Isuzu G-series Twin Cam

Hi guys.....

I have entered the world of the twin cam with a G200W I picked up for $200 with 5 speed and Microtec computer,just needs new rings.

I have been researching through here and OzGem etc but am left with a few questions.Any help would be hugley appreciated!

- Tailshaft....Can I use a normal 5 Speed tailshaft?

- Exhaust....What size exhaust did they use on the ZZ/R's etc

- Fuel pump....Being EFI upgrade obvious,can I use a VL pump?

- Bottom End....Bottom End bearings same as G200z?

Il post some pics up of the motor and a few parts Id like to clarify what exactly they are....

Cheers

Todd.

1.tailshaft yes you can use it.
2.i don't know what they used if it's standard go either 2 1/4 or 2 1/2 with extractors or if it's got a manifold just match it to that.
3.i used a vl with a microtech and it was perfect.
4. bottom end bearings are the same as the g200z make sure they have two oil holes because the twin cam rods are shot peened.

thats an awesome buy dude
i agree with all that was said except maybe about the tailshaft
It might just be with the twin cam box's that i can remember but i thought they were different spline?

you could be right all the one's i have had just had standard 5 speeds with the twin cam bellhousing and i used the fine spline. if its the proper close ratio box that would make it an even bigger score.

i have never seen the close ratio box, all the ones i got are normal (10+ 5 speeds so far)

so i am guessing prolly not, but hey u might b lucky!

the "gt" box was a special option that musta cost a bit, prolly only bought new by the racers

cheers

elky wrote:i have never seen the close ratio box, all the ones i got are normal (10+ 5 speeds so far)

so i am guessing prolly not, but hey u might b lucky!

the "gt" box was a special option that musta cost a bit, prolly only bought new by the racers

cheers

woah does this mean i have some twin cam stuff that elky doesnt have!!
i think i have a few of them!!

Yeah just reiterating what's been said:
G200Z lower end bearings should be a go yeah, just check oil holes line up as BAD44U said.
I can't imagine gbox output splines being a problem, I'd say like the rest they'd either be coarse or narrow, I'm told the gearbox I bought is a ZZR close ratio (supposedly) and the output is coarse spline I believe.
I'll be using VL fuel pump with my G180W.
Looks like you picked up a steal dude, just don't get bogged down with it like me. Is the Microtec all wired up with sensors and a tune?

I wonder if the close ratio ZZR gearboxes have different sandwich plates to normal twincam or something... Because the sandwich plate I had sent isn't lining up with the bellhousing, I'll rip the b*stard out and figure out wtf is happening, I just hope its not the gbox...

[/hijack]

Good luck with it dude.

Cheers for the prompt replies.....

Yeah it was a steal....

I never heard it running,but my mate I bought it off did drive it before removing it from a Gem he is putting a CA18 into.The Microtech hasnt been touched and the loom is complete...hoping its simply plug in and start

One of the sensors on the water manifold (above exhaust) is broken so that needs replacing.

I dont have a water pump drive belt,though thats easy enough to sort.I was given a Nissan alternator with it,on a custom bracket,which I havent checked to see if its to suit the Isuzu block.

The extractors are in about 5 pieces,Ill hopefully get one of the blokes here at work to weld me up a nice stainless set using the ones I have as a template.

I have taken the rocker cover off,and with a sigh of relief its extremely clean inside,all the cam lobes look fine,timing chain is sweet and the oil laying in the head is reasonably clean.All good signs the motor was looked after in its previous owners hands.

The big thing will be bore condition...If alls good,Ill send the bottom end off to be balanced,the block honed and then reassembled with new rings etc.I have a VRS kit I found for $130 ready to go.With the cam bearings are they right to reuse?Our toolmaker at work reckons he could make me some brass ones easy....so I may have to put him to the test if mine are worn.

The gearbox is a fine spline,Im guessing its an aussie rear as the bellhousing is a different colour (dirtier) than the rear,plus it has no remote shifter and gasket goo around the centre plate.

Ill put some pics up over the weekend....

Thanks again !!

Todd.

Greengem20B wrote:The extractors are in about 5 pieces,Ill hopefully get one of the blokes here at work to weld me up a nice stainless set using the ones I have as a template.
...
I have a VRS kit I found for $130 ready to go.With the cam bearings are they right to reuse?Our toolmaker at work reckons he could make me some brass ones easy....so I may have to put him to the test if mine are worn.

Ouch about the extractors, how'd that happen? lol. Oh well.

The VRS would include a head gasket wouldn't it? Can you tell what kind of material it's made out of, and who made it?

As for the cam bearings, these are pretty hard to lay hands on, so I'd say if you have the means of getting spare sets made, do so. I'm sure you'll be able to sell a few sets as well, I might be keen on a set depending on the price.

id be keen for a set of cam bearings but i have re-used them in two different motors and no-dramas yet. where did you get the vrs gasket set.

