask on norbos forum, you'll get more LC guys to answer there and many have had LCs for 30+ years so someone will be bound to have done this.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

yam4l0
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Joined: Sun Jun 01, 2014 1:40 pm

Re: boring out cylinders

#9 Post by yam4l0 » Tue Nov 01, 2016 7:25 am

The DT piston pin to crown dimension is shorter than on a standard LC piston so the barrels require shortening by a similar amount which is approximately 5mm.

Bare
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Location: vancouver

Re: boring out cylinders

#10 Post by Bare » Tue Nov 01, 2016 11:46 pm

AZRD350LCGUY wrote:How far can the RD350LC cylinders be bored and still be reliable?
A 66.5 bore brings the cc out to 375.25.
A 67 bore out to 380.92.
And a 67.5 bore out to 386.63.

IF?? yer looking at boring as an easy path to Mo' Power?
IMO you are pissing up the wrong tree.
Displacement/power increases thru Boring on such a teeny engine are simply Not worth the trouble involved.
You need get into stroking.. For which there is a LOT of info available

evan_calgary
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Re: boring out cylinders

#11 Post by evan_calgary » Wed Nov 02, 2016 2:06 am

Are stroker cranks available for the LC? Tons for RZ but haven't seen any that fit LC...

Hooligan
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Re: boring out cylinders

#12 Post by Hooligan » Wed Nov 02, 2016 3:44 pm

I'm still a bit fuzzy on why stroking a crank works? The exhaust port height is still at the same level and so no compression is realized until the piston closes off the port. Crank stroke doesn't change that factor. Thus the compressible volume does not change regardless of crank stroke.

The only thing I can surmise is that stroking works by increasing the suck and blow volume which increases the air-fuel to residual exhaust ratio?

There are two potential downsides to stroking the crank. Reduced rpm redline and slower rev generation.
'82 RD350LC in '81 colours, OEM pipes, UNI filters
'85 FZ750

evan_calgary
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Joined: Tue Nov 12, 2013 2:34 am

Re: boring out cylinders

#13 Post by evan_calgary » Wed Nov 02, 2016 4:21 pm

Guessing the exhaust pulse that is essentially stuffing the previous stokes back into the motor effectively closes off the port. Just my top of the head guess..

MK
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Re: boring out cylinders

#14 Post by MK » Wed Nov 02, 2016 4:52 pm

My race bike needed a last rebore and I purchased +2.5 mm (66.5 mm) Woessner pistons.
Unfortunately older rebores were carried out with a non parallel axis, so I ended up in need of an even bigger bore...
As Woessner only had +3.25mm (67.25mm) in stock I now use that size (had nothing to loose with them cylinders).
The liner is thin as paper at some locations and I would not recommend to rely on it working for your pair of cylinders.
I have used it for some 3-5 track days so far and it's still running.

Btw: If someone needs a pair of +2.5 mm forged pistons ... I have a set 4 sale.
Bye
Martin

Bare
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Re: boring out cylinders

#15 Post by Bare » Wed Nov 02, 2016 7:35 pm

evan_calgary wrote:Are stroker cranks available for the LC? Tons for RZ but haven't seen any that fit LC...
'Some' 4y3 cases accept a RZ/banshee crank as a drop in fit.
Other LC cases need a wee bit of flycutting (~100$) alteration to accept RZ/Banshee cranks.. Happily.
Little real world reason to even try to rebuild an LC crank.. stock stroke ones too

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