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Compression test results -- opinions?

Discussion in 'The Garage' started by shewheeler, Apr 12, 2004.

  1. shewheeler

    shewheeler 1/2 ton status

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    Apparently, I have a bad valve or somethin' goin' on that's gonna require some major work no matter how much I try to convince myself otherwise /forums/images/graemlins/crazy.gif I haven't had any other tests done to narrow down the exact cause. Basically, I know nothing about any of this so that's why I'm asking /forums/images/graemlins/dunno.gif

    The numbers:
    #1 - 61 lbs.
    #2 - 120 lbs.
    #3 - 110 lbs.
    #4 - 120 lbs.
    #5 - 119 lbs.
    #6 - 120 lbs.
    #7 - 120 lbs.
    #8 - 111 lbs.

    A little more info here

    #1, #3 and #8 look not so good to me, but are the others that much better? Would it be worth spending the time/money on this motor? I know it's not the original motor, but I don't know how many miles are on it or when it was swapped in.

    Thoughts? Opinions?

    Thanks /forums/images/graemlins/thumb.gif
     
  2. Beast388

    Beast388 1/2 ton status

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    Well, obviously something is amiss in cyl. #1. The others are all close enough that I wouldn't worry too much about them.

    Somewhere, you are leaking compression. That could come from a burnt valve, bad head gasket, crack in the head or block, broken valvespring, broken piston or bad rings, etc etc.

    Is there any steam or white smoke coming from the exhaust? Any coolant in the oil, or oil in the coolant? Any funny noises? /forums/images/graemlins/thinking.gif
     
  3. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Are there any other symptoms along with the bad compression reading on number one? Such as popping in the exhaust or carb? Those symptoms would also go along with bad valves. How about oil in the water or water in the oil? These would suggest a bad head gasket or cracked head maybe. How about fuel in the oil? This would suggest bad rings or scored cylinder. Just some suggestions as to how to diagnose the problem further.
     
  4. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    Was the test run dry or wet? Either way you should have got similar numbers, just the wet is usually higher by a few pounds. Regardless, you are right, major work is needed. #1 is at half of the rest of the cylinders. So its either Rings, burned valves, or a blown head gasket. Good way to check is to run a cylinder leakdown test. Pretty similar to the compression test, except you are filling the cylinder with air and measuring how much leaks out and where from. Listen to where the air is escaping from and you should have a pretty good idea what the problem is. Air escaping from the exhaust is an indication of a burnt/bent exhaust Valve. Air from the Carb/throttle body and you would be looking at a bent/burnt intake valve. Pop the oil fill cap off the valve cover and If you hear air escaping there you probably got some wiped out rings. The other thing that could be happening is a bubbling to the cooling system if the leak is at the head gasket. That would usualy be found before the leakdown with a loss of coolent and possibly fouled plug along with milky oil.

    Its a good place to start, before tearing the engine out. You may just need to pull the heads for a burnt/bent valve.
     
  5. shewheeler

    shewheeler 1/2 ton status

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    [ QUOTE ]
    Is there any steam or white smoke coming from the exhaust? Any coolant in the oil, or oil in the coolant? Any funny noises?

    [/ QUOTE ]

    No steam or white smoke and no funny noises other than popping from the exhaust (on the driver's side only)

    [ QUOTE ]
    Was the test run dry or wet?

    [/ QUOTE ]

    Dry.

    My truck has always run pretty crappy (usually manifesting as a "pinging" problem), but it has never burned oil or given me any other problems other than a general lack of power and that incessant popping /forums/images/graemlins/doah.gif

    The bottom line is that it's gonna need some major work and for me that usually means major $$$. To further diagnose the problem, I will have to take it to a shop and I would also probably have to pay someone to take the heads off and then reinstall them. I could probably get a break on the actual valve job (if that's what it ends up needing).

    I'm wondering if this motor is worth putting the effort into or if I should just suck it up and throw some more cash at the POS for a new motor? /forums/images/graemlins/1zhelp.gif
     
  6. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    Yes its going to cost $$$ to fix. But If you did the compression test, you can do a leakdown test. Fittings and Gauges and hook it up to a air compressor. If you don't have a compressor take it to a buddy that does. Trust me, you will save money in the long run. If you pin point the problem and then take it to a shop just think of the diagnostic time you saved. The popping could just be from the leak from the #1 cylinder popping through a tweaked valve.
     
  7. unclematty

    unclematty 1/2 ton status

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    good plan, but you forgot to loosen the nuts that hold the rocker armsdown on that cylinder, otherwise you may get an erronious result (just make sure the valves are closed all the way) /forums/images/graemlins/hack.gif /forums/images/graemlins/weld.gif /forums/images/graemlins/grind.gif.
     
