Isuzu G-series Twin Cam

Hi, I own a G200W with a points type distributor. I have discovered that the mechinal advance unit is worn out and only advances 5 degrees throughout the rev range, therefore not allowing the engine to rev properly.

Since most people go with fuel injection rather than carbs I imagine someone would have a points ignition type distributor sitting around that is in good condition and would like to sell it to me

If anyone can help me out, or have any information to whether or not parts would be interchangable from another distributor it would great to hear from you.

Cheers, Coley

Hi Coley,
This is probably 4 months too late, but I just noticed your post using the "unanswered" tool.
I was going to mention a programmable electronic ignition kit from SiliconChip & Jaycar that features vacuum and mechanical advance, and even has knock sensing. But before I get to that, .....

I wonder why your mech advance is limiting the advance?. They are pretty simple and normally only suffer from two problems – broken springs or seized flyweights. (My 1960s Isuzu mech advance units suffer from further problems – like oversized flyweight pivot holes (due to wear), springs wearing a groove all the way through the tang where they attach to the springs; sloppy cam and sloppy shafts. But hopefully your dizzy isn't that worn!)
In your case I'd suspect partial seizure. If it's the flyweights, it should be easy to remove, clean and re-grease.
But it could also be the distributor's cam that is seizing. This can also be removed, cleaned and re-greased. (Remove screw that attaches the cam section to the dizzy's shaft. It might be worthwhile marking the cam orientation with respect to the dizzy's shaft since it can be re-fitted 180 degrees "out", but this should not be a problem on the DOHC since the dizzy timing can be changed through its toothed drive – old Isuzus have an offset key instead of a gear so you cannot change its "position" wrt the engine; if the cam is 180 degrees out, then you need to rotate the dizzy leads by 180 deg.)

Alternatively one or both springs have broken. Usually this means going to full advance (the engine usually starts okay, but when revved, the engine pings until you get up to about 3,000 RPM or more), but sometimes the broken spring bits can jam the mechanism thereby limiting the advance. Whilst the springs should be "the proper ones", I have replaced springs with "similar" springs from other dizzies. (Usually one spring is heavier than the other and may be match to its particular flyweight.) But usually it's okay since most things are worn and out-of-spec. And if it's a new modified engine, then the original timing characteristics probably aren't optimum anyhow. (Besides, what fuel and octane rating were the original specs for, etc?)

FYI – as posted on http://workshopmanual.org/twincam/viewt ... highlight=, a mate in QLD fitted a Honda dizzy to a DOHC. I still don't know which Honda, but he merely shortened the shafts & body, and redrilled a hole to fit the DOHC dizzy driving gear. (It was a 2L DOHC in a GT Bellett which was later bought by Dave in Adelaide.)


And finally, if all else fails, there is a circuit for a electronic programmable ignition that can be used as a simple add-on to existing ignitions, or to modify or replace mechanical and/or vacuum advance. It also has an optional knock sensor.
It's described in SiliconChip March-May 2007 with the knock sensor being described in June 2007.
Jaycar list the kit (KC5442) for $89.95 plus the ignition coil driver (KC5443) for $44.50. The knock sensor kit (KC5444) is $16.95. They don't mention that for programming you also need a (modified) Hand Controller which is about $69 (I think). It doesn't include the knock sensor itself (maybe up to $20 from wreckers?), and I'm unsure if the vacuum sensor is included.
This kit still requires the distributor to distribute the spark, but it doesn't need the mech & vac advance.
It will trigger from virtually any sensor (points, hall effect, reluctor, optical).
I'd recommend an optical setup if you want to convert your points, but it depends on what's available at the right price.
Unfortunately the kit won't do away with the dizzy, and unfortunately the programmed code is not available (it's pre-programmed into the kit, or available pre-programmed into a separate "PIC" chip for about $25 from SiliconChip.
I'd like to modify the unit to fire twin coils (for 4-cyl engines) and trigger off some other sensor (I'd use the engine's flywheel), but since the code is not available, it'd be too hard. (Though two kits could be used instead.) Then there is no need for a distributor, rotor buttons, dizzy caps etc.

Cheers,
Peter.

Problem sorted. I machined down a g161 single cam distributor to suit. Simply adapted up the drive gear from the twin cam distributor to the single cam and shortened the shaft. The old distributor was stuffed anyway. It made alot of difference. It made 110hp at the wheels on my mates dyno at his workshop. I don't know if that is good or not. Its fairly stock. Does anyone have any figures on what their engines have put out?

