Isuzu G-series Twin Cam

Anyone ever lined up a sohc head gasket on a dohc block?

Appart from the timing cover (easy cut away), a couple of water/oil holes and not much meat on one side - the sohc gasket would bloody well fit.

My question is, can you by headgaskets with no holes in? A head gasket before it had the holes punched and the shape cut - A "Blank Headgasket"?

how handy would this be? or is this really dumb!!!!!!!

I don't think you can. I know you can buy gasket paper for things like inlet, carby, etc but this is for low-torque low-pressure applications as far as I know. My SOHC head gasket seemed to have different materials/rings and thick and thin spots on it too, which could not be cut into a blank piece at home.

I'm not 100% sure about this. I'm probably getting a head gasket custom made for around $150. Kinda sucks to pay that much for something of stock strength, but oh well.

Now don't take my advice as gospel - this info is from over 10 years ago....
I'm certain that DOHC owners used to add an extra hole to SOHC head gaskets, but I don't know if anything else was needed.

Most head gaskets have some sort of reinforcing around holes.
This may be to seal the gasket to prevent oil/water/gas penetration, or to prevent the hole fraying (kinda like how your feet stop your legs from fraying).
But the reinforcing may also “seal” around the hole – the gasket itself might not have enough “thickness pressure” to stop whatever from eventually edging by – like oil under pressure, or a cylinder’s combustion crap.

I think the extra hole was a water feed. So, for example, you could cut or punch a hole in the required spot making sure that there’s enough gasket remaining around the new hole. This assume of course that the hole is required – many gaskets have holes but for "blank" galleries – eg, there may be a water gallery in the block and gasket, but the head has no corresponding gallery. Hence the hole isn't needed.

If it’s an oil feed hole (ie, under pressure, not a drain hole), then maybe insert an O-ring. (EG - G150, G160 & G161 OHV engines used an o-ring around the single oil feed hole “inside” the gasket hole.)

I don’t know if a water hole would require reinforcing. But I suspect nothing was added. But maybe some gasket-gunk around the gasket edge? (But don’t use gunk or silicon around an oil hole!!!!)

I did buy some SOHC gaskets intended for my DOHC. But I still haven’t replaced any DOHC gasket.
But back then, SOHC gaskets were common & $25 whereas DOHC’s were rare and $110 or more, so it was worth the risk. (Just keep an eye on water leaks, oil contamination, engine temp etc and it’s unlikely that a gasket-hole leak will cause severe damage.)
Note that the cylinder has the highest compression (say 200psi), then I presume the oil feed (90psi max?), then water (15psi?). Oil drain and engine breather pressures should be negligible.

If gaskets are equal or similar prices (or cheap), I’d stick to the old rule – use the correct part.

But there are worse issues with gaskets – like NOT having a hole, or like my 4ZE1 engine into which someone installed a 4ZD1 head gasket – ie, the gasket’s cylinder diameter was 1mm less that the cylinder bore. Not very smart!

I don’t like adding any sealants etc to head gaskets (unless required, or maybe Hylomar or similar if reusing a head gasket) – it’s too complicated.

And I do not like any gasket hole being smaller than its gallery hole – eg, round water holes being smaller than the oval block and head galleries (though it’s okay if one side is smaller than the gasket hole) – the gasket will erode away hence fail or contaminate the “gallery”.
In the case of the 2.3L 4ZD1 head gasket in my 2.6L 4ZE1, there were gasket “rings” sitting on top of the pistons.

Hopefully someone with “real experience” will add to this post.

Cheers,
Peter IZU069

Use the Hylomar spray can shit - works the good. Rodeobob was telling me they sometimes use it to make up the difference/level out the block slightly on old trucks or some shit like that. You'd have to ask him but i just used it on a 4ZC1 and a brand new gasket and it looks the shit! Give it 10mins to dry and its all blue and plasticky, looks cool.

Nick-

Good to hear some endorsement, but I would never use Hylomar on a new gasket.
Whilst it may not do harm – it’s just a waste. And it may be difficult to “break” on next head removal. (Ever had to hack-saw a head off the block? Admittedly that was on a Toyota 4WD that had been using bore-water as coolant for a few years! A slight case of the head “welding” onto the block!)

My view is that head gaskets are better “dry” with clean degreased block & head surfaces – this was endorsed recently by RodeoBob Esq. Though sometimes I have added THIN sealant around the front side timing of chain/belt galleries. But then need to make sure that any sealant does NOT get into oil galleries (etc) – how do you know it hasn’t been squeezed in? Silastic has done some amazing damage to engines due to this!

