504 cylinder pressures
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  1. #1
    Fellow Frogger!
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    Default 504 cylinder pressures

    I pulled my third (and last) 504 out of storage and started to prepare the laundry list of the items needed to convert it to Megasquirt. I was surprised when we took cylinder pressures, which were (cylinder 1 closest to the driver) 155 psi, 150 psi, 145 psi, 80 psi. The last one was indeed a surprise, when I let the engine turn for another 5 seconds it sort of crawled to 100 psi. I squirted a bit of oil and it went up to 120 psi. Valve measurements were on the button, and I am fairly sure I followed the correct procedure while checking the valves and cylinder pressures. The engine runs pretty smoothly, but it seems to lack low end torque. Exhaust gas analysis indicated a slightly rich mixture, but low hydrocarbons, even at high rpm's. Carbon monoxide was also pretty low at idle (1%), but spiked up to 7% at high rpm's. I was thinking that perhaps the valve is not seated well, but my mechanical ineptitude has been well documented. Is any other possibility immediately obvious to someone? Any suggestions and diagnostic methods will be greatly appreciated.

    Thanos

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    Last edited by Thanos; 19th October 2005 at 03:53 AM.

  2. #2
    1000+ Posts 504-504-504's Avatar
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    Default cylinder testing.

    Quote Originally Posted by Thanos
    I pulled my third (and last) 504 out of storage and started to prepare the laundry list of the items needed to convert it to Megasquirt. I was surprised when we took cylinder pressures, which were (cylinder 1 closest to the driver) 155 psi, 150 psi, 145 psi, 80 psi. The last one was indeed a surprise, when I let the engine turn for another 5 seconds it sort of crawled to 100 psi. I squirted a bit of oil and it went up to 120 psi. Valve measurements were on the button, and I am fairly sure I followed the correct procedure while checking the valves and cylinder pressures. The engine runs pretty smoothly, but it seems to lack low end torque. Exhaust gas analysis indicated a slightly rich mixture, but low hydrocarbons, even at high rpm's. Carbon monoxide was also pretty low at idle (1%), but spiked up to 7% at high rpm's. I was thinking that perhaps the valve is not seated well, but my mechanical ineptitude has been well documented. Is any other possibility immediately obvious to someone? Any suggestions and diagnostic methods will be greatly appreciated.

    Thanos
    Compressed air.
    Gut a spark plug, weld on a piece of pipe with airline fitting on other end.
    Cylinder under test at TDC firing stroke, first gear, handbrake on and wheels chocked. Pressurise the cylinder with compressed air and listen for air leaks at carburattor, exhaust pipe and oil filler.

    Paul,
    504-504-504,
    Northern Outpost.

  3. #3
    Fellow Frogger! PCOATES505's Avatar
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    How long has it been sitting since you last started it? Could be stuck rings.
    How was the snow mate?
    Pete

    I am gunna get another 403 on the road........one day

  4. #4
    1000+ Posts edgedweller's Avatar
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    Quote Originally Posted by Thanos
    but my mechanical ineptitude has been well documented.
    Thanos
    Yeah sure Thanos, we are all very sorry you are not a mechanical engineer, meanwhile you seem to put most of us in the shade.

    cheers ed ge

  5. #5
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    Quote Originally Posted by PCOATES505
    How long has it been sitting since you last started it? Could be stuck rings.
    How was the snow mate?
    Pete
    I was thinking along the same lines...

    The compression increased a little with a squirt of oil (which would indicate poor ring sealing) but I'd let it warm right up and take it for a drive and repeat the comp test before going any further...

  6. #6
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    Quote Originally Posted by edgedweller
    Yeah sure Thanos, we are all very sorry you are not a mechanical engineer, meanwhile you seem to put most of us in the shade.

    cheers ed ge
    Thank you for your kind words, Edge, but the only way I can put you guys in the shade is send you an umbrella.

    Thanos

    Quote Originally Posted by PCOATES505
    How long has it been sitting since you last started it? Could be stuck rings.
    Pete
    The engine had not been started for about 18 months, Pete. If it is stuck rings, do they ever come loose with use? I gave the car a pretty good workout on the twisties for 45 minutes hoping that this would be the case.
    The mechanic said that if it was stuck rings the compression would go up more when we sprayed oil, but I figured it was easy enough to try.

    Quote Originally Posted by PCOATES505
    How was the snow mate?
    Pete
    The snow was awesome for this time of year, firm and plenty of it so I had a great week. Except for the part when the Austrian Polizei decided they wanted 250 euro of my money for a minor speeding incident.

    Thanos

    Quote Originally Posted by mistareno
    I was thinking along the same lines...

    The compression increased a little with a squirt of oil (which would indicate poor ring sealing) but I'd let it warm right up and take it for a drive and repeat the comp test before going any further...
    Thank you for the suggestion. I took the drive already, so I will repeat the comp test and report. If it has gone up I will take another drive and repeat, as I do enjoy this type of repair.