The VRS kit I sourced through Bursons...part number being V2032KC.

The head gasket is similar to one found in a normal G Series VRS kit,nothing special.

Have a few pics Ive uploaded....Im pretty happy with its condition so far.

This is how I bought it....been sitting around for a bit. Notice the gearbox has a steel carrier plate....does this mean its a strengthened unit?



Cylinder condition is good....light hone marks present.



Pistons are good....nice looking factory piston!



Old school Microtech



Combustion chambers....



Few more questions.....

Does anyone run stock Gem brakes?

How does it pull up?.....looking at doing rear disc conversion in the future,will upgraded discs on the front with good pads be sufficient in the meantime?

How do you get the valves out! I have no idea,guessing I need to take the shims out and their under there yeah?

Thanks again

Todd.

i hope you saved the old head gasket because it's totally different to the g series and is one of the parts that has to be made.
to get the valves out you need a double over head cam remover. if you are using the old valves and cams make sure you label the shims that go under the buckets so you can put them back in the right place. if you get them mixed up its a big job getting the clearances right. standard brakes are fine if there fixed up unless you can afford to upgrade.
thats similiar to the microtech i run in my twin cam i think mine is older still.

bad 44u wrote:i hope you saved the old head gasket because it's totally different to the g series and is one of the parts that has to be made.
to get the valves out you need a double over head cam remover. if you are using the old valves and cams make sure you label the shims that go under the buckets so you can put them back in the right place. if you get them mixed up its a big job getting the clearances right. standard brakes are fine if there fixed up unless you can afford to upgrade.
thats similiar to the microtech i run in my twin cam i think mine is older still.

I hope he means its similar to the 161 gaskets in material and style, because yeah, the water and oil galleries just don't line up. Agreed on labelling the valve bits.

As for brakes, it depends on what kinda driving you're gonna do. I find standard brakes in good condition have plenty of stopping power if you're just cruising and suddenly need to pull up, fast, but they have absolutely shocking heat dispersion. Soon as you give them shit in the hills or (I assume) track, the heat just won'd dissipate, and you'll end up overheating them real fast and getting massive fade or worse, total failure. I got my stock brakes glowing red hot, as in, bright red, in like five, ten minutes in the hills with a stock engine.

I really would advise doing a conversion to at least vented brakes, preferably slotted and/or drilled.

When I say its similar to a sohc I mean as in the material used.....its like the monotorque looking ones.....cheap papery,fibre type with metal insert around cylinders.....def. not sohc pattern.

I have the whole thing pulled down now and ready to go off to the machine shop to be balanced.It has a heavy duty clutch on it that is worn and the flywheel looks to have hairline cracks through the contact face.Gather it is the same as a sohc flywheel?

Cam bearings were measured at work and found to be suitable for re-use,they have worn on one side more than the other,but only 5 thou which Im told will be fine....

I worked out the buckets simply slide out and did of course label the shims accordingly.When I took the timing case off a piece that looks to me to be a valve retaining collett fell out.....they arent used for any other reason anywhere else other than the valves are they?

Cheers

Todd.

get your oil pump clearanced and rebuilt when the twin cams drop oil pressure the first thing to go is the exhasut cam bearings and that can be costly. can you post up the details where you got the head gasket. keep us posted. While your rebuilding it put an xf throttle bodyon the manifold the standard throttle body is tiny.

can you post up the details where you got the head gasket

Bursons do the VRS kits however i think theres only like two sets left in AUS. Be quick for that.

Agree with the XF throttle bit as the standard throttle bodys are fair shit, especially if its the twin butterfly type. XF MIGHT be a bit big for an n/a setup, VN V6 [65mm] is not a bad one to use plus the TPS is compatible with most aftermarket ecu's - not sure about your microtech though, never seen anything that old

Valve collet could only be a valve collet, the heads on those motors are pretty simple and consist of cam, valve, shim, spring. Easy

Flywheel is same as SOHC [Eli you should know this because, like always, i told you so haha]. Doesnt hurt to grab a G200 flywheel, pretty sure all DOHC's ran this one although i could be wrong.

Fuel pump run the standard Gem pump on 12V into a surge tank and run a VL/Camira pump [yes they are the same!] to the fuel rail. Definately go surge tank, you can make one yourself for fook all or buy a nice pretty shiny one for 150. Good insurance.

Bottom end bearings as already said are the same as G200z, crank mains should be the same as any G series SOHC.

Mm thats it i think?

GeminiCoupe wrote:Flywheel is same as SOHC [Eli you should know this because, like always, i told you so haha]. Doesnt hurt to grab a G200 flywheel, pretty sure all DOHC's ran this one although i could be wrong.

Haha, yep. G200Z flywheel is the go IMO, better clutch, bigger clutch dumps if you're into all that, nuts to lighter flywheels.