FYI - I knew a dude that swore by coating head gaskets with graphite powder on his Alpha Romeos.
I asked why? - “Because they are too hard to remove and scrape off.”
But it’s such a rare occurrence... “No, mine blow every 3 months.”
I’d rather scrape a few hours every few (tens of) years. Maybe he enjoyed wasting time & money.

Anyhow, I was told that Hylomar was developed during WW2 (that’s the pre-WWW network that engulfed the world from about 1939 to 1945) to enable gaskets to be reused in Spitfire engines etc.
Resources were pretty rare then.
Not sure if it was developed - or just used – by Rolls Royce (a brilliant German car – lol).
But good enough for aero engines, probably good enough for me. (Granted – we may have different alloys etc and have added or different coolant etc.) I have used it once on a pre-loved G150 head gasket. No problems – it outlasted the car!

If the head or block is rough it should be skimmed. But yeah - Hylomar would be excellent as a "cheat" filler etc.
[ FYI – I would never deck a head – I would deck the block. But that’s because I have heaps of 30-40 year old blocks. But try to find a good head – and then find it’s been decked so you have to use two (rare or expensive) head gaskets! A block is easier to replace and rarely needs skimming. Heads need skimming after bad overheats etc. ]

The only recent habit I have changed is to use thinners etc to clean the head/block surfaces as petrol (etc) is “greasy” – not that that seems to impact gasket seals.

Sometimes “silver (spray) paint” could be used on the gaskets for extra sealing, but these were the older “metallic” OHV G-series gaskets, not the DOHC types.

Reminds me – a mate used Silastic instead of head gaskets in an old Honda F750 motorcycle (air cooled). I reckoned that the fuel and oil and heat would have made Silastic useless – but it worked!
(But old bike gaskets tended to be thin and almost metal-to-metal head-cylinder contact. My old GT750 Ducati has no head gasket – it’s just a metal-metal seal!)

Best wishes.
P.

I didnt want to risk the thing not sealing so i thought fook it, ill just coat it with the Hylomar. I only had one dowel on the block and was pressed for time so i was about worried about the gasket being damaged [unlikely, but like i said didnt want the risk] upon installation. Not worried about having to remove the head as i doubt ill be pulling that engine apart any time soon - it IS an Isuzu after all, and well, if it fucks up ill just get a Shuttle 4ZC1 bottom end and screw the manifolds onto that.

My dad welded his pistons to the bore once on an old G161, fucked it up nice and proper. This was early 90's, Gemini engines were still worth some money so he went and got it rebuilt. Like the einstein he is he took it to the Motorsport students at some now-defunct tafe. Not sure what they did to it, all we know is [hey, i was 5 at the time im not in a position to remember anything] it scored 84mm G180 flat tops. The fucking thing FLEW.

Theres also CRC gasket stripper that you can use to break down the gaskets, thats what i used and it did a pretty good job.

I asked why? - “Because they are too hard to remove and scrape off.”
But it’s such a rare occurrence... “No, mine blow every 3 months.”

Thats classic Alfa's for you - prone to it. And the thing that irks me is people SWEAR by the fucking things. They dont go THAT good, they dont handle THAT good [Gemini was comparable to the late 70's alfettas] and they like to rust more then a Russian likes Vodka. GET THE fook OVER EM.

Nick-

Hmmm...

I had a good long read of this thread, learnt a bit, but couldn't draw any firm conclusions.

Put shortly, what would everyone say is their preferred head gasket option? G161 hg's go for about $26 on their own, and to my knowledge twincam ones are either unavailable, or cost more than having a custom one made - which would be around $150. Would people recommend:
-Having one custom made for ~$150
-Modifying a G series SOHC gasket by cutting a few holes as neccessary
-As above, but using Hylomar around the new galleries
-Putting a layer of Hylomar on an old gasket (mine's in g/c)
-Using just Hylomar in place of a gasket - sounds odd to me but that said everyone knows I'm a noob

I'm thinking of grabbing a G161Z gasket just to have a look, and to figure out what/how much modification is needed, or even to take it to my local car parts place and ask if they can modify it. Maybe if I show them how similar it is to the SOHC gasket it will cost less to have one made/modified.

why dont you use the Bursons part No. V2032KC?

Because from memory theres only 3-4 of those DOHC VRS sets left in the country and they are about 150-180.

Eli you cant use the G161 gasket because the bores are 75mm as opposed to 84 for the G180. Get the G180 SOHC gasket and give it a go.

No you cant use just hylomar between the head and block. Expansion factors are too different, youd get leakage as soon as the engine is warm.