  8. kennyw

    kennyw N9PHW Premium Member

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    How about another low buck option? Pull your motor and re-ring it with all new gaskets and re-build the heads. Re-ring kits are about $100 for a small block chevy, you already have an offer on the nor-cal site for help with pulling the motor and possibly even redoing the heads. This way things could be put back together cheap and done right (compared to RTV carb gaskets). This would also help avoid the problem of rebuilding the heads and causing problems with the rings later.
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Cheryle, just get someone to help get the heads off then bring them to me. /forums/images/graemlins/thumb.gif
     
  10. shewheeler

    shewheeler 1/2 ton status

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    [ QUOTE ]
    Cheryle, just get someone to help get the heads off then bring them to me. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Sheesh, you make it sound so easy... like I got some kinda line forming to help me /forums/images/graemlins/doah.gif

    I haven't decided what I wanna do yet /forums/images/graemlins/1zhelp.gif
     
  11. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I will make this easier for you. I will come down and help you take the heads off. I have done it before and I can do it again. The pizza and soda is on you though. /forums/images/graemlins/deal.gif I think I could help you on the 25th of this month if thats not too late for you. I figure this isn't your DD so time isn't that important.
     
  12. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    [ QUOTE ]
    (usually manifesting as a "pinging" problem),

    [/ QUOTE ]

    That sounds like my heads before I replaced them. Would ping no matter what I did, wasn't gears too high and lugging ping, wasn't timing ping , wasn't bad gas ping, just constant ping after warmup. Alls well now with replacement heads, old ones had several burnt valves as the PO overheated it at some point and most heads from mid 70's on were thinwall castings prone to cracking . If 4x4high wants to help let him. Heads aren't that bad , hardest part is reaching into engine compartment of lifted trucks /forums/images/graemlins/k5.gif
     
  13. MarcS

    MarcS 1/2 ton status

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    Pull the spark plug out to see if there is any oil or water on it. It probally won't look to good anyway because of the low compression but it may help rule out rings or cracks. Then take the valve cover off and check the valve springs are not cracked/broken. Also check to see if you can spin the pushrods going to the rocker arms or if the rocker arms came loose. These are easy and free ways to diagnose the problem. Don't go through removing the head just yet. /forums/images/graemlins/cool.gifIt may only be a spring.
     
  14. shewheeler

    shewheeler 1/2 ton status

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    [ QUOTE ]
    I will make this easier for you. I will come down and help you take the heads off. I have done it before and I can do it again. The pizza and soda is on you though. /forums/images/graemlins/deal.gif I think I could help you on the 25th of this month if thats not too late for you. I figure this isn't your DD so time isn't that important.

    [/ QUOTE ]

    HAHA... it's ok - I didn't mean to guilt you into helpin' /forums/images/graemlins/whistling.gif There's no rush on this as the truck still runs and I can use it if I need to make a dump run or whatever. I'll let you know about the 25th, but I'm not sure what I'm gonna do yet /forums/images/graemlins/crazy.gif

    [ QUOTE ]
    That sounds like my heads before I replaced them. Would ping no matter what I did, wasn't gears too high and lugging ping, wasn't timing ping , wasn't bad gas ping, just constant ping after warmup

    [/ QUOTE ]

    Wow! That's good to know cause it pings no matter what I've had done to it and I was beginning to think I was crazy and/or everyone was a lousy mechanic /forums/images/graemlins/doah.gif

    [ QUOTE ]
    Pull the spark plug out to see if there is any oil or water on it. It probally won't look to good anyway because of the low compression but it may help rule out rings or cracks. Then take the valve cover off and check the valve springs are not cracked/broken. Also check to see if you can spin the pushrods going to the rocker arms or if the rocker arms came loose. These are easy and free ways to diagnose the problem. Don't go through removing the head just yet. It may only be a spring.

    [/ QUOTE ]

    The plug was pulled when they did the compression check and the plug in #1 looked surprisingly clean considering the lack of compression. No water, no oil and not black.
     
  15. kennyw

    kennyw N9PHW Premium Member

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    [ QUOTE ]
    The plug was pulled when they did the compression check and the plug in #1 looked surprisingly clean considering the lack of compression. No water, no oil and not black.

    [/ QUOTE ]

    That is actually a sign of water getting into the chamber (spark plug being exceptionally clean). So good chance you have the typical cracked head... I think my truck has the same problem but I have been driving it that way for 2 years /forums/images/graemlins/whistling.gif /forums/images/graemlins/doah.gif I guess it is time to get something done about it though.
     
  16. Beast388

    Beast388 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    The plug was pulled when they did the compression check and the plug in #1 looked surprisingly clean considering the lack of compression. No water, no oil and not black.

    [/ QUOTE ]

    That is actually a sign of water getting into the chamber (spark plug being exceptionally clean). So good chance you have the typical cracked head... I think my truck has the same problem but I have been driving it that way for 2 years /forums/images/graemlins/whistling.gif /forums/images/graemlins/doah.gif I guess it is time to get something done about it though.

    [/ QUOTE ]

    When I cracked the head on my old 350, I had a good amount of white smoke/steam coming out of the exhaust. When I tore the head off, the piston, combusion chamber, and spark plug were all nice and "steam cleaned"! /forums/images/graemlins/doah.gif It was very easy to see the crack in the head too. /forums/images/graemlins/doah.gif /forums/images/graemlins/yikes.gif
     

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