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Yamaha YZ250 - done :)


Will Vale
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Hi folks,

A bit late to the party because I wanted to be sure my Swedish GB entry got done (amazingly, it did!) but I really want to build this in company:

8452025871_67fd52637c_c.jpg

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I'm totally clueless about bikes, both model and real, but I figure I can ask questions if I get stuck. It helps that nice Mr. Tamiya explains what all the parts are, so I can say "I need to strip the paint off the cylinder head" or whatever rather than refer to it as "that bit with the fins".

So far I've mostly cleaned up one of the frame halves - it took about an hour of scraping because the mould wasn't perfectly aligned, I still need to do the other and round it off with sandpaper again. I think I'll maybe add a bit of putty to the welds since they seem to be a bit cleaner than pics of the real one I found.

Oh, and does anyone know if the thicker tube on the lower front of the frames is just that - tube - or if it's castings? I don't want to remove the mould line if it represents a real one.

Exciting stuff. I can't wait to open the "cool bag" with all the rods and springs and things in it :D

Will

Edited by Will Vale
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Hi Will, Better late than never! I don't think I've ever seen this kit built, so I'm interested to follow your build thread. I hope you're going to add lots of extra detail?

Colin

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Hi Will

Now heres something new..

Definately be watching this one with interest and welcome to the mad bikers club

oh, the lower front of the frame, is basically a strut for the frame, its a hollow tube so yes you can remove the mould line.

Steve

Edited by MAD STEVE
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Thanks for the warm welcome all! Been a bit busy today but I'm eyeing up the kit box - maybe a movie and scraping the other half of the frame tonight?

Not sure how much extra I want to do - there's enough new stuff to worry about in terms of dealing with the chromed parts, and finishing up something on this scale. I was considering a muddy "just ridden" version but I've just done a muddy IFV. I really like the finish on this bike - obviously used, but in excellent condition:

http://www.mxworksbike.com/1973%20yz250.htm

I love the wear on the lower part of the frame - might be able to reproduce that by painting black over silver and sanding it back gently - and the welds on the exhaust. Gorgeous.

Am I right in thinking that as this is a works bike it'd differ a fair bit from the production bike in the kit? E.g. the cylinder head is different, and it sounds like the production bikes are more nearly (yet cheaply) constructed, from less space-age materials?

Will

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Thanks for the warm welcome all! Been a bit busy today but I'm eyeing up the kit box - maybe a movie and scraping the other half of the frame tonight?

Not sure how much extra I want to do - there's enough new stuff to worry about in terms of dealing with the chromed parts, and finishing up something on this scale. I was considering a muddy "just ridden" version but I've just done a muddy IFV. I really like the finish on this bike - obviously used, but in excellent condition:

http://www.mxworksbike.com/1973%20yz250.htm

I love the wear on the lower part of the frame - might be able to reproduce that by painting black over silver and sanding it back gently - and the welds on the exhaust. Gorgeous.

Am I right in thinking that as this is a works bike it'd differ a fair bit from the production bike in the kit? E.g. the cylinder head is different, and it sounds like the production bikes are more nearly (yet cheaply) constructed, from less space-age materials?

Will

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hi will,yep as a factory works bike these would have been built with little consideration to cost as it would have been a "one off" so to speak and it would have been scrapped at the end of the 1973 race season to make way for the 1974 works bikes.remember works bike are designed to win races at all cost above all else [as is the case with all works bikes] so as long as they win races the company can go on to make cheaper "production" bikes for us mere mortals to buy and race,and if the production bikes look the same as the works bikes then even better.it was a concept yamaha knew only too well...think of it as "win on sunday,sell on monday"..you see a works bike win races on a sunday and then you go and buy a production bike on monday :analintruder::blink: [great looking kit buy the way and hope it turns out well for you!]

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Cheers, that was about my understanding as well. I finally found some pictures of what I think is the right bike - a '76 production model - although the front forks are different in the kit, they have a web on either side of the tube below the rubber boots.

