DT125R ARCHIVE

yamahadt125 · DTR Senior Member

Top end rebuild

Calum122 · Guru

56.40mm standard 3mb00 cylinder.

Assumptions are the mother of all fùck ups. For the sake of £10 i'd have it measured then honed.

Most piston kits do. Although i would never assume that the piston ring end gap is clear. Again for the sake of £6 for diamond files and ten minutes before building. Better to be safe that sorry.

You'll want a genuine head gasket. And a small rnd bearing and base gasket. And exhaust gasket.

Calum122 · Guru

Also moved to correct section!

yamahadt125 · DTR Senior Member

oh okay where or how do i measures it£ 10 thought it would.be.more full gaskit kit 19.00 but not genuine kit

Calum122 · Guru

Nah. Yamaha charge £35 for a rebore and hone. So just to measure shouldn't be too much.

That head gasket has got genuine or Athena. Base gasket doesn't matter.

yamahadt125 · DTR Senior Member

http://m.ebay.co.uk/itm/301062396259?nav=SEARCH&sbk=1i

Calum122 · Guru

No. Athena or genuine. You can buy that if you want the base gasket but that's pointless. Just buy the Athena top end kit.

AndyYam · Guru

Go for a mitaka or better piston and genuine Athena head gasket. The rest can be cheaper pattern but tbh you might as well buy a full athena top end kit.

Mitaka pistons come with RIK rings and gudgeon pin and circlips but no small end bearing. Buy a quality small end bearing. Make sure you remove all old gasket from the mating surface with a plastic scraper and clean them thouroughly before assembly. Lubricate the bore, piston, small end bearing and crank with 2 stroke before assemlby.

Follow the instructions in the Haynes manual to the dot and dont leave anything to chance.

yamahadt125 · DTR Senior Member

m.ebay.co.uk/itm/360759793960
Athena top end gaskit 21.99 sound not to bad if all the crosshatching visable will i need to message cylinder ? It all looks fine just trying to save money

AndyYam · Guru

Yeah Athena top end gasket. It says 91-95 so if thats your year then go for it. Its not just bout if the cross hatching is visible. Those are the marks from the honing which is done to allow oil to be retained in those grooves in the bore. You need to check the cylinder all over and makre sure there are no scores etc. A detail, in focus photo of the bore from each end and we should be able to tell you but the only real way is to feel.

Saving money is good but it often leads to more expense later. You need to accurately measure the bore to make sure you order the right size piston. Checking the ring gap before you re assemble is also advised.

yamahadt125 · DTR Senior Member

Mines 2007 but they have my year but ill try to take a pic

yamahadt125 · DTR Senior Member

www.ebay.co.uk/itm/Yamaha-DT-125-RE-MX-Everts-2005-2006-Athena-Top-End-Gasket-Set-8467367-/360758658000

Yamaha DT 125 RE MX Everts 1D03 2005- 2006

Athena is an original equipment leading Italian motorcycle manufacturer.
The seals are manufactured to European quality standard ISO 9000 and are under constant quality control.
Consistent quality is guaranteed.
High-quality materials.
High quality Reinz and Elring sealing paper.

This is Athena top end gasket but it says 2005 - 2006 mines 2007 but its the same thing right?

Calum122 · Guru

To clarify this for you mate. Yamaha only made 1 cylinder for the 1989-2007 DTR for the UK and that was 3MB00. Some DTR's have a 3BN cylinder but from my understanding this is rare and a outdated model.

Any Headgasket from yeard 1989-2007 provided they are for a 3MB will do. In all fairness could just go to Yamaha and they'll take your reg and do that. Even AJSutton will do that for you. Although I've noticed that their head gaskets have shot from £15-25 now!

yamahadt125 · DTR Senior Member

my cylinder says on it 3MB00

AndyYam · Guru

Yeah that kit will be fine. As Cal says the cylinder was 3mb for most of the bikes but always best to order the one that has your model year in the title. Just in case. I would strongly reccomend reading up on some theory on engines and watching some videos on rebuilds before attempting it.

