Isuzu G-series Twin Cam

I have had no personal input into this information, but it's food for thought. In a thread on Just Gems, Sammy uploaded a document that I believe he was sent by the previous owner when he bought his twincam:




Isuzu twin cam G180W dummy cam modifications




The reason the cam bearings seem not to survive too well in all Isuzu twin cam 8 valve is two fold;
• The engine was designed as a pushrod engine and the oil pump was designed to supply as such, however the extent of modifications to the oil system when the twin cam head was adapted in 1966 was minimal and as such the cam bearings wear the brunt of the damage due to oil starvation.
• The oil gallery supplying oil to the head runs through the dummy camshaft (which I affectionately call the third camshaft of the Isuzu Tri - Cam engine) however the port for the oil feed to the head runs through an offset gallery within the dummy cam itself. In effect this allows a squirt of oil to the head once per every cam revolution, or once per every two crank revolutions.
To obviate the later issue, I have ground a circumferential gallery within the bearing surface of the dummy cam 5mm deep to allow a constant flow of oil to the head and then restricted the flow to the head at the block's deck by way of a drilled port blank / alloy grub screw (the port was tapped to suit) with a 2.5mm port. (I have some photo's lying around somewhere of this work; one day I may even get around to scanning them in and showing you the work itself...)

Make sure your 'groove' is radiused.





...

It's an interesting thought. It would explain why the cam bearings seem to go in a hurry. Two things instantly come to mind - could a similar outcome be achieved, without the need to remove the head (to insert the grub screw) and in doing so need to chase up a replacement head gasket? Perhaps, rather than machining a groove all the way around the "third cam", the factory single feed hole could be complemented with a second one in an inverted position?

My second thought is, would the increase in head oil flow deprive the lower end of valuable oil pressure?

Funny, I can't say that I am aware of cam bearings being a problem.

Then again, the twincams were quite reliable.
Were.

And I don't know what to make of "the extent of modifications to the oil system when the twin cam head was adapted in 1966 was minimal and as such the cam bearings wear the brunt of the damage due to oil starvation".
That's partly due to not being aware of oil starvation problems, and also that as far as I am concerned, there was no need for major modification because the head etc was designed with and for the OHV oil system.

If there was an oil starvation problem, what changes were made to the later engines?

Granted, the G161Ws had crank-vent breathing issues, but they were fixed.
So over their 15 year history, what changes occurred?
Isuzu were quick to address issues like that. Besides - I think they took great pleasure winning those endurance races - we certainly did!

Also, the only revving issue I'm aware of was the breakage of the magnetic disc in the reluctor dizzy above 7500RPM.
The only seizures issue I knew of were 3 DOHCs with seized bottom ends - but that's to be expected when you run a good G-W engine up the Hume fwy thinking your imperial speedo is metric, and using 50W oil - but never a cam.


I know lots of DOHCs seem to be breaking down, but I put that down to the mods that are being done.

The only cam problem I know of is getting the bearings - not that I have gone through with the order I was offered a year or 2 back ($14 per shell so $280 ex. per set).

But modifying is tricky - it's all about balance.
But if it is merely the ducting, it should be fine - you should be able to open up the pipes etc as much as you want (balance wise) since it's the bearings that determine the delivery (pressure).

And I'm not so sure about that oil route...
I only remember extending a blanked "3rd cam" oil feed when converting a Florian G161 for a GT Bellett cam....

And why not run the feed from the filter/chain tensioner to the head etc?

Thinking cap time. (Read - brain scraper search)

It actually sounds like a logical modification to me. The 5mm groove is to allow unrestricted oil flow and the restrictive block in the head deck is the regulator to control flow rate to the two overhead camshafts and prevent oil pressure dropping at the bottom end. I would certainly look at this closer if I were in a situation where I needed to rebuild and engine.

Good find there Eli. Any chance of finding those images mentioned?

I didn't get any pictures with it unfortunately The text was provided by Sammy.

I wonder if there's any way of restricting the increased oil flow without having the head off...

I didnt get any pics with it either, and i think the owner of the engine before me wasnt given any either (Pretty sure it was written by that owner)

The engine might have even had it done, however i never looked for it.

