Isuzu G-series Twin Cam

Hi everyone , got my first Twincam the other day . It was last in a Gemini about 7 years ago until it blew a headgasket , might still have a good bottom end if im lucky . The top end is in pieces but its all there , I just sat the cams ,head , & manifold on for a photo . Its got a points dizzy and some funky extractors. I saw some cam bearings in the head .

Welcome to twincam!

At first I thought yours looked a contender for sparts and I was going to suggest getting another complete GW if you want a working GW unless you find someone with all the missing sparts. (But afaik cam bearing caps need matching to the head - ie, line boring.)
You could have gotten another G180W else G200W. The latter is my choice for its lowdown torque though imo the G180 twincam & Japanese SOHC G180W & G180S (not G180Z) blocks are handy for 2L rebores. But the G180W can develop the same power as the G200W

It looks like a Gemini G180W (ZZR. ZZT etc) with the blue cam/rocket cover.

You have the over the top inlets and Gemini rack sump that most want as well as the Gemini/Piazza style oil filter. (I want the upward filters.)

Some seek the points dizzy. IMO that's a nice simple fallback or test dizzy if available, but otherwise the "RG" dizzy is the beez neez. That's an electronic Gemini dizzy - early FWD RB Gemini dizzy guts in a traditional RWD Gemini points dizzy (as I recently mentioned here on twincam). Its shaft can be cut down to suit all G-series engines - ie, G-W, G-S & G-OHV aka G-U or G-B - and original driving gear mounted in place of the original shaft retaining collar.
I'd suggest collecting a couple of Gemini points dizzies just in case - they are getting somewhat rare.
They can be used with ignitors or without for EFI, but their mechanism and reluctor is superior to alternatives (eg, original twincam dizzies; Delco Camira, Nissan, commodore dizzies, etc).


As to the rest, there are - or were - full engine gaskets kits, and cam bearings. Both seem to have become stalled issues on twincam...

Main and big end bearings are no problem, and the dummy cam bearings are the same as the G-U & G-S engines.


Your cams look contenders for a regrind.
If you want a cheap engine capable of 170kW/230HP with ~400Nm torque then a G200W with L1-profie cams and st'd exhaust manifold will do it.
That torque is doable with a mere exhaust modification and appropriate fuel (mine was 300Nm@2k & 383Nm@3k RPM using twin Weber DCOE45, but a Delco EFI should match that).
The kW/HP requires the cams and a minor port job, but should also use forged pistons - the originals are only rated to 180HP.


For Geminis, apparently using a diesel cross-member means the original exhaust manifold can be used. Otherwise extractors are needed and few of those meet the performance of the original manifold.

BTW - I suggest utilising the torque of these 8 valve DOHCs rather than trying for RPM & top end power.
Excluding the Webers and their manifolds (which was cheaper than EFI) it cost me $200 to beat V8s, rotaries, WRX's, and heavily spent Geminis.
And be wary of what other twincam owners do or say regarding modifications. Except for one case, I have only ever bought unmodified engines.
If someone complains about their unreliability, someone has done inappropriate work or maintenance on their engine.


PS - for EFI, IMO a Delco with modern high impedance injectors and a new fuel rail is the way to go.

Thanks for the reply , I have read about 8 hours worth of posts on here before joining . Got another motor coming for more bits . Still another cam and stock exhaust in the box I have here .. We dont have a Bursons here in Perth , but i will probably call up and buy a full gasket kit myself ..

Came with 2 boxes , both have the correct bellhousing . Think I have both engine mounts i need.. These Extractors are 4into1 with a sexy collector . Look Tuned length - dunno if this is what the Japs do or if its any good though .

I have been eyeing these off (pic below) .. But still undecided , I have plenty of EFi spares around the shed and zero Webers , Might end up cheaper to go EFi - see what happens .

Ah - forget Bursons if it's for gaskets (Permaseal).
The Permaseals have a thin inter-cylinder gasket width and are reputed to blow (more easily). (I did a sample/theoretical comparison somewhere - 22% thinner hence 44% weaker if I recall..?)
And the Permaseals omit the cam chain tunnel rubber gasket at the front of the head (at least for the VRS kits, though I do not recall them in their full kits either).

See elsewhere for MDS gasket kits.
In fact funny you should mention that... Maybe a certain Member should continue their negotiations for a bulk buy of MDS twincam kits?
Or if those old wankers are still wanking - or too busy with legit things - maybe we should get together for a buy?
(WARNING - I am fiscally very distressed, and those MDS kits were a few years ago.. I think. But I am in Melbourne...)

The MDS kits are complete engine kits and include the cam valley gaskets. Not that I can vouch for their quality, but they looked ok web-wise, and I am unaware of complaints. (Unaware does not mean I am aware of the latest goss - I do not visit other sites that may have updated info.)


4 into 1 extractors imply high RPM. The key to the nearly 400Nm torque (at low RPM) is based on extending the OEM 2 into 1 section from the st'd exhaust manifold. (As I learned years later, my implementation carried on from the HDT implementations - eg, the Brock etc G180W rally etc racers - but from someone that did unbelievable things; but I''ll avoid that for now.)


