Isuzu G-series Twin Cam

What cars did the G-series engines come out of ? Are they from Australian built cars aswell as japanese, or are they an inport only ? i know nothing about them and i have been reading posts on this forum, to learn more. Are they an expensive engine/box combo ?

Thanks in advance.

All imported.

Been developed from the same base as the G series SOHC engines were. Both types were based on the old OHV G series engines used in cars back in the 1960's.

There is a range of different G series engines many never being used in Australia.

G130, G150, G160, G161, G180, G200. These were in various layouts of 8 valve OHV push rod engines, SOHC and DOHC engines.

Denny will probably be able to lay out the time line as to the engine development... (data input - Denny)

G161s, G180s and G200s (I'm not sure if this applies to DOHC or just SOHC) can be found in:

Holden Geminis, Rodeos, Jackaroos, and the Japanese Gemini - ZZ/R and ZZ/Z (this has a DOHC)

As I'm sure you have gathered, the "Z" depicts single cam, and the "W" twin cam. The G180W and the G200W are both excellent motors capable of great performance, even with mild mods, but it can get very expensive. The majority of parts are not interchangable between the SOHC and DOHC engines, and a lot of parts are very rare. If you plan to keep the engine fairly stock they are a good choice - they should perform well, and shouldn't break in a very expensive way.

G130,G150,G160 are OHV motors out of the the Isuzu Bellett,Florian,Wasp family. The G160 & G180 were also released with SOHC using the OHV block with a dummy cam, these motors were popular in the Chev Luv and the Bellett GT from the early '70s. The G161z,G180z & G200z are SOHC found in Geminis,Rodeos & Jackaroos. The G161w, G180w & the G200w are twin-cam motors, the G161w being out of a Bellett GT type R, the G180w & the G200w are found in the 117, early Piazza and the Gemini ZZ/T, ZZ/R & ZZ/R Rallye (not in the ZZ/Z this was a Holden)

The DOHC cylinder head is either a Lotus design ... or a good copy of a Lotus Cortina one. Differences in head bolt spacing and other dimensions but the basic layout and design are too similar to be co-incidental.
Besides which GM was suposed to "own" Lotus in the time frame of the head's design.
Anyone have more solid info??

The Isuzu DOHC is a totally Isuzu design.
I has once heard that Isuzu had Alfa start the design and that Lotus finished it, but this is wrong. (When has Lotus ever built an engine etc?!) The Isuzu designer is alive and well.
Whether Isuzu based their design on Cortina etc (like Bellet and the G-series engine is Hillman etc, and Yamaha XS650 is Triumph) is another matter.

Are they similar enough for any parts to be interchangable? ie valves?

archangel62 wrote:Are they similar enough for any parts to be interchangable? ie valves?

are you talking bout from g180w and g200w or sohc and dohc??

Nah, to Jay Dee and IZU069's last posts, about the Lotus Cortina engine. Just curous.

Sorry for the delay archangel62 - I wasn't emailed - or was it due to my multiple Windoze crashes? WARNING - get XP-SP2+ (W2k-SP4+) roll-ups if you use big disks (ie - greater than about 130GB)!!!

I have a 2L DOHC which had (allegedly) $9,000 spent on it by some "expert" in Dandenong (Vic). I use it as a paper weight.
Apart from replacing the DOHC cam-chain idle sprocket with a specially machined "cotton reel" (like the standard cog but with the teeth machined off - "because the chain will just slide over it"!), the <insert-appropriate-sex-fallus>-head used Ford parts for the cam buckets (and maybe springs, shims etc).

Whilst apparently these Ford parts are close (I don't know which Ford), seasoned experts warn that this is not the way to do it.

I'd suggest bite the bullet and get the real parts. I have heard that the expensive DOHC cam shells are available relatively cheaply (source: RodeoBob?) It may be the same for related bits. (I haven't checked for a few years, but if anyone knows of good 2L DOHC pistons that handle 220HP-plus for well under $1,000, please let me know!)

I won't even use the Hillman cam-tensioner (rubber over spring steel) in my old Isuzu OHVs (besides, the Isuzu part doesn't disintegrate!).

And I'm wary of so called experts - like the abovementioned, and the other Dandenong expert that built a "hot" G161 DOHC for a Gemini (really hot after seizing piston #3 after 1,000km - he/she didn't relieve the piston skirt after linishing for piston/engine balancing!!).
Likewise I have heard these experts say that you have to have increase oil presure for hotted engines - and whilst I won't go into the validity of such claims, I will shoot down any person that says you do it by "bending and crimping" the oil-pump outlet! (It's like getting more delivery and pressure out of a crimped garden hose - yeah - the tap (equivalent to the oil pressure guage) is under greater pressure, but your plants will die of thirst and eventually seize up.
Geez - it's like the old crap about daining your carby before "car storage" so you don't get stale petrol!
Ooops - I digress.

