DT125R ARCHIVE

hairdoo · Guru

RE: Engine Failure

Malc · DTR Senior Member

Looks like a classic seizure, very likely due to lack of 2T oil or looking at the exhaust port far too lean a petrol/air mix - check your oil pump is okay once its all back together, and check all your carb settings, etc. to make sure the pertrol/air mix is good too - all that white in your exhaust port should really be black! What colour is your spark plug electrodes?

Used to see these seizures all the time, even before power valves were in there! ;)

delve91 · DTR Senior Member

That hasnt hit the powervalve, i hear lots of bahhhhhhing going on on this forum bahhhhhhhhhhh, does ur bike have a coolant bottle! lmao, if it dosent then ur gonna get lynched!

woll · Guru

i hear you delve :D i've made people fully aware i think that unless you bore past the limit then you won't hit the pv lol.

Spartan · DTR Senior Member

Right chaps, after a recommendation I found a local bike shop today that specialises in mx bikes, the workshop was full of em. The place was called 'In Chains' if anyone is interested it's in Ringwood - http://www.in-chains.co.uk/index.htm
A good place they seemed to know their stuff.

Anyway, he suggested it to be heat problems that was the main cause and not a piston collision with the pv, the head gasket has gone too on further inspection.

He pointed out this bit on the cylinder head, scorch marks where it had blown through:
Cylinder head.jpg

It sounds like there was not enough coolant circulating either, it was leaking and burning away in the cylinder.

Sure do have a coolant bottle Delve lol, it's weird because the bottle looked full to me so I thought there was enough coolant in there, turns out that the plastic had melted slightly at the bottom and prevented any coolant from going down the hose. I took it off, filled it with water and jammed a thin screw driver through the hole until the water free flowed out.

Well it's getting a rebore today, he's going to supply me with a new piston, rings and gaskets and I need to get a small end bearing. Should have it back by monday for a fresh rebuild.

@malc, checked the spark it's like a brown color which I think is normal. I've bought a new one anyway - br8es. You've got me thinking about the mixture now, I was playing around with it just trying different settings - I settled with 1 full turn out with the screw...hmmmmmm

biggrin

-- Edited by Spartan on Saturday 17th of July 2010 05:22:53 PM

woll · Guru

ah good news mate, always good to have a professional oppinion :D

Spartan · DTR Senior Member

Yeah man good news biggrin

Just realised something, I no longer have the circlips that go on either side of the piston. One broke when I was removing it and the other pinged off somewhere, do they normally come with a new piston or will I need to get new ones. Completley forgot about this.

Malc · DTR Senior Member

Spartan wrote:
@malc, checked the spark it's like a brown color which I think is normal. I've bought a new one anyway - br8es. You've got me thinking about the mixture now, I was playing around with it just trying different settings - I settled with 1 full turn out with the screw

Brown/tan colour is about perfect right enough. What year is your bike? I feel its always best to leave carb settings as standard (except main jet if necessary).

@delve91 - what is bahhhhhhhing?

Spartan · DTR Senior Member

hey malc, year of bike is 2007.

DeeTee · DTR Senior Member

You can buy circlips on their own from many places, for example PJME @ £2.23

http://www.pjme.co.uk/acatalog/Yamaha_DT125R_Engine_Parts_Top_End.html

-- Edited by DeeTee on Saturday 17th of July 2010 07:59:22 PM

woll · Guru

Malc wrote:

Brown/tan colour is about perfect right enough. What year is your bike? I feel its always best to leave carb settings as standard (except main jet if necessary).

@delve91 - what is bahhhhhhhing?

Think sheep wink

craigbulmer · Guru

Circlips normally come with the piston kit mate, mine did.

Spartan · DTR Senior Member

Thanks for the link Deetee. Alrite craig cheers, I will make sure when I go collect it hopefully tomorrow or tuesday. I'll let you know how it goes, can't wait to get it back. Compression will be better and I should get abit more out of the bike after the rebuild.

-- Edited by Spartan on Sunday 18th of July 2010 07:08:17 PM

Dickhead · Nonce

make sure the clips dint drop in the crank or ur be wasteing ur time

Malc · DTR Senior Member

Spartan wrote:
hey malc, year of bike is 2007.

A quarter turn out is yer lot on the airscrew. Is your main jet the right size?

