DT125R ARCHIVE

Boxing · Guru

RE: DT won't go past 40MPH. :-(

Calum122 · Guru

How about some pictures?

Boxing · Guru

Calum122 wrote:
How about some pictures?

Phone's dead, and can't find the charger. Will upload some tomorrow or something.

The piston is all black and full of oil not a pretty sight when you just paid £1100 for the bike. disbelief

Going to rebuild the top end and get a new CDI and loom to get rid of the rev limiter.

Lesson in life learned, don't buy a bike without test riding it. And don't pay £700+ in insurance before checking the engine out.

MDK · DTR Legend

yep kinda what some of us suspected .

it is a common case if some one is selling a dtr cheap or even at a good price is that they know it is on its way out . they will say its just had a new topend so dont ride it fast when they realy mean its on its way out .

haveing a good look at the bike in some cases you can see if there has been work done are the head bolts clean or look like they have been removed recently can you see the gasket poking out do,s it look new look at exhaust bolts do they also look well rusted and untouched along with threads on the bolts .
you can usualy tell if there has been any work done just by looking at bolts covers gaskets or screws .

maybe it is good you spotted this now or it could have turned in to a full rebuild .

Boxing · Guru

Now I have some n00b questions to ask.

You reckon the bottom end will need doing as well? Or just the top?

And anyone got links to the parts I need? Piston and rings etc?

I'll drop the engine out when I have the parts and clean it up a bit.

MDK · DTR Legend

best to first get your top end of and past some good pic.s

check is any of the rings or piston have broken away the last thing you need is any small bits of metal falling in to the bottom .

sure some of the other lads will best advise you how to check your bottom end or bearings ect for any play or wear and what the best option piston rings kits along with good gaskets .

Calum122 · Guru

You have to find out why yhe top end has failed before you decide whether or not a full rebuild is due.

You have 14 days to cancel your insurance with just a £50 admin fee. It may be worth doing that.

Get some pictures of the barrel. The bore. The piston. And I'll tell you what the crack is.

Also £1100 for a dtr isn't bad. Ypu can do a top emd rebuild for £100 so the bike cost ypu £1200 and it will be great. Stop going on about the rev limiter. Some DT's are made to rev out at 10k some at 12k. You dont really want to be riding at 12k revs anyway. Get the bike running as it should and it will do 70+mph really quickly and you wont really be bothered about a 10k limiter.

Like said. Thousand times the CDI's ARE NOT EASILY CHANGEABLE. So don't fúck about wasting money on them.

Calum122 · Guru

Boxing wrote:
Now I have some n00b questions to ask.

You reckon the bottom end will need doing as well? Or just the top?

And anyone got links to the parts I need? Piston and rings etc?

I'll drop the engine out when I have the parts and clean it up a bit.

Also stop being lazy! We've given you plenty of help. There are a 1001 threads about doing a top end rebuild with links in those. So how about reading up on them before asking and asking.

You WON'T know what piston you want until it is all apart.

Just use the search function to find what you need. If you get stuck the. Ask. And POST IN THE RIGHT SECTION AND WE WILL HELP YOU!

Nathlaad · DTR Legend

Cal goin sik

MDK · DTR Legend

sounds like you have already given up cus of a little bit of work maybe your better sticking to the mopeds .

Calum122 · Guru

Boxing wrote:
The rev limiter is 6,000 RPMs, not 10,000.

And I've stripped half of it out. The bikes a complete shed. The bolts are all odd, someone's been messing around with it. The petrol tank is leaking and all sorts.

I'll be looking through the threads in a minute.

And insurance was done three weeks ago now.

It doesn't matter, I'll see what will happen in the future.

I can't do the bedding in process, I'm a speed demon. So I think selling it would be the best solution once its fixed up, I don't know.

I'll see if my opinion is any different when its sorted out.

/thread

-- Edited by Boxing on Monday 1st of April 2013 05:43:26 PM

Lmao! No it isn't. The rev limiter isnt 6k rpm mate.

Boxing · Guru

In neutral it revs up to 7,000 RPMs, in gear it'll only rev up to 6,000 RPMs. It should be higher?

As I said I'm a n00b with DT's. And the bike will be sorted.

I don't know if I'm selling up.

I don't want to be stuck at 30MPH on it. But I'll probably do the running in process and be sorted with it.

Still not got the lump out, I'll know more once I've dropped the engine.

And I'm not bothered about the work, I'm just annoyed the bikes got odd bolts here and there, so its been stripped before.