Nick-

I'd get whatever gaskets you can get now. I'd get VRS rather than getting them made - that can always be done in the future (and maybe in bulk!).
Keep your "good second hand" gasket for when you really need it.
Can't use 1600 or 1800 gaskets - the bore is to small.
And you will need a gasket - otherwise valves hit pistons or compression is to high etc.

Try a search for Bowden Engineering (NZ) - they had various gaskest last time I looked. I have some pdfs or something with various gaskets pics - I'll see if I can locate and post.

As for price - how much is $200 compared to getting another engine? That's intended as a tip - I have seen a few enthusiasts not wanting to "buy the last" parts whilst they are there. Later they find a substitute part costs way more - like $2.50 "shrink rings" for Bellett rear axles - later cost ~$80 each in 2-off lots; or (DB52) GT Bellett disc pads for $5, then $15, then $30 per set via the club; now commercially unobtainable.
My tip - get whatever gaskest you can get NOW if there is a chance of eventual "no stock". (EG - I have ~10 sets of GT disc pads.)

What's included in the VRS and who should I contact?

GeminiCoupe wrote:Eli you cant use the G161 gasket because the bores are 75mm as opposed to 84 for the G180. Get the G180 SOHC gasket and give it a go.

Whoops, my bad. Thats the one I meant!

IZU069 wrote:Can't use 1600 or 1800 gaskets - the bore is to small.

Oh... Damn, there goes that idea.

G180z gasket should be fine for G180w Pete

Sorry – I was referring to G200 above when I said G161 & G180 gaskets would be to small.
I only use G200s, though I intend to use a G180 rebored to 2L (‘cos I put them in G160 & G161 OEM vehicles and I don’t want to exceed the "+10% rule" do I?).
But I used to use G161 head gaskets in G150s (OHV varieties) – that’s 82mm vs 79mm bore.
G180 & G200 bores are 84mm & 88mm respectively (I think). If G180 gaskets were a problem, I’d try G200 gaskets in a G180 - but I’d check for other differences too.

But anyhow, I bought 2 head gaskets and 2 VRS kits for the G200 twincams in case they were in short supply.
Burson didn’t have them in any store, but had them the next day (from AA Gaskets who in turn get them from NZ).

I was expecting to pay just over $500 RRP and I thought this to be good value - I do not want to be caught without gaskets. As it is, I got them 25% off RRP so I’m real happy!

PartNumber Description RRP
S2032KC Head Gasket “Isuzu 4” $78.55
V2032KC VRS “Isuzu G200Z 1949cc 1984 on” $173.20

These are ‘Permaseal’ kits supplied from AA Gaskets Pty Ltd.
The head gaskets (from NZ Gaskets Limited?) are carbon fibre and include the rubber O-ring for the oil feed.
The VRS consists of the following gaskets: head (carbon-fibre plus O-ring for oil-feed); cam-cover (cork); exhaust manifold; 2 intake manifold, 1 (not 2?) water jacket; thermostat cover.
It also has 8 valve stem seals.
The VRS does NOT include the front chain case gasket. This was apparently not supplied in the OEM kits.

AA Gaskets reckon they sell approximately 6 sets a year Australia wide and carry an average stock holding of 2 sets (4 months sales). It’s about 6 weeks to supply from NZ. (If I were operating under modern busines theories, I probably wouldn't carry stock for mere "6 per year".)

Assuming you can use the G200 head gasket, since they are only $80 and seemingly available, just get one! (It’s less than 2 tanks of petrol!) Save second-hand gaskets and conversions until you really need them!

By the way - it's easy to reverse the gaskets - be careful!
And I still reckon put them in dry (unless advised otherwise). I use thinners to clean the gasket surfaces (not te gasket!). (I used to use petrol till I found out how greasy it is!)

Thanks for the heads up on apparent rarity! Although I have a couple of G200 twincam head gaskets, I probably wouldn’t have gotten spares until it was too late! (I intend to machine two G200s (or G180s) in preparation for later use.)

On advice given to me by my machine shop crew, (this is referring to G161Z engines by the way) the standard Gemini head gaskets dished out by Permatex and ACL just don't cut it. I tend to agree with them. I've stripped and repaired a dozen heads in the past month or two and they all fail in a similar way. The bridge between cylinders 1 & 2 or the one between 3 & 4 seems to let go most times. So they suggest to use a coating on each side of the cheaper gasket, of VHT Copper Gasket Cement (SP-21A) to help keep the gaskets from failing. They don't use these fibre type gaskets at all because of the higher than normal failure rate. They recommend and use a graphite type head gasket.

My G161Z regular fibre type head gasket seemed pretty sh*t to me, and the car overheated since the change... My mechanic thinks that head gasket is either blown or never actually sealed properly, and it's hmm, not quite a year old?