I'm in the process of forcing a Camira TPS only a stock G180W throttle body, it should work, I just need to make myself a little wooden/metal adaptor plate. For me, with no access to a welder, it's easier than getting another throttle body! But in hindsight I probably would have just got another one welded on, it'd make things easier as far as inlet piping goes too.

what do you need exactly ive probably got one lying around rather than make a wooden adaptor.

I think that whoever built the thing last must have dropped a collet down the front of the motor on assembly.....

Ill take the flywheel down to get checked out,at worst Ill have to find another 2Lt flywheel,my SOHC has a 1600 on it.

The sump seal looks pretty good,has a split up near the front that Ill have to try glue together with some flexible sealant.

I have a VL pump ready to go and will go hunting for a VN V6 throttle body over the weekend....the stock piece is rather small!

Thanks again all!

Todd.

I've covered some of the original questions elsewhere - maybe look through my posts? EG - the splines might be course or fine, but there are various solutions (though I have no Gemini experience with this).
However yours looks like a Piazza or similar (fine spline; maybe large) - my G200 DOHCs were mainly older ones from 117s etc.

I used a heavy-duty Rodeo clutch, but I'll use hydraulic actuation next time (the cables tend to break, and I don't like the linkage systems).

I tuned extractors for torque. Standard exhaust manifold into about 26" of 2:1 and then a 2" system (though a bigger diameter is better). (With twin DCOE45s, she put out well over 300Nm torque from 2,000 RPM upwards.)

Gearbox ratios - ZZ/R is same as Bellett GT and apart from 1st gear, same as many others.
I prefer the Gemini with 0.782 5th gear.
Piazzas are also okay and have the stronger steel centre plate (as per Aussie Piazza turbo manuals).

Here's a gearbox-ratio table: (was in a Word.doc table converted to tab separated but stuffs up here...)
And the parentheses after the vehicle denote the (main) source of the information.

Gear: Gemini(2): PR91: ZZR(3): Piazza(4,5): Piazza(6): Piazza(13)
1st 3.467 3.207 3.207 3.312 3.174 3.431
2nd 1.989 1.989 1.989 2.054 1,963 1,963
3rd 1.356 1.356 1.356 1.400 1.364 1.364
4th 1.000 1.000 1.000 1.000 1.000 1.000
5th 0.782 (2) 0.855 0.855 0.840 0.775 0.775
Rev 3.438 (2) 3.592 3.438 (3) 3.550 3.402 3.402

Refs for above:
(2) Rodeo(?) & World Cars 1984 & 1985 – Japan Isuzu Gemini 110HP – 1984 LG, LJ, LS, LT & 1985 LJ, LS; also PCA Gemini TF Diesel.
(3) World Cars 1984 & 1985 – Japan Isuzu Gemini 130HP – 1984 ZZR, ZZT & 1985 ZZR).
(4) World Cars 1984 & 1985 – Japan Isuzu Piazza 120HP – 1984 XJ, XL, Belia & 1985 ditto & XN).
(5) World Cars 1984 & 1985 – Japan Isuzu Piazza 135HP – 1984 & 1985 XG, XE.
(6) World Cars 1985 (only) – Japan Isuzu Piazza 180HP – 1985 XE & XS.
(13) Piazza Workshop Manual (Aussie)

Best wishes.
PS - I hate you. $200! Yep - I hate you.

PeterA

Sorry - forgot:
I bought a few sets of those Bursons full & VRS gasket kits (as posted elsewhere). They were through AA Gaskets (Melbourne) who I think get them from NZ Gaskets from the East Islands (aka NZ).

One criticism others have of them is the thin walls between the cylinders - they tend to breakdown.
I haven't yet used them however.

And the cam shell bearings are expensive and difficult to get, though there was a posting where someone thought they may have a cheaper source or solution.

Yeah the box is a fine spline....

Was more concerned on the length of a Gem one behind the twin cam box.Im assured they will fit up no probs.

Been chatting to the machine shop (Russell Jones) and he suggested removing the balance shaft?

Has anyone ever heard of such a mod on these motors.....

Thanks again

Todd.

Why do you need a different length - or is it just a concern? The box should be the same length as Gemini 5 speed boxes, and I think the 4 speeds too.

Otherwise if you can measure the length needed (say from diff flange to end of box shaft), I can see if something might fit. Also supply the length of the rear piece (either the rear shaft's uni flange to flange centre, or diff flange to centre of the central shaft mount).

Else what length of front shaft do you need - can you measure the difference in the gearbox gearbox length?

And, do you want a 2-piece shaft, or is a single shaft okay?

what is the balance shaft. if its what i think it is needed as part of the timing chain arrangment. this is the first ive heard of such a mod.

Yeah initially just a concern...whether a Gemini tailshaft with the same fine spline would fit up alright,which it will.

Im going to have a chat in person with the machinist when I take the bottom end down to him,though when I asked if the balance shaft is needed with crank etc to balance his reply was that a lot of people simply remove them...not sure on how yet but will investigate it further.

Todd.