Isuzu G-series Twin Cam

hi,
trying to find out the inlet valve size so i can size up a set of carbs for my motor, any help much appreciated. Its the zzr type g180w.

cheers,
danny

From memory, it's 44.5mm.
But careful if using "normal" engine formula for the GWs, they just don't seem to work.

The HDT tuning using twin Weber DCOEs should be fairly well known however - the key ingredient being the F2 emulsion tubes (or was it F12 - it's been a while!).
For a stock G200W tuned for road-use & torque, I used DCOE 45s with (as I recall...) 36-38mm chokes. (DCOE48s should have been used, but IMO the expense/gain wasn't worthwhile. But that was before Webers were re-released at half price!)
I suspect similar for the G180W since the overall power can be the same. The big difference between the G180W & G200W was the torque at low RPM. (I think head port & valve size were much the same. And I'm certain HDT used DCOE45s on their G180Ws.)


However, I'd suggest EFI using a Delco, but it depends why you want to use carbies.

cheers for the reply,
The engine is already running 40mm idf webers and i prefer carbs over efi anyday. I found this rule of thumb info for sizing carbs on another site:
For hot engines, vent size=(intake valve-2mm)
For moderate street engines, vent size=(intake valve size-4mm)
For mild engines, vent size=(intake valve size-6mm)

Does this sound right? Atm im leaning towards a pair of 44mm idf with 40mm venturi's, the 40's deffinately feel a bit small for the motor atm.

cheers,
danny

I'm no expert, I merely built according to the directions I was given - namely that for street use for a st'd G200W, merely extend the 2:1 exhaust section (from the st'd manifold) to ~26-29" for ~400Nm torque at 3,000RPM. The dyno showed 300Nm @ 2,000 RPM and 383Nm @ 3,000RPM with torque reasonably flat (though decreasing) above that to 6,000RPM.
That's double the st'd torque but at half the RPM (IOW double the acceleration to 3,000 RPM).

That was combined with the twin DCOE45s that alone increased power from 135HP to ~150HP.

The next step was an L1 cam profile and a slight port job which would bump the power to ~230HP, but that required forged pistons since the st'd G200W pistons were only good for ~180HP.

That tune meant leaving most cars for dead whilst getting 24-27mpg (28mpg = ~10L/100km).
And excluding the carbs and manifolds (which I was gonna use since EFI was rare at the time and I didn't have the st'd ECU), that torque increase cost a mere $200 exhaust (the 26" 2:1 into a 2" with hotdog & muffler).
A big part was having the right manifolds (a special batch of G161W-replicas extended ~10mm for better Weber clearance and angle dropped to 10 degrees (the max for DCOEs) and tapered bores) plus the correct jets - especially the emulsion tubes (I was told to forget trying to use any others).

From what I understand, the racing version was similar but with a different cam (but NOT an L2 profile!).
But the emphasis was always to use the GW torque rather than try for "high end power" (hence no 4:1 exhaust/extractors etc). For high end power, get a 16V engine.


I intend to build another performance G200W - and this time I have the forged pistons - but it will be EFI since the DCOEs had too much fuel splatter etc. And EFI should crap on carbies.
Back then my advising guru was using a Haltec with twin-injectors on his G180W since single injectors weren't enough.
However later my guru eventually settled on a Delco system, and - as I recall - he reckoned single injectors should be fine, and certainly crap on Webers etc.


As to your ROT, I can only repeat that the GWs are not like other DOHC engines.
Certainly when I first heard of twin 45s for a mere 2L engine, I thought "$#%#@ crap!". However I now understand that even 48s weren't too big for the G200W.
I think even the dyno-tuners thought the setup was a bit of a joke. But after having their dyno checked (they thought it was faulty), they were simply awestruck.

cheers for all the info.
Being an 1800 i think ill lean towards the 44idfs, the motor deffinately seems to want alot of airflow. As the carbs at the moment run rich at idle almost to the point of fouling plugs and lean out above cruise.
I read in other threads u mention an f2 emulsion tube, do you know if the downdraft and sidedraft f2 are similar? As i can source an f2 for downdraft.

cheers,
danny

Nah, sorry - I don't know enough about carbs & Webers.

But I suspect 44s to be the better choice. As you say, the GWs are big breathers.
Besides, they can always be choked down.

