Triumphrat

ifras · 03-09-2010, 11:33 AM

Hi I have a triumph 3ta can anyone tell me what is the max. size the cylinder can be bored out to.

Marc Beaudry · 03-09-2010, 05:27 PM

call your local parts supplier and find out the largest over pistons they stock - thats usually the max overbore...
or are you asking the the max. overbore the liner will take ?

GABMA · 03-09-2010, 07:01 PM

I believe Triumph supplied a max of +.050 on most all models. Some Jap and Italian accessory makers supplied +.060 on some bikes. You don't want to bore unless you have to. There are all sorts of ways around this for a not-ridden-very-often classic.

Are you considering this because the bore is rusty, oval, tapered, or simply loose with the pistons?

ifras · 03-10-2010, 06:01 AM

The piston has +0405L stamped on it,when I checked the piston ring in the bore the gap was about 2mm. I do not have any precise measuring instruments so I cant say what size the bores are.

GABMA · 03-10-2010, 09:01 AM

Ring gap is the worst possible way to gauge bore diameter.

1) No doubt the rings on a bike that old have a large gap. That's OK, even expected. New rings are easy to acquire because piston rings are somewhat standardized. You simply need to find the bore (usually in mm) and have an engine specialist cast around for another modern engine with the same bore. You might even be able to do that on-line these days. Finding rings by bore dia is much easier that looking for official 3TA ring sets!

2) Then as to the pistons, turn them up-side-down in the bore, and see what size flat "feeler gauge" you can put between the front of the skirt and the front of the bore. In other words, measure your front-to-back clearance at the bottom of the piston at a point in the bore about 1/2" down from the head gasket.

Tell us what those results are.

ifras · 03-22-2010, 07:07 PM

Itook the engine block to an Engineering company and they told me the pistons were the wrong size they should be +60.They have supplied me with the correct pistons and rings so now its back to my garage,thanks everyone .

Quote:

Originally Posted by GABMA

Ring gap is the worst possible way to gauge bore diameter.

1) No doubt the rings on a bike that old have a large gap. That's OK, even expected. New rings are easy to acquire because piston rings are somewhat standardized. You simply need to find the bore (usually in mm) and have an engine specialist cast around for another modern engine with the same bore. You might even be able to do that on-line these days. Finding rings by bore dia is much easier that looking for official 3TA ring sets!

2) Then as to the pistons, turn them up-side-down in the bore, and see what size flat "feeler gauge" you can put between the front of the skirt and the front of the bore. In other words, measure your front-to-back clearance at the bottom of the piston at a point in the bore about 1/2" down from the head gasket.

Tell us what those results are.

GABMA · 04-07-2010, 07:34 PM

Most shops these days will simply sell you what they have in stock, and not what you actually need. Boring is a real big thing for shops because they get to rip you off on pistons, rings, bore job, which some times doesn't even need doing.

On these old bikes is highly unlikely that you'll actually ride the bike 20,000 mile to find out, so they'll make the sale and never see you again.

Repair of old bikes as practiced by the bulk of the players is simply a con game. If you don't believe me ask for the cylindricity and ovality measurements of your cylinder. They probably won't have them because they probably never measured the cylinder.

toxic · 04-08-2010, 08:54 AM

My machinest gave me so many measurements for each cyl I had to ask him to explain what it all meant. Basically my bores were pear shaped, out of round and oval. It was facinating watching him take the measurements with his equipement. Plus it is a little reassuring when you are in the company of someone that knows what they are doing and is willing to explain it to a stranger.

We have lots of shops in my area but I wasn't happy with the "just leave it with us and we'll take care of it" approach.

I finally got a solid lead after a month of asking around. Local member of the Vintage Motorcylce club pointed me in the right direction.

GrandPaulZ · 04-08-2010, 12:22 PM

Absolutely best to find a machinist that works on MOTORCYCLE engines.

My friend has been in the business for over 30 years, and is a Harley collector. He's never done me (or anyone else) wrong, that's why he's still in business.

RetroRod · 04-09-2010, 01:31 AM

Quote:

Originally Posted by GABMA

Most shops these days will simply sell you what they have in stock, and not what you actually need. Boring is a real big thing for shops because they get to rip you off on pistons, rings, bore job, which some times doesn't even need doing.

On these old bikes is highly unlikely that you'll actually ride the bike 20,000 mile to find out, so they'll make the sale and never see you again.

Repair of old bikes as practiced by the bulk of the players is simply a con game. If you don't believe me ask for the cylindricity and ovality measurements of your cylinder. They probably won't have them because they probably never measured the cylinder.

I truly wonder why we offer up advice sometimes, when all they have to do is run down to the nearest machine shop (that has never seen a set of Triumph barrels before), and get all the solid advice from them. RR