Head Gasket Info From Anyone ?

[IanCornwall]

Hi can anyone tell me if the head gasket on the Mk1 GS300 2JZ-GE 1994 is the same as the head gasket set for the 1997 to 1999 version

The engine types match but is there an internal difference to the engine ?

Thanks

Ian

[IanCornwall]

Well I have spent a few hours dismantling my GS300 to do the head gasket

surprisingly quite easy in many parts as I think due to the build quality of the original I have only had a problem with a few things

The front cambelt cover is a bitch it the slotted head bolts are to tight, but a little perseverence and they did come out (eventually)

a code of tippex on the multitude of air and vacuum pipes I hope will make reassembly easier and less of a drain on the memory

A couple of really inaccesable bolts under the inlet manifold simply because the mountings for the air pipes is in the way

So now all ancialliaries are off, and the cam covers removed waiting for me to remove the cam belt, this has been nicely marked and the engine put into position, again hopefully to make refit easier

Now a few questions, come on people help me out here please, pretty please

Do I have to remove the cams from their bearings to get to any of the head bolts ?

between the spark plugs are hex sunk large bits these could be covers or just plugs, are there anything under these ?

What if any is the best way to remove the cam belt from the pulleys ? does the cam lock or is there some other way ?

All being well the head will come off in the morning then a check, new gaskets and back together, once i finish I should have a nice proceedure with good pictures that will help others out in the same boat

[winnie]

Are you 100% its h/gasket?

http://www.lexusownersclub.co.uk/forum/ind...showtopic=26586

[IanCornwall]

Hi Winnie

Unfortunately 100% sure, I can feel the power dropping as quick as the temperature rises and it is just to bad to be anything else

I was trying to convince myself it wasn't the head gasket, but it definately is, all the symptons are there and now is the time to change it, although it is time consuming doing the gasket change it is relatively simple unbolt / clean / check / rebuild job on the engine, the main problem is lack of info on the engine, but I have managed to find a lot of stuff on here and the Supra web site

But like all engines there are always the unexpected bits that pop up, like hidden bolts and where that "O" ring or seal is meant to go that you find in the kit when you have changed everything you can find

Also I feel if I am going to fit the NO2 set I have then a new steel gasket will be cash and time well spent, especially as I have a suitable kit already

I actually like NO2 set ups as unless you really floor the pedal a lot then it is probably the best £ per bhp value power increase available, especially as the GS has ample power to start with, just there for the extra push on overtaking or when you just want to pi** of mercs on slip roads

[BigRoj]

Hi Ian,

Just a thought for when you fit the Nos kit, does it come with an extra injector to fit in the inlet manifold?

Cos when you upgrade it to 150hp it will need all the fuel you can give it and more besides to stop your pistons becoming part of the atmosphere. The ignition may need re-mapping as well.

[IanCornwall]

I have been thinking about thw NOS and the electronics on the Lexus

On the Ford it was dead easy, another injector to dump fuel in each bank (V6) and I never had a problem

The Ford V6 though was a bit agricultural being honest and I didn't cause a problem, shoved the probe in the exhaust on a rolling road and tweaked fuel load until near enough normal as the injector opened a split second before the NO2 opened

As the NOS only kicks in on full throttle pedal it really only needs one fuel setting

I do have a sneaking feeling that it will confuse the hell out of the Lexus ECU though, or will it be easier in that the O2 sensors etc will automatically adjust everything ? wouldn't that just be so easy ?

Do you know anywhere that is capable of checking the ECU against NOS against mixture

The nice thing about the NOS is all I have to do is not switch the system on and it will drive exactly as standard so I can take it anywhere to get set up correctly

Last thing I want to do is melt the pistons and valves after just doing the head gasket, which was remarkably easy once you work out where all the vacuum hoses go back

[BigRoj]

Hi Ian,

You're right about it confusing the ecu and sensors, with all that extra oxygen from the nos plus the airflow meter getting a cold blast of dense nitrous, giving the knock sensor a work out and on full throttle/kickdown, going to be a bit exciting one way or the other! just imagine all that with variable cam timing as well.

I don't know anyone offhand who does that sort of checking but I'm sure there will be, somewhere.

