DT125R ARCHIVE

Spartan · DTR Senior Member

Engine Failure

RudiRulez · DTR Senior Member

sounds to me like you had a semi siezure, chances are youve ****ed your piston rings and possibly damaged your piston and bore, basicly your engine wont fire up because theres no compression.

thats just my conclusion from the info youve given us.

woll · Guru

Rudis right your engine has seized, that's why the back wheel locked up. And chances are if the wheel locked up at 60 you'll know have a flat spot on your rear wheel. And i think if the chain had come off you would of lost some teeth of one of the sprockets or smashed the stator and the engine casing.

Spartan · DTR Senior Member

Picked up a new spark plug on the way home today just as something to try, but still no change. Do you think it's best if I open up the cylinder and check the piston? Have been thinking about it all day today whilst at work, kinda dreading what I mind find if I check the piston.

How would I test compression?

Dickhead · Nonce

try roling it in 1st gear take ur exhaust of and take a picture of it and post it

Spartan · DTR Senior Member

Ok mate will try tonight.

Spartan · DTR Senior Member

You were right guys, my piston is shot. Hope you can see in these pictures, it looks to me like a big chunk missing right up by the rings:

I'm going to need a top end rebuild now aren't I

EDIT: Forgot to ask what might cause this, I have recently hit 13k on the clocks. Surely this can't be the bikes way of telling me the piston and rings needs changing. Thought it was more subtle than that haha.

-- Edited by Spartan on Monday 12th of July 2010 07:04:18 PM

DeeTee · DTR Senior Member

Another piston PV collision, these events are far too common for comfort

Spartan · DTR Senior Member

How could the piston collide with the PV. Could it be that the piston had become slightly warped?

DeeTee · DTR Senior Member

I dunno my friend but its always damaged at the exhaust port side of the piston. I have seen it several times now. These bikes seem to be a bit fussy about something, maybe the rings were worn...12000 miles is a long way on one set but I dont know if they had been changed before...do you?

Just a guess mind bu my bike wont be going past about 6000 on one set of rings I know that much.

Spartan · DTR Senior Member

No they haven't been changed before so they have done all this mileage on one set. Well i've been reading through darkangel's post in the 'how to' section about top end rebuild. It's really useful so i'm going to the get the parts I need and follow the steps. Was thinking what I might need but it's all there:

Top end gasket set
Piston kit
Top end bearing

If the cylinder is damaged in any way i'm guessing it will need a rebore too?

I've never attempted anything like this before, I understand it's important to get the right piston diameter, do I just measure the head of the old one or shall I just speak with the yammy dealer.

Dickhead · Nonce

i wouldent use a yammy stealer

dout the pistons hit the powervalve looks like heat has done the damage here take the barrekl of and sent it to pjme

DeeTee · DTR Senior Member

robin wrote:

i wouldent use a yammy stealer

dout the pistons hit the powervalve looks like heat has done the damage here take the barrekl of and sent it to pjme

Could be but 60 isnt exactly caning it, either way yes PJME will make a nice job of a re-bore and supply the piston kit and gasket, dont forget to ask if you can have a discount on the re-bore, you may get 10% off if you tell them you are a memmber of the DT125R club .

craigbulmer · Guru

10% discount my arse, more chance of a discount if you do show them your arse haha.

Looking at that, id say a rebore is needed. But you would need take the barrel off and inspect it to see any different. Id never done anything like this before either, its honestly easy enough to do, follow the guide carefully and you will have done it and be starting it up without realising

http://www.activeboard.com/forum.spark?aBID=66365&p=3&topicID=30312484&page=3
Page 3

fray · Guru

Looks nasty, the thing is tho will bits off metal etc have gone down into the bottom end?

Dickhead · Nonce

dout it i had a piston skirt fal in to my botom end at 10000 rpm engins stil in my bike now

RudiRulez · DTR Senior Member

DeeTee wrote:

Another piston PV collision, these events are far too common for comfort

damn, what the hell is going on! I've got a big(3 hours) ride upto leicester in 2 weeks and im actually worried now.

Spartan · DTR Senior Member

That's a point fray I hope not though, I think some of the bits have settled in the exhaust port looking at the pics. It's very oily in there too.

I might start taking it apart tonight and get the piston out to have a look. I'm kinda worried about the barrell I understand if there is even the slightest of scorches or dents then it will need a rebore.

