Gs400 head swap

[Anonymous]

i currently own a 78 gs400 twin and i heard about the 8 valve head and the 4 valve...mine has the 4 would it be worth swapping the head to an 8 or is the performance gain to small to bother...plus since i hear the valve adjusting is critical and cam wear is more expectable on a head like this is it worth it.....plus if i found a old 500 or 550 and used the pistons tub and head on my 400 body would it fit or would i have to bore out my tub and just get bigger pistons what do i do about my head then.....this bike is fast enough just wondering.... if somthing like this would be worth the time....i dont have anything right now and budget is low plus finding these parts wouldnt be easy im almost thinkin its not worth it but somone please tell me because id really like to know..

[KW]

The 16v head probably wouldn't fit. Even if it did you're likely to have to machine the pistons to give clearance for the extra valves. Likewise the 500 (if you're talking about the GS500 twin). The 550's are 4 cylinder bikes.

[SqDancerLynn1]

I don't know I think your best bet would be to forget about it. If you want to do something look for a complete GS500 twin motor and do a swap

[focus frenzy]

I just got the newest motorcycle mechanics magazine and they have a article on the GS twins (the original ones) and the 400 with the 8 valve head is a hybrid, it uses the bottom end from the 450 and the bore is the same as the 425.
so it's bore and stroke is totaly differant from your first generation 400, and to top it off, the shape of the pistons is totaly differant due to the 8 valve head.

[Anonymous]

Help needed

im talking about the twins with the 4 valve heads and the 8 valves...they did make both in gs400 models mines a 4 im sure you can convert the 8 valve to mine...the most extra work you might have to do is swap the pistons for the clearance....
what i meant was a 500 twin with any amount of valves...swaping the pistons tub and head to make it a 500 cc on the original 400 base...i dont see how that wouldnt work...isnt it the same except the top end is a little bigger in bore to make the extra 100cc's


Plus do all gs bike use roller bearings i know the 450 doesnt..also you said the 8 valve bikes used 450 and 425 parts as a hybrid why do they do this?

[SqDancerLynn1]

I think all of the twins used plain brgs NO rollers

[focus frenzy]

Re: Help needed

im talking about the twins with the 4 valve heads and the 8 valves...they did make both in gs400 models mines a 4 im sure you can convert the 8 valve to mine...the most extra work you might have to do is swap the pistons for the clearance....
what i meant was a 500 twin with any amount of valves...swaping the pistons tub and head to make it a 500 cc on the original 400 base...i dont see how that wouldnt work...isnt it the same except the top end is a little bigger in bore to make the extra 100cc's


Plus do all gs bike use roller bearings i know the 450 doesnt..also you said the 8 valve bikes used 450 and 425 parts as a hybrid why do they do this?

nope nope nope won't work, here are the numbers for the 4 valve versions
77-78 GS400 low pressure roller crank, bore/stroke= 65mm/60mm, 398cc
79 GS425 low pressure roller crank, bore/stroke= 67mm/60mm, 423cc
80-83 GS450 redesign! high pressure plain bearing crank 71mm/56.6mm, 448cc
89-2005 GS500 high pressure plain bearing crank 74mm/56.6,487cc
and for the 8 valve 400
80-87 GSX400 high pressure plain bearing crank 4 valves per cylinder bore 67mm/ stroke 56.6mm 399cc

the gs 400 and 425 4 valve engine is the first generation big GS twin, the 400 8 valve, 450 4 valve and 500 4 valve are from the second generation, and the 500 is borderline being a third generation due to the top end being of somewhat modern design.
Suzuki also made a GS 250 thats design is based from the 400 8 valve engine but does not share any parts that I am aware of.
there was also a GS500 four cylinder made, from what I have found it was only available in Germany and is pretty rare, also there was a four cylinder AIR COOLED GS400, I have found a few for sale on www.ebay.co.uk and some more info pointing to-wards it being also sold in Japan, but for some reason it is not listed in the my Suzuki pages web site.

it is possible to put the 4v 500 top end on a 450 or even on the GSX 8 valve 400 bottom end but it may require changing the rods on the 450 and 400 8v to work.
you can not put the 500 or 450 or even the 400 8 v top end on the first generation bottom end.
you are limited to going up to the 425 top end.

PS: 9

[focus frenzy]

Re: Help needed

Plus do all gs bike use roller bearings i know the 450 doesnt..also you said the 8 valve bikes used 450 and 425 parts as a hybrid why do they do this?

not actually parts other than the 450 crank and stroke dimensions, it's bore is the same size as the 425, but it uses different pistons due to being a 4 valve per cylinder engine.
Lynn, the first generation twin made up to 79 used a roller crank, twins made from 80 to current have a plain bearing crank, they are not interchangeable.

PS:8

[KW]

Here's a slightly different possibility to "up" the capacity of the 400 4v motor. And before I start I haven't tried this or checked out any measurements(yet!) , but I may have to in an attempt to repair my GS425 (oversized pistons are not available anymore and my cylinders are shot).

OK, here goes:

1. GS400 4v pistons are the same as the GS750 8v pistons (65mm dia.)
2. GS850 8v pistons (69mm dia.) will fit the GS750 4v if your bore out the cylinders.
3. 1 & 2 above should mean that the GS850 8v pistons will fit the GS400 4v motor if you bore out the cylinders to 69mm.

This would increase the GS400 4v to approx 448cc.

The only problem I can see is that there may not be much thickness left in the liner skirt (where it fits into the crankcase) - I've been advised not to have a wall thickness of less that 2.25mm or you run the risk of the motor "nipping up" when it gets hot due to distortion of this part of the liner.

I'll be measuring all this up tomorrow so I'll let you know what I find out.

[Anonymous]

thanks for all that info im better off probably leaving the motor stock and yeah i like the fact that the crank and tranny run in roller bearings with low pressure oil pump its vertually indistructible and long lasting they should have never strted making them with plain bearing inserts

[Scooter]

KW, I'm new here, but not to engine building. How did the measuring go? Were the pin to crown heights the same on the gs400 pistons compared to the gs850 pistons? What about dome shapes? Do you have any more info? I'm attempting a big bore project on my gs400 and you had the best info I've found in a month of looking! For me to swap on a set of 450 pistons and cylinders would have required machining in an o-ring groove, and two holes drilled and tapped in the centering dowl holes. Along with boring the holes in the case coves to suit. The smaller intake and exhaust runners would have made killer torque along with a few other mods(Performance cams, header wrap, free flowing mufflers, and K&N air filters). The only hold-up? Pistons. I wanted to bore up to 425, but couldn't find pistons anywhere(and I mean anywhere). So then I thought about the 450 conv. but my machinist buddy is reluctant. I could really use some more info if you have any. Thanks!