BTW - try to get the correct tune specs before getting the carbs.
As my guru pointed out, back then F2s were $120 EACH. Hence add $480 to two 2nd hand DCOE45s at about $500 the pair and I may as well have bought the DCOEs new configured to my - er, I mean my guru's - spec.
Since then however Weber prices have halved, and I've seen sets of emulsions and jets for well under $100. But at the time, since the emulsion tubes were the essential foundation for all else, it was a valuable tip. (I bought my DCOE45s off a Datsun rally driver that had heaps of stuff, so he set it up with the F2s, the chokes (36 or 38mm?), the mains (120?) and the other jets that I wanted. The dyno tune changed little other than fitting a fuel pressure regulator (to drop the st'd mech pump from ~4psi) and replaced the main jets with "proper" ones - the ones I got had been drilled out!)

But consider costs as well. EFI is now probably cheaper - ie, a Delco 808 etc. And I suspect the original EFI inlets are of good design, though all I recall was that the there was nothing better than the st'd G200W exhaust manifold (it would take a really good extractor design to beat them) since I wasn't using EFI anyway, and I had ordered 2 sets of those replica GTR (actually 117) inlet manifolds. BTW - I was fitting to a Florian (else Bellett) so I did not have the exhaust manifold issue that Geminis have, though I think the Gemini diesel cross-member solves that issue.
But you may have your reasons for carbs. I'd however recommend the Delco for performance, and no need for "mechanical" retuning as the engine develops, or wears.


Poida is probably the person to speak to. He has a Delco'd G180W, and AFAIK, is quite knowledgeable re Webers.
Of course Delorto is better than Weber - the Sydney Bellett/Gemini club (now the ICCA) always got a few extra horsies from the Delortos - but getting jets etc may be more difficult.

cheers for the info,
The extractors seem to be a nice size, quite large 4-2-1 that finish up around the passenger seat.

What oil do you run in your twin cams? i seen mentioned they require 20w50, so im running penrite hpr 20w60 which is recommended by them for 20w50 engines. Just curious as the motor has a topend rattle and from posts on this site it could be the chain or the oil pump wearing out and starving the exhaust cam.
Does this sound right?

Cheers,
Danny

I'd like to know why anyone would recommend a 20W/60 for 20W/50 applications. Maybe they get kickbacks from repairers?

The original spec was SAE30W which is now 20W/50.

I tend to use Castrol GTX, or GTX-2 if it's a new (but run-in) engine - ie, its detergent in an old engine makes a mess and causes misdiagnoses like blown head gaskets.

Not that I'm suggesting or sanctioning it, but 20W/60 may be ok if you are not revving high.
A mate used to run a 50W oil thinking that was good "for an old engine". Even after his 3rd blown G-W he didn't get the hint. (They all seized their big-ends. He was known for VERY fast cruising.)


Older GWs without the ratcheted cam-chain tensioner often rattle on start-up until the oil pressure builds up.
A constant rattle could be a worn chain or - maybe more likely - incorrect cam-bucket clearances.
Worn chains should be replaced, and clearances set to standard.

If cam bearings are that worn that a noise occurs (ie, cam flex; lost oil pressure), that too should be rectified before other cam bearings wear & big-ends seize etc.


Thicker oil is a good trick to reduce some engine noises and smoke, but it's also a good way to wear everything - ie, shafts, bearings, bores, oil pump, etc - especially if high-revving and racing the engine.
Sticky oil is probably a better option - ie, the "rings and bearings" (aka Stop Smoke etc) oil additives until the engine can be repaired.


PS - your extractors sound ok with the 2 into 1 ending under the passenger seat. That suggests a longish 2:1 twin-pipe section which increases the torque at low RPM rather than high RPM - ie, a low-RPM high torque (8-valve) engine rather than the high-RPM hi torque/power that favours 16V (4 cylinder) engines.

cheers for the oil info, just changed in hpr20w60 so will have to drop it for some gtx by the sounds of it.

Diverging this post further lol

Can i just swap cam buckets out in a twincam?
I jsut checked the clearances on my twincam as it was a bit tappety and found the following:
no1: inlet 0.18 ex 0.15
no2: inlet 0.25 ex 0.25
no3: inlet 0.18 ex 0.30
no4: inlet 0.20 ex 0.25

was only using feeler gauges so could bea slight variance, but it seems that when the head was built they have mixed up no2 inlet and no1 ex.

Anyone have any suggestions?