[IanCornwall]

The NOS goes into the manifold after the throttle body, not into the air intake, so surely it will miss the flow sensors , or will it ?

Does the Mk1 have Variable valve timing ? i thought that was on later model GS300, although I must admit having just stripped the head there was no sign of variable valve timing gear unless thats down the bottom end on the crank, where I havent been

Please correct me if I am wrong

Thinking of the fuel control, won't the O2 sensors and knock sensors pick up a weak mixture and add buckets of fuel to compensate ? or don't they work fast enough

Exciting? I do hope so

Catastrophic ? I do hope not

[BigRoj]

Hi Ian,

No, the standard Mk1 isn't vvt, that came with the end of '97 mk2.

Theoretically, in a "normal" car engine, the knock sensor detects pre-ignition, often called detonation or pinking, particularly in a forced charge (turbo etc) engine, and adjusts the ignition timing accordingly (until it stops basically). But pre-igntion can be caused by, as you quite rightly say, a weak mixture but also by too high a cylinder compression and residual heat from a localised hot spot in the combustion chamber-the latter of which will be caused by a weak mixture. As for the O2 sensors if the Nitrous is only going to kick in on full throttle and the sensors detect a weaker mixture and try to put more fuel through, there aint going to be any as you are at full throttle. That was one of the reasons I asked about a supplementary injector, just so you have the back-up if you need it.

[IanCornwall]

Hi Roj

I have been looking at the NOS stuff again today, amazing how I forget all the bits and pieces

on the V6 I actually ran with 2 x plus 50bhp units, one for each bank and 2 fuel nozzles into the manifolds

I am now planning on running with 2 x 50bhp units on the Lexus after the throttle body where the manifold splits sideways

Apparently the +50bhp is based on a 4 cylinder 2,000cc engine, with one nozzle set, so in theory I can deliver with 2x50 units 150 bhp extra if I want to

also I do have the extra fuel nozzles that came originally with the kit so I will be fitting these as well

basically the fuel and NOS are both delivered by solenoid valves that can be adjusted easily with an allen key to tune the set up

In my experience of stock fuel injectors, they normally run at about 60 - 75% capacity when on full throttle, so maybe enough fuel in reserve, time will tell

My son had a brief chat today with the garage that set up his Cosworth when he went and upgraded his power chip, they are apparently capable of setting the NOS as well, but they do say that they don't think they will have to play with the ECU on the GS300, just make sure its not going to run at all weak for a 20 second run at full power, and with a possible 350+BHP on tap, that 20 seconds means I will be travelling quite a way in that time

Working on 3000 cc Supras done in the past they say the engine itself if in very good condition will handle more than 450 bhp as long as it is in balance, possibly more as the NOS means for 95% of the time the engine will be running stock power, if it shows any sign of being out of balance they will shut it down before it wobbles its way out of the car

[BigRoj]

Hi Ian,

Thats brilliant, sounds logical to me. And lets face it, if you hear any "ball bearing in a biscuit tin" or " two skeletons fighting in a dustbin" type noises when the nitrous hyperdrive is engaged you aren't exactly going to ignore it!

Best of luck with it, going to be FUN!

[IanCornwall]

after dodging rain clouds for a few days I have competed the change of the head gasket

I was actually quite amazed how easy it was, only a few little things to take care over really, and timing the engine up once I was certain of the settings was a doddle

As in all engines a few akward nuts and bolts that were obviously put in the engine before it was installed in the car, but a few universal joints on the extension bars and off and on they went

One everything was back together, turned the engine over and it started in literally a second, so I was well chuffed

The distributor has only been roughly timed, but it can't be that far out as it started so easily and runs sweet

Now can anyone help and let me know if have a problem with vacuum hoses, the throttle body is fine,

it is the set at the rear of the engine behind the inlet manifold, when I took them off to remove the bits and pieces there was one without a vacuum hose on it,

I have looked all around and cannot find another empty pipe that a hose if it was fitted to the pipe would mate with, does anyone have a schematic of the vacuum hose system to the Mk1 GS300 that would be excellent

I reckon that the GS300 head gasket is one of the easiest that I have ever done, and as soon as I sit down and write out the steps proceedure and mate that with the digi photos, anyone with spanner experience can do it if they are unfortunate to need to change a BHG