Removing Lower Frame Rails On Tl125

[bunyan]

i'm restoring my current tl for gentle trail use only, but i have another very battered one which will be a bit more for action. anyone cut away the lower frame rails and replaced it with an ali bash plate? it was quite a common mod years ago. what else can i chop off to save weight? (dont say get another bike. i like tl's!) i have a 150cc conversion in my shed as well. apparently, early ty forks are an improvement as well.

[craigcorolla]

Hi, I am too wondering about this mod ! and also steepening the steering angle by cutting and welding the headstock, just wonderd how far you can go and it is still road legal ? Any info would be great, Thanks, Craig.

[b40rt]

Hi, I am too wondering about this mod ! and also steepening the steering angle by cutting and welding the headstock, just wonderd how far you can go and it is still road legal ? Any info would be great, Thanks, Craig.

TL1215's, that must be a big bore kit !

[tlrider]

Hey bunyan,

I have a TL125 with a 168-170cc big bore and have both chopped the lower frame rails and the steering angle. I bought the frame modified and the modifier had cut about a 5/8" to 3/4" wedge from behind and below the steering stem. He pulled the lower portion towards the rear of the frame thus steeping the rake. I thought the bike steered like a Yamaha TY175. It was very responsive and the bike did not fall into the turn as does the stock geometry. My dislike to the mod was doing any kind of drop off or dropping into a gully where the front wheel had to go back up the other side immediately without a flat spot at the bottom. The sensation was that the forks were going to fold under the bike. I did measure the angle compared to a stock TL and have it written down somewhere. I'll have to find it. The wheelbase shortened by about 3".

I rode it like this for a year or so. I decided to de-rake the bike. I cut the weld and moved the lower portion of the steering stem forward about half the distance of the original mod. I made a steel U shaped bracket that slid on from the bottom and welded it all the way around. I like this much better. The bike still turns tight and does not fall into the turn. Drop offs are much more comfortable but the stock forks are still lacking. I haven't figured out what to replace them with. Mariocchis off a Fantic have been suggested.

I can't comment on what rake is legal, is there even a legal spec? I'm in the States. What I can tell you is the bike seems to handle fine wide open in 5th gear across an open field. I run a 12 or 13 tooth front sprocket and a 60 tooth rear. Am hitting 40 MPH or so?

I also cut out the lower frame rails and added a 1/4" AL bash plate. I modeled it off what BPS Engineering of France shows on their TL Pro kit. It's a nice mod adding more clearance in the front and it slides off rocks and logs better. Another important mod I got from BPS is adding supports from the sub frame, the portion going from the footpegs up to the rear shock mounts, to the main vertical backbone near the rear engine mounts. These are also visible in the BPS photo but you have to look closely. These stiffen the ride imensley and I just recalled I made a triple tree brace. Modeled it off the image from the parts list that shows it as an option for the bike. Mounts between top triple tree pinch bolt on one side and lower triple tree pinch bolt on the other fork. This gets rid of the 'wiggle' in the bars when doing drop offs.

Sorry to be so long winded, hope you find this useful.

Scott

[craigcorolla]

Hi Scott,

Thanks for getting back and not at all long winded, it was an interesting read.

Well spotted B40RT ! Now corrected !

Scott, I dont want to be a pain but have you got any details of the 170cc bore ? Did you do it yourself or is there a kit you can buy ? If so is it a difficult job to do and set up for good running?

Thanks again for reply,

Cheers, Craig.

[bunyan]

thanks for the replies. the french BPS site is interesting so i will go ahead and chop them frame rails.

[tlrider]

Ooops!

I didn't realize I was not directly addressing the original poster of the thread, sorry guys.

170cc Big Bore....here's what I know.

My engine was built by Hoyt McKagen, may he rest in peace.

I met another builder but have lost contact with him. Being a machinist I'm planning on doing another one to put in the Fraser MkII frame I have.

An ATC200 large fin cylinder is used as well as a dished piston from said ATC for low compression. Depending on which overbore you have displacement should be 168-170cc.

The jug and barrel are shortened to match the TL125 stroke. Same height as stock cylinder I presume.

The cases are bored to fit the larger jug.

The oil passage in the case that feeds the head must be welded and re-machined as it was cut in to during boring of the cases. I only know this from having been told so by the engine builder.

Put it back together...and yes it is a good set up for running. A few people have said 'This is what Honda should have built.' It does make for a very nice ride, you lose the off idle cough and the bike has enough grunt to loft the front end when you need to. If anything I'm timid on the throttle, the bike will pull itself out of trouble.

BPS offers 'Our 180 big bore kit complete with piston and gaskets (exchange only).' at 396 Euros. I was to get cylinder, piston and all machine work for $500 US about 3 years ago.

This article on Thumperpage has a lot of info on Honda piston and cylinder combo's for the TL. http://www.thumperpage.com/articles/tl125faq.html

I've also been told that installing an XL125 exhaust valve and reducing the intake diameter with an epoxy or Devcon aluminum to increase velocity aids in reducing off idle cough.

Here is another option that seems to have worked.

I was running 93 octane pump gas with octane booster and lead additive. The motor ran great at low rpm's with no cough but I would get detonation at higher speeds on the loop. Recently I tried CAM2 race gas which is something like 108-110 octane with lead. I picked up top end performance but seemed to lose some low end response with just a little cough.

A few years ago I made some pattern carb insulators with o-rings on the head side. They allowed me to lock down the carb nuts without distorting the carb and get a good seal. With the lose of low end I decided to make some new carb insulators with a straight hole rather than with the taper as the originals have. This seems to have corrected my problem, the straight hole seems to add just enough velocity to eliminate the cough using the race gas.

[tlrider]

Craig, where is Bolton?

[craigcorolla]

Cheers TLrider, Great info on engine mods. Bolton is in England ! Thanks again gives me something to thinkabout. Craig.