Hi. I

If you are going to remachine the cases I recommend getting the big fin ATC 200X cylinder and piston, 65mm bore I think. You will also have to shorten the cylinder to match the 125 stroke but you end up with a 166cc engine. I have one in my TL and am building a second one for a Fraser frame I have. Quite a few people have ridden mine and commented 'This is what Honda should have built'.

Scooter

If you are going to remachine the cases I recommend getting the big fin ATC 200X cylinder and piston, 65mm bore I think. You will also have to shorten the cylinder to match the 125 stroke but you end up with a 166cc engine. I have one in my TL and am building a second one for a Fraser frame I have. Quite a few people have ridden mine and commented 'This is what Honda should have built'.

Scooter

Hi This kit is a drop in with no boreing of the cases required.Sammy Miller motorcycles in England and Powroll in the states have both sold a kit like this for going on three decades now. This price is very good. I have the Powroll version with a stroked crank for 175 cc which is much more powerful than stock. Localy many people have used 145 kits for the last 25 years with no problems, highly recommended.

Ok, thanks tlrmark and TLrider. Is compatible the atc200 cylinder with the tl125 head? Where can I buy an atc200 cylinder and piston(complete kit)?. I don

I had a Powroll bore and stroke done to a stock TL cylinder in the early 80's to 161cc or there about; it made a significant difference.

I have no experience with the drop in 145cc kit and I'm sure it works fine and it's probably the less expensive route.

I bought my current TL with the 200cc cylinder kit installed and like it a lot, being a machinist I decided to build another. It is quite a bit of work as there are fixtures to be made and you also have to recut the valve pocket in the piston. When boring the cases you break into the oil passage on the back of the spigot hole which feeds one of the transmission shaft internals.It is recommended that this be welded and recut but my bought one was not done that way and I rode it for 10 years before tearing the engine down due to a broken kick start gear.

sherpagorri, to answer your most recent question there is not a kit available to my knowledge. The stock TL head will bolt right on with no mods necessary though there are several you can do. I bought mine off ebay, piston and cylinder together so I beleive they came off the same bike. The seller had good photos and the parts looked in decent shape, there is a little pitting on the cylinder walls. It honed nicely and the bore is well within tolerance so I'm going to leave it as is.

If you're really interested in doing this I can write you a detailed list of what you need to do.

Many thanks for your help TLrider. I don

Many thanks for your help TLrider. I don

man, that kit IS a bargain, hope it works out good for ya

Thanks friends, I have found another interesting kit in ebay. Is a 165 cc. kit, but more expensive:

http://www.ebay.com.sg/itm/Kit-165cc-pour-Honda-125cc-OHC-Big-bore-kit-165cc-Honda-125cc-OHC-CB-XL-/230735623659?pt=LH_DefaultDomain_23&hash=item35b8ea35eb

I

Thanks friends, I have found another interesting kit in ebay. Is a 165 cc. kit, but more expensive:

http://www.ebay.com.sg/itm/Kit-165cc-pour-Honda-125cc-OHC-Big-bore-kit-165cc-Honda-125cc-OHC-CB-XL-/230735623659?pt=LH_DefaultDomain_23&hash=item35b8ea35eb

I

For me too, but don

sherpagorri,

That kit looks like what I described using the ATC200x parts, nice thing is you will get all new parts in the kit. They state prior to year ?, I can't recall but your TL is prior, that boring of cases is required. Having said that I surmise shortening the cylinder to match the 125cc stroke would be necessary as well.

I'm not positive about that but it is something you should consider along with the valve pocket in the top of the piston may need to be recut.

Food for thought...

The kit's listed as being for all the 125s but the combustion chamber volumes are quite a bit different between the models. I'd be surprised if the kit just bolted straight on without some other sort of work as TLrider has pointed out. If you're using the standard TL head on a big bore kit you'll be raising the compression ratio quite a bit unless the piston is dished.

A Honda xl185 barrel will go onto your cases after boring them out (sleeve diameter 69mm), with an ATC 185 (dished) piston it helps to keep the CR down, see the picture below.

It's difficult to lower the CR on the ohc engines as you're restricted by the cam chain length.

This is what TLrider means by cutting into the oil gallery, this is one I did last year. I've since had it welded up but the project has kind of stalled.

1.5mm sleeve thickness is fine, especially for a trials engine. Pete Arnold at PACRE http://www.pacre.co.uk/ won't go lower than 2mm but he's building high spec road race engines that have won championships out of the CB motors.

To be honest, it's easier to just fit an xl185 engine or even better the post '79 xl125 6 speed bottom end with the 185 crank and top end (no casing boring required), but where's the fun in that!?!?

Edited January 31, 201214 yr by craig10

craig10,

Thanks for pointing out the dished piston, I completely forgot about it. That being said the big bore engine I have been running the last 10 years has a domed piston in it. I was quite surprised to see this when I tore the engine down as all information I had led me to expect a dished piston. The second engine I'm building will have a dished piston, until then I won't be able to comment on performance differences.

Thanks for posting the pics, worth a thousand words!

Hi TL rider,

If it's a standard TL head with the domed piston on your big bore engine, the CR must be pretty high! The standard TL piston is dished, or at least the one I've got in the garage is.

Some interesting info here http://www.kaila.net/tl125/tl125bigbore.html

I've actually got an xl125k2 but the engine architecture is basically the same. I've got various projects on the go at the moment using xl185 and ATC185 parts. I've also just line-bored a head to take roller bearings on the camshaft just to see if it was do-able, I'll upload some pics once it's finished and tested.

Like you, I'm also in engineering so these things just have to be tried!

Edited February 2, 201214 yr by craig10