I no longer own the engine

Hmmm - overcoming the restriction then reapplying it....

Remove the central cam mounts and restrict those.... (The single head feed splits to the 2 cams.).

Well your all in luck people, i was actually the one who bought that engine off Sammy. I have seen these modifications and will take some photos for you. I have all the parts wrapped up in storage at the moment untill i am ready for assembley, so i will pull the parts out and take some photos.

Cheers,
Damo.

You bluddy legend

Ok so here are the modification pics i promised.

This is the standard vs modified cam.



This is where the oil is restricted at the block deck. It's just a grub screw with a 2.5mm hole drill through the center, then tapped and screwed into the original oil gallery.



A bit closer.



And this is just a pic of a standard oil gallery for comparison.



Sorry about some of the pics, but my stupid camera would'nt focus properly, it was the best i could get out of about 50 photos.

Have fun,
Damo.

What about an extra line to the head galley from the block galley (or filler assembly)? (Both are Imperial grub screws if I recall...).
Hence no need to mod the lower cam.

I was chatting to someone from Russell Jones' machine shop about having the twin cam balanced, he brought up that he has heard of people totally removing the 3rd cam in race motors...

Nice!!

Well, I guess with that recess carved around it, there's no point in it rotating (or being there at all, really) although you'd have to put something in it's place to direct the oil up, or it'd just blast out of the dummy cam chamber and leave the head dry (I think, haven't seen the guts of a W for far too long!)

And again, there's also the possibility of drilling a second hole in it, rather than the whole recess, and perhaps not having to mod the head? Just for those of us who erm, don't want to destroy that fresh head gasket or clean up the copper gasket (depending which motor I'm talking about).

Awesome pics, thanks for that! And Peter, I'm sure I'll get what you're talking about when I go outside tomorrow and look at my engine. Right now I can't remember anywhere the oil enters the head externally - only the line to the timing chain tensioner.

Eli

Greengem20B wrote:....he has heard of people totally removing the 3rd cam in race motors...

Find out how they drove the oil pump (electric?) and re-routed the oil passage to the head.

Re-chaining the cams would also be interesting.

Or does "heard" mean I "heard of people talking about totally removing the 3rd cam in race motors"...?.

So the idea would be to run a external belt driven oil pump (wet sump), run a oil line to the 2 grub screws in the back of the head, have a valve to adjust/restrict the flow?
Electric oil pump to prime & supply pressure during startup, no more rattles....

Chop the third cam straight after the first bearing, & hope the timing chain pulley still spins balanced, would losing 90% of the third cam make any noticeable difference to performance?

Bullet proof idea or a waste of time?

I hate it when good topics die....

If it's only to get rid of the rattle, get a later tensioner & front cover.

As to G-W oil issues - I'm not aware of any. (Though it's on my list along with cam bearings...)

I am aware of GWs blowing up, but AFAIK that's only "rebuilt" engines (LOL)....

I finally met up with my Guru after many years...

He confirmed that there are no issues with the GW oil feed - certainly unless talking about 500bHP etc - though we did discount the G161W (as a piece of shit, but that is a relative statement!)


As to oil going through the dummy cam or even removing the dummy cam - CRAP. (Besides, why double the cam-chain speed? And I'd love to see what cam or crank gears those alleged "dummy cam removers" used!)
Only the usual rules applied , eg, NOT having the oil feed hole underlap the shell's oil fed hole.
(He'd drill out oil feeds (but not at bearing exits!) and align double-end drilled holes and taper joins. But that was the only "mod" and he dealt with very high performance engines.)


As to what GWs to get - any with the later (triangular) ratchet-fitted cam chain tensioner (ie, Piazza G200W, and the later blue G180W version).


And as too short-straighting to 180kph into a needle-hairpin (on Kangaloon Rd?)... What can I say, absence makes the heart grow fonder??


PS - there was once someone questioning the use of the "mild" L1 profile cam (410 thou lift?) for the GW.
Higher lifts or the L2 profile etc run into issues.
And as usual, what I could never understand is why get opinions compared to a well tried and proven base build? At least start with that unless you KNOW something better (but IMO the G200W's 400Nm & 230HP is pretty good for "minor" mods!). (Celica cams indeed!)