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post #1 of 9 (permalink) Old 07-28-2011, 08:22 PM Thread Starter
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piston and ring size?

OK I have a leaky gasket on my front cylinder. I put some Bar's stop leak in it and it worked pretty well. Anyway after I (hopefully) get through the rest of this riding season I'm doing a tear down and rebuild and a bunch of custom stuff to the bike over the winter.
While I was looking at parts breakdowns I saw that there are 3 different piston sizes and three corresponding ring sets listed. Anyone here know why? I figured they might be for use after a cylinder sleeve re-bore but it doesn't give bore sizes and I'm kinda skeptical that those little sleeves have enough meat on the walls to even bore out. But, I havent seen them so I'm ready to be wrong.
Bike is a 99 with 36000 miles on it so the list of parts to replace is getting pretty long. The last thing I want to do is tear this thing down and only replace the gaskets and then have some old worn part break after putting it back together.
Anyway, any info anyone has on these 3 piston and ring sizes would be greatly appreciated.
BTW first small engine rebuild. All my experience is automotive/heavy duty.
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post #2 of 9 (permalink) Old 07-28-2011, 10:34 PM
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Quote:
Originally Posted by Devil_Hwy View Post
OK I have a leaky gasket on my front cylinder. I put some Bar's stop leak in it and it worked pretty well. Anyway after I (hopefully) get through the rest of this riding season I'm doing a tear down and rebuild and a bunch of custom stuff to the bike over the winter.
While I was looking at parts breakdowns I saw that there are 3 different piston sizes and three corresponding ring sets listed. Anyone here know why? I figured they might be for use after a cylinder sleeve re-bore but it doesn't give bore sizes and I'm kinda skeptical that those little sleeves have enough meat on the walls to even bore out. But, I havent seen them so I'm ready to be wrong.
Bike is a 99 with 36000 miles on it so the list of parts to replace is getting pretty long. The last thing I want to do is tear this thing down and only replace the gaskets and then have some old worn part break after putting it back together.
Anyway, any info anyone has on these 3 piston and ring sizes would be greatly appreciated.
BTW first small engine rebuild. All my experience is automotive/heavy duty.
Stock bore is 82 mm. The two oversizes are .5mm and 1.0mm, so the bore sizes would be stock 82mm, next oversize 82.5mm, and then 83mm. And yes, there's enuff meat there for an overbore of 1 mm; possibly even another .5mm. Finding pistons that will work above that in those sleeves might be a problem, altho I've got some ideas along those lines.

Jim

J.D.
Kerrville, TX
'95 Vulcan 750 "Therapy II",
aka "Raggedy Ann"
'95 VN750 project
'03 VN800B "The Little Black"
'04 VN800E Drifter project
'93 VN1500A custom project
VROC #16185
GCVROC #33

Photo album: http://www.flickr.com/photos/leekayd/sets
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post #3 of 9 (permalink) Old 07-28-2011, 11:49 PM
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Quote:
Originally Posted by J.D. View Post
Stock bore is 82 mm. The two oversizes are .5mm and 1.0mm, so the bore sizes would be stock 82mm, next oversize 82.5mm, and then 83mm. And yes, there's enuff meat there for an overbore of 1 mm; possibly even another .5mm. Finding pistons that will work above that in those sleeves might be a problem, altho I've got some ideas along those lines.

Jim
That info seems to jive with what I remember of what Ron/lance328 posted a couple of years ago.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/11-vn750-general-discussion/9127-top-ten-items-you-would-suggest-new-owner-do-his-new-ride.html

Last edited by OlHossCanada; 07-29-2011 at 12:17 AM.
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post #4 of 9 (permalink) Old 07-29-2011, 08:05 AM Thread Starter
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Perfect! Thanks guys!
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post #5 of 9 (permalink) Old 07-29-2011, 10:09 AM
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Quote:
Originally Posted by J.D. View Post
Stock bore is 82 mm. The two oversizes are .5mm and 1.0mm, so the bore sizes would be stock 82mm, next oversize 82.5mm, and then 83mm. And yes, there's enuff meat there for an overbore of 1 mm; possibly even another .5mm. Finding pistons that will work above that in those sleeves might be a problem, altho I've got some ideas along those lines.