Cheers,
danny

If I read the G200WE book right, they should be 0.13mm & 0.23mm. And knowing Isuzu, they'll be cold & static figures.

Although an excess gap may not be too bad other than possible noise and heavier impacting, it's the under-gaps that can be damaging - eg, valve burn.

If it's a newly built engine with valves reseated etc, I'd be tempted to take it easy, run it in, and then fix the clearances.
You could fix the clearances now, but that might mean 2 jobs and disturbing the cams twice. (It's different with simple screw adjustables.) But if you have a good assortment of shims - I mean buckets (LOL) - then why not now?

But certainly a re-check later to ensure it isn't valves & seats settling, or cam-bridge bolts pulling out etc.
And check that the bridge (cam bearing) bolts aren't stripping BEFORE you put in a thicker bucket.


If it was recently rebuilt, I'd call that a fairly crap rebuild based on those clearances. (What else does it have - unwashed bores, crap machining, silastic on gaskets, unrounded linishing?)
But if it's after settling which can result from amateur rebuilds - ie, not the right tools to press in valve seats or lap valves etc - well, yeah - I know my limits too.
But bucket shimming should stay in spec far longer than adjustables...

that was cold settings, i swapped my turbo sohc for this twin carb dohc. So im unsure on age since rebuild, it was apparently rebuilt not long before the previous owner but he couldnt confirm this. The motor is clean inside with no obvious wear etc on the cams, buckets, chain guide.

I was just going to swap the two and measure the gap to see if they had been mixed up, having never pulled a g180w down before do the buckets/shims jsut lift out once the cams are out???

swapped them over and no change somehow......

Also do twincams have adjustable cam sprockets standard? as this on does but it has an offset little bush made up to locate the cam, making it not adjustable??
Also how do you tell which tensioner is which? searched and found out there are 2 types but how do u tell which is which?

The st'd cams are not adjustable.


below is a pic of the ratchet tensioners. The non-ratchet types are longer & round with a big hex nut at the end.

hmm looks like i have the hydraulic type, is there anyway to adjust/modify it? as i believe this is where my loud rattle is coming from. When it starts up there is a slight tapping but after the motor and oil has really warmed up the tapping gets extremely loud, the exhaust cam bearings did show signs of worsening wear from front to rear also.

You need the complete front cover from a later GW.

Maybe try a new chain if it's stretched that much.
Unless the hydraulic seal/ring is worn an leaking more than it should.

hmm the chain looked new and in perfect nic, as did the cams. Will pull it down and give it a clean to see what the go is.
Cheers for all the help so far.

pulled down and cleaned the tensioner, all was good and made no difference....
could an adjustable bolt setup be made to suit? basically thread the brass nut and install a threaded rod/bolt to tension the chain?

Also with cam timing i found this http://workshopmanual.org/twincam/viewtopic.php?f=8&t=8

since my cam sprockets are adjustable, what position should the cams point at tdc? ie for a closed valve should the cam lobe sit perpendicular to the bucket or should it be at a right angle to the head???
just trying to double check the inital setup since it appears 2 of the buckets are wrong...

cheers,
danny

A bolt should be ok as a tensioner.
Though I've heard it mentioned as being done on the early DOHCs, I've only seen it done on other engines.


As to valve timing, chain-wise it's as per that link's marks - ie, crank-pulley mark aligned with idler/dummy-cam mark, and both can gear marks centered vertically up.
From their you dial in the cams to get the book settings or whatever opening/closing spec you are after.

Ok got some pics to hopefully help sort this out, on inspection the inlet cam seems to be retarded a tooth or 2 maybe....
The chain has no bright links that i could see to line em up so i will have to go off what orientation the cams sit at tdc??

Sorry about the pics my camera was being a pain.
Inlet cam


Exhaust cam


Cam positions

That's not a nick on the front exhaust cam is it?

I forgot to say that yes, lift off the cams & remove the buckets.
The proper (Isuzu) way to adjust the clearance is with the correct thickness bucket.
But let's get real - shimming the clearance down is the practical way to go. And other engines use that technique - ie, placing shims under the bucket.
Not that I've done it myself (I've been lucky with clearances I had), and the concern I'd have is if the valve shaft tops are not flat so they crack through thin shims, but there should be other shims available. Measure the inner round diameter of the buckets and get the same diameter shim. Maybe a slightly smaller diameter is ok though that might mean some moving around.
However the shims should be hardened (and hence more brittle) and hence not wear (much).


