GS Big Valve head

[Big Jay]

GS400 / 425 head machined for oversize valves 38 / 32. Ready for the porting department for blending. These heads really respond to this mod as, stock, there is quite a restriction where the port meets the seat.

[Buffalo Bill]

Do go on with story, but please include before pic and specs.
Like to know how to do this to the GS650 and GS1000 heads.

[bitzz]

Kibblewhite has a 25mm and 30mm over size setup for a GS1000.
Just grind the seat for the over sized valves.

[Big Jay]

Do go on with story, but please include before pic and specs.
Like to know how to do this to the GS650 and GS1000 heads.

As you can see from the photos, the seat throat has to be opened for the oversize valves. You can't just cut the seat larger for the big valve. Then care must be taken to keep sufeciant valve to valve clearance so they won'y hit other when it is running.

[Buffalo Bill]

Yes, I have pics from the valve job I did on my 1100G last winter. Looks like no room for larger valves in that head.

[Chuck78]

Now we're talking! MORE INFO, PLEASE!
I have a few 425 heads and I think a complete 400 engine and maybe a 2nd 400 engine for parts awaiting me.
I've been wanting to build a hot rodded GS425 big bore for some time now.
I was contemplating oversized valves, but figured maybe a street porting job was the furthest level that it was reasonable to take it to...
Now you've got me convinced otherwise.

449cc with Wiseco K844 GS750 pistons, aftermarket cam grind with higher lift around .420", and some CR33 GS500 carbs or some RS34's modified into a 2 cylinder rack... that's what I'm talking about!
I actually have a pair of NOS slightly used 920cc GS750/850 pistons from MTC Engineering to make a 489cc GS425 with 850 sleeves or perhaps 450 sleeves machined into the 425 cylinder block...

I really want an old school roller crank GS twin stripped down and hot rodded out, a lighter weight very flickable, braced-frame, upgraded wheels/tires/brakes/suspension, kinda twisties machine... possible WERA Formula 500 racer as well as Vintage 3 or Vintage 4 or whatever class I could competitively fit it into... AHRMA would limit it to 449cc iirc? WERA would allow a GS400-425-450 up to 550cc, but that's insane on a 400/425 cylinder stud spacing, only do-able on a very hogged out 450 with 500 cylinder jugs and a base gasket spacer.

[Chuck78]

GS400 / 425 head machined for oversize valves 38 / 32. Ready for the porting department for blending.
These heads really respond to this mod as, stock, there is quite a restriction where the port meets the seat.

Is this a customer's bike you are working on?
Is it a vintage race bike?
Or just a hot rod?
Thanks for the additional inspiration/motivation, Big Jay!


Just seeing this and reading your 2 topics in this twins forum on these has really rekindled my desires to build a 500cc GS400/425 with a street port job, .410" lift street performance cam, big valves, big bore, braced frame, wide rims, and top notch suspension...
Running out of cornerning clearance on the big cc (wide engines) GS fours was the other big motivating factor after my 2nd 2020 trip to the Eastern US mountains, ripping a modded GS750 through all the twistiest roads and mountain passes that I could make it to....
Yoshimura prepped race bikes ran a cut down stator cover with the bottom angle milled and a plate welded on for extra cornering clearance, and a custom low profile magneto setup for the ignition, as well as extending the length of the fork tubes by welding extensions onto the tops of the forks to be able to run a taller ride height...
my GS750 is around 465lbs with 2.5 gallons of gas, which is about the same as what you can get a GS1000 down to.
The GS400's aren't featherweights, but the dry weight (w/o fluids) is 133lbs less than my '77 GS750B started at, 378lbs dry weight stock with spoked wheels (382lbs for E models with mag wheels),
so I think I can probably get it down to ~335lbs dry weight after mods:

*wider alloy rims and wider tires but also going tubeless (same weight as stock)
*2-into-1 exhaust and alloy muffler can (-14lbs)
*centerstand delete (-8lbs)
*lighter weight modern 310mm single disc rotor and twinpot brake caliper up front, swap drum rear for underslung GSXR rear disc (same weight)
*smaller bars than stock, or alloy clip-ons (-1lb)
*GS400X gauges to eliminate the center indicator light cluster, alloy bracket, Tomaselli style headlight brackets and rubber isolators, drilled out chaincase cover, additional Yoshimura-style holes and divots drilled into head/cooling fins (-1lb)
*lighter modern chain + alloy rear sprocket (-2lbs)
*alloy rearsets from a Hayabusa or aftermarket + passenger footpegs/frame delete (-4lbs)
*lighter deltabox style chromoly swingarm or GS1100E longer aluminum swingarm (-2lbs)
*Airbox delete - K&N pods added, Mikuni RS34 custom twin rack'ed carbs or GS500 CR33 Keihin smoothbores (both significantly lighter than the zinc-aluminum alloys used in OEM carbs, -2.5lbs)
*Lithium Iron Phosphate battery and starter motor/gear/drive delete (-10lbs)
*bigger cylinders and pistons, but hollow core cams (same tradeoff)
*Will be adding longer shocks (Fox Factory Shox) and bigger forks (GS500 in GS1100E triples, or CBR600F4 in VMax 1200 triples), so some mods add a slight bit of weight... (+3lbs)
*add bronze-welded chromoly frame bracing (+2lbs)
*minimal turn signals (-2lbs)
Lots of little weight savings here and there... approximately 40-45lbs there.


