Compression test results

[dom14]

Hi Guys,

I did a compression test on my RB30 Patrol today.

These are the readings

6 ---> 180
5 ---> 175
4 ---> 175
3 ---> 175
2 ---> 165 oil squirted 190
1 ---> 190


I warmed up the engine before the compression test & opened the throttle wide.

My concern is the number 2 producing low compression than the rest and jumping to 190 with an oil squirt into the bore, indicates worn rings?!! Or can it be something else(head gasket on it's way?)?

Is it time for a new head gasket and head reconditioning?
Or can I hold onto it bit longer?

Thanx in advance for any tips/advice guys.

[Patrol'n]

Hey Dom,

From my memory (been a long while since I rebuilt an engine), a low compression reading that increases with oil being injected into the cylinder is an indication of worn piston rings. That's just from my memory though, and not a mechanic by trade, so I jumped on the net and found the info below.

http://www.freeasestudyguides.com/compression-test-injecting-oil.html

The link above seems to support the worn piston rings, or maybe worn cylinder or bad piston.

http://www.popularmechanics.com/cars/how-to/a8520/cars-101-how-to-do-a-compression-test-14912158/

This link suggests that total variation between cylinders highest to lowest shouldn't exceed 10%, your figures suggest closer to 14%, so maybe some wear there. Maybe worth getting that rechecked by a good mechanic before spending any significant cash?

As to whether you can hang on to it a bit longer, I suppose it depends how it's running, whether you have any serious trips on the cards, if you have a bunch of folding stuff laying around etc etc...

Not suggesting it, but I remember my dad telling me a story years ago about his old HQ Kingswood, the red 202 blew a hole in the top of number 4 piston, he drove hundreds of miles before he fixed it, just kept stopping to refill the oil...

[dom14]

Hey Dom,

From my memory (been a long while since I rebuilt an engine), a low compression reading that increases with oil being injected into the cylinder is an indication of worn piston rings. That's just from my memory though, and not a mechanic by trade, so I jumped on the net and found the info below.

http://www.freeasestudyguides.com/compression-test-injecting-oil.html

The link above seems to support the worn piston rings, or maybe worn cylinder or bad piston.

http://www.popularmechanics.com/cars/how-to/a8520/cars-101-how-to-do-a-compression-test-14912158/

This link suggests that total variation between cylinders highest to lowest shouldn't exceed 10%, your figures suggest closer to 14%, so maybe some wear there. Maybe worth getting that rechecked by a good mechanic before spending any significant cash?

As to whether you can hang on to it a bit longer, I suppose it depends how it's running, whether you have any serious trips on the cards, if you have a bunch of folding stuff laying around etc etc...

Not suggesting it, but I remember my dad telling me a story years ago about his old HQ Kingswood, the red 202 blew a hole in the top of number 4 piston, he drove hundreds of miles before he fixed it, just kept stopping to refill the oil...

Thanx mate.
I'll read through the links.
I'm planning to do a leakdown test and a combustion gas leak test tomorrow.
I'll see how it goes.

[gaddy]

For what it's worth , i view any new or rebuilding of heads as a temporary fix , you still have a bottom end with wear that will only be put under more stress now that the top is in as new condition , had a mate who ran a engine reconditioning shop , a hell of alot of their work came from people putting on new / reconditioned heads only to have the bottom end fail shortly after . I'd be doing the sums to work out viability and options .

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[mudnut]

Find a wrecked or rolled 4.8 U and transplant all the running gear into the Q. Best of both worlds : a lighter body and extra grunt.

[dom14]

Find a wrecked or rolled 4.8 U and transplant all the running gear into the Q. Best of both worlds : a lighter body and extra grunt.

Do they bolt in straight? I mean the engine, gearbox, diff, etc etc?

[dom14]

For what it's worth , i view any new or rebuilding of heads as a temporary fix , you still have a bottom end with wear that will only be put under more stress now that the top is in as new condition , had a mate who ran a engine reconditioning shop , a hell of alot of their work came from people putting on new / reconditioned heads only to have the bottom end fail shortly after . I'd be doing the sums to work out viability and options .


Yep, totally agree with that mate.
That was one of the reasons I didn't fully recondition the head last time but mildly ground the valves & seats manually with grinding paste. I thought, it was a waste of money.
All Heads cylinder head reconditioners offered me a head reconditioned for LPG, with head gasket, valves, valve guide seals, exhaust & intake manifold gaskets, etc for $600 or so(five years ago). I decided not to go for it and instead kept the quickly and cheaply reconditioned old head 'cos I wasn't sure about the bottom end and still not too sure.

Five years later, those concerns are more valid now.

In the past I've had dramas with putting reconditioned heads to old worn engines and ended up with trouble within few months.

I'm thinking about getting an RB30 engine and rebuild it slowly in my spare time from bottom to top.

[mudnut]

Do they bolt in straight? I mean the engine, gearbox, diff, etc etc?

Dunno, but it would be fun to find out. At the very least I would suspect you would have to modify engine mounts and the tranny tunnel to accommodate the gear shift.

The wiring loom for the ECU and Transmission control and gauge cluster would be a headache.

[dom14]

Dunno, but it would be fun to find out. At the very least I would suspect you would have to modify engine mounts and the tranny tunnel to accommodate the gear shift.

The wiring loom for the ECU and Transmission control and gauge cluster would be a headache.

Sounds like PITA job mate.
Probably better off getting a GU as it is.
GU's are generally better built machines than GQ's, aren't they?