It's more annoying that the seller said it'd be fine, and I've done near enough all the stuff you guys said to do, and the reed switch and all that doesn't even exist on the '97 models as far as I'm aware. :/

Calum122 · Guru

Yeah he's hardly going to tell you the truth now is he.

Yeah mate its shagged. You said yourself the pistons shagged. If its damaged you'll damage the bore. If you have a shagged piston its not going rev propely now is it.

MDK · DTR Legend

you guys kinda beat me to that point and thought we got past the rev limiter thing once he found out the piston is fckd . its clear the bike will not rev high cus of the piston problem .

you will see this once its sorted and the revs are totaly normal again ..

Boxing · Guru

P030308_20.00.jpg

P030308_20.00_[01].jpg

-- Edited by Boxing on Tuesday 2nd of April 2013 05:34:30 PM

Boxing · Guru

Meh. I give up on it.

Going to see if I can make any £££ back on it by stripping and selling parts off of it.

I ain't no mechanic, and this bikes out of my depth. And I ain't got the money to get a mechanic to do it. So fuck it.

Calum122 · Guru

Doesn't look too bad mate. Get me some pictures of the bore now. The piston doesnt look too badly scored. Possible heat seizure due to incorrect warm up procedure or other.

On the cheap you can get away with new piston amd rinfs. Or preferrably send it away for a rebore.

Stop being a baby. Its only a two stroke. Dont need to be a mechanic to do piston and rings. Thats just maintenance on two strokes. You've done well by getting the cylinder off.

Get me so shots of the bore and the pistons please.

If you stop being so defeatist and listen to me and others i will be more than happy yo talk you through it. Wont take longer than a week and you'll be on the back wheel ripping it up!

First you need about £100. Thats not a lot. Depending on how badly its damaed. But it doesnt look that bad to br fair.

Calum122 · Guru

It's not black and white mate.

What you do is this. Take the barrel off the bike and wad the bottom end with kitchen paper to avoid dirt getting into the bottom end.

Have a look at the piston. On the top it will have an arrow and a number. The number will tell you what oversize the piston is. If its 1.5+ then the powervalve will need modifying if you go down the rebore route.

If not then just take the studs out. The powervalve and send it off to PMJE for a rebore. You can get a rebore and correct piston for about £60-£100.

You'll want a genuine HEAD GASKET and might as well grt a genuine bottom end gasket. No more than £20.

Place the bottom gasket on correctly.

Remove the circlip on the con rod. Remove piston. Replace small end bearing. Insert piston by making sure the arrow points towards the exhuast port. And make sure the piston ring end gap is within tolerances. Also check that the piston fits in the bore nicely. I.e. its the correct oversize.

Install cylinder. Install genuine head gasket with UP readable.

Install head and tighten to spec. If unknown then friggin tight.

Do a heat cylce. Then retorque head nuts. Then run in for 500 miles. After that you'll be good to go.

Boxing · Guru

Bikes mostly stripped now, still not got the engine out to get to the piston. But yeah.

P030308_21.36.jpg

Struggling with the swingarm now. Need a rubber hammer which will be sorted tomorrow.

This nut seems to be on tight or welded up? confuse

P030308_22.45.jpg

Been whacking it from the otherside, its not freeing.

Going to see if can get the head apart without dropping the engine now.

Going to finish it up tomorrow. And who is PMJE?

Some idiots owned this bike before, the screws and bolts have all been over-tightened and locked on, had to smash the heads off of the screws with a hammer and chisel.

Odd nuts here and there, but oh well.

Will be all sorted soon. biggrin

stillbroke · Guru

**** ****

Calum122 · Guru

Dont need to drop the engine out for the cylinder mate. Will come out with the engine still on the bike.

And thats the wrong side of the swing arm. The other side loosens up mate.

eG x LoGiKzZ · Guru

you need to undo the swingarm bolt from the other side, you should be undoing the nuts instead of the bolt end

Boxing · Guru

Yeah, I've undone the other side, it won't come off, we're suspecting someone's welded the other side on. The bolts off on the other side. :|

eG x LoGiKzZ · Guru

ohh, have you tried taking the weight off of the swingarm? there is a spot weld next to that bolt to stop it turning but it should come out

MDK · DTR Legend

yeah lean the bike over to the stand side and slip some box -stack of breeze block or a crate under the bike to lift the back wheel of the ground .

with the weight of the bike on that bolt it will be like a vice grip ..if still stiff once lifted find a poker metal bar or even a large + screwdriver put in the hole and tap the bolt out with a hammer if needed althou I use a good lump of wood so not to slip and smash the engine .

pic of bolt

but as said above the head should come of with engine in place move kicker so piston is realy at the bottom of the stroke .

cant wait to see the inside of the bore as the piston dosnt look all bad althou the pics are blured .