And your pic reminds me a lot of the manifolds that my aforementioned but unnamed Guru had manufactured. They were based on the G161W (117) intake manifolds but were extended ~10mm and reduced to ~12° to cater for Webers (as opposed to the original Jap DCOE-type carbies) and had my Guru's characteristic tapered ports, plus provision for a brake booster etc takeoff. AFAIRecall about 45 sets were manufactured and I believe they are still the best manifolds. (Though as Guru & I argued, EFI should be able to match and exceed any carby implementation.)


As to bell housings - NEVER discard them. My favoured box was the (early?) Gemini 5-speed with 0.782 5th gear (as opposed to the more common 0.855) but with a LHS-startermotor twincam type bell housing. (Also in diesels up to and including the C190.)
The ZZR etc Geminis had the 0.855 5th ratio. (Shit man, even in my G161-OHV Wasp - albeit with OEM std 4.55 ratio diff and a torquier than OEM cam but otherwise st'd - needs lower than a 0.855 5th!!)
The only other boxes I'm interested in are the 0.775 5th gear Piazza boxes else MU (2.6EFI) 0.809 5th boxes, but they are for hi-torque twincam strength and the MU is the later (stronger) MUA(?) box with different clutch actuation offsets. (So too the Aussie 4ZC1-t Piazzas as opposed to import & NZ G200W Piazzas).
(There I go again - I confuse my MSA, MSB, MSG, MUA (TFR?) etc boxes! There's not enough stimulation on my Isuzu forums to keep those details in RAM, and my ROM knowledge predates all those learnings.)


I'd suggest EFI though Webers now are far cheaper than when I got them. (New F2 emulsion tubes as required for GWs were $120 EACH. Now you can get entire kits for far less than that!)
And Delco is the way to go ('808 types as in Camira etc). There are GW BINs (G180W?, or G200W?) on the DelcoHackers website - member Antus as I recall.

I will take pictures of the other set of extractors soon .. Ill be keen on a gasket set , might see if i can get one from Japan ..

Petrol Gemini(left) vs Diesel Gemini(right)


Current g/box stash
1 x Diesel 5spd
2 x Rodeo MSG 5spd (Box1 Came bolted to a 4ZD1/Rodeo) .. (Box2 has a Rodeo G/box mount?)
2 x G200w 5spd (unconfirmed)

Im tempted to try the rodeo boxes down the 1/4 mile with my other Turbo Gemini .

Have you seen the gear-sets in the Piazza and Rodeo MSG type boxes ? Are they H/D like the Gemini Diesel ?

I'm just wondering if the purple GW is out of a purple Bellett. I was amused at the purple Bellett with its grafted Camira or Nissan or whatever dizzy. Poor sods - the RG dizzy is just so superior, plus a lot cheaper (ie, it's easily DIY).


Anyhow, I only ever exchange complete gearboxes. Currently I have a Rodeo box which was overhauled (EXCEPT for the farken center mainshaft bearing - the one you can hear over the engine whenever not in 4th gear or without the clutch depressed). It had a LH starter though obviously a reduction type. (TIP - use Isuzu reduction starters as found in 4ZE1 engines for all pre 4ZE1 Isuzus including all G-series and 4Z engines.)
Otherwise I swap GZ (RH starter) bells with the GW else diesel (up to & including C190) bells for the LH starter.

May favourite box is the early Geminis with 0.785 ratio 5th - even for my current 1965 G161-OHV Wasp (with typical commercial 4.55 diff albeit later 1985 Jackaroo LSD).
However I intend to use later MUA types (4ZE1 etc) since they have an output shaft that my G200Ws might not twist, plus stronger 2nd gears compared to earlier boxes. Not that the later boxes line up properly - I know their clutch lever alignment (for hydraulic slaves etc) is about 25mm lower, and gearshift extensions and bell to body clearances are different, and they use the 17mmID version of the (6203? 6205?) flywheel bearing.

As I recall, my most favoured box was the later (1992 onwards?) MU box. It was for the 4ZE1 and had a lower ratio 5th than the earlier MUs, and Piazzas.

The Piazza 5 speeds were stronger. I'm not sure about the G200W version but 4ZC1-t manuals should have a steel center "gear carrier" plate as opposed to the usual alloy.

I've never swapped gear sets though I do have some now rusting gear sets still awaiting comparison.

Man this place is quiet .. Ah well . My friend in Japan enquired and The full gasket kits are discontinued . I can however get a water pump or a VRS kit ex Jp

Picked up Purples other half .. . Looks much more complete ..


Dizzy closeup

Bought a Durapro VRS kit from my Local AutoOne for $154 .. And thats the running Total thus far .


Found this http://www.mdsperformance.com.au/image/ ... -G295_1537


My friend in Japan enquired and The full gasket kits are discontinued . I can however get a water pump or a VRS kit ex Jp

Double post

Gi'damn - I happened to review recent updates and saw your last 2 replies were awaiting approval!
Geez I hate slack Admins! (Sorry! I know HolGem doesn't notify me of updates but I've had no troubles with twincam!)

