Well, my SR was running like a dog for a while. It was a late-model 400 with a K&N air filter, and for much of it's life, a supercrap, erm, supertrap style muffler on it. That kept melting and falling off, but another story for another day. Anyway, I was getting a little sick of how the thing was running and wanted something with a bit more "oomph" and more of the thumping feeling that everybody talks about when riding their 500. Compared to the 500, the newer 400 feels a lot more revvy and less of the 'thump' from it's bigger brother. Anyway, something was feeling wrong with the bike. It'd been loud - top-endy and valvey sounding and I'd set and reset the valve clearences dozens of times and they were always in spec. I spend half my life watching bike videos on youtube and plenty of others sounded as loud as this, so I figured it was normal... turns out I was wrong. I had tossed up doing the rebuild myself, but figured that by the time I'd stuffed around, sourced the parts and buggered just about everything up I might as well send it to a pro. Just about everybody I knew recommended a guy called Carl, at Cafe racer (Blatant plug - check out www.caferacer.com.aú) Despite the name he does shitloads of MX and VMX stuff as well as road going stuff He also knows singles like nobody's business, so I figured that I'd trust him do to do the work. I dropped the engine off and we ran through what I was after. I'd sourced a FCR 39mm flatslide carb and a SR500 crank in good nick so I drove that up with the old donk in the back seat. We sat talked for a few hours about what I wanted from the engine, where I wanted the power and the torque and I left him to it. There's something unbelievably cool about walking around a workshop and picking a rod, a piston, a cam grind an exhaust and choosing an end result. Ended up getting... Carillo Rod. I could have gone with a standard but apparently that will mean cleaning up the bottom end when I next get it looked at. So I figured the extra cash would be justified. Ported Put the flatside Keihin on New cam New Exhaust (Old one was far too restricted) I ended up getting one that Carl recommended as he had them made specifically for his SR500's. Figure I can't go wrong there... Put the new crank in with a hi comp piston. After a bit of deliberating I didn't go for an overbore as I figure the new engine will keep me entertained for a good while anyway, and I can go for plenty of top end rebuilds without any hassle. Anyway, so I left him, and then a day or two later I got a call after taking the head off It turns out I'd near killed it, and myself! He said that in years of working on SR's he hasn't found a head as exhaustively rooted as mine was. I'll leave a little pause in there for your admiring cheers. I'd pinched a valve and cracked it, and spewed metal all through the head and the rest of the engine. Left the thing just chewing away at itself. Bloody lucky I dropped off the engine anyway as he said I could well have had a lock-up at high speeds. That wouldn't have been much fun. Anyway, here's a pic... Nasty eh? Carl said... "Have you leant it to anybody who's revved the tits off it, thrashed it for long periods?" Er... I thought. That was probably me. Anyway, I've spent a bit of time mulling over what has caused it and it was probably a number of things.... - Shit jetting. - Thick header wrap. (Maybe, but even if this didn't help it rooted a perfectly good standard Yamaha doubled-walled header pipe, so don't do it kids) - And something else, which I've forgotten. And all compounded by way too many long rides at high RPM's. I've done a few 900k+ days on the SR, all at 120kph or so stopping only for smoking, urinating, eating and gaffing my muffler back together. I should have noticed it early as the top end was always bloody loud. I did and redid the valves a number of times, but after listening to some other SR's, and watching some videos on the bike on youtube I figured some were just like this. I was wrong. In retrospect the other loud SR's I'd heard running were buckets of shit, and I shouldn't listen to anything youtube says anyway. But it's a testament to the SR that it can keep running and running without blowing itself up. So, if y'all can learn from my mistakes - it be these two. JET YER BLOODY MUFFLER PROPERLY. Close enough isn't good enough. IF YOU HEAR OR FEEL SOMETHING THAT DOESN'T SOUND RIGHT It probably isn't. Don't listen to what some other people say. Go with your guts. Taking the SR head apart is a pretty easy job. I should have done this 18 months ago. Anyway, I sourced a new crank and he changed the oil pump and some other bits and peices. A couple of weeks after getting the head and he's finished it, and here's some pics of the bike... Balancing the crank... Shiny Rockers Mmmm, port... And finally, on the dyno with the new exhaust So the end result? Well, I'm as happy as a pig in shit because it's now putting out well over double the horses a stock one does. Peak power is available immediately and it doesn't stop until you hit the rev limiter (Yep, the later SR400's have a rev limiter!?!) As far as pissing contest figures goes it makes 33 horse power at the rear wheel. Doesn't sound good until you realise that a new WR450, stock, puts out 28 horses on the same dyno (A notoriously skeptical one) :demon: Anyway, she'll be back soon and I'll be cleaning up some bits and peices on the frame before taking her on some trips. I'll post up a full ride report and a video when she's back.