I think G180W is 83mm bore, and G200W 87mm bore. Was this what you were wondering IZU069? Or were you referring to the SOHC gaskets being 84 and 88mm?

Sorry you've lost me.. Which SOHC gasket would you match to which DOHC?

Oh and so I take it you can get off-the-shelf graphite gaskets for G180Z/G200Z?

Thanks again for the advice. I did note the very thin gasket between 1-2 & 3-4 – I measure it as 4mm. Maybe because it’s virtually ‘all metal’ on the AA/Permaseal/NZ_gaskets means that it compresses and gives way.
I’ll find the other G200 gaskets that I have and compare (one day…. I’ve just recovered my PC after another failure. If it wasn’t for some windoze-only software I just purchased, I’d be fully Linux this time!)
Though I’d get different gaskets instead of trying to “seal” crappy ones.
Then again, SOHC & DOHC gaskets are quick to replace (it’s a 4 hour job for the OHVs).

And re SOHC – DOHC interchangeability – it’s for same bore (obviously!?), though this may have been based on G180 (later DOHC – ie, blue rockers – not green) and the G200s.
There was only one extra hole needed for the DOHC.
My bore info may be wrong – it was just a quick reply (got the bore info from “World Cars”). But from memory all G series had the same bore for the same capacity (irrespective of SOHC & DOHC – ie, the blocks are the same – except for G160 vs G161 etc.)

Sorry for the confusion. I’ll get back to my windoze recovery….

Cheers, Peter.

G161z and G161w - 82mm bore
G180z and G180w - 84mm bore
G200z and G200w - 87mm bore

So, the conclusion thus far is.................

Is it possible to use a modified SOHC headgasket on a DOHC without it being too DODGEY?

Or do we all do group buy at Bursons?

Mike.

Ok I bought myself a copper G???Z head gasket (I did ask for a G180z gasket), erm, the labelling was up the sh*t, it even said "holden 6 cylinder" on the pack despite blatantly having four pots, although it scared me for a minute...

By ACL. Model number "BC220CU16-GTR" it is a 1.6mm copper gasket to decompress a little, I personally wanted this because I want to go turbo. There's also a 1mm version available. Apparently RRP is $299 but I got it for $200. However I'd check how much custom made copper gaskets are because I think it might actually be less than this, am kicking myself but oh well.

I counted, there are 13 holes which need creating/extending. One hole, which looks like oil, links to one of the middle head bolts on the new gasket, but I'm thinking this shouldn't pose a problem as the bolt will be so torqued it won't leak anywhere, and whats more neither the oil nor the bolt will be contaminated.

The bores actually look 1-2mm smaller on the copper head gasket, I don't know if it's for the wrong G-series or not, but the pistons are recessed a little around the edges so hopefully it won't it. If it doesn't hit it should make the gasket more resistant to blowing between 1&2 etc...

Well, fingers crossed. I'm going to make a few calls to try to find someone who can modify copper head gaskets. Any ideas???

I wish I could get a pic for everyone but I don't have a digital camera. I'll see what I can do but it won't be soon.

-Eli

Top Marks for doing this.........

Glad to give back something after being such a pain! Hahah.

Update: O.G. Speed Shop, a local hotrod/drag orientated place said they will either be able to modify it for me, or will know someone who can. I'll be taking it (and my G161Z sump gasket, oh and a piston for a rings measurement) in on Friday.

Here are the pics (click to enlarge)




13 holes need to be made/modified to incorporate everything. Interestingly, on the twincam gasket, a head bolt and what appears to be an oil line are linked on the SOHC gasket. I guess this doesn't matter, oil in the head bold shouldn't go anywhere or do any damage seeing you're supposed to oil head bolts first anyway.

I'm taking it into a mob called O.G. Speed Shop some time soon, apparently they can modify it for me. Does this look like it will work alright, or will it be dodgy?

Thanks,
Eli

Hi Eli,
Just some comments (many of which are repeats from earlier) - but please note that experts may spot the errors!

Most G-series head gaskets have the oil feed hole separate to the bolt hole.
Isuzu fit and supply an O-ring that sits in this oil feed hole – though maybe this is based on old head gasket materials?.
Whilst the “oil into the head bolt cavity” shouldn’t go anywhere, but if there is a leak, you will lose oil pressure to the head and other bearings. EG - If this bolt loosens or the washer cracks, the head is likely to seize first, though main and big-end bearing can also be damaged or seize.)