Summary - other (DOHC) parts may fit or be close, but is it worth the risk unless engineered/machined properly?
PS - I know that the Isuzu DOHC breathes very differently to other DOHCs including Lotus. Apparently only the Isuzu DOHC will "not be lumpy" (ie, it'll be street-friendly) when using L1 (race) cams.

I have a 2L DOHC which had (allegedly) $9,000 spent on it by some "expert" in Dandenong (Vic). I use it as a paper weight.
Apart from replacing the DOHC cam-chain idle sprocket with a specially machined "cotton reel" (like the standard cog but with the teeth machined off - "because the chain will just slide over it"!), the <insert-appropriate-sex-fallus>-head used Ford parts for the cam buckets (and maybe springs, shims etc).

Whilst apparently these Ford parts are close (I don't know which Ford), seasoned experts warn that this is not the way to do it.

I'd suggest bite the bullet and get the real parts. I have heard that the expensive DOHC cam shells are available relatively cheaply (source: RodeoBob?) It may be the same for related bits. (I haven't checked for a few years, but if anyone knows of good 2L DOHC pistons that handle 220HP-plus for well under $1,000, please let me know!)

Care to elaborate on all this? I assume by bucket/shim you mean the cups over the springs on which the cam lobes push? Whats wrong with the ford items and what actually goes wrong? I would have thought springs wouldve been fine if they were the right diam, spring rate and length. Also, whats the reason for replacing the tensioner? I thought the G dohc's used a hydro tensioner like the FJ20. Also not following on the cam shell bit. Shano has found an alternative for the cam bearings, maybe ask him more questions?

Looks like ill be bombarding you with questions when i go to build my turbo engine

Nick-

By Ford parts, are we referring to the Ford DOHC Kent based engines with Lotus heads for the alternative parts? I'd be inclined to think their components might even be harder to get hold of than the Isuzu ones. There is a bloke running a company in Frankston that specialises in Ford Lotus twin cams but take a healthy wallet with you. He isn't one to drop prices and let you have a bargain. He's damn expensive and the reason why... he's about the only one who has what Ford Lotus people need. I have owned the ford Lotus twin cam and I still have a factory workshop manual. I can refer to it if need be but the two twin cams are not alike really.

Still can't paste pics - I was gonna show the "cotton reel" idler "sprocket". Note that it was the idler sprocket - not the tensioner - that I was referring to.
Re tensioners, the DOHC ones should be okay as they have a return-limiting ratchet. Early SOHCs didn't have this so they'd rattle until they pumped up with oil.

I can't elaborate too much on other details as I'm going on what I was told and I still haven't rebuilt a DOHC, nor inspected the described shit heap. But since the Ford parts close but different, I took te inference to be that either they were substituted without appropriate modification, or that it doesn't make sense to modify unless you are bluddy rich or can do it yourself. (Pay someone else $9k on an engine that was never used - you can decide. I'd love to see what was done on the bottom end - I only have the head.)

As for the pistons, these are apparently expensive for the 2L DOHC. My original rebuild plan was to fit twin 45DCOE Webers (increasing output from 135HP to 150HP), and then a cam and port job which increases output to 220HP. Unfortunately stock pistons apparently only handle about 180HP, so either I had to fork out $1k+ for forged pistons, or $2 for a wood block to be placed under the loud pedal. (I'm a great bush mechanic, but....)

See ya in another 2 months...

Send an email (or contact RodeoBob) if you want to contact me...

Peter (IZU 069)

At last - my cotton-reel idler sprocket.

The following shows what was in the head of the alleged "$9,000 2L DOHC".



Unfortunately I haven't got a conveniently removed DOHC original to compare it to, but the two central raised "tracks" should be the teeth for the chain.

A Bellett cam sprocket is shown here for comparison...



The person that allegedly machined and fitted this apparently reckoned that the cam chain would just run over the "cotton-reel" and spin it. I tend to disagree, but if my stereo was loud enough, I might be prepared to entertain the idea.

The other thing that I wonder about is how the assembly can be removed once the bearings “stick” a bit to the head? There is no central threaded hole to enable simple extraction.
Otherwise, it’s a cute idea.

I wish I could show other similar beauties like:
- deliberately kinked and restricted oil lines to increase oil pressure,
- radius-relief removed when machining the crankshaft (main and big-end bearings),
- radius-relief removed on stub axles (aka uprights).

Hopefully things have improved since I spied the examples above. Though after recently seeing some slotted (disc) rotors that were only slotted on the outside, I’m not too sure – noting that this isn’t a catastrophic problem like the above, it's just an observation that it seems like looks are everything, functionality nothing!

And I’m rapt – I finally got some pics posted.... Thanks Poida. (It's easier doing it than "learning" how to do it! Welcome to the education - and the IT - world!)