SR250 Cafe build

Hey Cosworth, just wondering seeing as you did the warrior cam swap, do you have any side by side numbers for lift, duration and overlap? Wait, I have the numbers for the stock SR250 somewhere but do you have them for the warrior cam?
 
Stock cam specs: valve lift 0.322”, duration 260, duration at 0.050” 240.

Niche Warrior 350 stage one cam specs: valve lift 0.390”, duration 274, duration at 0.050” 244.

PartsDiscounter on eBay sells the cam and the entire valve trains for a smoking price.
 
Love the build, hopefully starting my own soon. How much of the stuff on motolanna for the other SR series bikes will fit on the SR250? Did you have to mod the seat to fit onto the frame?
 
I modded the seat just a bit to make a custom "latch" for the front but in retrospect, the stock one is fine. Not much for the SR400/500 fits. The seat is just in the general ballpark for dimensions.
 
JadusMotorcycleParts said:
Awesome. Thanks for that!
Click to expand...

Also I think the main air jet will have to be changed a bit to account for the extreme loss of vacuum from a bigger cam like the warrior 350 cam. I'll know more tomorrow.
 
Stock cam again. Warrior 350 quad rockers. XS650 rings. All back together, rebuilt, and broken in:

xZsJuXs.jpg
 
Stock cam (presuming either good-used or NOS), not the Warrior cam? And Warrior rocker arms, not your spare SR250's?
 
The warrior cam may get another shot. But it didn't run right. The warrior rockers are cheaper, better and available. Plus they fit perfectly.

Better because they have bonded pads instead of forged pads. Now that I have the warrior rockers, I will order a warrior cam. I think the warrior cam and the SR250 rockers is not a viable metallurgical marriage.

I wore the cam to a nub in 30kms and killed the rockers.

I have also enlarged the feed hole from the head bolt to the cam roller bearing to assist feed. There is not much pressure but high flow in this motor. Drilling this hole makes more oil available to the cam to chuck about. Also it can stop any swarf from clogging the hole.
 
Thanks for documenting all this info on the warrior cam and rockers. It's a shame it hasn't been as simple of an upgrade as it could have been. Would you recommend the oil feed hole enlargement even without the cam mod?

I really like the details and proportions of your bike. I think a pretty nice touch is the gold anodized rear-set plates, matching the rear shock gas cylinders, then, the fact that the stainless header is bronzing nicely and matching those details too! Plus the shot gun shells and bar weights ;)
 
I think everyone that has the chance to get their head off should mod the feed hole. A cam and rockers can be pricey for this bike. Keep them bathed in yummy oil.

I'm pretty certain the warrior cam needs to have warrior rockers since the sliders are bonded and most likely a more complimentary Rockwell hardness.
 
I'd like to add Janus that I also think the oil capacity should be upped a bit after doing this mod. Possibly to 1500ml and covering the window. With more oil in the head there should be less in the bottom end.

Any thumper with oil supply issues, should have the oil checked every ride and a bit more added. Not enough to fog the case, just a wee bit of insurance since the single cylinder action creates an oil fog pumping action of positive pressure/negative pressure in the case.
 
Just trying to follow...
Previously you noticed that the exhaust oil feed hole inside the OEM cam was restricted where the aftermarket Warrior 350 camshaft was not. Did you drill the good/used SR250 cam internal oil feed path (and to what size), or the head's feed hole from the hollow head bolt (and to what size), or both?
 
I don't know what oil mods Yamaha did but personally I always found the SR250 to have a very poor oil feed to top end, even worse than CB360's :eek:
Main difference though, the bearings would wear out with excessive clearance rather than seize up so motor kept running (but sounded like someone shaking a tin can full of bolts ;D )
 
zap2504 said:
Just trying to follow...
Previously you noticed that the exhaust oil feed hole inside the OEM cam was restricted where the aftermarket Warrior 350 camshaft was not. Did you drill the good/used SR250 cam internal oil feed path (and to what size), or the head's feed hole from the hollow head bolt (and to what size), or both?
Click to expand...

Yes, I forgot to add that. I matched the stock sr250 cam feed holes to the warrior cam size. Added two sizes up on the hole that is drilled to feed the cam bearing and the cam (entire head). I don't recall the exact size of drill bit but it was imperial, not metric. I'd go one size bigger even.

CrazyPJ - the only mod Yamaha did was add a roll pin to the crank to force more oil to the head. Which was restricted by the feed hole off the head bolt.

I think this solves the SR head issue, long term.

**edit - I'm gonna order another Niche cam..and give it a go**
 
Ah, I knew they did something.
I only every worked on a few of the early ones, luckily we still had two strokers in Britain so sold the hell out of them ;D
 
I'm unaware of any oil supply problems with the SR500, but if you made it (the hole) a bit bigger and increased your capacity by say 200cc, it would be a safe mod. Not a lot of pressure in these motors, just lots of flow. Drilling the hole may drop the pressure to levels that aren't nominal on an SR500 though.

Thanks for the interest in the bike.
 
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