Jim
Quote:
Originally Posted by OlHossCanada View Post
That info seems to jive with what I remember of what Ron/lance328 posted a couple of years ago.
Something was bothering me after this response last night so I checked the specs.
I can`t find any reference in the Clymer manual to the 0.5 and 1.0 mm oversize pistons, but I do remember lance mentioning that one time.

J.D.`s reference to a bore size of 82 mm is correct for the 1985 vn700.

However, all the vn750s, including Devil_Hwy`s `99 model have a stock bore size of 84.9mm.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127
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post #6 of 9 (permalink) Old 07-29-2011, 10:16 AM
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Quote:
Originally Posted by J.D. View Post
Stock bore is 82 mm. The two oversizes are .5mm and 1.0mm, so the bore sizes would be stock 82mm, next oversize 82.5mm, and then 83mm. And yes, there's enuff meat there for an overbore of 1 mm; possibly even another .5mm. Finding pistons that will work above that in those sleeves might be a problem, altho I've got some ideas along those lines.

Jim
Quote:
Originally Posted by OlHossCanada View Post
That info seems to jive with what I remember of what Ron/lance328 posted a couple of years ago.
Something was bothering me after this response last night so I checked the specs.
I can`t find any reference in the Clymer manual to the 0.5 and 1.0 mm oversize pistons, but I do remember lance mentioning that one time.

J.D.`s reference to a bore size of 82 mm is correct for the 1985 vn700.

However, all the vn750s, including Devil_Hwy`s `99 model have a stock bore size of 84.9mm.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127
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post #7 of 9 (permalink) Old 07-29-2011, 11:41 AM Thread Starter
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Quote:
Originally Posted by OlHossCanada View Post
Something was bothering me after this response last night so I checked the specs.
I can`t find any reference in the Clymer manual to the 0.5 and 1.0 mm oversize pistons, but I do remember lance mentioning that one time.

J.D.`s reference to a bore size of 82 mm is correct for the 1985 vn700.

However, all the vn750s, including Devil_Hwy`s `99 model have a stock bore size of 84.9mm.
Back to the drawing board then I guess. I'll try calling one of the parts store's tech support and see if they can tell me. here's the parts breakdown with the three different ring sets and pistons

http://www.bikebandit.com/houseofmot...m4537#sch63144
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post #8 of 9 (permalink) Old 07-29-2011, 01:21 PM Thread Starter
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OK here's what I found out. The oversize pistons and ring sets are indeed .5 and 1mm overbore. So therefore if the 750's stock bore is 84.9 I need to rebore to 85.9 to use them. I'll be doing it this winter.
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post #9 of 9 (permalink) Old 07-29-2011, 02:00 PM
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Quote:
Originally Posted by OlHossCanada View Post
Something was bothering me after this response last night so I checked the specs.
I can`t find any reference in the Clymer manual to the 0.5 and 1.0 mm oversize pistons, but I do remember lance mentioning that one time.

J.D.`s reference to a bore size of 82 mm is correct for the 1985 vn700.

However, all the vn750s, including Devil_Hwy`s `99 model have a stock bore size of 84.9mm.
Argh...I was wondering why 84.9 was sticking in the back of my mind; thanks for the reminder, Hoss. Like a dummy, I didn't look far enuff along the same line where it shows that very thing in the spec section of the manual. That would make the stock bore 84.9mm, first oversize 85.4mm, and second oversize 85.9mm.

Altho it doesn't mean it isn't there, I don't recall a reference to the oversize pistons/rings in either manual, but they are referenced in the parts catalog.

Jim

J.D.
Kerrville, TX
'95 Vulcan 750 "Therapy II",
aka "Raggedy Ann"
'95 VN750 project
'03 VN800B "The Little Black"
'04 VN800E Drifter project
'93 VN1500A custom project
VROC #16185
GCVROC #33

Photo album: http://www.flickr.com/photos/leekayd/sets

Last edited by J.D.; 07-29-2011 at 02:05 PM.
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