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Old 02-05-2010, 06:25 AM   #31
brucifer
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I think you've lost your mind... J/K

The 600 engine is much bigger and I seriously doubt there's enough room to cram that thing in that bike, although it would make for an entertaining ride if there was.
The XT350 engine is a completely different design. It has double overhead cams, two carbs and twin exhaust ports.
You might be able to get it to fit but I don't think the end result would be worth the effort.
If you're intent on turning this bike into a hot rod, just use the engine you have. If it's your only transportation, maybe pick up another SR250 engine and mod it as time and money permit, then swap it out.
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Old 02-05-2010, 10:11 AM   #32
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Quote:
Originally Posted by brucifer
I think you've lost your mind... J/K

The 600 engine is much bigger and I seriously doubt there's enough room to cram that thing in that bike, although it would make for an entertaining ride if there was.
The XT350 engine is a completely different design. It has double overhead cams, two carbs and twin exhaust ports.
You might be able to get it to fit but I don't think the end result would be worth the effort.
If you're intent on turning this bike into a hot rod, just use the engine you have. If it's your only transportation, maybe pick up another SR250 engine and mod it as time and money permit, then swap it out.
yeah i took a closer look and there isn't any room in the bike to grow upwards, i will try to find another SR250 engine to play with
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Old 02-07-2010, 08:38 PM   #33
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btw, i still cannot figure if the SR250 has the same bore as the XT250... there are some places that say that they both have 75mm bore, and others say that the SR250 has 73,5mm.

are the cylinders the same?
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Old 02-28-2010, 08:50 AM   #34
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anyways, in the mean time unable to find a complete SR250 engine, i found instead a cylinder and head, researched more about overboring this engine and found out that the best option was the 84mm YFM350 overbore piston and thats what i bought :)

here it is (hasn't arrived yet)
http://img714.imageshack.us/img714/5...1002231728.jpg

a little upgrade on the clutch:


also, i inverted the original bars for a preview of the looks with clipons




i already have the clipons but i have to figure out another way to mount the headlight directly to the forks and lose the complex stock mountings... i quite like the looks of the bike now
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Old 02-28-2010, 12:55 PM   #35
eric123
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Use a pair of these...

http://www.jcwhitney.com/motorcycle-.../p2003822.jcwx
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Old 03-27-2010, 12:48 PM   #36
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Updates:
- started porting the intake and exhaust:



- clip-ons and headlight bracket:


- wheels -
before:


after:


how it is now:






on the wheels alone, i managed to take off about 4kg on the back and 2kg on the front with the alloy rimms and by decreasing the previews rear 120/80 R18 tyre to an 90/90 R18 and in the front i decreased from 90/90 R19 to 90/90 R18. also by ditching the original complicated headlight mount and bar, i also removed almost 2kg from the front

it made all the difference in the world, it is getting faster and faster and i haven't got to the engine insides yet but this has arrived last week:




it is a 10.25:1 84mm YFM350 overbore piston and guess where it is going

Cheers
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Old 03-27-2010, 10:46 PM   #37
Zecatfish
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Don't forget your going to have to bore the engine cases to fit that larger cylinder in there.

I tore down two of my 250's and found the XT250 with a gaulded piston, and the TT250 had suffered a lean condition that started to hole the piston, and there must've been some pre-ignition because the piston crown was also cracked.

Seems that XT250 and TT250 pistons are scarce, not mush to choose from on ebay.
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Old 03-28-2010, 08:21 AM   #38
oc_nightmare OP
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Quote:
Originally Posted by Zecatfish
Don't forget your going to have to bore the engine cases to fit that larger cylinder in there.

I tore down two of my 250's and found the XT250 with a gaulded piston, and the TT250 had suffered a lean condition that started to hole the piston, and there must've been some pre-ignition because the piston crown was also cracked.

Seems that XT250 and TT250 pistons are scarce, not mush to choose from on ebay.
if the SR250 bore was the same as the XT/TT, i could sell you the used piston pretty cheap if it was in good shape, but the SR has 73,5mm bore

im also thinking very seriosly about using YFM350 valves and have webcamshafts to regrind my cam to an agressive profile as i dont think that only porting will compensate the cc increase on the middle and top rpm range.

a 4 valve head would be great though, but i have lots of doubts that the XT250 or XT350 4v heads would fit and then timming it would be a pain in the arse...

these thumpers are so simple that it is a joy to work on them :)
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Old 03-28-2010, 09:57 AM   #39
brucifer
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Quote:
Originally Posted by Zecatfish
Don't forget your going to have to bore the engine cases to fit that larger cylinder in there.

I tore down two of my 250's and found the XT250 with a gaulded piston, and the TT250 had suffered a lean condition that started to hole the piston, and there must've been some pre-ignition because the piston crown was also cracked.

Seems that XT250 and TT250 pistons are scarce, not mush to choose from on ebay.
What do ya suppose caused the galling on the XT piston Zecatfish?

Not MUSH to choose from? Ya been drinkin'? Just kiddin'!

I recently picked up a 1980 XT250. It's all there but looks pretty crappy.
Went through the carb and attached the accelerater pump rod correctly, now it runs great.
Needs fork seals and swingarm bushings. I removed the swingarm last night and found that it needs the steel sleeves as well. I had ordered the bushings, pivot bolt and seal beforehand and had them here so I could do the job without having to wait for parts. Well, so much for planning....

