1981 Yamaha SR250 Cafe Racer

Man, you are turning that thing into road-going jewelry! 8) Keep spinning those wrenches... I can't wait to see the next set of photos... you really pay attention to the details, and I'm enjoying watching this build.

man that looks awesome!!!! love the motor... the accent pieces on the sides of the jug as well as the starter really make it pop nice detail!

Details, is what make a nice bike look even better. Good work!

Thanks guys! I ordered all my engine bits and the last bits and pieces for my forks yesterday .. the bulk of which should be here tomorrow!

Not to sound like broken record.... but that looks real Pur T.

It's amazing how you can get engrossed in something like engine assembly and start to feel hungry, walk inside and find it's quarter past one in the morning and three hours have gone!

I've got a lot done on the engine today .. This morning I finished off the ports and polishing the combustion chamber (subtle reprofiling of the exhaust port, smoothed out the intake and polished) And this afternoon I honed the cylinder and this evening I got started on assembly!

The engine is together and timed, compression looks healthy and everything is looking good. I just need a few bolts (I'm replacing everything with high tensile cup head bolts) and a sump plug (mine was rounded off and cracked) and it's ready to fire up!

Pics tomorrow.. actually today, when I've had some sleep ..

Here's some pics as promised of the engine assembly ..

$280 of Yamaha genuine parts (new piston, gudgeon pin, rings and all gaskets and o rings, plus an oil filter) ..



Everything laid out for assembly ..



Take one piston, preheat the oven to 250 degree's and season to taste .. well actually, the gudgeon pin was an interference fit so it went in the freezer and the piston in the oven and they slid together perfectly.



The best way I found to assemble everything was to put the cylinder on the bench upside down, flip the piston upside down in the ring compressor, line the valve reliefs up appropriately and leave it out just enough so I could pop the gudgeon pin in and pop the snap rings in.



I smoothed and polished the combustion chamber ..



The head on .. I popped the starter back in and put it's drive chain back on, ready to put the side covers on ..



It's almost ready to start but I have decided to tape it up once more and give it another coat of paint (I chipped it in some spots during assembly) so it's perfect and glossier ready to go back in the frame.

Regards,
Ben

man that looks GREAT!!!!

You'll be happy when it's done.

Hey,

I've got the engine back in the frame and wired up .. having ignition issues I'm almost on top of.. should start tomorrow!

AWESOME!!!!! man that looks great!

I have a 1980 SR250 that I picked up last fall for $150 that had been sitting in a shed for about 15 yrs and needed lots of work. I spent last winter getting it running and doing a basic cleanup of the bike. After stumbling across this thread and seeing the amazing work you've done on your bike so far I've decided to spend this winter painting the engine and stripping the rest of the bike down to the frame for a proper restore. I'll be following with great interest as your project progresses. Again keep up the great work. Can't wait to see the final results.

Noah

Thanks guys!
Noah, to get you started .. here's a pdf of the full service manual (it took me a while to find the complete manual) http://www.manualz.info/Manuals_pdf/YAMAHA/SR250%20G%20Service%20MAnual%20ENG.pdf

If you have any other queries once you get started you're more than welcome to ask!

Regards,
Ben

Hi all!
I traced the ignition problem to a wire I mixed up when splicing in a new connector on the stator, once that was rectified I hung an IV bottle of fuel to the carb, primed it with a squirt down the carb and it fired right up and blew foot-long orange and blue flames
I'm stoked.. now I have it running and know everything works, I've pulled it back out of the frame to tidy up an oil leak and tape it up for a final coat of paint, then it goes back in for good.

I followed the instructions from the site Ken's Electrolysis Setup at http://twinoak.altelco.net/~jacil/clay/motorcycle/KElecSetup.html and made up a petcock blanking plate this afternoon and an anode out of coat hanger wire, and I have the tank on the bench being electrolysisised as we speak. It really works!

Once that's done the tank will go back on the frame with the motor and I can start on the rear section and seat .. once my friend gets back from overseas he will sandblast my hubs for me so I can finish off my wheels and it will go back up on it's wheels again .. getting closer to being able to ride it again!
Cheers,
Ben

lunar_c said:

Thanks guys!
Noah, to get you started .. here's a pdf of the full service manual (it took me a while to find the complete manual) http://www.manualz.info/Manuals_pdf/YAMAHA/SR250%20G%20Service%20MAnual%20ENG.pdf

If you have any other queries once you get started you're more than welcome to ask!