Spartan · DTR Senior Member

Thanks malc, i'll stick it back on quater turn out. If the mixture is wrong, could it cause major problems then?

I can't remember what size the jet is, 220 maybe, tbh i'm not sure how to tell. Is it printed on the jet because I think I remember seeing that number when I had my carb apart.

Malc · DTR Senior Member

If the main jet is too big it'll run too rich and you'll lose power. If its too small it'll run lean and you'll lose power as well as risk just about every trauma you can have with a 2T engine. Lean mixtures on 2T can and usually are fatal.

210 is correct for a 2007 RE, but if the exhaust is non-standard sometimes it will be rejetted to suit.

The airscrew has an effect across the entire rev range and too much out leans the mixture across the entire rev range out.

Spartan · DTR Senior Member

I laid a brick malc after reading that...fatal...holy s**t and heres me turning the air screw lean thinking it will increase fuel economy...doh!

Thanks.

I'll check again at the weekend, whilst waiting for my barrel i've put everything back on the bike and stored it at the back of me garage again.

-- Edited by Spartan on Wednesday 21st of July 2010 07:27:58 PM

fray · Guru

Read this. The chipped crown section.

http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

Explains why the piston proberly failed, does tally with your HG leak.

Spartan · DTR Senior Member

Thanks for the link fray, a really handy page to keep around. Sounds about right too.

Going to give the shop a call today I think to see if they have completed the rebore.

I still need to pick up a small end bearing too, I spoke with yamaha yesterday and they quoted £13.50 for a new one. I looked here:

http://www.pjme.co.uk/acatalog/Yamaha_DT125R_Engine_Parts_Top_End.html

PJME sell one for £4.50, but it's for a DTR. Will that matter? Abit worried about why it's so much cheaper, I don't want to get problems down the line.

biggrin

2strokecrazy · DTR Member

i'd stick to standard mate, yes its more expensive but is of a much better quality, dont get me wrong some pattern stuff can be better than standard but i don't mess about when its my own engine, i only use pattern on engines if i was going to sell it but thats my personal opinion

Dickhead · Nonce

that bering will last alot longer than your top end will aslong as its a ok brand such as koyo etc it will be fine

from a dealer i was quoated 34 pound each for genuwin main berings once i found out the numbers i got the samae ones up the road for 14pound each and thay are the same brand etc go figure ?

2strokecrazy · DTR Member

if you have a local koyo dealer then ideal but there isnt alot around, good to here yours is only up the road,ideal really

Spartan · DTR Senior Member

Still havn't got the barrel back yet, hopefully picking it up tomorrow now after speaking with the shop yesterday it kept getting delayed. Wanna get back on the bike now, there is only so much polishing you can do whilst waiting.

Spartan · DTR Senior Member

Finally got it back along with a new gasket set and piston kit:

It's had a 0.5 mm overbore so the piston is 56.5mm. The shop cleaned up the barrel for me along with the PV which came back spotless, spent the afternoon yesterday putting it all back together.

Getting the rings in the barrell was abit tricky but the bit that took some patience was getting the circlips into the piston, damn little things kept pinging away.

Changed the gearbox oil, coolant, fitted a new spark plug and swapped all the nuts for stainless steel ones haha, looks the bling now wink

Took it out for 10 miles yesterday after I finished and all was good. Went out today for 70 miles not going above 50. Have been taking it easy but already it feels alot better than before.

So there we go, top end rebuild complete. Just another 400 odd miles to go biggrin

hairdoo · Guru

where did you get rebore done spartan as im wanting to do mine next week , only place ive found in the area was SEP engineering at kegworth , did u av to buy a little end bearing seperatly or did it come with the piston ?? .. cheers Dave smile

fray · Guru

Glad you got it sorted bud!!

Its a pain running it in ay it, did my head in!

delve91 · DTR Senior Member

warning warning!!!! Non genny head gasket :o :o :o!!!!!!!!!!!

gooner78 · Guru

delve91 wrote:
warning warning!!!! Non genny head gasket :o :o :o!!!!!!!!!!!

I know what your saying i went through two off them in just over 100 miles i put a genuine one in and its lasted just over 2000 so far

Dickhead · Nonce

i was guna say that any one ever thought of geting a 0ring machined like on ktms nd rs 125s would make life much easyer