Cruzin Image GS400 Big Bore- Fit GS425?

[brit7.11]

As per the title, is there any reason why the Cruzin Image big bore kit for the GS400 would not fit a GS425?

I believe the 425 only differs in bore size, so can't see why not, but anybody done it?

I emailed Cruzin Image, but they were unable to confirm.

Many thanks.

[Chuck78]

Got a link for the kit?
Is it a 448cc or 449cc kit?

[Chuck78]

GS425 pistons are just a 2mm overbore size of a GS400 1977-1978 piston.
1977-1978 GS400 stock bore 65mm pistons are the same EXACT piston as the GS750 8V (2V/cylinder) pistons.

GS850 pistons are 69mm and otherwise exactly the same as all 77-79 GS750 pistons, but 4mm larger bore. GS850 1979 head is the same exact head as a 77-79 GS750.
You can bore 850 pistons into a 750, or grind the cases slightly to fit 850 cylinders and pistons into a 750.

[Chuck78]

See where this is going?
Two stock bore GS850 pistons bored into a '77-'79 GS400/425 will give you 449cc "big bore kit."

You'll have to check the actual cylinder sleeve wall thicknes of the 425, but you might be able to bore +1.0mm oversized GS850 pistons into a GS425 cylinder.
Also, two individual GS750 Wiseco # K844 pistons for the Wiseco 844cc big bore kit for a GS750 will be much nicer if you want more performance. You get 10.25:1 compression and deep valve pockets tonbe able to fit an aftermarket camshaft regrind profile from MegaCycle Cams or Web Cams.
You'd still be at 449cc same as GS850 pistons,but higher compression makes more power, and the ability to run bigger cams also means more power potential.

I think 470cc is what you'd get if you can bore 70mm GS850 +1.0mm oversized pistons into. If you won't be upgrading cams, and always wantvto be able to run low octane gas, this would be the best budget route if the sleeves are thick enough.


I've been planning for years to have 1 of my 425 cylinders resleeved larger to fit some old school MTC Engineering forged 920cc GS750 pistons into a 400 frame with 425 too end and ported head. The Wiseco K844 449cc route is also tempting.

By the way, APE Race Parts does the cylinder boring and some pretty trick head mods to these engines, and they sell custom big bore head gaskets to use the GS750 K844 pistons on a GS400/425, And also will sell you just two pistons out of a 4 cylinder GS750 set

[LAB3]

Haven't looked up any prices but go-fast parts usually sell for a premium. When I had me 450 the upgrade that seemed to make the most sense money wise was putting a GS500 engine in it with the 450 heads on top.

[brit7.11]

Thanks for the replies.

These are 69mm pistons, so only 2mm oversize for the 425, so i cant see any reason why they wouldn't fit.

I'm not looking for a performance upgrade, just a good rebore option for when I do a full rebuild. Genuine Suzuki parts are hard to find and really expensive.

I've used Cruzin Image pistons before with no problems.

[brit7.11]

Here's a pic of 'Little Suzy' in the Cairngorms.

[Chuck78]

Wow, that's CHEAP! Yes, that should work just fine as long as they are stock GS850 piston designs. They look to be. The GS650 big bore kit they sell is apparently just stock GS750 pistons, and has sane disclaimer "not design of original Suzuki pistons," and unfortunately are 100% not compatible with the GS650 closed chamber head and don't fit the bike they're advertised for.
This kit however should work no problem as they appear to be GS850 hemi pistons to replace GS400/750/425 pistons of the same valve spacing position.

[brit7.11]

I think I'll end up trying them.
Lil Suzi is running well, so no immediate plans for rebuild, but watching a slight head gasket misting with interest!

Kind of itching to pull it apart, but enjoying riding it too much.