I know this can all seem off putting and you may feel like fck it sell it but what your doing now will serv you well in the future and you may even earn money doing your mates bikes .

Boxing · Guru

Cheers guys.

Will sort it out tomorrow. I'll post some more pictures tomorrow as well.

Boxing · Guru

Scratched some of the black stuff off, no numbers on the piston. Just an "UP" sign.

And the head has "3MB00" written on it?

I don't think there is a YEIS bottle. Have you got a picture of one? So I can see what I'm looking for?

And what about the play on the bottom end? It move 3-4MM left and right, rocking. But it doesn't have any play going up. Is this normal?

Thanks for all the help and advice. smile

-- Edited by Boxing on Wednesday 3rd of April 2013 05:10:42 PM

Ralzy · Guru

YEIS (Yamaha Energy Induction System)
More power and better fuel efficiency

SUMMARY
This system utilizes the negative pressure produced in the intake passage when the piston moves up and
down to induce a part of the air/fuel mixture into and out of a special chamber. In this way the fluctuations
in the velocity of air/fuel mixture stream can be evened out, thus creating a more stable and effective intake
function for higher power and better fuel economy mainly in a 2-stroke engine.

BACKGROUND
When the intake port is closed in conventional 2-stroke engines, the negative pressure level in the venturi
rises and thus decreases the effectiveness of the venturi action in a certain rpm range during the next intake
stroke. The YEIS is a good technical solution to this problem. At first this system was adopted in motocrossers
so that their race performance could be increased, but its range of application has gradually spread to include
even the Yamaha Mate V50.
CONSTRUCTION
Its basic construction is very simple using a connecting pipe between the intake passage (carb joint) and the
special chamber. Power is increased especially in the low to medium speed range, without changing the
basic design of the engine.
OPERATION
Fig.1
When the piston moves down, the air/fuel mixture in the crankcase is compressed to close the reed valve. A
part of the air/fuel mixture is then induced from the intake passage into the special chamber while at the
same time giving a boost to the air/fuel mixture stream past the throttle valve.
Fig.2
When the piston moves up and the reed valve opens, a negative pressure is produced in the intake passage.
The chamber then releases the air/fuel mixture into the intake passage. This intake stream joins the stream
coming through the throttle valve and enters the cylinder, thus increasing the supply of air/fuel mixture each
time.

RESULTS
The air/fuel mixture flows through the intake passage smoothly and continuously so that the intake efficiency
is increased and fuel supply from the carburetor is evened out, thus allowing easier carburetor setting
for higher power and better fuel economy
especially in the low to medium speed
range.

-- Edited by Ralzy on Wednesday 3rd of April 2013 08:38:52 PM

Boxing · Guru

Top end of the piston.

Had the wrong spark plug in, and the previous owners an idiot.

The top end.

This the best top end?

Someone over-tightened the powervalve and put a pin in to hold it!

Tissue in the bottom end.

The rod has 3-4MM play, moving left and right. Its not tight.

All the parts from the bike.

Someone put a pin in the PV.

Piston

Inside the topend

Piston side view

Top of the piston.

Calum122 · Guru

Nice one matey. Looking good.

Looks like incorrect mixture of oil. Looks like too much.

The bore looks pretty sweet so good news there. No real damage done just needs a good service.

Doesn't look like there is a number on the piston. So that indicates it is standard size.

I notice you have got a 3BN head. If you want better power you're going to have to swap that over for a 3mb head. Worth while upgrade and can get one for about £30.

There are two ways you can go about this. The cheap and desperate way with risk of failure.

Or the proper way. When my bike got nicked and ramped i had to skimp out a bit and i went the cheap way. 5k miles later engine is still crisp.

My bore was prestine. Make sure there is no score marks on the bore. Doesnt look like there is which is good.

Have a look for me. See if you can see crosshatching on the bore. You'll needs to hold it in certain light. But you should see crosshatching on the bore. If not then its reccomended you go for a rebore.

The proper way is that you have that bore sent away for a rebore. This gains you extra cc and a fresh new top end. But if you can't remove the powervalve then its going to be trouble.

The cheap way which i did but worked for me is to get the same size NEW piston kit.

And install new piston and rings. New grudgen pin. And small end bearing. And put it all back together with a new genuine head gasket and a new bottom
Gasket.

Job done sorted. Defo worth getting a 3mb head as well.

Make sure there is no gasket left on any of the surfaces.