'69 650 T120R Overbore Possibilities - Triumph Forum: Triumph Rat Motorcycle Forums
» Main Menu

Discussion Forums
 » Twins
 » Tiger
 » General
 » RAT

Features
 » Blogs

Motorcycle.com Links

Contribute
 » Photo

Motorcycle Forums
» Insurance
» Sponsors
» Our Partners
»ATV Reviews
»Motorcycle Games

Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

Reply
 
LinkBack Thread Tools Display Modes
Old 02-21-2014, 07:31 PM   #1 (permalink)
Senior Member
Grand Prix 500
Main Motorcycle: Triumph Thruxton
 
Ipswitch's Avatar
 
Join Date: Jul 2013
Location: Home of the $30,000 millionaires
Posts: 109
Other Motorcycle: A sweet Honda Accord
'69 650 T120R Overbore Possibilities

I've searched for the answer to this but I could not find any definitive answer.

I have cylinders that are bored +.040 factory spec. Haynes manual only gives tolerances up to +.040 which leads me to believe one can only go .040 over without compromising cylinder wall thickness. However, I'm seeing pistons for sale all over the place for +.060 and even a few +.080 foe 650 cylinders. My cylinder walls already look somewhat thin to my eyes compared to cylinders at +.010 (but I don't know f*ck all about vintage motos).

I do have another set of jugs (huhuhuh) which is only +.010 so either way, I'm going to need to buy pistons.

In the EXPERIENCE of you classic Triumph builders, what is a safe and long-lasting overbore size that is acceptable for a 1969 650 T120R cylinder?
__________________
A THESAURUS IS NOT A DINOSAUR
Ipswitch is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 02-21-2014, 08:51 PM   #2 (permalink)
Senior Member
World SuperBike
Main Motorcycle: 1977 Triumph Bonneville
 
Join Date: Sep 2011
Location: Grass Lake , Michigan,USA
Posts: 2,377
Other Motorcycle: 1996 Ducati 900ss/cr
Extra Motorcycle: 2000 H-D Superglide
Well, I agree they look thin, and I'm not advocating huge over bores, but I'd easily go .060" or .080" rather than buy a new cylinder unless I was doing long distance touring . Hot Rodgers have been running them so thin you can watch the pistons for years. I have a friend who claims he's using 73 pistons in his 650, which sounds pretty crazy. That would be really, really thin.
duc96cr is offline   Reply With Quote Quick reply to this message
Old 02-21-2014, 09:47 PM   #3 (permalink)
Senior Member
Moto Grand Prix
Main Motorcycle: T120RT
 
KADUTZ's Avatar
 
Join Date: Feb 2006
Location: in my house
Posts: 2,609
Other Motorcycle: T140V,T140D,T140E,T140J
I believe Triumph used to offer .20 &.40 as oversize pistons. The aftermarket use to go up to at least .80 over. If I remember correctly after .40 over it was suggested that the crank should be rebalanced

K
__________________
TRIUMPH
"THE WORLDS PRE-EMINENT MOTORCYCLE"
KADUTZ is online now   Reply With Quote Quick reply to this message
Old 02-22-2014, 12:54 AM   #4 (permalink)
Moderator
Team Owner
Main Motorcycle: Rickman T120
 
Join Date: May 2010
Location: Victoria Australia
Posts: 4,274
Other Motorcycle: T160,TR6
You could be better to leave the barrel at + 0.040",if it's not badly worn.
I'd just buy + 0.040" pistons,if the wear is less than 0.006".

I think you're getting some loss from cylinder distortion when you exceed + 0.040".
Mr.Pete is online now   Reply With Quote Quick reply to this message
Old 02-22-2014, 01:45 AM   #5 (permalink)
Senior Member
Grand Prix 500
Main Motorcycle: Triumph Thruxton
 
Ipswitch's Avatar
 
Join Date: Jul 2013
Location: Home of the $30,000 millionaires
Posts: 109
Other Motorcycle: A sweet Honda Accord
Ideally, I would leave it at +.040. But the cylinders are badly worn and need to be re-bored. I will re-measure everything to be positive about the measurements. Either way I'm going to be buying pistons so I'd rather buy pistons to fit the cylinders that are +.010.

Quote:
Originally Posted by Mr.Pete View Post
You could be better to leave the barrel at + 0.040",if it's not badly worn.
I'd just buy + 0.040" pistons,if the wear is less than 0.006".

I think you're getting some loss from cylinder distortion when you exceed + 0.040".
__________________
A THESAURUS IS NOT A DINOSAUR
Ipswitch is offline   Reply With Quote Quick reply to this message
Old 02-22-2014, 04:46 AM   #6 (permalink)
Senior Member
SuperSport
Main Motorcycle: T110 Triton
 
Triton Thrasher's Avatar
 
Join Date: Nov 2012
Location: Darkest Pulteneytown
Posts: 1,343
+60 thou on a Unit 650 9 stud barrel is pretty safe. Certainly safer than buying a new barrel.

