Replace head gasket on a 6MGE as preventative maintenance?

[MS112]

Hello

I am trying to decide if I should replace a head gasket on a 6MGE as a preventative measure. It was bought from a wrecker as an emergency spare, with unknown milage, just that the compression test was ok (this was about 3 years ago and I was/am a nieve idiot, so didn't ask any further questions. Hindsight sucks)

It has a fairly large oil leak originating somewhere behind the back of the timing cover, prompting me to buy a gasket overhaul kit. Said kit includes a head gasket.

Considering I will be replacing the majority of gaskets, I wonder if as a preventative measure, I should also change the head gasket.

The reasons for wanting to do so:

• The engine is currently not in a car. Easy to work on now.
• Even if it is in good condition now, the M motor apparently has a reputation for blowing head gaskets in general. I was under the impression it was just the 7MGE, but was quickly corrected on that matter.
• I will be replacing the majority of gaskets on the engine. If the head gasket does go down the track, I will have wasted time and gaskets.

After speaking with two friends, their opinions concurred that it was best to leave it alone. A quick google search reveals the majority opinion is of also of the "leave it alone" school of thought.

I suppose the difference in this case, is that the starting condition of the motor is not known. The only clue is that it claims to be from an MX73 previously, so the engine was likely a swap job already. There is also evidence it was run on LPG.

Thoughts?

Cheers,
Brendon

[andrew_mx83]

if you have the gaskets and the time why not, its a hell of a lot easier on the stand than in the car. you will be up for about $100 to deck the head, if you wanna do it properly deck the block too but its a fait bit more work. for a couple of hundred you get rings/bearings and have a fresh healthy motor

if you dont change the gasket at lease retorque the head

[MS112]

Hey Andrew, thanks for quick reply

I will keep the re-torque in mind.

With regards to rings and bearings, I suppose that's the other half of the equation: if you are prepared to take the head off, perhaps refreshing the entire motor is probably a good idea at that stage.

As far as I know, the engine doesn't appear to be in bad shape (but then again I'm no expert either). There was no sign of being cooked (solidified gunk in cams towers, oil pan and gauss cover for pump), and the oil was not milkshake coloured. It's mostly an exercise in reducing the unknown and hopefully increasing reliability.

[andrew_mx83]

i dont like putting 2nd hand motors in cars... if you have the time, tools and dosh why not freshen it up and know its reliable?

[MS112]

Alright

Did a compression test. Seems the head definitely has to come off for a look. I note now I should have done this before posting a thread. Sorry about that.

Values are in KPa. These are from the second test.

• #1: 1500
• #2: 1300
• #3: 850
• #4: 950
• #5: 1050
• #6: 1450

Not only is there too much variance between cylinders, #3 and #4 are suspiciously low. Also, #4 improved by 100KPa after spraying CRC into cylinder. I realised after the fact I am supposed to use small amount of oil. But I think the general idea is there: HG is suspect, rings might also be done.

Cheers,
Brendon

[hickozGT4]

you should alway do a dry compression test aswell as the wet test use oil not crc(too thin)

good way to see how the rings are....

as said above F#*k putting an engine in the car if your dont know the state...

the added cost now is major saving in future when the engine goes and you have to pull the prick out again...
if you have never done one before its a good learing curve...
there are alot of good part out there for the 6m.... may aswell beef it up a little

[derekjay]

Here's one I prepared earlier: 6m-ge | MZ12GT

Actually I just put the head back on on Saturday.
Assembly

It has taken me ages to get the engine to this state, but generally I only work on it on the weekend and I have very limited space in my garage, which means I have to wait for it to not be raining so I can create enough space to do work in.

I can't tell you at this stage if it is worth the effort, because I am not finished with it yet. But at times it has felt like building an engine twice due to stuffing stuff up and having to redo it (ruined piston rings, crushed gaskets, etc).

As has been said above there are heaps of spares available for this engine. The only real trick is that the front crankshaft oil seal is actually from a 7M rather than a 5M.

[CrUZida]

Don't waste your time doing a compression test on a motor that has sat around for a few years.
It can easily give false results due to a bit of rust building up on an open valve and therefore it wont seal 100%.

You need to give the motor a couple of full heat cycles before doing a compression test to get realistic results.

[MS112]

you should alway do a dry compression test aswell as the wet test use oil not crc(too thin)

good way to see how the rings are....

as said above F#*k putting an engine in the car if your dont know the state...

the added cost now is major saving in future when the engine goes and you have to pull the prick out again...
if you have never done one before its a good learing curve...
there are alot of good part out there for the 6m.... may aswell beef it up a little

The first test was done without adding anything to the cylinders. The second test (shown above) usually only improved the cylinders by 50 KPa, excepting #4.