    Thanos
    Last edited by Thanos; 19th October 2005 at 02:59 PM.

  7. #7
    1000+ Posts Wildebeest's Avatar
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    Default 504 cyl pressures.

    Quote Originally Posted by Thanos
    Thank you for your kind words, Edge, but the only way I can put you guys in the shade is send you an umbrella.

    Thanos



    The engine had not been started for about 18 months, Pete. If it is stuck rings, do they ever come loose with use? I gave the car a pretty good workout on the twisties for 45 minutes hoping that this would be the case.
    The mechanic said that if it was stuck rings the compression would go up more when we sprayed oil, but I figured it was easy enough to try.


    The snow was awesome for this time of year, firm and plenty of it so I had a great week. Except for the part when the Austrian Polizei decided they wanted 250 euro of my money for a minor speeding incident.

    Thanos



    Thank you for the suggestion. I took the drive already, so I will repeat the comp test and report. If it has gone up I will take another drive and repeat, as I do enjoy this type of repair.

    Thanos
    Thanos,
    Is there a possibility that fuel has washed the bore of the last cylinder checked, giving the low reading.

    After thoroughly warming the engine check the compression while the throttle is held wide open. But then you already knew this eh?

    A cylinder leak down test using the "SnapOn" equipment or similar is the way to go. The gauge will give a % readout. Also as previously posted you will be able to detect the leakage by listening at the [1] carb intake [open]. The [2]engine oil filler or dipstick tube and the [3] exhaust outlet.

    [1] Inlet valve leak.
    [2] Piston ring blowby.
    [3] Exhaust valve leak.

  8. #8
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    Quote Originally Posted by Wildebeest
    Thanos,

    After thoroughly warming the engine check the compression while the throttle is held wide open. But then you already knew this eh?
    That is the way it was done.

    Quote Originally Posted by Wildebeest
    Thanos,

    A cylinder leak down test using the "SnapOn" equipment or similar is the way to go. The gauge will give a % readout. Also as previously posted you will be able to detect the leakage by listening at the [1] carb intake [open]. The [2]engine oil filler or dipstick tube and the [3] exhaust outlet.

    [1] Inlet valve leak.
    [2] Piston ring blowby.
    [3] Exhaust valve leak.
    I will take this information to my mechanic and see if he has the instrument. Thank you for the thorough explanation.

  9. #9
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    Quote Originally Posted by 504-504-504
    Compressed air.
    Gut a spark plug, weld on a piece of pipe with airline fitting on other end.
    Cylinder under test at TDC firing stroke, first gear, handbrake on and wheels chocked. Pressurise the cylinder with compressed air and listen for air leaks at carburattor, exhaust pipe and oil filler.

    Paul,
    504-504-504,
    Northern Outpost.
    Thank you, Paul. Somehow, I missed your post earlier.

    Thanos

  10. #10
    Fellow Frogger! 123abc's Avatar
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    try loosening all the head bolts, dont remove them, just back them off, (AND DONT MOVE THE HEAD UNDER ANY CIRCUMSTANCES), then put a drip of oil around the washers and down the bolt shanks, then re-tension useing the correct patern and tourqe, also after this re-check valve clearances, they may have closed a few thou. because the head may have pulled down more once retightened.

    sometimes gaskets will settle over time after not being used for a while.

  11. #11
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    Quote Originally Posted by 123abc
    try loosening all the head bolts, dont remove them, just back them off, (AND DONT MOVE THE HEAD UNDER ANY CIRCUMSTANCES), then put a drip of oil around the washers and down the bolt shanks, then re-tension useing the correct patern and tourqe, also after this re-check valve clearances, they may have closed a few thou. because the head may have pulled down more once retightened.

    sometimes gaskets will settle over time after not being used for a while.
    Will give it a shot, thank you.

    Thanos

  12. #12
    Tadpole
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    Default 504 cylinder pressure

    it should be 11Kg/cm2 whith 1 Kg/ cm2 diffrence

  13. #13
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    Quote Originally Posted by 505 turbot inj
    it should be 11Kg/cm2 whith 1 Kg/ cm2 diffrence
    Thank you, I also saw the 11 bar (which works out to around 160 psi)reference in the workshop manual. And BTW, following the advice I received here, I took it to the hill and gave it a good work-out near red line for forty five minutes, then drove it in a "spirited" fashion for another 150 km and the cylinder pressure is now 155 psi, same as the other cylinders. If all fixes were as easy!

    Thanos

  14. #14
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    How long has it been sitting since you last started it? Could be stuck rings.
    How was the snow mate?
    Pete
    Lots of interesting information in this thread. Pete, what do you mean by stuck rings and how does this affect compression?

    Cheers,

    Matt.
    On the internet, no one knows that you are only wearing a fez.

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