I've made a bit of progress, the frame is together following a lot of scraping and sanding - I still need to fill some of the joints for the cross members and where the two halves meet at the extreme rear. Wasn't too painful so far but I'm sure primer will show up lots more work to do. The fuel tank went together well but needs some filler on the inside - the lining part wasn't quite as big as the outer halves. Plus all the seams need sanding out and polishing.

I also fitted the two halves of the engine block together, and the cylinder head. There's a horrible seam to deal with on the engine block, but the cylinder head is actually pretty nice. I need to clean up the inlet though - the two halves weren't very well aligned - but mostly that'll be hard to see with all the gubbins in there.

Lastly, I've been picking over the chromed parts. I think the wheels are probably fine, they have chrome on both sides, and all the pin holes and sprue attachment points are hidden when assembled. The hubs are on the wheel sprue but need to be de-chromed and painted black, so I'm not sure why they did that?

Everything else is either round and will need the attachment points and seams sanding off, or flat and blessed with pin holes, plus it's only plated on one side, so I need to get all that stripped and learn how to get a nice metallic finish.

I'll try and get some pics of the bits I've worked on at the weekend - not very exciting yet, but for every dodgy bit there's a really nice bit, so I think it'll turn out OK.

W

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Nice metallic finish? Gloss black, either enamel or Alclad's primer, give it at least a couple of days to dry properly. Make sure the finish on the black is perfect as the Alclad finish will not hide any flaws, no matter how tiny; then thin sprayed coats of Alclad lacquers of the required type. Perfect metallic finish done! It is as easy as it sounds, but you have to be patient. Let the black dry thoroughly and apply the Alclad in thin layers.

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are the parts moulded in the correct colours?.i had both the 1/12 scale tamiya honda cr 250 and suzuki rm 250 mx models some years ago and if memory serves me right they didnt need painting as they were moulded in the correct colour plastic....build straight from the box,put decals on and job done....while on the subject of these model bikes does anyone know if the rm and cr 250 mx bike models are still in production

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Cheers, that was about my understanding as well. I finally found some pictures of what I think is the right bike - a '76 production model - although the front forks are different in the kit, they have a web on either side of the tube below the rubber boots.

I've made a bit of progress, the frame is together following a lot of scraping and sanding - I still need to fill some of the joints for the cross members and where the two halves meet at the extreme rear. Wasn't too painful so far but I'm sure primer will show up lots more work to do. The fuel tank went together well but needs some filler on the inside - the lining part wasn't quite as big as the outer halves. Plus all the seams need sanding out and polishing.

I also fitted the two halves of the engine block together, and the cylinder head. There's a horrible seam to deal with on the engine block, but the cylinder head is actually pretty nice. I need to clean up the inlet though - the two halves weren't very well aligned - but mostly that'll be hard to see with all the gubbins in there.

Lastly, I've been picking over the chromed parts. I think the wheels are probably fine, they have chrome on both sides, and all the pin holes and sprue attachment points are hidden when assembled. The hubs are on the wheel sprue but need to be de-chromed and painted black, so I'm not sure why they did that?

Everything else is either round and will need the attachment points and seams sanding off, or flat and blessed with pin holes, plus it's only plated on one side, so I need to get all that stripped and learn how to get a nice metallic finish.

I'll try and get some pics of the bits I've worked on at the weekend - not very exciting yet, but for every dodgy bit there's a really nice bit, so I think it'll turn out OK.

W

if you can findit you should try and find a copy of a book called "yamaha dirt bikes" by collin mckeller.the book came out in 1986 [try amazon,e-bay or second hand book shops].i have it and it tells the story of all yamaha 2 and 4 stroke mx,enduro,trail and and off road play bikes from 1968 up to 1986 and has a wealth of info on the real bike that your model depicts

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  • 2 weeks later...

The parts are in colour, but white and black styrene really aren't a substitute for polished GRP or painted metal, so I think (apart from maybe the spokes) I'll paint the whole thing.

Thanks for the book tip - it looks great but is eye-wateringly expensive as far as I can see. If I get lucky and spot a cheap copy I might grab it.

I'm afraid I've been pretty useless, still haven't really done much after the initial rush. I've put this up to shame myself into progressing...