Excellent! And well done.
Others might be interested in how difficult it was to machine the SOHC dizzy. Though I assume a lathe was used so it's not a normal "backyard" fix.
Update 27Nov12: No fancy tools are required, just cut off the shaft ~10mm below the collar, remove the collar and and fit the DOHC drive gear using a 4mm spring pin (4x20mm is a common size) and preferably one wrap of 0.15mm shim or something else to take up the 0.4mm shaft to gear diameter difference. The DOHC gear's pin hole may need drilling out to 4mm.
It was after this thread was posted that I realised the G-Z DOHC dizzy could be used for any G-series engine except the G200W Piazza with locked optical dizzy (same guts as 4ZE1 Jackaroo/Trooper). The "standard" G-series dizzy for all but the ITEC G200W G-series engines has become known locally as the RG dizzy. It has the RB FWD Gemini reluctor guts (from the earlier RB model) and ignitor fitted to the G-Z points dizzy. The ignitor can be omitted for most ECU/EFI applications (Delco, Microtech, Megasquirt etc) and the dizzy locked for ECU timing. For non-reluctor input ECUs, keep the ignitor as that is the reluctor sensor's "digital conversion" (as built into Hall and optic ignition sensors) noting that the firing is on the negative going pulse - ie, select -ve trigger on the ECU else or invert the ignitor's output. end update.

As a guide, a standard G200W is about 99kW (135HP; 6,200 RPM) with max torque (JIS) 167Nm (17kgm, 123 ft.lb; 5,000 RPM). These figures are from "World Cars 1984" for a 1984 Piazza.

My G200W from an Isuzu 117 (late 1970's) was similarly rated, but I had more double the torque at half the RPM (at the rear wheels). The engine was standard except for twin DCOE45 Webers with "Bellett GTR replica" inlet manifolds, and a 2-inch exhaust system with approximately 26" of 2-into-1 from the standard exhaust manifold.
The dyno tests (in a 1969 Isuzu Florian) were:
RPM Nm kW
2000 300 37
3000 383 56
4000 324 79
5000 320 98
6000 270 100

With cams and a port job, it should have output 220HP. But I never got around to that - better pistons are required as they'll self-destruct at about 180HP.

I'm not sure if the above dyno test was with unassisted points ignition, or the electronic dizzy. It was probably a GT (or GT-R) 40 coil. But there wouldn't be too much difference.
However spark and timing can make a big difference. Mending a broken spring in my old Florian improved performance, and increased fuel economy by 15%. Fitting a CDI ignition to a Bellett in the 1980s forced me to retard the timing (the engine would reverse whilst cranking!) and there was heaps more torque at idle etc.

These days, I run a $50 High Energy Ignition from points in my Isuzu Wasps etc. (Silicon Chip design; available fro Jaycar, Dick Smith etc.)

Best wishes,
Peter.

110hp @ wheels is a fair effort considering it makes 135hp @ fly standard.

The carbs take it to 150HP.
I can't recall what typical transmission losses are (I know for motorcyles with drives shafts it used to be about 15%, and chains much less unless they are really worn.)
But the tests from Tates Automotive are as posted above. The report doesn't say if it's at the wheels, but being in the Florian I would assume it is. (Why rerate for flywheel, especially without stating the actual dyno readings?)
I tries to confirm with Tates, but alas they no longer exist - they were in Hawthorn (Melb) and used to build and test race engines. And they had a pretty good reputation....
The Tates' dudes said how impressed they were - they actually thought their dyno was wrong.
BTW - the Florian had its standard 4.1:1 diff.

And that power/torque in a 1-tonne vehicles certainly explains why I was leaving V8s behind.

[ ^d8 6Mar11 - corrected "st'd RN ignitor" to "st'd RB ignitor". & BellettNet/HDT ref added /^d8 ]

Update:
I now run a Gemini dizzy with RB guts in my G161 OHV.
It's so good that I haven't bothered with my CDI (my Wasp cranks & starts at 5.2 Volts cold! - st'd RB ignitor and blue coil).

The Gemini dizzy can be modified to suit DOHCs - very similar to OHV conversion (just cut the shaft 10mm lower).

And since the above, it seems the 300Nm @ 2kRPM and around 400Nm @ 3kRPM for G200Ws, and 230HP output with forged pistons (flywheel assumed) has been confirmed elsewhere - eg HDT; BellettNet.