Regards,
Ben

Click to expand...

Thanks, I already have that file plus the owners manual and the parts manual that I put together. I also work at a print shop so I've printed off a couple of copies so I don't have to worry about getting them all greasy. Any idea compression should be on this bike? I'm currently getting 135 psi on the compression tester. Trying to decide whether it's worth the hassle to hone and put new rings on it this winter. What did you use to polish your cylinder by the way?

135 doesn't sound too bad .. it should have 8.9:1 compression so that's not too far off what it should be. It'll be fine til next winter

Geez does mine rev hard since I ported it! The stock ports are really quite a knife-edge climb up from the valve seat.

I always have to think of what you guys mean by "winter" .. being from Western Australia, it doesn't snow anywhere here, and the coldest it gets is about -3 centigrade. 45 in summer though..!

Over in the eastern states it snows, like Melbourne, VIC (Mt Hotham etc) and in the Blue Mountains in NSW .. but not here! So if you can live with the rain, you can keep riding. Still, it's freezing riding in -2!

I visited New Zealand recently and I went quad biking on the snow and ice around the mountains where they filmed parts of the Lord of the Rings trilogy .. it was so cold (about -7C) I was wearing my road jacket underneath an offroad jacket!

Funny you should mention New Zealand. I just ordered a part from there to put a kick start on my SR250.

Boy do we ever have winters here in the midwest of the US. It's currently -7° celsius here with a wind chill of -14° with light snow.

According to my manual the 1980 SR250's had a 9.2:1 compression ratio. What formula do you use to determine the the compression?

When you say you ported it, did you bore the cylinder out bigger and put a bigger piston and rings in?

This is awesome! Keep it up. I like the attention to detail and the fresh paint on everything.

Noahdog, tell me everything you know about putting a kick start on an SR250 .. *grabs you by the collar* EVERYTHING! I really want one on my bike
By "porting" I mean I reshaped and enlarged the intake and exhaust ports on the cylinder head to increase the gas flow into the cylinder. Reducing restriction here means the engine can draw in more air/fuel mixture every cycle, increasing it's volumetric efficiency and thus producing more power. Smoothing the combustion chamber with a more uniform finish and polished finish reduces "hot spots" and deters pinging.

Anyway I've been really busy with the bike .. Since I got it running and checked everything was okay, it was time to put a final coat of paint on the engine and get it ready to put back in the frame for good! I am so sick of painting and taping .. I did manage to chip it once while putting it back in the frame but I can touch it up easily enough.


I also followed "Ken's Electrolysis Setup" and it turned out very well. Here's a pic of my setup using a car jump starter, some test leads, the rubber gasket from the bottom of my old fuel cap, a coat hanger and some washing soda! I love MacGuyver.


Here's the motor on the bench, painting and cleaned .. valve clearances and cam chain tension done, final torque'ing done, starter in and ready for the side cases.


And here it is back in the frame all plumbed up .. I am so happy with it! I used a spring to stop the fuel line kinking (it's a fairly severe turn from the petcock into the carb) .. there's a commercial product called the Unicoil for this purpose, which I bought and had to cut up and modify anyway. I think it looks really cool .. I kind of wish I had more hoses!



All fasteners on the motor (besides the crankcase bolts, I didn't want to disturb the seals as I wasn't planning on splitting the cases) have been replaced with high tensile cup head set screws with a black oxide finish. A lot of them are specific lengths and dimensions for this model, so I've had to modify their lengths and the shoulder bolt that goes in the bottom of the oil filter cover I had to turn down in a lathe as it's an odd size that was not available from the usual fasteners suppliers.

All of the original bolts for the motor mounts were assessed, cleaned with a wire wheel and then polished by hand.

Here's the frame, tank and motor all together at last .. also notice you can't see the wiring .. it's there, painstakingly hidden I just realised that I'd already wired it up ..



Cheers

One day I hope to be where you're at! That thing looks really, really good. I'm with ya on taping up stuff. It's getting old already and I've really just begun.