SR500 vs SR400 - what's the diff?

[Wired1]

I've just picked up my next rebuild - a Yamaha SR400. It was the one that was on Trademe last week and is bloody rough but just what I wanted for the basis of a good rebuild. I'll start a thread for the restoration and do the usual videos on youtube, but for now I'm keen to pick the collective brain regarding variation in engine design between this SR400 and the more common SR500.
From what I've found out they both have 87mm piston and bore, but the SR400 has a shorter stroke. They both put out 27 horse power, the SR500 does it at 6500 and the SR400 at a slightly faster 7000 rpm.
There are loads of parts available for SR500's and a lot of aftermarket goodies to increase the bore to close to 600cc but virtually nothing for the SR400's so I'm hoping they share the same barrel and head etc.
Any info on this would be gratefully received.

[Motu]

Is the 400 2 valve or 4 valve?

[Wired1]

It's 2 valve, identical in appearance to the TT500 I have in the shed. I'll do some rudimentary measurements in the next few days to see if the barrel is the same height as the TT500 one. I have heard that the SR400 was designed to slip under an insurance break point in Japan, and that's why they were only ever sold there.

[cowpoos]

100CC's ??????????????????

[HTFU]

100CC's ??????????????????

couldn't help yourself could you :Pokey:

[Motu]

Probably similar differences to the 400/600 4 valve.The top end should be the same,seeing as the bore is the same as the 500,it would be easier to raise the comp ratio with a domed piston rather than a reduction in chamber volume.Shorter stroke crank of course - the rod will be longer,and the sleeve shorter or relieved to clear the longer rod.

[SixPackBack]

Contact 'badcat' dude, he built a fantastic SR. From memory he had lots of parts/contacts.

[Wired1]

Thanks, I've left him a message.

From the wonderland of google I have found the Deus SR400 page - they specialise in building SR400 cafe racers - and have this to say:

"Being almost 17mm shorter in the stroke than its SR500 sibling, the 400 donk doesn't do much torque-wise until it hits around 4000rpm. Then the response comes on clean and strong (you wouldn't call it a "rush" but it certainly starts to haul for a 400). The short-stroker doesn't vibrate as much as an SR500 either."

[Sensei]

Have a manual with all the hot up stuff to do to these from when I had my XT/TT 500's can copy it if ya keen , tryed the 620cc kit in my TT500H .

[Bren]

was that the burnt out one with knobblys?

[Wired1]

was that the burnt out one with knobblys?

Yes that's her - what a beauty. And they're actually high performance all terrain traction systems not knobblys.
It runs, starts first kick and runs strong. It's the first time I've bought a project bike that actually runs. The plates are dead but at least LTSA managed to find it so it won't require the full bollocks rego, just the revival job.

[xwhatsit]

Don't know anything about the engines, but yes, they were produced to get under the 400cc laws in Japan; to get your full license there is near impossible. So most people ride around on 400s. That's why we get all sorts of weird imports here from NZ that nobody else gets; 400cc Ducatis etc.

The SR400 is still being produced now, I think. Or at least was until very recently. Being made since the 70s -- still with the TLS front drum (I don't think the SR500s ever had drums, they had disc brake from the beginning?) -- lovely drop-in replacement front-end for CB250RS (drum brake more powerful than the RS disc, beefier forks). So if anybody has an SR400 front-end lying around I'd love to hear from you.

The GB400/500 story is similar; in fact, you hear of people who prefer the 400 for the same reasons Deus mentions -- the 400 vibrates much less. I've heard a couple of people now suggest that 400 is the largest size for individual cylinders if you want to have a nice smooth engine.

[Pwalo]

Don't know anything about the engines, but yes, they were produced to get under the 400cc laws in Japan; to get your full license there is near impossible. So most people ride around on 400s. That's why we get all sorts of weird imports here from NZ that nobody else gets; 400cc Ducatis etc.

The SR400 is still being produced now, I think. Or at least was until very recently. Being made since the 70s -- still with the TLS front drum (I don't think the SR500s ever had drums, they had disc brake from the beginning?) -- lovely drop-in replacement front-end for CB250RS (drum brake more powerful than the RS disc, beefier forks). So if anybody has an SR400 front-end lying around I'd love to hear from you.

The GB400/500 story is similar; in fact, you hear of people who prefer the 400 for the same reasons Deus mentions -- the 400 vibrates much less. I've heard a couple of people now suggest that 400 is the largest size for individual cylinders if you want to have a nice smooth engine.

You are quite right. I had a FT400, the Japanese market version of the FT500 (certainly less than my friends SR500). I actually enjoyed my time on the thing, and it was pretty good in the vibration stakes. But for some reason I haven't had a Honda since then.

I'm pretty sure that the SR is still being produced. Those Japanese are really crazy guys.

I've heard the suggestion that 400cc is about the biggest piston size you want for a bike. The SV's 325cc jobbies work very nicely.

[Bonez]

I'm pretty sure that the SR is still being produced. Correct, here's a time line.

http://home.vtown.com.au/~sross2/

Next years model may have EFI. Wonder if it will have a fake carb ;)

[Wired1]

Yes they are still making them. Mine is a 1980 bike according to the LTSA who managed to trace it yesterday. It appears to have everything pretty much as it was for the 500 of that year including mags - the modern ones have spoke wheels.

[Badcat]

i have a 500 crank here....
and a tt500 carb that would make a big difference.

ken

[Wired1]

i have a 500 crank here....
and a tt500 carb that would make a big difference.

ken


Thanks, from what I've been reading the 400 might be a better bike than the 500. I've ridden this a few times already and it is a very good engine so unless it blows to bits I'll probably leave it as a 400 for now.

[SixPackBack]

Thanks, from what I've been reading the 400 might be a better bike than the 500. I've ridden this a few times already and it is a very good engine so unless it blows to bits I'll probably leave it as a 400 for now.

My 400 run a lot better with a 500 carb, at the time I had a supertrap muffler and the standard 400 carb was not that flash.

[Badcat]

yep - and the sr500 goes a lot better with a TT500 carb.
my 600 cc race motor (ex f3) has a new FCR 41 flatslide for it - now, i just have to get around to sorting the chassis and brakes before i fit it!

woot!

[Wired1]

I have fitted the supertrapp from my TT500 and it sounds awesome - lets hope the vtnz guy agrees! Do you mean you fitted an SR500 carb to an SR400 or are you talking about some other bike? I think it's the same carb so I guess they have different jetting?