GS 400, 425, 450 compatibility

[Anonymous]

Hey y'all!

I'm considering selling my Yam XS650 and buying a 1979 GS 425. I have a couple questions. 1, are these bikes usually worth even looking at? (Can you highway ride on them? Are they reliable?) 2, how interchangeable are GS parts? I know of a 1979 GS400 and a 1981 GS450 I could buy on the cheap for parts bikes. I was espcially interested in finding out if the GS450 bodywork (esp gas tank) and the GS400 engine would fit on the 425 frame. What about brakes, wheels, etc? I would really appreciate some advice. If I buy a bike, I need something with parts readily available for me. My XS is a nightmare in that area.

[snark]

I'm not an expert in this area, but my understanding is that the main difference with the three bikes you mentioned is the powertrain. When I posted on here about a 425 a friend was thinking of buying (he didn't) and a 450 engine I had, the replies I got back basically said everything should preety much swap right in.

[spots25]

I can guarantee the wheels and brakes swap, because I have '80 GS450 wheels on my '78 GS400 right now. Also, I have a '80 GS550 front brake on there.

for the highway, I rode my bike at 70mph two up, so with that extra 25cc, you should be better off even!

[Mastiff]

Here is a report on the GS425 from a British website:

Suzuki GS425s are quite rare, an interim model between the original 400 and the later 450 twin. I bought my 1981 machine as a two year old which had done a mere 5000 miles in the hands of an OAP. It was that kind of bike, with a simple DOHC engine and an utterly conventional chassis layout, that would appeal to motorcyclists across age bands. These days, they are useful second bikes for the hard winter chores and, when neglected, are perfect as cheap hacks.

My GS has, on the other hand, been my sole bike for the past eleven years and now sports 67000 miles! As well as a short commuting run every day, it's also had to suffer long holiday jaunts, weekend madness and enough country lane hustling of an evening to prove itself most worthy! This is the kind of twin the old British industry should've produced, had they the money and the wit!

My first impressions of the GS were of a smooth, mild twin that was very easy to ride. The chassis might not be to some tastes as Suzuki were convinced that removal of all road sensations was a Good Thing. The remoteness of the ride on wet roads with Japanese rubber was, to put it mildly, stomach troubling. My heart was in my mouth several times when I swung through a slow bend only to have the tyres slide away. The seat height was low, so a good chance of getting a boot down.

After a couple of days on wet roads I bunged on some new Avon Roadrunners. These removed most of the wet weather slides, although they were still remote, and I had little idea of when they were going to start sliding. At least they let loose in a predictable, progressive manner, unlike the Jap rubbish that would let go with sudden violence.

The Japanese stuff didn't seem to wear at all, the Roadrunners lasted 13000 front and 11000 miles rear. Next came a set of Michelins, which were on special offer. Initially, they were better than the Avons, tuning out a mild weave that had appeared on 90mph runs. However, after 6000 miles they seemed to go off, with some quite large weaves at the back and a wandering front wheel. By the time another 3000 miles had passed the bike had become very dangerous to ride and I changed them for a set of Arrowmaxes. These lasted about 10,000 miles but seemed no better than the Avons, which I've used ever since - although they become shorter lived with each new set!

The Suzuki is one of those bikes that goes better with newish tyres. The frame is quite strong but prone to a blitz of rust after five years, which became so persistent that I ended up having it blasted and powder coated. The suspension was on its last legs after three years, had not been stunning in its damping even when I'd bought the bike, but it remained reasonably controlled below 70mph.

Higher speeds were accompanied by some quite large wobbles, their degeneration into a complete lack of control dependent on the state of the tyres. The rear shocks were sorted out with a set of Konis, which after five years were replaced with Girlings. The stiffer springs actually allowed some idea of what the back tyre was doing and all but eliminated the weaves.

At least whilst the swinging arm bearings were in good shape. Not as frequent an occurrence as I'd like, some of them lasting less than 5000 miles, although the originals last over 10,000 miles. I always bung in plenty of grease but it doesn't seem to help. In the end, at about 20,000 miles, I bought an alloy swinging arm with needle roller bearings that has not needed any attention. A nice bit of kit, with eccentric chain adjusters.

That helps with the chain tensioning, as I usually put on the cheapest chain I can buy. The original chain lasted for 12000 miles but the replacements rarely do more than 8000 miles - needing an adjustment every 300 to 400 miles. I only wipe them over with an oily rag once a week. The sprockets usually last out two chains, although I had one set that shed teeth after only 7000 miles.