Craig was it PJME you sent your one off to, I have seen this name mentioned a few times now. Do they supply the piston and rings then aswell or do I need to get that from somewhere else. Noticed you got a mitaka piston kit. What's wet n dry and oven glass, something you said you used to get the cylinder head uber shiny, looks mint afterwards :)

Dickhead · Nonce

if the barrel aint to bad you will get away with a hone you sont want the barrel to be shiny or the rings wont bed in and you will lose power

craigbulmer · Guru

Nope mine wasnt sent off to PJME, it was sent to Grampian Motors in liverpool. (http://www.grampianmotors.co.uk/) The garage i use reckon they are the best in the country, ask different places, they all use the 'best in the country' but they are all different places haha. The rebore at this place with only £17.50, postage is quite alot to send though. Alot of places do this kind of work, just need to find a recommended one.
Ive not got a Mitaka piston, mines a proX piston. On the same level as Mitaka, the place i used like many others match pistons from several brands and find the best fit. Good fast service aswell.

Wet n dry is a type of sandpaper that can be used on metal (go to B&Q

). Cylinder heads have to be perfectly flat, oven glass is engineered to be 100% straight, its the best thing to use. If you seize your bike up, or in any case really, its best to skim the head down, which is why i used wet n dry to make it completely flat. Its best to have it machined flat but that costs money that i didnt have lol.

fray · Guru

PJME will supply a piston kit, they will rebore your cylinder to match the piston perfectly they will supply you a gasket set aswell. If it was me i would defo get it rebored while it is stripped, be stupid not to imo after whats happened! Id also get the head skimmed and fit a new genuine yamaha head gasket. Id get a new small end bearing aswell. May aswell go the whole hog! You have got a complete fresh top end then.

Give your conrod a wiggle up and down while youve got it apart to check for main bearing play.

Spartan · DTR Senior Member

Finally got it all apart it's taken me the best part of 3 hours I think.

Can now see the full extent of the damage to the piston, there appears to be scrape marks on the side of the piston and some in the barrel. Overall condition of the cylinder seems ok, it's all smooth in there.

Thanks for the input guys btw much appreciated biggrin

, a fresh top end sounds good to me plus it will only play on my mind if don't get a rebore done in case there was something I missed.

I might aswell just get the head skimmed at the same time as the rebore then, do you think it will be much more? I've been told of a local bike place too that can do this so i'm going to find out tomorrow hopefully.

Craig mate I still don't get the oven glass bit lol, i'm being an idiot aren't i confuse

Fray which part is the small end bearing?

I'll post some pics up tomorrow after work when it's abit lighter to take them.

fray · Guru

The small end bearing is the one that goes inside the piston in the top of the conrod, they are only £5

The oven glass that craig is on about is just a flat surface to rub the head on to get a perfectly flat surface (put sand paper on the oven glass then rub the head in figure of 8 over it) may aswell get the head skimmed properly tho its only like £15 at PJME its £25 for a rebore there aswell just to get an idea of prices.

Dickhead · Nonce

you should not need to get the head skimed unles it was warped

woll · Guru

robin wrote:

you should not need to get the head skimed unles it was warped

You shouldn't but there's always a chance it's slightly warped. If he wants to get it done then let him. I would put money on it improving compression and making the bike run better.

2strokecrazy · DTR Member

this looks like a heat seizure, normally caused by incorrect 2 stroke mixture or pump failure, i doubt it would be the pv as its a 2007 reg bike and if its on its 1st bore it would be well within tolerance

Spartan · DTR Senior Member

Some pics for you:

Cylinder

Looking down cylinder

Further inside by exhaust port, looks like it was scraping against the side

Piston, scrape marks on the side

Cylinder head

So there we go biggrin

How much do they actually take off when they do the rebore and skim the head, is it a few mm?

Spartan · DTR Senior Member

PJME say that all studs need to be removed aswell as the PV assembly.

Does this mean I need to remove the PV from the barrel, have just removed it anyway to have a ganders at it, it's filthy:

What do you think would be the best way to clean all the crap off, that goes for the cylinder to. Would something like carb cleaner or wd40 do the job?

-- Edited by Spartan on Wednesday 14th of July 2010 08:00:27 PM

woll · Guru

wow that frames in good nick lol. If i was going to clean it up i'd use either some fine wet and dry or a wire brush on the drill

Dickhead · Nonce

ive found the easyest non damageing way to clean the pv roller is with a one of them mettal brillo pads