DT125R ARCHIVE

PatMan · Guru

Rebore sorted but need some advice!!!!!

NEV · Guru

Pat did you also hone out your head gasket to suit the re-bore?

PatMan · Guru

Hello Nev mate, am just waiting for the gaskets from Yamaha, but thats a good question though what you just said about the gaskets, would I need to do this, I just thought they would fit no problem evening though the bore is now 58mm

NEV · Guru

Nah deffo need to do mate, or it leaves a lip, everyone and his dog who knows about bikes have all asked me if I'd done mine as you can't get oversize gaskets, when cornish motorcycles did mine, I took them the whole engine in, so they could do everything together, for porting and gas flowing etc, whereas alot of people just drop their barrel, piston and head in with workshops, and then get a gasket afterwards, and put it all together themselves. just out of interest though Pat,did you go for the 2mm oversize makita dt piston or the tzr?

PatMan · Guru

I got the TZR piston mate, well I didnt took it to a place local to me who deals in all custom stuff, but thankyou so much for the tip on the gaskets, have you got to do both gaskets please mate? and also got to dermal the powervalve down to in the middle, mind you did put that in first message

NEV · Guru

Nah just the top one, you'll aready know to get the athena/genuine type rubber coated one yeah? as scrimping on the taiwanese ****e ones, only ends up in tears.

PatMan · Guru

I do mate thankyou I get all my gaskets on my bike from a proper Yamaha dealer mate

NORFE · DTR Trusted Engine Builder

so whats the dirrerence in the tzr /dtr piston mate. i noticed a few people doing the same??

PatMan · Guru

The place I went to, the bloke said you cant get a DT 58MM PISTON, but I am sure you can, (could be wrong), and as the TZR and DT are almost the same, the TZR do a 58MM piston, not 100% sure mate on all this, please someone step forward and explain to NORFE the correct thing for this

NORFE · DTR Trusted Engine Builder

ahh ok

i thort there was sumet special about the tzr piston or sumets

dtr pistons go up to 58.90mm then theres the athena 65mm after that

this is the guy who does all my rebores and it shows the sizes they do so they must of been miss informed some where along the line

http://www.ebay.co.uk/itm/SERVICE-BARREL-NEW-REBORE-PISTON-KIT-FULL-GASKET-SET-YAMAHA-DT-125-R-DTR-/280746462717?pt=UK_Motorcycle_Parts&hash=item415dcb0dfd#ht_684wt_1037

hes does a good job and i can drop and collect same day some times if im in the area cant beet the price either

PatMan · Guru

Well if they go over 58MM mate on a DT piston I am not sure either then.

this is the bloke I use near me. www.mbcustoms.co.uk

NEV · Guru

Both Dave at roadanddirtbikes who supplied the piston, and Jason at Cornish motorcycles both told me that the TZR piston is a higher compression piston, same again as the RD piston, the difference between the RD piston is the skirt windows, and yep you can get a 2mm oversize DT piston, I got a new one knocking about in the garage, but its an ebay one I was told to stay clear of, after I'd bought it, sods law eh. Oh and you need the older TZR125L 1987-1992 Standard bore size 56.4mm not the later TZR125R which has a standard bore size of 56.00mm

NORFE · DTR Trusted Engine Builder

ahh okidoke mate cheers

satelliteone · DTR Senior Member

PV, shaping is a right pain, patman, you have to get the sides right too. Not just the middle of the PV. If u slide the piston in the bore and move the pv back and forth u can see, i just used half of the PV to see, mirrors the other side too.

Nev the TZRR uses the exact piston as the DTR`s, i just rebuilt mine. the compression is only done by the head. its very different to the 3mb00 3BN head, the 4dl has its own P marking only version. No idea on the 4FL heads. Think its the same as the DTR.

Close is the 3MB heads. to higher compression.and one step further is the true 4DL00 barrel and matching heads, if ur lucky enough to own one. :)

here is my tzr with an dtr piston

NEV · Guru

Hey I'm just going by what one bike shop parts owner and one bike workshop owner told me,
I have searched and found this though, it shows a 0.5 mm oversize, but says theres a difference between the tzr125l and the tzr 125r. pistons
http://yambits.co.uk/tzr125l-050mm-piston-kit-p-8289.html
Do me a favour though, ring Dave at road&dirtbike 01274 530282 , or Jason at Cornish motorcycles 01752 666234 maybe they can explain what I'm trying to get over by the TZR piston being higher compression piston.
As when two different blokes with about 60 years experience between them tells me something, I generally take their word for it.
I do know though, that although I'm still running in the bike, the engine is running sweet as a nut, so whatever piston is in it, and whatever has been done to the top end, works very very well, and at the end of the day thats what matters to me.

PatMan · Guru

Thanks once again satelliteone mate for the info and advice

I shall be doing this very careful but doing it like your step by step guide, well actually my mate whos wicked at this stuff will be doing it I will be just watching

satelliteone · DTR Senior Member

ahh nev its the "L" version. older engine, very simular to the DT125LC , yup yor right, the pistons would be different, the tzr comes in many versions too. The FU/4DL/FL/HW/JB etc.. trz`s range are quite close to the DTR.

kweel patman.. will be sorted! :)

Seanyftw · Guru

rawr all this talk of rebuilds and rebores etc is making me itch to get mine sorted!

PatMan · Guru

hahahahaaha mate

1990dtr (aka THIEF) · Do not trust me or buy from me

quick question might be stupid its just the barrel that gets rebored right not the head ???? or am i missing summin cuz iv just sent my bore to be rebored to 58.9mm ???

satelliteone · DTR Senior Member

58.9mm oooerrrr, you might need to very sight work to the gasket, so it dont overlap into the bore. the head should be ok, but if u have a handy lathe! lol.. ask the guy at the machine shop see what he thinks.

Ta patman chapperz, looking good.

NORFE · DTR Trusted Engine Builder

just the bore and maybe the gasket, wait n c when it comes back put te gasket on the barrel and feel for a lip

head only needs doing if the size gets to big

1990dtr (aka THIEF) · Do not trust me or buy from me

ohh ok cheers guys :)

bagpuss · DTR Respected Member

if you are looking for the pictures of how to grind your power valve read the topic power valve fail. smile

NORFE · DTR Trusted Engine Builder

yes mate forgot to say you will have to do the valve drum aswell with the bore that big.like the other post read the 1 i did about it

when you get ya barrel back bench it and assemble it all as normal then with the pv in the closed position use a bright coloured marker to draw on pv on the area needin modding, pic 1 shown in red!

then remove the power valve and it exposes the area needing a fettle seen in pic 2

you can either use a dremel. die grinder with a carbide burr or a file

while removing material keep installing the pv halfs now and again until you have removed enough of the surface to have 1mm clearance from the piston/rings

jobs a gooden !

http://dt125r.activeboard.com/t47212329/power-valve-modification-for-over-sized-bores/