Not the kind of behaviour associated with a 38hp vertical twin that doesn't have an ounce of brutality in the manner of old British bikes. The engine begins to go harder come 6500rpm, but even in second or third it never comes close to wrenching arms out of sockets. The GS still has an excellent gearbox that allows maximum abuse of the clutch and ratios, all the way into the red.

As the bike weighs only 375lbs it's a snap to throw about, either in town or down country roads. It feels safe and predictable in curves (on good tyres and with sorted suspension). The front wheel started to wobble exiting corners, a consequence of rotted steering head bearings and worn out front forks, at 18000 miles. The steering head bearings were easily fixed with a set of taper rollers but the forks needed to be taken right down, fitted with new bushes and seals. I ended up with stiffer springing and damping as well as a fork brace. That set the front end up very nicely, along with the other mods, making the GS feel much more like a British twin in its feedback and tautness.

The front disc brake used to twist the forks and cause massive dive on the stock set-up, but after the rebuild of the forks it was much superior, allowing me to take the wheel right to the edge of locking up. The lever needed a firm grip, but with Goodridge hose and Ferodo pads there was plenty of power and no noticeable lag in the wet. The stock pads had a two second delay and before the Goodridge hose was fitted the lever became very mushy. Ferrodo pads lasted for 9000 miles against 14000 for the originals.

Engine maintenance was laughably easy, although I did have to change the oil every 2000 miles. Engine problems were mainly related to the top end. The camchain doesn't last for much more than 25000 miles but the tensioner went for 40,000 miles before the rattles became too much to bear. The exhaust valves tried to dig holes out of their seats at 16000 miles but only succeeded in destroying their edges. A pair of used valves lasted only 4000 miles whilst the next new set managed 22000 miles. There's quite a lot of warning of their demise from the popping in the exhaust on the overrun. The first time it happened I spent hours sealing up the exhaust, thinking that it was leaking.

The top end's by far the most troublesome area of the engine. The bottom end's bulletproof, with both gear primary and balance shaft drive plus a much heftier crankshaft than in the later 450 twins. The bores and pistons are still original, with no apparent wear. The earlier GS400 had even more trouble from the top end whilst the eight valve GSX400 used to have head material made from cheese! To my biased mind that makes the GS425 the pick of the bunch.

It many ways it's a motorcycle that surprises. For instance, although the acceleration is never shocking, once it's gained a reasonable turn of speed it holds on to its velocity with relative ease. I used to cruise at 80mph until I realised that it was just as happy at 90mph! The vibration starts to come in after that, although I've ignored it and put as much as 110mph on the clock.

Not something I'd care to do with the stock bars and pegs, my machine now sports flat Vincent bars and pegs moved back a good five inches. It's a compact bike that leaves me feeling perched atop it, but the modified riding position means it's much more comfortable and controllable. I can do about 400 miles in a day without going crazed with the pain, but I usually have to pull over for fuel after 150 miles.

Economy's pretty good. I rarely achieve less than 60mpg, usually around 65mpg with 70mpg possible under a very mild right hand. Chucking the standard silencers in favour of some old Triumph pipes is worth an extra 5mpg, the engine running leaner and freer flowing. With its off-beat exhaust note it can't be confused with a British bike.

The GS and I have grown old gracefully together. Apart from a couple of head rebuilds, the bike's been a brilliant companion that is much more a natural retro that the somewhat pathetic imitations the Japs are trying to pass off. There's nothing on the market for reasonable money that offers the build quality of the GS, modern Jap bikes look, to these cynical eyes, like throwaway junk. I know someone who blew up a GS450 engine in less than 20,000 miles. That's just not good enough in my humble opinion.

George Hutchings

http://www.umgweb.com/0sgs4065.htm

[andyjohnson]

Mastif,
I am looking to change the riding position on my '87 GS450L, I've already ordered daytona bars to get forward. I wondering though, what the best way to move the footpegs and controls back and possibly up a bit. could you fill me in on the specifics of what you did with yours?
Thanks,
Andy johnson

[breny426]

1978 Gs400

I have a '78 GS400 and have had the same question about compatibility of parts. The biggest changes through the late '70s to early '80s 400/425/450 that I've seen has been the bore and the carbs. I've been able to find used and new parts on ebay and at local shops. It can be difficult sometimes, but if you have the time and the patience you'll be able to find and sometimes modify your bike the way you want it. Just be sure to look real close at pictures before you order anything off of ebay or any other website.