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Gut Check- I Have Two Dead Cylinders

Discussion in 'Early CJ-5 and CJ-6 Tech' started by IRQVET, Jul 8, 2018.

  1. Jul 9, 2018
    IRQVET

    IRQVET Member

    Left Coast, with...
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    - I've owned this Jeep for 3 years and I bought it as a non-runner/ project vehicle.

    - Did the compression check to see what condition of the motor was in. I was hoping to get it to fire and get it running around my property before I dive into anything else needed during this project.

    - Rest of the Jeep is very solid. I can't speak for the gear box. If your curious about the condition, see my build thread so you have an idea of what I'm working with and what I've done:

    Some headway on the 67, slow and steady!

    As far as a leak down is concerned, what kind of tool or attachment would I need to go on my air compressor?
     
    Last edited: Jul 9, 2018
  2. Jul 9, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    You could rebuild it yourself. Difficult part - deciding what is needed and what is not.

    If you tear it down and do the work yourself, your local machine shop will probably recommend more than you need, since they benefit from your business and the CYA aspect.

    If you want the absolute best possible outcome, doing it yourself puts your evaluation into every step.

    Note that, if you buy a short or long block, your local shop will probably sell you a reman block that has been sourced from overseas (or across the border). This is not neccessarily a bad thing, but you should realize what you are getting.

    Make the calculation that benefits you most ...
     
    Vanguard likes this.
  3. Jul 9, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    30 psi is pretty darn bad. Does it run? Put it together as it is and drive it around. If you have oil fouling problems, add anti-foulers to the offending cylinders. Dorman Products - Search Results

    Run it. See what you've got.

    If it does not run, then you can maybe fit new rings after you hone the cylinders. Depends on what the oil pressure is.
     
  4. Jul 9, 2018
    45es

    45es Sponsor Sponsor

    Naches, WA
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    One hidden benefit if you decide on this option and you talk real nice to Chris (ITLKSEZ who lives close to Spokane) is, maybe he will let you come by and see the Fat Hippo project and Varg. :D
     
  5. Jul 10, 2018
    Alan28

    Alan28 Sponsor Sponsor

    Ch√Ętillon en...
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    I believe that your Jeep was running. Maybe better to sell it and buy a CJ in good condition, because the cost of repair can become high.
    Check with some members living around, it can be a good idea!
     
  6. Jul 11, 2018
    termin8ed

    termin8ed I didn't do it Staff Member Sponsor

    Mason, MI
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    On mine i was running on 2 cyl. Pulled the intake and the cam had 2 lobes worn down to nothing...

    I ended up rebuilding but probaly could have cleaned it up good and slapped a new cam, lifters on it and called it good
     
  7. Jul 11, 2018
    71CJ54WD

    71CJ54WD Member

    DC
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    Ive seen an engine make equally terrible numbers and then after soaking the cylinders in some solvents and oils the rings became springy again and it had perfect compression again for many years. You could have some stuck rings from sitting.
     
  8. Jul 11, 2018
    IRQVET

    IRQVET Member

    Left Coast, with...
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    You know what guys, I think I goofed. After watching more youtube videos on compression testing and leak down testing I think I know where I went wrong.

    I'm no mechanic, I think I said that ready somewhere. This is embarrassing to omit. It just dawned on me I screwed up the compression test. I'm 99% sure I forgot to repeat the process of bringing each piston to top dead center before testing each of the cylinders. I'll go ahead a re-do the compression test, see where I'm at. Then all call around to all the auto parts stores to see who rents out a leak down tester if the compression check goes tits up.

    Can anyone confirm what psi each cylinder should be at to be consider healthy? 90, 100, 120?

    Heres your sign.png
     
    Last edited: Jul 11, 2018
  9. Jul 11, 2018
    termin8ed

    termin8ed I didn't do it Staff Member Sponsor

    Mason, MI
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    Its not going to matter on compression if they are at top dead center. I usually let the engine spin about 4 times to get a good reading. Wide open throttle.
     
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  10. Jul 11, 2018
    termin8ed

    termin8ed I didn't do it Staff Member Sponsor

    Mason, MI
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    Leakdown, yes since you want the valves both closed
     
  11. Jul 11, 2018
    IRQVET

    IRQVET Member

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    The more I thought about it, it dawned on me I'm confusing the TDC thing is more for leakdown than compressing testing.
     
  12. Jul 11, 2018
    tarry99

    tarry99 Member Sponsor

    Northern California
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    Yep..........the key to a compression check is having the motor at operating temp...........all plugs out , battery charged , and then turning over the motor in a manner of repetition............meaning at the same speed and number of revolutions on each cylinder during the check............your looking for an average to compare so consistency is important.................

    Leak down at TDC.........in simple terms your just blowing a 100 psi or more in each hole looking for a leak.........the starting air pressure (psi) has to be the same at each cylinder before starting the test.......that normally will require an adjustment at the gauge prior to each test.......as your compressor builds air above that starting point.
    The second gauge will show a percentage of leak.......
     
    IRQVET likes this.
  13. Jul 12, 2018
    montanacj

    montanacj Sponsor Sponsor

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    IRQVET likes this.
  14. Jul 12, 2018
    Warloch

    Warloch Did you say Flattie??? Staff Member Sponsor

    Falcon, CO
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    On the compression test, your not looking for a 'specific' number per se, but I like to have them within about 10 -15% of each other. You have to realize that different builds will result in different compression in engines. I will say that a real 'low' as in under 90 across the board would cause me to look much deeper into things as a whole. Typically all the cylinders will not wear 'the same' so you will be able to tell when a motor is wearing out based on one or two being really out of synch with the others.

    Post what you get - your close to sea level so others should be able to help there. I like mine to be between 110 to 120 to call it a 'good motor'.
     
    IRQVET likes this.
  15. Jul 12, 2018
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
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    Checking in late. Re variance between gauge and cylinders. The 10% to 15% between cylinders is a good thing. Now, because many gauges are not calibrated and most out there are of the cheap sort I would not bet on the number shown on the gauge is the actual psi. The only way I know how to test a compresson gauge is to take it to a shop that has a "good" gauge on their air system and set their pressure to 50# and 100# and 150#.
    At each setting shoot air into your gauge and record the reading, from that plot a correction curve and keep it with the gauge. I've done the same with tire gauges. I own no less than 10 tire gauges (6 stick and 4 dial), none show the same pressure. Compression testers I own 3, none read the same.
     
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