DT125R ARCHIVE

FunkeyMunkeyDavid · Guru

RE: What shall I do?

NEV · Guru

Funnily enough when I had my rebore done at Cornish motorcycles, I ordered the piston and had it sent down from road and dirtbike, luckily the lad doing the re-bore clocked it as being an RD one due to it having windows in it, and sent it back to be swapped for the right one, but apparently it was packaged as the wrong piston in the right box, maybe there was a duff batch of wrongly packaged pistons.

GADGET · Guru

Wunt be the first time fellas

Harry · Guru

Sweet thanks lads

Will be measured tomorrow and see if the rebore can be done at work, although most of the machines are cnc so unless a program is written it can't be done, then skim and new piston :)

Is there any guide or anything in what sort of things to do when rebuilding it, as in to drop oil it in and running it in etc

GADGET · Guru

Yeah put 2stroke on everything ,and grease on the base gasket,oh and put a rag in the bottom cases until the barrels ready to slot right down so you don't drop anything in th bottom end (bloody circlips)

FunkeyMunkeyDavid · Guru

+1 biggrin never done that before

AndyYam · Guru

I have. dropped a circlip in the crank when rebuilding this one. sent about an hour with torches and hooked wire trying to get it out.

NORFE · DTR Trusted Engine Builder

all you need is a smear of oil on the skirts of the piston, if you drizzle oil all over every thing like i see every one do its way ott,, enough oil comes thru off the pump to lube it

look up dry rebuild on tinternet

helps the rings bed in better aswell so i was told or read some where

Nathlaad · DTR Legend

treat it like gash kid!

GADGET · Guru

Yeah man just a smear make sure you lube the small end bearin ,but yeah know what u mean Norfe people cake it on sometimes then spend an hour kickin it over and cleaning th plug wondering why it won't start

AndyYam · Guru

I don't think I put anything on my small end bearing :/ never have done before.

NORFE · DTR Trusted Engine Builder

GADGET wrote:
Yeah man just a smear make sure you lube the small end bearin ,but yeah know what u mean Norfe people cake it on sometimes then spend an hour kickin it over and cleaning th plug wondering why it won't start

EXACTLY HA... smile

Harry · Guru

Bit of oil on the piston and bearing, got it :)

Going in today to get skimmed and rebored so shouldn't be too long now

Harry · Guru

Few questions, bear with me...

The barrel got measured at 56mm by the engine builders, that's standard right?

So the first oversize I am looking at is 0.5mm..

So is this the correct kit? It's for an older TZR like said, but the advert suggests the first 0.5mm oversize brings it up to 56.9 not 56.5.

http://www.ebay.co.uk/itm/YAMAHA-TZR125-MITAKA-5mm-PISTON-KIT-/270877208006?pt=UK_Motorcycle_Parts&hash=item3f118a2dc6

I'm guessing this is just a measurement error, but best to check before I buy.

Also will the powervalve need grinding down it will it be fine for this amount?

At the end of the day I will just take the piston if it's the right one and say make it fit the barrel perfect but it's nice in my head to understand what's going on.

NEV · Guru

Now then Harry, somewhere in another thread I pointed this out to somebody, about the early TZR and DT bores being different to the later ones,
You'll need to bore the barrell out to suit the larger bore TZR piston, and yes you'll also probably need to grind the powervalve to suit, although probably not that much on its first size up, on mine I went maximum bore, so a fair bit had to come off the powervalve, only a suggestion, but if you live near the place doing the bore, take the whole engine to them, that way they can bore and skim to suit everything in front of them, you may also need the head gasket reaming out on the next bore up, and also the head may need machining as the cylinder volume needs changing too.

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Harry · Guru

Cheers mate

I'm trying to get this sorted ASAP so will probably opt for the smallest oversize with a dt piston that way there's more room for more rebored and the power valve won't need to be touched at all.

Sadly they won't be able to skim the head, but seeing as the gasket never went and it never got hot the garage looked at it and said it shouldn't need doing

Energized · DTR Legend

Yeah np's mate. It only needs doing if it's been warped etc :P

Harry · Guru

I can hope haha

Another problem is I cannot find a mitaka 0.5 oversize piston... only one on ebay is from a seller that is away for another 5 days :(

Any site I can get one from? Can't seem see anything just other piston manufacturers or different oversizes

NEV · Guru

Energized wrote:
Yeah np's mate. It only needs doing if it's been warped etc :P

No Enny yer right, it'll not need skimming unless its warped, but it'll still need machining out to adjust to the re-bore mate, again I had to have mine done as it was on max rebore, not sure if it needs it on the first size up mind, but 0.5mm is a fair bit when everything is talked about in thousandths of an inch, same with the gasket its set for a 56.00 bore, but you are adding 0.5mm to the bore therefore the gasket will need reaming out, as for some reason they don't make oversize gaskets anymore.

Harry · Guru

Ah what a pain!

Ok, so if I oversize by 0.5 the gasket will need doing as well and maybe the head?

The garages concern was that they wouldn't be able to clamp it down and get decent reference points due to the odd size

NEV · Guru

Go elsewhere then mate, as a good 'un will have.

GADGET · Guru

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

Harry · Guru

Sadly they are the only ones near, I don't have massive time outside of work to travel anywhere else before they close so I don't have a choice :( they are decent though, my mate who runs his own engine re build business uses them all the time for refurbing parts

Nice one gadget that's brilliant :)

NEV · Guru

Well if you're happy Harry fair enough, but I would still suggest taking the whole engine in to them so they can re-bore it, then build up the top end properly, if at all possible.

Harry · Guru

They don't seem too keen on bikes, not sure if it is something I would trust them to do more than myself - I am giving them the new piston so they can check the clearances so as long as I can bolt the barrel back on alright it should be ok

Another question, I've got a genuine yam head gasket, what should I use for the barrel to crankcase? I already had one from a set but it's one of those paper ones

gooner78 · Guru

FunkeyMunkeyDavid wrote:

premix all the way.....oil pumps are poop...... if you still want to use a pump,you can get the parts to rebuild them from yam and not massively expensive. not compared to a top end rebuild anyways

I will be using premix once my huskys engines been rebuilt the pump never failed though the infeed pipe melted to the exhuast stopping the 2 stroke getting to the carb all because a small clip snapped that held the infeed pipe away from the exhaust i,ve got £280 bill coming my way as a result

Harry · Guru

I'm leaning towards premix, but just a bit worried about the topping up as you can't just pour it in because it won't mix right and will end up just staying on top of the petrol?

Calum122 · Guru

Harry wrote:
I'm leaning towards premix, but just a bit worried about the topping up as you can't just pour it in because it won't mix right and will end up just staying on top of the petrol?

You'll also have to clean the carb out as well every so often.

NEV · Guru

Calum122 wrote:
Harry wrote:
I'm leaning towards premix, but just a bit worried about the topping up as you can't just pour it in because it won't mix right and will end up just staying on top of the petrol?
You'll also have to clean the carb out as well every so often.

Erm, no ya don't!!

eG x LoGiKzZ · Guru

Calum122 wrote:
Harry wrote:
I'm leaning towards premix, but just a bit worried about the topping up as you can't just pour it in because it won't mix right and will end up just staying on top of the petrol?
You'll also have to clean the carb out as well every so often.

maybe if you ride it once every 4 years haha