OC-
Good to see you're making progress. Lookin' good.
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Old 03-28-2010, 11:44 AM   #40
Zecatfish
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Quote:
a 4 valve head would be great though, but i have lots of doubts that the XT250 or XT350 4v heads would fit and then timming it would be a pain in the arse...
The XT350 engine has the timing chain on the wrong side compared to the old XT/SR/TT250. So that idea is a pipe dream.



Quote:
Originally Posted by brucifer
What do ya suppose caused the galling on the XT piston Zecatfish?

Not MUSH to choose from? Ya been drinkin'? Just kiddin'!

I recently picked up a 1980 XT250. It's all there but looks pretty crappy.
Went through the carb and attached the accelerater pump rod correctly, now it runs great.
I got it as a project machine.
The side case was patched with JB Weld.
These engines oil the crank from to right side cover. The crank goes into a seal. That seal was damaged, bent. I think it is the underlying cause of the oil system failure and the galling of the piston. I still hadn't gotten the wrist pin out yet either, its fairly stuck.

That is the best I can determine with what I've found so far. I'm not going to fix that engine. The TT was in better shape. So if I fix one I'll move the XT electrics over to the TT engine and fix it. I haven't pulled the cams yet to examine the damage on the top end. The TT will need a piston, rings, and one rocker arm.

Wish I could say more but that about sums it up.
There was a Yamaha recall on these engines concerning oil starvation in the topend. The fix involved a small dowel pin to restrict oil to the crank and force more pressure to the top end.
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Old 04-24-2010, 05:05 AM   #41
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well i was in work and school holidays so i chose to do one of the things i like to do the most... noise

photos:


i left my hometown Leiria and soon after Ansião i was lost


what, im in "vermelhos"? (red) really helpfull


pretty funny village names... "Picha" (d*ck)

the roads were alright, but later it just got even better, great mountain roads... i was enjoying the road so much i didnt take many pics but these work as a teaser:






"Wow!"



lost again, good looking little village though


after that i really started to worry as the great road just converted to this


land of miners, after all im on the right track! because of the huge amount of trucks using this road, the dust and the pot holes meant that i and my SR took a lot of beating if it wasnt for the goggles i'd be blind...


later the scenery got a bit more green....


...and yellow


after 195km, my SR drank 5.85L, im happy :)


Serra da Estrela, the highest mountain in Portugal


as i was taking photos i noticed i was being followed...

by a "Serra da Estrela" dog

close to the top



snow! crunch crunch crunch!


i went to Viseu to stay at an old friends house, she got me a garage to set the correct valve clearance


and she came with me to Leiria aswell


filling up again



last stop before arriving to Leiria


just being silly


last pic of the day


after 495km, my back wasn't broken and my ears weren't bleeding... i guess a 250 café racer is a pretty good tourer
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Old 04-24-2010, 05:24 AM   #42
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anyways,
the cylinder is ready for the 84mm piston:



comparison between the SR/XT250 valves (sides) and the new Warrior 350 ones (middle)



the head porting is almost done
on the intake side im going to leave some small bumps for better atomization of the air and fuel:



the exhaust side, im going to try to do as close as i can to a mirror finish to prevent carbon deposits:



the copper 0.021" gasket is on the way and the piston pin hole is being opened to 20mm for the stock SR250 pin. im going to do a 3 angle valve job aswell
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Old 04-24-2010, 06:50 AM   #43
brucifer
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Looking good, man! Nice ride report, and great pics.

Your port work looks nice. Professional results achieved at home.
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Old 04-24-2010, 09:56 AM   #44
Bud Tugly
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That bike looks like it would be perfect for exploring the backroads as long as you aren't riding with guys with much faster bikes. Trying to keep up with them on a 250 would get very frustrating.

If you try to push the performance too far you may start creating other problems like overstressing the transmission, clutch, or other parts of the drive system. Also, the frame and chassis might be inadequate for increased power and the handling could deteriorate as a result.

Before you go too far with modifications, it might be lots cheaper and less trouble in the long run to buy a more powerful bike for fast riding and keep this one closer to original for more relaxed and casual trips.
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Old 04-25-2010, 02:48 AM   #45
oc_nightmare OP
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thank you brucifer

Quote:
Originally Posted by Bud Tugly
That bike looks like it would be perfect for exploring the backroads as long as you aren't riding with guys with much faster bikes. Trying to keep up with them on a 250 would get very frustrating.

If you try to push the performance too far you may start creating other problems like overstressing the transmission, clutch, or other parts of the drive system. Also, the frame and chassis might be inadequate for increased power and the handling could deteriorate as a result.

Before you go too far with modifications, it might be lots cheaper and less trouble in the long run to buy a more powerful bike for fast riding and keep this one closer to original for more relaxed and casual trips.
im not trying to push the performance too far, i know it is just a 239cc air cooled mono, it is just a way to have very light café racer with some hp to have more fun and afaik if i stick with the stock power band through the rev range i will be doing pretty much the same mpg and having the same reliability... at least thats what i hope

ive talked to the guy with the frankenbike yz/xt250 and he has been racing the xt312 engine forever and hasn't died or gave any problems yet so im confident about this

btw, ready for the machine shop:
exhaust side, after sanding with 1000grit


intake side:


before:


after a little bit of cleaning:


;)

oc_nightmare screwed with this post 04-25-2010 at 03:13 AM
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