[garett]

my boss would swap his 4.8 gu for my gq if it had a turbo....
both are good, i just like my tank. the boss hates his auto cos it keeps doing solenoids. only real problem we've come across (never seen a 3l with a problem but heard about it a lot). and someone here might even have a fix.

a gu has a safety rating.... my motto is the other car is my crumple zone.
the gu is a bit more comfortable but the gq just looks way cooler. :groupwave:

[dom14]

my boss would swap his 4.8 gu for my gq if it had a turbo....
both are good, i just like my tank. the boss hates his auto cos it keeps doing solenoids. only real problem we've come across (never seen a 3l with a problem but heard about it a lot). and someone here might even have a fix.

a gu has a safety rating.... my motto is the other car is my crumple zone.
the gu is a bit more comfortable but the gq just looks way cooler. :groupwave:

Agreed. GQ looks way cooler. That's why I've been sticking with mine for past seven years. :)

Any ideas about the cause of high compression of the cylinder 1 mate?
It's 190psi, and should be around 170psi. It was 170psi last year and before.

[Patrol'n]

A couple of thoughts about the 4.8 into GQ, I noticed that GVM is only 2800kg on the RB30 powered GQ, whereas it is about 3150 or so on the 4.2, (makes sense due to the much heavier engine and gearbox) the heavier 4.8 and gearbox might seriously eat into the load capacity, since I couldn't see the rego authorities upping GVM on a 20 plus years old vehicle with an engine swap? (Might be wrong I spose). I've heard that the 4.8 is taller and might require a body lift to fit into a GQ.

Wouldn't even consider swapping my GQ for a GU, the GU might be better in a bunch of ways but I love the old girl too much, RB30 and all.

[dom14]

I did vapour test(CO test) and exhaust gas is definitely leaking into the coolant.

So, it's clear the head/head gasket is stuffed. Right now I'm wondering whether I should just get a fully reconditioned head as well as well as have the bottom end rebuilt.
I wonder whether the old bottom end might go kaput soon after installing a reconditioned head.

[Patrol'n]

If it's got a lot of Kay's on the bottom end, then seems like it would be a better (albeit a bit more expensive) idea to recon the whole engine, at least then the extra expense would see the engine last a long time and be reliable for remote touring too.

Would really be frustrating to do the top end only to have the bottom end fail shortly after, I guess it always comes down to budget though

[dom14]

If it's got a lot of Kay's on the bottom end, then seems like it would be a better (albeit a bit more expensive) idea to recon the whole engine, at least then the extra expense would see the engine last a long time and be reliable for remote touring too.

Would really be frustrating to do the top end only to have the bottom end fail shortly after, I guess it always comes down to budget though

Technically speaking, that's what has happened, sort of (not the bottom end but the top end).
Since, I did the cylinder head five years ago, I haven't done an enormous number km's on it.
But, I knew it's gonna fail prematurely at anytime.(Hence the reason I've been carrying STEAL SEAL with me all the time as well as head gasket).
Yeah, I even carried a spare head on some tours(didn't have that el cheapo head checked though).
I've been kinda half heartedly prepared for head/gasket failure in the middle of nowhere.
The reason was the head had a visible crack after the rebuild job(partial) at the rebuild shop.
I opted to not fix and used STEAL SEAL instead.

I've been told the bottom end of these RB30 NA engines are pretty solid unless somebody's done something really stupid to it.
I'm assuming neither me or the previous owner(s) have done anything stupid to harm the bottom end. :)

I personally think RB30 bottom end is solid, but the top end is crap(prone to failure too often than we would like to).
300+ k's on bottom end on NA setup is probably not a bad situation for these engines. :)

Bottom end rebuild at this stage is bit too much for me.
I'm gonna have to wait few more months before I have coins or time for that. :D

I"m keeping my fingers crossed. Bastard's been good to me(Of course, I looked after him/her). :D

[garett]

from what i was told the nissan head on the rb30's was good but the holden head was hit and miss, this was comparing a skyline to the vl, not sure which head went on the patrol. something about the holden head made somewhere else.
if your not going to do the bottom end at least check the bore and that the pistons don't slop in the cylinders.

[dom14]

from what i was told the nissan head on the rb30's was good but the holden head was hit and miss, this was comparing a skyline to the vl, not sure which head went on the patrol. something about the holden head made somewhere else.
if your not going to do the bottom end at least check the bore and that the pistons don't slop in the cylinders.

If that is the case, the spare cylinder head I have is a better one, 'cos it's a from a Skyline.
So far from the feeler gauge and ruler test, there is no warpage in the spare head, but I would have to have it
tested for cracks.

[mudnut]

If that is the case, the spare cylinder head I have is a better one, 'cos it's a from a Skyline.
So far from the feeler gauge and ruler test, there is no warpage in the spare head, but I would have to have it
tested for cracks.

The Holden header tank was also too low, which allowed air locks to form in the head and cause over-heating.

[garett]

The Holden header tank was also too low, which allowed air locks to form in the head and cause over-heating.

that may even be the root of the holden head issues. didn't pay too much attention as i'm more of a ford man LOL

[dom14]

that may even be the root of the holden head issues. didn't pay too much attention as i'm more of a ford man LOL

The debut VL RB30 fitted the radiator slightly below the top of the cylinder head, which caused gravity induced cavitation issues inside the cylinder head water jacket, which resulted in frequent cracks in the head. They fixed it in subsequent models by raising the radiator just above the cylinder head.