DT125R ARCHIVE

endurodt125 · DTR Respected Member

RE: 1999 yz/dtr 170cc athena hybrid build

Calum122 · Guru

I've spoken to specialists about having this done to my TZR engine. Life time bike mechanic his words were DON'T. It's a black art and he won't pretend like he knows what he is doing. I asked if he would do mine but refused the work.

Basicallt the fly wheel acts as a harmonic dampener. Lightening the fly wheel will cause the crank to flex uncontrollably. Even more so whenspun up to 10k rpm.

Do as you please. But that was his advice. Lightening the fly wheel will not give you more BHPs. The flywheel smooths the powercurve and stores energy. My hands are numb can't type any more byt thats pretty much what I was told.

scrimsmustang · DTR Mechanic

If you do lighten your flywheel use the 99 to 03 type, drill the rivets out and separate the 2 pieces and machine the outer piece then get it balanced and re riveted. Like Cal says it wont give you more power but the motor will spin up a lot faster. Don't know about the rest of what his mate says that but I've never had a problem.

Calum122 · Guru

It was the Yamaha technician at Skellerns Cheltenham. Not a mate. I wanted my tzr wheel lightened and he refused to do it.

scrimsmustang · DTR Mechanic

He wont have had a lathe in the dealership workshop as they have no need whatsoever for one, you need to take it to a precision engineering shop to get it done unless you have a lathe.

Calum122 · Guru

I don't think they do. But he's massively into his smoker tuning.

scrimsmustang · DTR Mechanic

Ive had mine done, never used it yet though. I think it will be fine though, just look at the size of the flywheel on your brothers YZ125 the 250 is no bigger and they have no probs. Mind you lots of people do weight them on 2stroke MX engines when using them for enduro to smooth the powerband out for a bit more bottom end, I never have though.

Calum122 · Guru

It's nof the weight that's the problem. It's the inertia generated when its spinning. A fly wheel is designed to be in a perfect harmonic balance with the counter forces being exerted by the clutch and the piston. A crank is not balanced from the centre. The pistons throw is not central to the the crank. To balance out these forces you have a weight placed onto the crankshaft. That weight has been engineered to counter act the masses of other forces going on during its cycles. Disturbing that balance will undo all that hard work.

Harmonic dampeners are proven technology.

That's all I'm saying.

scrimsmustang · DTR Mechanic

Straight over my head, no I get what your saying but im still going to use it. It must work opposite with weighting a flywheel a few ounces on an MX bike also so im guessing taking a few off should be OK also. Well I hope it is Ile have to wait and see mate as I aint gone mad with it.

endurodt125 · DTR Respected Member

Ahhh do i dont i, ive literally got it all ready to go :/ i thought lightening flywheels was common practice with 2 stroke tuning ...i wasnt going to take a stupid amount off so i cant see it being that much of a problem ..theres tuners taking **** loads off blaster flywheels on youtube and alot of tuning companys actually sell lighter flywheels .......

Sam M · DTR Respected Member

I took about 0.5kg off my flywheel. Liked it revved up quicker was better for flat out attacking but.... stalled easier when crawling over bigish slow rocky areas and took abit more of a knack to stop it spinning up near the top of hills (just had to be more controlled with throttle). I do a lot more technical riding then full out attacking now days and have gone back to the standard flywheel with the outer ring. Lightened it myself at work using a 3 jaw chuck off a lathe mounted on a block in my vmc600 milling machine instead of using a lathe. I probed all the way around it to make sure it was level and clocked the couner bore for flywheel nut for centre so its spot on :)

Sam M · DTR Respected Member

A few pics il do a write up one day...

Sam M · DTR Respected Member

endurodt125 · DTR Respected Member

**** me thats some high tech **** lol im doing it on some old vintage lathe ...shes a good old girl thoe ...just got to set her all up properly and shes good to go ,it weighs 13.2kg so im guna take off about 3.5kg and get another one and take a bit more off and see which one suits my riding style

endurodt125 · DTR Respected Member

I cut a old cranshaft up and bolted flywheel on so i could get it all dead central 😏😏

endurodt125 · DTR Respected Member

Ignore that last bit lol in the end i took 430g off

endurodt125 · DTR Respected Member

I

endurodt125 · DTR Respected Member

Right do i need to get this ****er balanced cz i got some saying yer and some saying no :s

scrimsmustang · DTR Mechanic

I don't think it will matter to much if you have skimmed it on a lathe, should be fine.