340lbs dry weight + massive engine power upgrades should make this thing quite the screaming sleeper...unsususpecting! When I was still planning on building this out of my stock GS425, I had gotten a nice set of GS400-badged side covers, thought that would really make it even better, someone seeing 400cc model designation on the side after seeing how fast it was... But now I've got a '77 or '78 GS400 frame to build this out of, and a GS450 wiring harness and a crate of GS400 and 450 parts from a tear-down, since I really wasn't needing much stock that I don't have spares of already, or significant upgrade parts in lieu of the stockers.
I have 2 or 3 of the highly sought after GS450S knee dent tanks on the shelf, and a GS400 Guiliari aftermarket seat... GS400 badged side cover, and a GS400/425 tail section and inner fenders to cut down...

I actually have pretty much all these parts, but would just need to buy some new tires (Pirelli Sport Demons 130/80-18 & 100/90-18), cylinders re-sleeved and bored for 72mm pistons, pistons lightened (they're ancient MTC forged pistons, a bit heavy), cylinder head work, custom cam regrind... a little custom machining with my home shop mills and lathe here and there, maybe a lighter rear rotor and a custom center for it. And of course all new engine gaskets, seals, cam chain, and some fresh piston rings (I ran these pistons in a GS750-920cc until a shoddy valve job by a car machine shop caused severe detonation, ruining my #4 piston and combustion chamber).


2017-03-02 23.09.33 by chuck_lambert78, on Flickr

2017-03-02 23.32.44 by chuck_lambert78, on Flickr

2017-03-02 23.29.26 by chuck_lambert78, on Flickr

2017-03-02 23.11.33 by chuck_lambert78, on Flickr


I actually may build up a second one of these as as more budget build and retain rear drums and stock cylinder sleeves, since I have two bikes worth of parts now (1 complete stock 79 GS425E). 449cc Wiseco K844 GS750 pistons and stock GR650 Tempter (Suzuki twin, same cam fitment but substantial lift for more street torque).

[Chuck78]

Rich Graver's last GS450 incarnation:


Rich Graver, GS450 racer, Grattan, 1991:

Graver-Rich-Grattan-91 by chuck_lambert78, on Flickr:


An AHRMA raced GS400:


GS450 racer:


food for thought.... with the Wiseco pistons bumping it up to 449cc and ~10.4:1, Big Jay / APE's big valves and head work, Megacycle cams, a MAC exhaust + performance baffle (or some of those trick GS400 exhausts on Japan.webike.net), some GS500 forks in later GS1100E triples or GS550/650 forks/triples, twinpot brake mod single disc upgrade, K&N filter or pods, and a dynojet kit, these little bikes can be really really potent screamers... Bridgestone Battlax BT45 or Avon RoadRider tires... Hagon or YSS shocks spring/valved for the application, Racetech Gold Valves in the fork. VERY FUN for riding in the twisties for sure, or around town...if you can keep your right wrist controlled in moderation!

I've read a lot of comments online where people describe a GS450 as being "pretty fast for a 450..." - so with the same displacement but high compression, a worked over head, MegaCycle cam grinds, DynoJet kit, performance exhaust, etc... it should impress quite well and hang with the big bikes at least up to interstate speeds...
,

[Chuck78]

Big Jay are you still doing these big valve GS400/425 heads?
Rapid Ray is no longer on this forum apparently, so my choice of who to hire the head work out to is you...


After riding primarily just 2-stroke woods bikes for the past 4+ years, I'm really wanting to build up my 400 parts pile i to what I'd originally envisioned for my stock GS425, especially with me getting so accustomed to & loving the light weight flickability of the KDX220R dirt bikes.

[Chuck78]

Big Jay I'm also wondering if you could get some custom JE Pistons made in 73mm & fit some GS450 sleeves (71mm stock bore) or GS1000 sleeves (70mm stock bore) into the GS425 jugs?

I also have 2 of my 4 original MTC 72mm 920cc GS750 pistons, but unfortunately they ended up accidentally sitting in a box on my basement floor, and the furnace condensation drain leaked it's acidic water out and lightly corroded the skirts of the piston slightly. They may still be plenty usable, but I took them to a buffing wheel which I probably should not have done, as that removed a little bit more material.
Perhaps good enough as a basis for what to copy at least, along with an OEM GS850 "Big Bore GS400" 449cc piston.

Some MegaCycle or Web cams would go really well with this and some RA34's + a custom offset front sprocket to clear some wider tires and rims laced into GS750/1000 hubs & in a GS1100E narrowed swingarm.

THANKS!

[Nessism]

Sadly, we won't be hearing from Big Jay any further. He passed away recently, leaving a big void in the community. May he rest in peace...

https://www.cycledrag.com/godspeed-ape-jay-eshbach

[Chuck78]

Sadly, we won't be hearing from Big Jay any further. He passed away recently, leaving a big void in the community. May he rest in peace...

https://www.cycledrag.com/godspeed-ape-jay-eshbach

Oh no!!!! I missed this news

My condolences to Jay's family. What an incredible guy. He built up quite a business and reputation from the earliest days of Japanese 4 cylinder superbikes....wow.
Thank you for alerting me to the sad news.

[GregT]

Sad to hear. Condolences to his family. Only had contact with him a couple of times but we seem to have shared a sense of humor. Good guy to deal with.