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2006 DT125RE Full Engine rebuild and general re-vamp - Slow Progress


Yamahdan
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Hi all new to the forum, thought I'd start a thread on my DT rebuild.

I bought the DT about 8 months ago, when I bought it it looked like this.

IMG_0429_zps667995a4.jpg

IMG_5158_zps68ce7849.jpg

TOP SPEC AS FOLLOWS:

Powervavle pegged open, badly!

Rusty DEP full system

Wobbly back wheel (2 spokes missing)

Scuffed plastics

Rusted twisted chain

Home made number plate bracket that spun sideways :eusa_think:

Generally s#*t condition

Not in the best nick, but I wasn't concerned about that because it cost me £1050 with tax and MOT a full tank of petrol and a few spares!

I got it home, fixed number plate, un-pegged the YPVS and got it working properly and used it for work for about 6 months.

Then one day on the way to work the bike was getting progressively worse "burring" and "blipping" more and more often until a "ping" come from the exhaust. From then it was first and second gear "burring" itself along, got it to work and in the car park it died completely. No compression what-so-ever spinning over on the button with no resistance at all.

Excellent....

Anyway picked the bike up a couple of days later in the van, got it home and whipped head, barrell and piston off...

20130223_144217_zps98d14598.jpg

Excellent.

Clearly running very lean...

I am now in progress of re-building the engine in full...

Pics and write up's will follow as and when things happen, but don't get much time so it will be slow!

Thanks Danny

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Started the work on the DT tonight, (work nights) put the top end through the wash, and baked dry.

I began with the head, everything was removed thermostat etc, the dome de-coked and mild-ly polished, then the head sealing face was lapped to remove all of the "dinks" in it from previous work being done.

End result:

20130308_051850_zpsbcb901a7.jpg

I think in the picture below the glare from the light on the surface messed the camera up a bit! :babyha:

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You can see a pretty decent reflection in the pic of the light above the bench!

Surface is flat within 0.008mm, and mirror finish (going to try to decrease squish by not using head gasket)

Thanks Danny

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Surface is flat within 0.008mm, and mirror finish (going to try to decrease squish by not using head gasket)

You sure this is wise Dan?

Also looking at your piston, has it been hitting the powervalve? Is that an oversize piston, as it would make sense if it was, because before it was pinned open, it wouldn't touch the powervalve, but then you say you sorted it so it was servo controlled, and if its an oversized piston and the powervalve hasn't been shaved to suit, it will keep hitting it

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Give the powervalve a good clean up also, I was going to smooth mine out a little but my dremel gave up the ghost!

Ken

Started it yesterday, getting the polish out on it tonight.. should be easy, I'll wait until I get the barrell back from boring to relieve it to give it room in the bore..

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Surface is flat within 0.008mm, and mirror finish (going to try to decrease squish by not using head gasket)

You sure this is wise Dan?

Also looking at your piston, has it been hitting the powervalve? Is that an oversize piston, as it would make sense if it was, because before it was pinned open, it wouldn't touch the powervalve, but then you say you sorted it so it was servo controlled, and if its an oversized piston and the powervalve hasn't been shaved to suit, it will keep hitting it

Sorry I missed out a two in that figure, its flat within 0.0028, so under 3 microns, I can't get it much better that that, not here anyway...

Theoretically if I get the barrell mating face within the same flatness they will seal once the bolts are tightened down, people at work were saying they used to use a sheet of glass with wet and dry on top and that used to work!!

I want to decrease the squish to give me a little more compression, giving better bottom end punch (mildly), but losing a bit on top end, due to lower revs. I will build it without a head gasket, and turn it all over by hand to make sure nothing hits, then find tdc and check the gap I have got, if its too small I'll put a gasket in.

Should work, hopefully....

And regarding the P.V, I thought the same when I looked at it, but the powervalve hasnt got a mark on it, none at all, I 100% had the powervalve the right way in the chamber and it was turning the correct way from the servo. Also when I stripped it I put a steel rule down the bore on its edge in several places around the exhaust port and span the P.V, and there was plenty of clearence even with the P.V upside down!

The piston is in fact undersize!

I believe the barrell has been re-worked in the past as it is circa Ø56.6mm, (with a Ø0.015 taper in it!), which I suppose isnt too bad consridering, but then the piston is Ø56.1 up to Ø56.35, so in places half a mil Øclearence, which is far too much surely??? I mean the piston rattles around in the bore like a pr#*k in a sock...

I guess whoever did the work before just bought oversize rings instead of a new piston??

Danny

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I think leaving the head gasket out is a bad idea, if you want to reduce the squish, what distance have you measured the gap at, anything around 1mm is OK

if you find yours is above that figure you'd be better skimming the excess clearance from the head IMO

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I think leaving the head gasket out is a bad idea, if you want to reduce the squish, what distance have you measured the gap at, anything around 1mm is OK

if you find yours is above that figure you'd be better skimming the excess clearance from the head IMO

I'll take your word for it, I'll build it with a gasket and see what I've got....

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  • 5 months later...

Hi all,

Just an update of where I am after six months of no posts on this thread...

NOWHERE!!!

No time or money for this bike, now got a sprog on the way so its looking worse for it!

I have also taken on another DT which has eaten into my time massively when I didn't want it to, I'll get some pic's and get em on another thread soon..

I will be working on it before the baby comes so the next 6 months should be a bit more exciting for anyone whos interested...

Thanks...

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  • 1 month later...

Death ash...Great crack! What pooorick! Sold you that!. I hope you got that for an absolute bargain! Cheeky gits. Well it'll be an interesting one. But with a baby on the way projects like these become difficult, BUT not impossible. Hopefully you'll find some time to at least rebuild the engine and get it all legit.

I'm interested.

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