May not be engineering perfection, but I don't believe you'll get distortion that will actually affect your running.
Triton Thrasher is offline   Reply With Quote Quick reply to this message
Old 02-22-2014, 05:47 AM   #7 (permalink)
wol
Senior Member
Powerbike
Main Motorcycle: 2003 Bonneville
 
Join Date: Oct 2010
Location: Carmarthen UK
Posts: 369
Other Motorcycle: !979 T140D
The factory always said not to exceed plus 40 -- but i have run several engines at plus 60 without problem
wol is offline   Reply With Quote Quick reply to this message
Old 02-22-2014, 06:42 AM   #8 (permalink)
Senior Member
Moto Grand Prix
Main Motorcycle: 1971 t120r
 
Join Date: Mar 2005
Location: exmouth devon uk
Posts: 2,673
Other Motorcycle: triumph rocket 111
Extra Motorcycle: BSA Spitfire
I had one running OK at 60 thou.I also had seizure problems with a 40 thou.It seized one side,then a few months later,siezed the other side but I think it was weak mixture going up a long hill at 75mph.
My 750 big bore has very little metal between cylinders and it has seized once causing some light scuffing.Its still on there running well now with over 10,000 miles so far.
rambo is online now   Reply With Quote Quick reply to this message
Old 02-22-2014, 09:47 AM   #9 (permalink)
Super Moderator
Site Supporter
Commentator
Main Motorcycle: '67 Triumph Bonneville
 
Join Date: Aug 2005
Location: Laredo, Texas
Posts: 9,660
Other Motorcycle: British Iron
Extra Motorcycle: Dreer Norton Prototype
I've done many to .060, only ONE to .080. So far, zero issues, no smokers.
__________________
GrandPaulZ
Author of "Old Bikes"
Born Again Bikes
My Photo album
GrandPaulZ is offline   Reply With Quote Quick reply to this message
Old 02-22-2014, 08:37 PM   #10 (permalink)
Senior Member
Team Owner
Main Motorcycle: The one between my legs
 
Snakeoil's Avatar
 
Join Date: Feb 2009
Location: Upstate NY
Posts: 5,919
Other Motorcycle: A few
Extra Motorcycle: Yes
My jugs were 0.040 over when I stripped down the engine and I had some porosity in one jug. So we bored it to 0.060 and although we got rid of most of it, some still remained, but below the rings.

In hindsight, I wish I had left them at 0.040 over.

regards,
Rob
Snakeoil is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Triumph Forum: Triumph Rat Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter your valid email address, that can receive an automated confirmation message. Otherwise, you won't be able to gain full access.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
T100R overbore? calal Classic, Vintage & Veteran 5 07-24-2013 10:54 AM
camplate jam 1968 650 t120r jcford72 Vintage Technical Tips & Tricks 5 06-05-2012 10:24 PM
New Amals or Keihins for 650 T120R david_in_ky Classic, Vintage & Veteran 44 07-26-2011 07:44 AM
saveing t120r 650 triumph love Vintage Technical Tips & Tricks 7 05-11-2011 12:54 PM
Building a 650 t120R bzzrd2 Maintenance & Workshop Talk 2 12-18-2005 02:27 PM

Powered by vBadvanced CMPS v3.2.2

All times are GMT -4. The time now is 07:41 AM.



Motorcycle News, Videos and Reviews
Honda Grom Forum Harley Davidson Forum Honda 600RR Kawasaki Forum Yamaha R6 Forum Yamaha FZ-09 Forum
1199 Panigale Forum Roadglide Forum Honda CBR1000 Forum Vulcan Forum Yamaha R1 Forum Yamaha R3 Forum
Ducati Monster Forum Harley Forums Honda CBR250R Forum ZX10R Forum Star Raider Forum Yamaha Viking Forum
Suzuki GSXR Forum V-Rod Forums Honda Shadow Forum Kawasaki Motorcycle Forum Star Warrior Forum KTM Duke 390 Forum
SV650 Forum BMW S1000RR Forum Honda Fury Forum Kawasaki Versys Forum Drag Racing Forum Ducati 899 Panigale Forum
Suzuki V-Strom BMW K1600 Triumph Forum Victory Forums Sportbikes BMW NineT Forum
Volusia Forum BMW F800 Forum Triumph 675 Forum MV Agusta Forum HD Street Forum Suzuki GW250 Forum
Yamaha Motorcycles Victory Gunner Forum Honda Vultus Forum HD LiveWire Forum

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.

Search Engine Optimization by vBSEO 3.6.0