This bit may be trivial: If there is a continuous but slow leak (through the head bolt hole), this cavity will also have to be filled up before “pressure” gets to the cams etc. This may be negligible (how big is the cavity compared to the rest of the “empty” oil passages?), but it is an additional “oil supply delay” which causes long term shell (bearing) breakdown which affects not only the cams, but also the big end and main bearings.
Note however that oil usually drains back into the sump anyhow (eg, overnight), hence the effect may be minimal. And if it’s a “fast leak”, then oil starvation as mentioned above is a bigger problem.
(Opinion: I’d prefer that that head bolt is “dry” like all the others, eg: no oil cooling and no contamination into the oil feed supplying the cams.)

The gasket’s bore diameter MUST be greater than that of the bore. Any overhanging (or “inhanging”?) gasket can break off and score the bore, jam valves etc. (My 4ZD1 gasket in a 4ZE1 as an example.)

Is the gasket solid copper? Copper will cause electrolysis of the alloy head. I’d be wary of any copper content in a head gasket with alloy heads (or blocks), though it may be that copper granules suspended in new technology gaskets is okay.
(If solid copper, make sure there is no “cylinder overhang” as mentioned above. The copper may melt, or stay hot and cause engine overrun after switch off etc.)

Align and check the gasket with the both the head and the block. Some block & head cavities/holes are larger than those in the gasket. Hence you could have leaks – ie, putting all the required DOHC holes into the SOHC gasket may cause joining of different holes.

Now – just my opinion based on your pictures and the assumption that it is solid copper (or is of sandwich construction without the obligatory female in between), and that its for a 2L DOHC:
I would order a DOHC head gasket.
(I don’t know the availability of G180 gaskets. The G200 gasket could be used, but I’d rather the thicker G180 “bridge” between cylinders – see below…)

I recently obtained 2L DOHC head gaskets for under $80 (presumably manufactured by NZ Gaskets as supplied by AA Gaskets to Bursons).
The only reservations I have with these AA Gaskets is that they may be prone to failure as indicated by Poida (and others?), and that they do not include the cam case gasket (which was a separate gasket anyhow).
The apparent failure is between cyls 1 & 2 and 3&4 due to breakdown of the gasket in between.
I have noted that in the AA Gasket, this part is narrower than Isuzu gaskets, but only by about 0.5 – 1mm).
It also seems to have less gasket material than Isuzu’s; ie – it looks like the two metal reinforcement “veneer rings” meet without much - if any - gasket material in between (hence I suspect they get too hot and break down etc).

I would feel uneasy about modifying the copper gasket - I’d rather try the $80 AA Gasket version. If that breaks down, then I’d consider using the copper gasket.
I’d keep the copper gasket until I’m desperate – or until I resell it to someone that does want it (presumably racers that don’t care about long-term head electrolysis etc - they just want a re-useable gasket).

Best wishes.
Peter.

I guess I don't have a choice now. If the people modifying it reckon I have half a chance I'll give it a go. If it comes to it I can reuse the old one, look at how good it looks... But that might leak and will only hold out for so long/so much boost. I hope I havn't just wasted $200. Oh well if I have there are plenty of G whatever it is Z owners who might be interested.

I would love to buy a designated twincam item but from where??

Thanks for the reply!
Eli

Eli,

I got kits for a G200W through Bursons (August 2006) as listed below. The prices are RRP - you might be able to screw a further (25%?) discount.
The kits are xx203KC and are usually labelled "Head Gasket: Isuzu 4", or "G200Z 1984 on".
These came from AA Gaskets who apparently use "NZ Gaskets".
- Permaseal S203KC head gasket (RRP $78.55) - the gasket includes the oil-feed O-ring.
- Permaseal VRS203KC (RRP $173.20) - consists of head (and oil-feed O-ring); cam/rocker cover; water, exhaust & intake (2 of) manifold gaskets; and valve stem seals. The cam case gasket is NOT included.
The gasket bore/chamber diameter is 88.7mm.

I measured the width of the AA gasket between cyls 1&2 & 3&4.
The (VR)S203K was 4.0mm.
Another gasket (OEM Isuzu?) measured 4.8mm.
As to the reports that these gaskets have a tendency to blow, I wonder if the extra 0.8mm could make the difference? Even though it's only 20% greater width, could this mean it might increase strength by up to nearly 50% (44% actually - the same ratio of a car audio's output power at 14.4V as compared to 12V).

I don't know what the availability is for an 1800, but - except for the narrower gasket between the chambers (as mentioned above) - I don't see why the 2000 gasket couldn't be used. (My recollection is that the later 1800 DOHC blocks are identical to 2L, and the heads are mechanically interchangeable.)

Cheers, Peter.