Sam M · DTR Respected Member

Nice setup sure it will be true enough, when wer doing precise jobs like that on the manual lathe we put a clock on a magnetic stand on the lathe bed, take the lathe out of gear, slowly rotate by hand with the clock touching the front face of whatever your truing, the clock will go up and down as you spin it, a little tap here little tap there, here there, here there, until the clock stays on the same reading for a full rotation then you know your **** on :) abit of a pain and probly not that neccasary. Which is why I tend to use the cnc miller for jazz like this. Norfe lightened a few with a grinder and didn't notice excessive vibes so I really don't think you would notice it being slightly out of scew turned by a lathe.

Sam M · DTR Respected Member

You an engineer endurodt? or just got a mate with a vintage lathe :) me like either way

endurodt125 · DTR Respected Member

Nah just work at a college and get acces to all the motorvehicle workshops ...couple of bikers work there so there always keen to help out

scrimsmustang · DTR Mechanic

It will be fine, aint used mine yet but im not worried about it at all and I am going to use it .

Calum122 · Guru

NORFE used his all the time. But his was a weekend toy.

endurodt125 · DTR Respected Member

Ahh well ill give it a try and see what happens (bang ) lol ...mines a weekend toy aswell so willing to sacrifice a bit of reliabilty ....does anyone on here know of anyone thats actually corrected the port timings on the 170 and can get me in contact with them? Im kinda having second thoughts on doing it ???would like some sound advice

-- Edited by endurodt125 on Friday 6th of February 2015 06:09:13 PM

scrimsmustang · DTR Mechanic

Ive fitted loads of Athena 170 kits to peoples bikes never had a problem with any of them, all have ran sweet as a nut they don't give a lot of difference in top speed but give loads more bottom end power. Just fit it without f*****g about with it and see what you think.

endurodt125 · DTR Respected Member

I have man ,wasnt very impressed and i managed to heat sieze it when running it in so the top ends off and im sending it for a replate at the end of the month ...so while its apart i thought i would look at correcting the port timings ....ive been told the barrel needs raising by 3mm then 3mm needs skimming of the top ....ive put the piston at bdc and can clearly see that the piston covers the ports which will be blocking the flow? Ive made a 3mm spacer and now the piston lines up with the exhaust port perfect and uncovers the rest of the ports more ...ive read in graham bells tuning book the piston should be inline with the exhuast port at bdc or the port should be slightly lower ..so ive done right thing? ....the thing is alot of people are telling me to raise it 3mm but ive not come across one single person thats done it even after hours of research ,maybe the ports are supose to be like that ? Looking at it it kinda makes sense but im no expert

Calum122 · Guru

This is where I got my info from. Not hugely reliable but as said I just skimmed it and iit made sense cause I was so disappointed with the 170 kit.

www.125ccsportsbikes.com/forums/index.php

endurodt125 · DTR Respected Member

Cheers bud i did come across that ...think im just guna have a think about it all and do some more reading ...cz theres no turning back once the 3mm has be taken from the top of barrel ...really dont to waste a £500 kit ...it all makes sense but i dont want to be missing somthing

Calum122 · Guru

Worse case scenario you have a spacer made at the top of 2.5mm and run two head gaskets.

Or you have an o-ring machined into the head. A match spacer with an O-ring machined in. And then clamp it all together using 1 head gasket. Either way nothing broke can't be fixed.

And what you and that chap described is not the way a two stroke should work. I'm confident that what you've done is correct. Even you only machine off 1-2mm and see how that went. That's the way to do it. Do little by little. But Graham Bell, the legend, descirbes what you're looking for in a cylinder. And the Athena kit ain't it!