DT125R ARCHIVE

SkinBobUk · DTR Respected Member

Dead piston.....

Calum122 · Guru

Looks like not enough oil mate.

SkinBobUk · DTR Respected Member

Sweet, ill make sure the autolube and everything is working. Thanks for the advice.

Calum122 · Guru

Mate summits amiss.

Let me check the haynes

Calum122 · Guru

Sorry I'm wrong.

Overheating mate.

Need to check the cooling system. There is something about the oil. But the bore would be oily.

Check the cooling.

Has the bore got cross hatching on it?

SkinBobUk · DTR Respected Member

Nah the bore is mint, no marks of any kind, just the usual up and down ware from the piston.

I did wonder about oil as when i took the head off the piston and bore were not very oily at all, a bit too clean really.

Calum122 · Guru

Right. Well the bore should have cross hatching down it. If it doesn't then you should consider a review. The idea is to increase friction giving better compression. Naturally has the rings wear away at the bore the cross hatching is removed.

Check the autolube. Ive got a video of how it should be set up.

Also check the cooling system. I reckon you're overheating.

Also check the fuel. An insufficient fuel mixture can cause the cylinder to run hot.

Calum122 · Guru

And introduce yourself in the newbies section. It's a bit rude expecting people to help you when you're clearly just using this site for your own enrichment.

Calum122 · Guru

http://www.youtube.com/watch?v=WwFUzgr2xnA&sns=em

SkinBobUk · DTR Respected Member

Thanks again i'll look into all those you mention.

Also i've posted in the newbie section a day or so ago...... http://dt125r.activeboard.com/t51474015/new-from-lincoln/

But for some reason when i post pics it says as mod needs to approve my post as it looks like spam, so maybe it hasn't shown up as new posts or something.

Calum122 · Guru

Ok well that's not too bad then. I obviously havent said it buy welcome to te forum.

SkinBobUk · DTR Respected Member

Actually having looked again with some light I can see cross hatching. I've attatched some pics just to be sure.

Calum122 · Guru

Bore looks pretty good. Which is an indication of appropriate oil. I would say its over heatig or foul fuelling.

Have a look at the carburettor. Is it clean. Of not then it could just be foul fuel and you might just get away with a new head gasket. Else it could be coolant. Worth checking the cooling system

superted · DTR Respected Member

looks like there hasnt been enuff fuel so the spark has been arking out on the piston causing it to start burning throught the piston

Calum122 · Guru

Are you just using a normal spark plug?

You should consider using an iridium one.

Alright. Well then. You know what you need to do. Like I said. A lack of fuel can lead to overheating.

louisBOSS · DTR Senior Member

Would suggest to premix it .

Also make sure its running the corrtect jets. You never know it could have been rode about for months with the wrong size jet or plug,Then corrected it sadly to late.

Calum122 · Guru

Autolube is gammy. But convinient.

SkinBobUk · DTR Respected Member

Thanks for the advice chaps. Im taking it all onboard ready for when i get a day off to get the spanners out.

DT-R_bradders · Guru

ohh look at the transfer ports on it, knife edged... maybe i should finish off the one i started doin.

looks odd tht piston tho. wat was ur temp gauge sayin at the time it cut out on ya?

SkinBobUk · DTR Respected Member

It barely moved above bottom. But the bike has some electric problems so it may have been reading wrong.

But ill make sure to sort out all the little problems before killing it again lol.

One thing that has confused me is that my piston measures 58mm and bore 58.4. And the pistons come in sizes 57.9 or 58.4, so im not sure which one to get.

FunkeyMunkeyDavid · Guru

has it dented the top of the piston a bit,or does it just look that way? looks like a golf ball lol

SkinBobUk · DTR Respected Member

Yeah the piston has a big dent in, if i shine a light on top i can see it through the piston.

FunkeyMunkeyDavid · Guru

not good lol i'd be tempted to say its detonation caused that. hard to say if the destroyed plug caused it though,or the detonation destroyed the plug? you'll defo need to sort the electrics before you run it again. what sort of electrical problems did it have?

SkinBobUk · DTR Respected Member

Well all the seller told me was that the electric start didnt work due to a flat battery, but i put a new battery on and there is still no life. No lights when turning the ignition on, just the ypvs whirr. The fuse is fine so im thinking a break in a wire somewhere or maybe the ignition switch.

Calum122 · Guru

Hmm.

If you turn the power on an you get the YPVS but no other electrics then it sounds like a rewire. I'm no expert on this but I'll say this. If there was a fault I.e. exposed wire it would short circuit blowing the fuse. So a loose wire would be easy to experience. When the engines on the lights no longer run off the battery. They run off the coils. So here we'd have a seemingly working bike.

So what may have happened is he's rerouted the wiring to bypass something that was giving him grief. Something I haD to Do my last DT.

NEV · Guru

Does the starter motor have a relay/solanoid? maybe thats whats buggered, is the starter motor clicking? has it jammed on the bendix? sometimes giving it a sharp tap with the arse end of a hammer on the starter motor body can free it. other than that whip the starter motor off and test the two terminals on it with another fully charged battery, see if it spins

DT-R_bradders · Guru

will make a difference wozz smoother flow for the air/fuel mix,

skin bob try removing the starter solanoid, there will be 4 wires goin into the part wer the solanoid plugs in, 2 skinny wires n 2 bigger ones, bridge the 2 connections for the 2 bigger wires, use a bit of wire thats as thick as the 2 wires or use 2/3 smaller wires wound together at the ends to make it take more amperage, if the starter fires up then its the solanoid thts fooked, if not then the starter has problems , might jus need removing then cleaning out n spray a bit of WD on the shaft the the small gear runs on think these motors have a one way bearing that the gear runs on unlike a normal car starter moter has wer the gear slides out to engage the fly wheel

best if you can get yourself a multi meter to check if power is getting to wer it needs to be, u can diagose the problem without removing any parts with a multi meter

SkinBobUk · DTR Respected Member

Thanks for the awesome advice all. Ive got a day off on tuesday so can finally get out and have some fun with the thing. Ive got a multi meter so can check all feeds, etc. Hopefully by the end of the day i can post back with some good news!

NORFE · DTR Trusted Engine Builder

that looks like an ignition system fault like its advanced to far and been sufferuing pre ignition melting the piston crown,its not lack of oil if it was lack of oil the first place to melt/siez is the intake side of the piston and the bore would be shagged

the rest of the piston looks fine

the bore will be marked due to the particles of alloy floating about off the crown, it would of been like sand particles

a leaky head gasket can also cause the piston crown to deteriorate like that as the cooler temp of the coolant hitting the red hot piston crown can cause it to contract/cool quickly and make it brittle and flake off

but im guessing looking at the pics it will be the ignition to blame, check the timing with a strobe light before it goes back on the road

start with a new piston /rebore, make sure you get every bit off alloy out the bottom end, if id of had a piston done that tho idd be completely stripping the bottom end to make sure its all free of bits as any bits of piston particles will wreck a bottom end may aswell tip some sand in the bottom end and run it , atleast if u rcheck and rplace wht needs be the engine will last longer in the long run, no point chukkin a new top end on if the bottom end fails 2 weeks later

SkinBobUk · DTR Respected Member

Thanks norfe ill definately check out the timing. Im going to strip out the bottom end like you said and ensure there is nothing floating about. Just one question tho, do i need a rebore? There is no damage to the cylinder itself. Although ive measured it and the bore is 58.4 but the pistons on sale are 57.9, 58.15 or 58.4. So im not sure if the cylinder should be bored to match a piston or if one of the above would fit.