Parts dealer says 1981 suzuki gs400 parts discontinued

[GregT]

Engine parts are rest of world GSX400. All same, L, S, and E.

[Sandy]

Contact.Murray or Aaron at Modern Motorcycles in Vancouver. They could possibly have the largest stock of NOS Suzuki parts in the world. Just google them. And your bike is not a unicorn, the US imported 2 valve.model for.those years is. Everyone else got the 4 valve.model.

[John Park]

Contact.Murray or Aaron at Modern Motorcycles in Vancouver. They could possibly have the largest stock of NOS Suzuki parts in the world. Just google them. And your bike is not a unicorn, the US imported 2 valve.model for.those years is. Everyone else got the 4 valve.model.

I think Murray ran dry a few years ago; we were down to piecing together a complete[ish] gasket set. I think Suzuki Canada may have a few bits left, but I decided to move on and convert mine to a 450. That involves replacing everything above the crankcase....

As Greg says, check the head for cracks from the exhaust seat to the plug hole. I've come to the conclusion that 4 valve heads and air cooling were a bad idea.

[GregT]

As Greg says, check the head for cracks from the exhaust seat to the plug hole. I've come to the conclusion that 4 valve heads and air cooling were a bad idea.

Only the early small capacity engines seem to have this problem. The GSX400, the Yamaha TX500, the Honda CB250RS all do it. I suspect the designers were simply a bit miserly with material thickness in the heads. The bigger engines from the same period - the GSX750 and 1100 Suzukis and the 750/900 Hondas have no problems. Pity really as the small capacity 4V/cylinder engines are sweet running units.

[John Park]

Only the early small capacity engines seem to have this problem. The GSX400, the Yamaha TX500, the Honda CB250RS all do it. I suspect the designers were simply a bit miserly with material thickness in the heads. The bigger engines from the same period - the GSX750 and 1100 Suzukis and the 750/900 Hondas have no problems. Pity really as the small capacity 4V/cylinder engines are sweet running units.

I differ on this. There is no viable heat path for the web between the exhaust valves. Down leads to the combustion chamber and up leads to the floor of the cambox. You can see the hot spot inside the head where the oil has cooked just above the web. The web is a thermal disaster in waiting as it picks up exhaust heat and has nowhere to put it. I doubt that miserliness had anything to do with it, other than that four pipes would have been complicated and costly.

Valve seat gets hot, expands and cracks head on hottest side - toward plug. Give me a hemi that, while it may be old school, blows intake at the exhaust valve, and has a valve angle that allows for finning on top of the combustion chamber. And don't try to sell me a SOHC design that puts a cam where those fins should be.

One way to deal with it is to run two exhaust ports rather than siamese the port. Even the old XL250/350 did this. SP250 also, I think. The bigger motors are a different situation because you can't hold them wide open for all that long. For those that did, the oil cooled GSXRs did okay at dealing with it, but water works best.

There are also no fins worthy of the name on the top of the GSX400 combustion chamber. I'm currently working on a 1949 Velocette MAC 350 [hemi] which has an iron head but the whole shebang is finned.

Sure, lots of designs run anyway, but I'm into design elegance. The original Aermacchi cylinder head was a paragon of cooling strategy and facing into the wind, much like Moto Guzzi singles. Some pinhead redesigned the head with an 'ashtray' valve cover which was a disaster for cooling, totally eliminating the internal finning. Competition bikes retained the original design - who knew? - and the consumer bikes cooked themselves. Form can follow disfunction.