(click for bigger)
I did finish a plane, but that's not helping with this bike is it?
W
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Thanks for the encouragement (and thanks also to Steve for not ticking me off when I started building the LCAC...)

I've done some eating-my-greens tonight and spent a couple of hours sanding the pin marks off the insides of the mudguards, number plates etc.

The tank thankfully ensured all the ejector pins were on the inside, and the main seam was very clean. That said, I ended up with a biggish (just under 1mm in places) gap around the inside where the inner saddle fits into the outer tank, so I've just filled that with putty. It's not like it's going to be very visible but I'm trying to get better at smoothing and cleaning things, so it seemed like a good idea.

Once that's dried and sanded I also need to dribble a bit of CA to build up the flare where the seam runs through it front + back.

At this rate I might be able to apply some white tomorrow. We'll see...

Will

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I sanded the inner seam on the tank at lunchtime, did a bit of touching up with CA, and this evening it's had some white primer and a couple of coats (on the inside) of TS-whatever-it-is pure white. As have the other bodywork pieces with the exception of the front numberplate, which needs a pin hole removing first.

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(click for bigger)

The pictures show the tank before paint - not very exciting, but it is progress! You can sort of tell from the putty that it isn't perfect inside the gap - it's a fiddle to try and sand in there against the inside of the curve - but I think it'll at least stop there being cracks visible when looking through the frame from the other side.

I am currently trying to stop myself playing the "is it dry yet?" game, to which the answer is always "no" :)

Will

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Got two wet coats of paint on today, punctuated by wet sanding with 2000 grit to remove dust. It's looking good, I think the tank needs another coat though to remove some earlier marks around the filler cap where I spotted some scratches and sanded them out.

8536255848_b8957e2f09_c.jpg

(click for bigger)

Still wet in the picture, so the gloss isn't representative but it's pretty good and I see to have mostly avoided the orange peel. Looking forward to polishing these now.

Will

(edit: fixed link oddness, I think I deleted a ']')

Edited by Will Vale
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Lookin' good there Will, there is something satisfying about getting a good finish with a Tamiya rattle can. To get an even better gloss finish, I've been using Autoglym Super Resin polish applied with a cotton wool ball (no grain) and light rubbing/polishing. It's got a very slight abrasive quiality but ideal, the paint must be hard (two/three days) and don't leave any wet residue it will 'burn' the paint. Wash after with dishwash liquid and tepid water.

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Thanks for the tips, I like the rattle can paint because it's a) really robust and B) sticks to bare plastic, so you can avoid primer - reduces the risk of cutting through to primer with the white paint. I'll probably polish it with Tamiya compound rather than try something else since I've got it to hand.

Cotton wool is an interesting idea though - I usually use a bit of T-shirt fabric but I like the idea of something softer, at least for the Finish compound.

Cheers,

W

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Good to see more progress on this one.

A good bit OT, but this one brings out a lot of memories, reminding me of the 1/4 scale RC-model of this bike that Kyosho (via Graupner in Europe) brought out in the late 70's. I did a lot of RC of all sorts back then, even competing high level in RC-boating. Anyway, Kyosho came with the first true two wheeled RC-bike then, a 1/6(?) scale road racing bike with electric motor. I got my hands on the first one that came to Sweden and it worked quite well! After some preparation and modifications, lowering the center of gravity and fitting the new hollow air filled tires that came out as accessories it even worked superb, and I great fun driving it a lot.

Soon then Kyosho brought out this large YZ250 with a glow engine. I had to get one of course. But it was nothing short of a disaster. The engine was built into a complex scale like gearbox casing and was hopeless getting any reliability from, despite it being a well known quality OS engine inside. And for the short moments the engine worked the bike just kept falling over like a long tall card tower with about 58 weak links...

They then released an electric version so I got the alternate parts and rebuilt mine to loose the engine problems and concentrate on the handling, but it was completely hopeless. A total mess. I never heard of anyone getting it to work, but maybe we did something wrong. The smaller road racer kept driving like charm though, and brought me much joy. Good days :).

Sorry for the rant, but I just had to get it out :). Keep up the work, It gives me nice memories and will look great when finished.

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