GS400t with 4 valve cyl head

[Guest]

I have a rareish GS400 bike here. it is a Canadian model and is 400 cc 1981. In Canada, they sold the 400 CC model for a few years different from the USA that went to 425 cc then to 450 cc. The rarity of this bike is that it is a 4 valve piston cyl head combo rather than the more common 2 valve head. I am in need if a std piston to replace one that has a broken ring land. Anyone here know of one that might be available? and failing that can I replace the cyl head with a 2 valve and a pair of pistons that match? Has anyone got a pair of two valve pistons and cyl head with all attachments? (such as cams, valve cover, chrome end caps?) and anything else you might think I need? Thanks in advance for any help you might offer.

[John Park]

As well as the piston, you'll need a head gasket which is particular to that motor; the base gasket is the same [I think] as a US 450. Rings may be scarce as well. I think ones from a Yamaha XT225 may??? fit. Suzuki Canada still has some things, and cmsnl.com has reasonable inventory.

The whole US 450 top end will fit the 400 block. I'm running one. This solves a lot of parts problems.

[mikestp]

Well if your reply is as I see it. A 450 cylinder, a pair of 450 pistons, and all the misc parts that go on the head will fit the crankcase of the 400? Or are you saying the 450 head will bolt to the 400 barrel and if I also replace both pistons with the 400 two valve type all will be fine? That might be the easiest route for this.

[GregT]

Rest of the world it's a GSX400. The heads eventually crack from the exhaust valve seats to the plug holes so if you are planning on keeping it, the 2 valve top end is a good option. You will lose some performance though.

[John Park]

Rest of the world it's a GSX400. The heads eventually crack from the exhaust valve seats to the plug holes so if you are planning on keeping it, the 2 valve top end is a good option. You will lose some performance though.

Depends on how you define performance. The 4 valve head is rather compromised by the port angle so for peak power it's pretty much a standoff; for torque in especially the 4000 to 7000 range the 450 wins easily, maybe because it sucks the carbs open sooner. On the street the 450 is a better motor and the cooling 'system' - fins - are conspicuous by their near absence on the 4 valve. IOW, the rocker boxes ate the cooling fins.

There's just something about hemis....but @10,000 rpm the 4 valve is pretty intense.

[John Park]

Well if your reply is as I see it. A 450 cylinder, a pair of 450 pistons, and all the misc parts that go on the head will fit the crankcase of the 400? Or are you saying the 450 head will bolt to the 400 barrel and if I also replace both pistons with the 400 two valve type all will be fine? That might be the easiest route for this.

The barrel is different. Bigger bore - 71mm? You need the front chain guide and the rear guide is different too, but the 400 will work but you may have to make a spacer to move the cam chain tensioner out about 3mm or so. Carb boots are different; exhaust bolts right up.

[mikestp]

I am attempting to buy a 4 valve piston, it will make it easier to repair knowing what parts fit. At this time I am not certain of what will or will not fit. The 400GSX barrels are not measurably worn, and all I need is a replacement piston. I am not sure a 450 barrel will fit onto the crankcase. I found piston replacement candidate here:

https://www.ebay.com/itm/PISTON-GSX-400-1983-12111-33300/132372800567?epid=1526283216&hash=item1ed208a437%3Ag%3AENsAAOSwl9RZ7chd&_sacat=6000&_nkw=gsx400+piston&_from=R40&rt=nc&LH_TitleDesc=0

The ebay advert says it is for a 1983. I can hope it will match the other piston i have. the bore size is 67mm, same as my bikes bore size. My head gasket was a good removal and with copper spray I can reuse it. I hope this ebay advert for a 4 valve piston is te correct one

[TxGSrider]

Just out of curiousity , what caused the ring land on your old piston to break? It'd not a very common issue on most engines I've seen outside of ring gap issues and such.

[Gorminrider]

Be Very Careful. That part number does not match as for a GSX 400. a TWIN .Goto parts suzuki motorcycle accessories spares replacement aftermarket

BUT a google search for "suzuki 12111-33300" comes up as possibly for a GSX 400F which is a FOUR CYLINDER bike

[mikestp]

Be Very Careful. That part number does not match as for a GSX 400. a TWIN .Goto parts suzuki motorcycle accessories spares replacement aftermarket

BUT a google search for "suzuki 12111-33300" comes up as possibly for a GSX 400F which is a FOUR CYLINDER bike

https://www.bikez.com/motorcycles/suzuki_gsx_400_e_1981.php

This shows it is a twin... and 67 mm in size.....

And this 1983 shows as a twin also 67 mm in size

https://www.bikez.com/motorcycles/suzuki_gsx_400_e_1983.php

[Gorminrider]

re-read my post?
an F is not the same bike as an E

there's an "F" on homepage this monthhttp://www.thegsresources.com/

[mikestp]

ahhhh placng an underscore under in message under the letter F makes it look like an E. My error, I would have asked to have the piston in question measured to see if t was 67 mm

[Gorminrider]

yes it's not very plain with the line under it!... But main thing is, don't have the wrong part showing up!

[mikestp]

broken land

DSC05929.jpghere s a pic of the broken piston

[Gorminrider]

nice picture of disaster! Lots of these bikes in Canada, you know, but just tearing it down to get the piston is a lot of work...you might want to get the whole engine as scrap cheaper if there's a boneyard near you.