I don't know what those metal bits/arms are under the cam sprocket bolts. That's not part of the dialable cams is it? The dialable cams I've seen are 2 piece (inner shaft part and rotatable outer teeth) with a lockable thread adjustment.
I wonder if they'd upset the balance (albeit minor?), or if they could be noisy if they flex - though that doesn't seem like the "chain" noise you are hearing.

Check too for good rubbers.
That top chain "guard" has rubber underneath though that shouldn't be that important unless the chain is hitting the metal. But that pat of the chain is usually tight except at low RPM (eg, when hand rotating the engine) because the first cam (exhaust) can rotate itself after a lobe high point is reached - ie, the valve spring pushes down on the trailing face of the cam hence rotating the cam until the normally slack trailing chain segment loses its slack.
But the cam tensioner is rubber ended, and if that's excessively worn...

Check too that your cam idler sprocket (LHS under the inlet cam) isn't worn, and does have teeth.
I mention that because I have a G200W that was given to me. Someone had spent $4,000 on it, but the dork that did the work was a fool! The fool had removed the idler sprocket teeth so the idler looked like a cotton reel - a cylinder with 2 raised diameters that the chain rollers would slide on. The theory was that "the chain will simply slide over the idler". Yeah - right it will - it will wear flat spots else the links will carry the lateral (teeth) force instead of the
rollers. And geez, I wonder how noisy that would be?
Not that I expect anyone to have been so lucky as to have met such an idiot, but this idiot was one of the "expert" engine rebuilders in a well known automotive street in Dandenong - Melbourne. (Yep - certainly a dandy-Nong!)
Not that IMO those sprockets should cause noise even if worn - unless the teeth are hooked (...over and catching the rollers). Their bearings might wear, but that's a bearing noise. (Were they 6203 bearings or similar??)


And non-Isuzu replacement chains won't have the polished link plates. But its the position of the pulley marks that is the key. The polished links just make it easier to confirm that the correct link is lined up with the "dot". That helps overcome the exhaust cam catch-up issue I mentioned - ie, you might just about have them lined up and then the exhaust cam rotates forward.
But there is a link-count that applies between the 2 cams. I don't recall how many, but I'm certain is was an odd number of rollers (ie, involved a 1/2-link count). I think archangel62 posted a confirmation but maybe on another forum.
I looked for an image to no avail, but I did find the following:

First, the cotton-reel chain tensioner (ok, so it was the inner shaft that was modified; the geared sprocket was removed or missing):




And from a certain pdf... Whoops - I forgot the lower (primary drive/chain?) chain tensioner - also a rubber end.

Nah thats just an odd reflection, cams are in perfect nic cant say that about the cam bearings though.

I will deffinately be investigating in modifying or using shims from another motor when i get a chance to reco a head, just to be sure its right. Hopefully i can find something close to replace it from a more modern engine maybe, fingers crossed.

They appear to be lock tabs for the offset bush on the cam locating pin, u can just see one on the inlet cam pic. Not sure why they have it like that though. I just finished rotating the engine to watch the chain slack u mentioned and i noticed it as you described but that pic the slack came up just before the exhaust cam was at tdc so im positive the inlet is a tooth retarded but will have to fix that hopefully tomorrow.

Idler sprocket has teeth and appears in perfect condition, was quite shocked from your picture and was dreading the worst and the top chain guide has alot of rubber there.

Hopefully getting the cams right will alleviate the issue, perhaps the current config is amplifying the chain slack.....

Thankyou so much for the help, hopefully this will help others in the future.

The cam bearings and the oil pan gasket are the parts we have found difficult to source. One of the forum members found a few sets of what we think are the right bearings, still to be checked and verified but they look damn close!

If they are the right ones then we know what to look for in future. We'll also try to find a reliable source we can buy some stock from. It's a long term goal to find these bearings and oil pan gaskets and stockpile them for our future use. We also need to source supplies of gasket sets, new pistons and cam timing parts. Just about everything else is cross compatible with the G???Z engines. The idea is to buy in a way that a non profit co-operative would do. Members work as a team to buy up and stockpile the stock at a reasonable price and keep the price reasonable for other members.

If we don't work that way we'll end up paying through the nose to people (eBay sellers) with no interest in these engines other than seeing an opportunity to make a quick tax free profit.

Thanks Poida,

All seemed to go quiet on that front.

