89 yz490 drag project

[pushdogg]

long time lurker, first time poster.(dont look at my forum birthday, ive been following tsm since jan 2010) it seems i have come into a possible  yz 490 parts bike, i have a rolling chassis from a 87 yz 250. they seem very similar but im not entirely sure (i was 4 when the 250 was built), and i realize the 490 has a number of problems(which can be fixed through some simple machining). im really feeling the urge to make a dune dragster or possible hill climb project(being from ohio and silver lake dunes in michigan) out of this.

is this swap/interchange possible? i will continue to search part numbers and see which ones match up for possible swaps, but any knowledge or vintage 2 stroke wisdom is greatly appreciated.

EDIT: MORE PICS!
EDIT EDIT: i cant seem to get them to work, so photobucket link is in my next post, its been updated.

[opfermanmotors]

The 490, in all years was air cooled and the 87 250 is watercooled.  So that is one thing that will show there should be differences.  The year of the YZ490 was not mentioned though and also the reason for switching to the 87 250 frame?

We put a 1974 TS 250 motor into a 1976 TM100 frame and put 81 CR250 front forks on it.  So anything is possible if you have a welder.

[pushdogg]

The 490, in all years was air cooled and the 87 250 is watercooled.  So that is one thing that will show there should be differences.  The year of the YZ490 was not mentioned though and also the reason for switching to the 87 250 frame?

We put a 1974 TS 250 motor into a 1976 TM100 frame and put 81 CR250 front forks on it.  So anything is possible if you have a welder.

the 490 is an 89(just picked it up for $50), i do realize the 250 is water cooled. i would use parts from the 87 to complete the 89. the 87 is off site(ill try to retrieve some pictures of it), and the 89 is kind of dusty(ill take pictures and edit as soon as i get done here). i have a rag and a little bit of cleaner, im going to try to find any quirks.

needs a reed cage, carb, piston, rod, crank?...crank bearings?. im in the process of getting it taken apart now, ill have more pics as i progress.

http://s1183.photobucket.com/home/pushdogg

EDIT: latest is, the 87 pictures are accessible through my facebook, but im going to try to get it ready for you guys in the next week. if you want to see the 87, throw me a request....andrewleo7@hotmail.com

[SachsGS]

Back in those days Yamaha made it's motorcycles as "interchangeable" as possible and it wouldn't surprise me if that 490 motor bolted right in to the 250 frame - the engine mount pattern is probably very similar.

[factoryX]

Actually you'd be surprised whats bolts up with mid-late 80's yamahas. There is a guy on 3wheelerworld running a yz490 in his tri-z 250 three wheeler:

[TMKIWI]

Holy crap. Look at that exhaust.
Looks like a leg burner.

[opfermanmotors]

Holy crap. Look at that exhaust.
Looks like a leg burner.

Or a rock/log clipper

[factoryX]

Not every bike is built for woods riding 

[Coop]

Not every bike is built for woods riding 

You beat me to it. I was going to say look at the front tire, that is dune machine all the way.

[pushdogg]

Not every bike is built for woods riding  

You beat me to it. I was going to say look at the front tire, that is dune machine all the way.

which is what i had in mind for this 490. a little update, the rod bearing or a crank bearing is bad, it seems to go one way a certain distance but not come all the way back. i have pictures with the cylinder off, some of the ports look like someone went at them with a flathead

EDIT: doesnt eric gorr do the machinging on the 490's that fixes the pinging problem? im sure a port and polish are going to be in order as well.

[factoryX]

The only issue that I don't like about the 490's is their almost impossible to jet correctly.

[pushdogg]

ordered a flywheel puller today, and a clutch holding tool.....should be all apart by this weekend

[pushdogg]

The only issue that I don't like about the 490's is their almost impossible to jet correctly.

your profile picture looks like a 490 without the machining done(pre-ignition)....from what i understand is that if the cylinder/head is machined correctly it makes the 490 worlds easier to jet. either way it will be short runs with it, im more worried about starting it.

[SachsGS]

Years ago I had a Yamaha 490 and it wasn't a problem starting it.A friend had an early 90's Honda CR500 and that bike was hard to start!

[pushdogg]

well it appears that the flywheel key is twisted in, broken or non-existent(the flywheel will not come off). after mushrooming and twisting the bolt in my new flywheel pulling tool(it twisted so badly and after looking at it im surprised we didnt shear the bolt off). me and my associate have determined that we may need to figure out a way to modify it into a slide hammer(a big one), im not sure if this is best course of action(but may be the only way to remove it), any ideas or insight would be awesome. whats nice is the other side isnt even close to  being as bad. that said it fits beautifully into the 250 frame and it took mounting it to get it to sit still enough to work on.

im less a carb, reed cage, and the boot in between. ive heard that you could use those parts from a wr500 and they will fit up perfectly....can anyone here confirm that?, after looking at oem charts i cant seem to find a part number for the reed cage.....or find the reed cage at all.....boyesen doesnt make a reed cage for this old a bike from what i understand.....so any insight on that as well would be very helpful.