No offence intended and as im sure you'll realise the forum is all about people doing their own work, but if you're not sure on how to measure the cylinder its worth doing some homework before diving in as it will cost you if you do something wrong. When you do it, dont rush it and make sure you have plenty of time. If you get stuck, stop. post photos and questions on here and we'll all be happy to help. If you want a number then pm me and id be happy to txt back when i can to help with anything you get stuck on.

Its a good feeling when you get it running again for the first time after a rebuild!

yamahadt125 · DTR Senior Member

RE: Top end rebuild s

AndyYam · Guru

RE: Top end rebuild

Calum122 · Guru

Personally, just personally, measuring the barrel is a specialist job using lasers. I wouldn't use a vernier as it's not accurate enough, no matter how precise.

Take it to a dealer for £10 he'll measure it and tell you what the bore size is. Take it to a Yammy dealer and they'll tell you wether or not it's within limits or whether it needs a rebore. That's what i've done and they've just ordered a piston and honed it for me.

Victor · Guru

I think standard is 56mm on models after 98 or 97 and 56.4mm on models before

yamahadt125 · DTR Senior Member

Yeah i think your correct ebay standard dt re 1999-2006 56mm standed size piston

Calum122 · Guru

No it's 1988 DTR's that have 54mm barrels.

yamahadt125 · DTR Senior Member

Well ebay says 56 standed size ? And google and other websites

Calum122 · Guru

Aww FML I'm getting all muddled up mate. Sorry my bad.

Yamaha DT125RE 56mm

1988 Yamaha 56.40mm

Sorry about that.

-- Edited by Calum122 on Friday 17th of January 2014 09:05:26 PM

yamahadt125 · DTR Senior Member

Haha its fine i just thought google was corret

yamahadt125 · DTR Senior Member

Only thing i can't find is a thermosta gasket found on ebay one but wasn't 3 hole gasket had 4holes also do i need to clean carb and check reedvavles but been running fine so carb should be alright but also is it worth changein 2
Stroke oil like get something to drain out the bottle and put some top quality oil because don't know what stuff owner before had in it its green dunno if its cheap **** ?

Calum122 · Guru

Firstly for the thermostat gasket. It is fine to just make one yourself using some quality gasket paper. Usually found at motorworld or halfords.

You would only need to check/clean if you suspect a problem. Every time you take the inlet off you're suppose to replace the gasket. They're quite thick so not sure whether you can make it. So i'd just leave it alone.

When doing any time of engine rebuild you're suppose to use low quality oils during the break in period. This will wear out any imperfections in the bore and help the rings seal better. Obviously during the break in period keep the engine load t a minimum especially when using low grade oils. I'd go for a cheap semi synthetic brand. Probably avoid anything less.

AndyYam · Guru

I'll have a look when i can to see if I have a thermostat gasket. As Cal says you could make your own but do it right!

If you're competent with stripping carbs then its worth doing as general maintenance whilst its off but without wanting to offend you I'd agree with cal and say leave it as it is if it is working fine.

I've not heard of using low quality oil during run in and although i can see the logic it also seems mad to me. The act of the metal passing the metal will run things in. Low quality may reduce the time it takes to run in but personally id rather use a high quality oil and just run it in for longer. I've seen green 2 stroke oil before and remember googling it. I dont remember it coming up as a cheap low quality oil but personally id want to know what oil i was running. I'd drain it and refill with a good quality oil. Personally I've been using Castrol Racing fully synth which is about £12-13 in halfrauds. Silkolene, putoline are all good brands.

You got a link to where it says about using low quality oil cal, just be interested to have a read. Is that racing bikes?

yamahadt125 · DTR Senior Member

Hmmm is it worth changing oil to castrol or leave the stuff in it which was init when i bought The bike and when gets low put good oil in the bike?

AndyYam · Guru

Are you not reading the full post or you asking for another opinion?

"...personally id want to know what oil i was running. I'd drain it and refill with a good quality oil."

yamahadt125 · DTR Senior Member

m.ebay.co.uk/itm/330948954734
thanks so gasket Paper just cut to size and would.work and seel up correctly