DT125R ARCHIVE

L_COLE · DTR Respected Member

Having some problems with my dt

Dt Danny · Guru

Have a look up the exhaust port and have a look at the piston

slob · Guru

I wouldn't ride it until you find out what's wrong, you will do more damage and end up getting stranded and it's not safe if it packs in for numerous reasons.

If you give us a bit more info like how many miles the bike has done and if you know it has had a top end re build ie piston replacement.

If the piston shatters like mines did it takes the bottom end with it, very much doubt it would still be running if that was the case though, but the symptoms you tell point in that direction.

More importantly take the exhaust of and take a pic of the piston as Danny said.

MDK · DTR Legend

I agree zaust off and have a look up that hole ..

it do.s sound like rings are maybe worn or on their way out be a good to to spot this now as said it can do a lot more damage if they shatter later

AndyYam · Guru

Agree with above. Check the piston and bore conditon.

Victor · Guru

Probably worth ruling out a fueling issue aswell

L_COLE · DTR Respected Member

Ok I'll get a pic up tomorrows. She's done 20,000 miles, 17,000 miles when I brought it. I don't believe she was looked after in the past tbh, finding out later when I brought it the coolant system was completely blocked up and the engine oil turned into think white sludge! All sorted now though. So I find it hard to believe it's ever had a top end re build, sounds like she needs one... so in the worst case scenario how difficult would a top end re build be? Or is that something I should leave with the mechanic?

Cameron · Guru

So the gearbox oil was emulsified when you first got it? Has the water pump seal been changed on it? My mate had a dt running like that and the gearbox **** itself, I had a to change all the gearbox bearings think it was the balancer shaft one that completely collapsed and locked the engine up. Might be something to think about. Does sound more like top end but make sure you get that water seal changed if it hasn't been already!

L_COLE · DTR Respected Member

The water seal was the first thing looked at by my mechanic and its fine lol so who knows, he said it could have been condensation from the window but Im find that hard to believe, personally I think It could have been sabotage as the thread on the screw cap was ****ed, I could get the oil tested but takes so long to do. Ill post a pic of the oil tomorrow show you what I mean.

dread123 · Moderator

pic of the oil is not needed! if it was changed 3000 miles ago then it has no issue here. your asking about rebuild-plenty of posts on here regarding that just check in the right section.not a hard job to do yourself as you'll see from the other members posts-have fun

MDK · DTR Legend

top end is not a massive or realy hard job and can be all sorted by your self by reading up on it on here ..

we will know more once we see the pics .

AndyYam · Guru

If the coolant system was fixed and no water can be leaking into the oil then that should all be good. Its easy enough to drain a little oil out of the gearbox ( not engine oil) and check. You can always pour it back it. For the cost of a new bottle of gearbox oil I'd change it anyway though personally.

As for a top end rebuild. As long as you are competent and willing to be patiant then you'll be fine and I'd say get stuck in. It's great to do it yourself but take your time, read up as much as you can before you start ( both on here and in the haynes manual). Keep the haynes manual with you at all times and USE IT. You'll be looking at around £100 for a top end rebuild.

Rebore £35 including postage
piston kit ( the cheapest worth using)£40
gaskets ( only use genuine or athena for head gasket) £20
Small end bearing £8

The rest is your own time.

L_COLE · DTR Respected Member

From looking in oil window on the side, the oil looks a nice gold colour like it should, but I drained some anyway and its looks awful

Everything was checked to make sure there was no water leaking, I had the oil seals replaced anyway and all gaskets.

The oil in the glass was the oil taken out when I just brought the bike

Going to run down town now just to get oil, what pacific oil do I need ?

Here's the piston pics

Victor · Guru

Pretty sure you could use new ring's and possibly a rebore looks like blowby on that piston to me

Dt Danny · Guru

i agree with victor, can you get a picture of the barrel and whats the compression like ?

L_COLE · DTR Respected Member

Good news, she ok now. just changed the oil and it's running perfect. although I'm still going to have to figure out what is getting into the oil?? I've had the water seal changed the first time this happened so any thoughts... going to change the oil every 1000 miles now until I get this fixed.