Don't waste your time doing a compression test on a motor that has sat around for a few years.
It can easily give false results due to a bit of rust building up on an open valve and therefore it wont seal 100%.

You need to give the motor a couple of full heat cycles before doing a compression test to get realistic results.

Thank you for that point of advice.

Unfortunately the engine is not in a vehicle to be started and warmed up. The TSRM did state that the engine needed to be warm when doing this. The compression test was done more or less to work out if the head should come off and further inspection done.

As I recall, based on the motor's last position, cylinder #4 was on an intake stroke, which can then explain the low compression. #3 and #5 were also showing below standard compression though, which both should have had closed valves. I had to estimate those states however, so I could be wrong.

I have entertained the idea of trying to run the motor on the ground, but the fuel supply would be the most difficult to rig up.

Thank you all for your input so far

Brendon

[CrUZida]

Fuel supply is actually very very easy to rig up.
Just drop a fuel pump in a 5 gallon drum and put the return line in there too, and job done.

The radiator is much more time consuming to rig up.

[andrew_mx83]

pfft radiator

or just borrow a fuel line off a running efi vehicle


so one cylinder did not pickup any comp when adding crc? most likely stuffed HG or valve.
can you post up the wet/dry results (ideally in psi) so we can compare?

[MS112]

Fuel supply is actually very very easy to rig up.
Just drop a fuel pump in a 5 gallon drum and put the return line in there too, and job done.

The radiator is much more time consuming to rig up.

Ok, it must be pretty clear now that I am inexperienced at this

The MS112 Crown has it's fuel pump external to the tank, so that complicates things a bit. I suppose I simply drop the engine into the bay of the receiving Crown and connect up the fuel lines. Could even attach the radiator that way.

Just to clarify (and perhaps because I am somewhat slow), are you recommending I at least perform a hot test before pulling the head off, or were you just telling me what I did was incorrect with regards to compression test?

pfft radiator

or just borrow a fuel line off a running efi vehicle

so one cylinder did not pickup any comp when adding crc? most likely stuffed HG or valve.
can you post up the wet/dry results (ideally in psi) so we can compare?

All cylinders picked up at least 50KPa on the second (wet) run, except for #4 which picked up 100. This would make the rings on #4 suspect, according to the TSRM. I will not be able to post up the first test run until tonight.

Thank you both for your replies,
Brendon

[CrUZida]

The MS112 Crown has it's fuel pump external to the tank, so that complicates things a bit.

That doesn't really change much, just means that you need to run a flexible hose from the suction side of the pump into the tank. In some respects it may make it easier.
Just don't let the hose hit the bottom, and potentially suck up small particles.

I suppose I simply drop the engine into the bay of the receiving Crown and connect up the fuel lines. Could even attach the radiator that way.

No reason why you can't, depends if you can be bothered with the effort involves.
In some respects it will be easier, in others harder.

Just to clarify (and perhaps because I am somewhat slow), are you recommending I at least perform a hot test before pulling the head off, or were you just telling me what I did was incorrect with regards to compression test?

More so just warning you to take those results with a grain of sand. If something has 0 compression, then chances are there is a problem (but once again, this could just be a stuck valve), but if its just lower than expected, it could easily be in need of a good heat cycle, blow the cobwebs out, etc.

[MS112]

Thank you CrUZida

Andrew, results table as requested.

           +------------+------------+
           |     Dry    |     Wet    |
+----------+------+-----+------+-----+
| Cylinder |  KPa | PSI |  KPa | PSI |
+----------+------+-----+------+-----+
|        1 | 1450 | 210 | 1500 | 220 | 
|        2 | 1250 | 180 | 1300 | 190 | 
|        3 |  800 | 120 |  850 | 120 | 
|        4 |  850 | 120 |  950 | 140 | 
|        5 | 1000 | 140 | 1050 | 150 | 
|        6 | 1400 | 200 | 1450 | 210 | 
+----------+------+-----+------+-----+

ASCII table for the win. Would be good if vBulletin supported tables though

#edit 2012/05/13
Hey look, it does now:

Cylinder	Dry (KPa)	Wet (KPa)
1	1450	1500
2	1250	1300
3	800	850
4	850	950
5	1000	1050
6	1400	1450

But I dropped PSI rating as I dunno how to do the merged columns

Cheers,
Brendon

[andrew_mx83]

yup i often wish i could paste tables in.

the wet/dry results looks good, 10-20psi is fine. concerning is the low comp on #3,4,5


just tear it down and freshen it up...