I notice that full G200W gasket kits are being sold on eBay for ~$380 albeit via Sleeka (Adelaide) and not MDS, but it's the same kit, just relabeled. IMO it's worth getting that rather than using the inferior Permaseal VRS or head gaskets (thin between cyls 1&2 and 3&4) and modifying G-Z sump gaskets.


BTW - do you know the roller count between the cam timing marks? Is it 19? (I know it's an odd number.)
It must be 19 since 17 or 21 would be too far out - eg, see this youtube as linked from nerdzblog - Cam timing for my Isuzu G180W Gemini engine.
That roller count should be added to our Master engine data page...

FYI - there was another youtube that showed the chain top slackening when rotating by hand as the exhaust "catches up" to the inlet. That is normal cam/chain behaviour. (And not finding references is now normal behaviour for me!)


And BTW nut161, to avoid ambiguity or confusion, that untoothed "cotton reel" was some fool's modification. It was not a worn OEM chain idler.

A mate also told me that certain Mitsubishi cam (chains and) tensioners or tensioner parts can be used for the GWs. (That sounds better than the Jaguar Sovereign bits I saw a few days ago!)

The bearings are still sitting on my shelf. Maybe Andy has tried out his set? I'm sure he'll let us know if he has.


The timing chain marks should be documented. Maybe pull a timing cover off one of your shed bound engines and dab some parts marking yellow ink on the links where they line up with the timing marks... then snap a picky and note the chain link numbers. I'm pretty sure that timing chain diagram Denny posted is here on the site somewhere, if not I am sure I have it here.




I think we should really begin to work on the 'co-operative' line of info and parts sourcing for the benefit of everyone who has these engines. There is nothing to gain by holding out on info or supplies of parts.

Lets not end up looking like an 'elite' (you know what I mean by this Pete, but lets not elaborate publicly) group of specific car enthusiasts who are individually looking out for themselves as individuals.


Those eBay gasket sets are G200W ones if I recall right Pete, so they won't really suit the G180W engines. I'm not even sure if they have the oil pan gaskets included. We also need to be careful any kits we find have reasonably fresh quality gaskets in them. Rubberised gaskets that have been stored for long periods can often shrink. That includes cork/rubber composite gaskets. I have NOS GMH/Isuzu G161Z rubber oil pan gaskets that are just like you find in new gasket sets, not hardened or shrunk yet are genuine off the shelf old stock, circa 1975-1984. And then I have other gaskets not even 10 years old that are crap, hardened and shrunk.

The timing marks on Denny's pic relies on having bright links and thus isn't suitable for those with new non-OEM chains.
PS - as per Dialing in your cams for a twincam...


Though the pic is enough to get it mostly correct, it's reasonably possible to be out by 1 roller between the cams at the top unless you know the spacing involves half a link, aka an ODD number of rollers.
(The top could be misaligned compared to the bottom, but at least with the cams correct relative to each other, it'd be easier to confirm valve openings and piston TDC etc.)

Workshop submission - the chain type/size with link count and the spacing between the shiny links. Readers can thus mark their own chains.


The G200W eBay gasket kit is complete. VIZ:
.

The sump gasket is visible as is the cam chain chimney's front cover to head (orange) rubber gasket that is so conveniently omitted from the Permaseal VRS kits.

Compare that to our older kit from G200W Full Gasket Set.

I got the impression they were fresh stock - ie, newly manufactured. Otherwise too I would be worried - 40 year old valve stem seals, cam-cover cork seals, and rubber sump & other gaskets tend to be somewhat useless (even if less dangerous than their equivalent brake seals LOL!).


The G180Ws could use the G200W head gaskets, though it may also be possible to source G180S head gaskets (ie, the Japanese G180 SOHC - NOT the "Opel" G180Z!!) and add the extra hole required (oil feed??).
If using the G200W head gasket in a G180W, some say the gaps will soon fill with carbon - not that I consider that desireable.
But in any case, these gaskets are wider and hence supposedly stronger between cylinders 1 & 2, and 3 & 4, than the Permaseals which I understand have been used is G180Ws without too much complaint.


As to eliteness, I'm even dealing with Triumph owners with GW twincams. Howz that - me dealing with Pommie cars! Not that that means I deal with just anyone - you know my attitude to time wasters, projection and transference, and sites with vested interests.
But you know my keenness to share information - especially when it saves time or money, and leads to a superior outcome.