THANKS for your updates.

Incidentally I have some NOS G200W (G180W) water pumps.
And I think that last gasket kit is from Moorabbin (Melbourne) for ~$380 which INCLUDED the head to cam-chain cover (orange) rubber gasket that no Permaseals have.
There was some dude called Poida that was looking into a bulk but or special deal for those kits....

Hi I am still plodding along here . Its time for an update .

Ok so i put the Silver motor onto a stand and had a great time stripping down my first Twincam , It was really interesting to see how strong and simple the motor is , very impressive , although this particular motor was in bad health as you will see .

Oil was leaking from this motor everywhere . Silicon was in abundance .


A few head bolts were missing and replaced with some random bolts .


The head looked freshly faced but had a hole exiting a water gallery near 1+2 . It was completely covered in silicon to try and stop it leaking down the side of the block . Majority of the Cam bearings are okish . Definitely usable still .


Next was the bottom end , Discovered some metal flakes and silicon pieces . All bearings worn down . Still standard sizing . Crank will need a grind . None of the piston rings were broken .



Alright so in Summary i need the Purple head welded and serviced and a the Silver Bottom end needs : Crank grind , New rings bearings , Hone??
I cannot bore this motor out because I cant get oversize pistons for it ??

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Hrmmmmmm.....
So next I Test fit the Purple block and a 5spd gear box to my TX . This is the PURPLE Block and SILVER HEAD - Coupe Video: http://youtu.be/sEO1s1UsVRs?list=UUODaS ... hsM1l2N7ww

Fit the engine mounts well , but the TX gearbox cross member is a fail . Have a few options here ..
1)Change to TX 4speed with Twincam Bellhousing ?? If it works ? .
2)Move mount back on the tunnel .
3)Fab a Mount up to fit as is .

I Test fit the 4-1 exhaust that came with it to see if they work or not . Also Test fit a set of Bellett GTR manifolds my friend sent me from Japan . Man they are sexy . I have a set of 48mm Solex ADDHE . Maybe over kill but were practically free , hopefully I can get this to work . Wasnt planning on having a all out Race motor but its looking that way so far .



After that i pulled the purple block out and ripped the sump off . The bearings in this block are much better , although the Silver Head has a few burnt and scored Cam bearings . One or 2 look new - rest stuffed .
Basically the SILVER motor was thrashed !! The purple motor for some reason lost its head to the silver block ...And the purple motor sat in the shed asleep .
Silver head - Fried






Ok So it looks like this .
Level 1
Rebuild PURPLE Block with new rings , bearings , hone , balanced .
Service and Weld Purple head . Light touch up port .
Buy KP Gaskets kit from somewhere (hopefully international is cheaper)
Kit Solex 48s
Buy linkage kit
Make a RB dizzy conversion
Make up the best set of cam bearings I can
Buy starter motor ???
Buy water pump
Try fit bellhousing to TX 4 speed ( Its not the TX 4speed with inspection plate .)
Make a pushrod for TX Master cylinder on firewall

Level 2
Port spare head
Regrind Spare Cams
Build Spare block
FIND FUCKING CAM BEARINGS AND A KP GASKETS RESELLER !

By the way Budget is on target !
2 x G200W = Free
1 x VRS kit = $154
Bellet intake = $140
Twin Solex 48s = -$25

Running total $271

Won't be needing those valve stem seals!

Also gotta watch out for new water pumps, the ones that pop up on eBay every now and then have a pressed impeller opposed to the factory cast ones which is also common in the G***z series motors, although NOS items might be alright. I know this has an effect on the water circulation, and therefore water temperature, in the G***z series motors and would probably have the same effect when installed on a twin cam engine. In saying that I have used these pumps in the past and did not have any problems but it is something to think about when contemplating buying a new pump or reconditioning the original pump. I guess it also depends on what your plan is for the motor whether it will see much track work and get a pounding...

Apologies for Reply approval delays. (I got no notifications and I just notified Poida that the site had been down for a few days...!)


FYI - I might have some NOS DOHC water pumps. Some were slightly different (for a LUV or KB ute or similar - a slight different in front flange thickness as I recall).

PS - a Piazza G200W!! I-TEC; locked optical dizzy with 1989 Jackaroo 4ZE1 optical module (not the 4ZE1 Rodeo!); later ratcheted cam chain tensioner; and Piazza "over the top" inlets instead of 117 G200W "out right & forward" that no Gemeni or Bellettian wants. Technically the 2nd best GW (only beaten by the very later blue G180Ws) but IMO the best for their G200(W) low down torque.

And yet another PS...

Starter motor - a reduction starter motor - eg from a 4ZE1 Rodeo or Jackaroo.
But beware; RHS starters mount with their solenoids or motors "horizontally leftwards" when moved to the LHS of the engine. That may hit the body (Geminis come to mind) or the exhaust may be in the way (Geminis without diesel crossmembers and (hence) standard exhaust come to mind).