This is what the oil looks like after 1000/1500 miles...

So how many miles would you usually do for a top end rebuild ? I'm guessing it's due one soon.

2strokemx · Guru

I change my oil once every 2 months, probably every 200-500 miles and i thought that was pushing it

slob · Guru

Think it was due 5000 miles ago mate. You need to do one your rings look very worn just for starters and your piston is scored. The rattle you explained is piston slap, when the piston is shagged basically.

Oil wise it could be the seal again, not really any other way water can get in other than the filler cap, or possibly clutch cover gasket but that is highly unlikely.

Your best to do the top end rebuild and new water pump seal and new clutch cover gasket plus water pump cover gasket.

Will cost you about £140 all in, me and others are more than happy to walk you through it.

If you don't and the piston shatters at the skirt which the always do in the end it gets metal bits in your main bearings and destroys them essentially. Then you are looking at about £400 and that's if you were lucky enough if Norfe on hear done it for you and the bike would be off the road for a while.

AndyYam · Guru

Ok, so the piston does look like it needs changing. Possibly just a new piston but maybe a rebore. You wont know until you get the top end apart and check the bore condition. My personal opinion is that if you do this then you might a well get a rebore anyway. The exhaust port looks very coked up with carbon deposits so make sure you clean this before you rebuild as it will be bad for air flow.

As for the oil. It could be that any traces of water still in the gearbox are responsible for the oil being as it is. If it were fully emuslified and white then you've probably got a leak. I'd change it and do as you plan to, keep an eye on it. If you had a leak it would be alot worse than that after 1500 miles and you'd be losing coolant. Have you checked that?

A top end rebuild time varies on models and how the bike has been treated, its never an exact science. Haynes/ Yamaha will hav timeframes but on some bikes you could strip down to find a like new engine, on others it could have blown up or seized in half that time.

L_COLE · DTR Respected Member

I did have a look at the coolant looks fine and yeh I see what you mean might as well get the lot done. Going to do a top end build when I finish college at the end of May, I've brought a Haynes manual so I can study it before I go ahead. Just gonna take it easy now a check the oil often until then.

Just wondering what you guys think of this?
www.ebay.co.uk/itm/SERVICE-BARREL-NEW-RE-BORE-PISTON-KIT-FULL-GASKET-SET-YAMAHA-DT-125-R-DTR-/360728879037

slob · Guru

Will be cheap for a reason, bad quality stuff.

Get genuine or Athena gaskets

Re bore wise use pjme, you send them the barrel they measure it and bore it out to the exact sized makita piston.

Never heard a bad word about them, and they done a great job of mines.

L_COLE · DTR Respected Member

Sorry mate only just seen your reply. So how much was your re-bore all in when bored for the makita size piston? I take it you had some performance gain when re-bored?

Going to be stripping her down soon for powder coating, so while the engine is out might as well get the bore done. I'm going to be Stating it all on the 20th April so I'll post something on here when I start.

madrevs · DTR Senior Member

Would recommend grampian motors in liverpool brilliant bunch of people and cheaper than pjme.they also supply and manufacture the reboring machinery for alot of the other places in the uk.i think from memory my barrel was £25 for rebore plus piston and free next day delivery back to me.they also modified the powervalve for me aswell for free.was around £75 all in and there mitaka pistons are cheaper than any other place I could find.i personally wouldnt use it until youve fixed it as It will cause alot more damage than just a rebore

Dt Danny · Guru

^^ ive used grampian motors

L_COLE · DTR Respected Member

Sounds good m8 thanks. I think this would be the fix, after showing 2 other mechanics my bike they are all saying piston slap but only very slight. I've got no other choice but to ride it, it's my only transport for now so goanna have to wait until the end of may when college is finished.

So when I get around to this what would be the best size to have it bored to?

Thanks for all the reply's guys.

madrevs · DTR Senior Member

Depends on what size its at now u wont know till u take it apart.if unclean the top of the piston tjey normally have the size stamped on top.might not even need reboring might just need a hone but the engine place that does the cylinder will do all this and supply a new piston to match.max u can go to on a dt cylinder is 58.4 which is what mines at now