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Thread: Compression test results

  1. #1
    Legendary dom14's Avatar
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    Compression test results

    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.
    Last edited by dom14; 7th July 2017 at 06:18 PM.
    RB30, some 2-3 inch lift auxiliary LPG tanks
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  3. #2
    Expert Patrol'n's Avatar
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    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/co...cting-oil.html

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

    http://www.popularmechanics.com/cars...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...
    93 GQ wagon, RB30, extractors, 2 inch tough dog lift, 5 spd, A/T KO2 32's, steel winch bar, rated recovery points, red arc dual battery set up, rhino roof racks, UHF etc etc. Slow and steady might not win the race but it gets me there eventually...

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    dom14 (7th July 2017)

  5. #3
    Legendary dom14's Avatar
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    Quote Originally Posted by Patrol'n View Post
    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/co...cting-oil.html

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

    http://www.popularmechanics.com/cars...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.
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
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    Patrol Freak gaddy's Avatar
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    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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    dom14 (8th July 2017), GQtdauto (8th July 2017)

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    Patrol God mudnut's Avatar
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    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.
    My advice is: not to follow my advice.

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    Legendary dom14's Avatar
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    Quote Originally Posted by mudnut View Post
    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?
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
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    Legendary dom14's Avatar
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    Quote Originally Posted by gaddy View Post
    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.
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
    Cheetah Outreach

  11. #8
    Patrol God mudnut's Avatar
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    Quote Originally Posted by dom14 View Post
    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.
    My advice is: not to follow my advice.

  12. #9
    Legendary dom14's Avatar
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    Quote Originally Posted by mudnut View Post
    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?
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
    Cheetah Outreach

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    Patrol Freak garett's Avatar
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    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.
    if its worth doin its worth over doin

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