Help! '05 Ranger 500 carb engine with too much compression?
Close
Login to Your Account
PRC Polaris Ranger Club - Powered by vBulletin

Help! '05 Ranger 500 carb engine with too much compression?

This is a discussion on Help! '05 Ranger 500 carb engine with too much compression? within the Ranger Problems & Solutions forums, part of the Polaris Ranger Forums category; Hi, I rebuilt the top end on a 500 ranger for somebody I know. The intake side of the stock piston and cylinder were scored ...

Page 1 of 5 123 ... LastLast
Results 1 to 10 of 43
Like Tree15Likes

Thread: Help! '05 Ranger 500 carb engine with too much compression?

  1. #1
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times

    Help! '05 Ranger 500 carb engine with too much compression?

    Hi,

    I rebuilt the top end on a 500 ranger for somebody I know. The intake side of the stock piston and cylinder were scored badly. Come to find out the air boot had fallen apart and was sucking dirt straight into the engine.

    So bought an oem replacement wiseco piston and a niche cylinder. Put the engine together timed it (which with the engine installed in the frame is difficult to verify the pin on the cam is inline with the crank center line) , and adjusted the valves per the manual.

    Once together, it started right up and ran smoothly. I let it run for 20-30 minutes in my drive way, checked oil levels and coolant levels and everything seemed good.

    The owner took it home, then 3-4 days later called me and said it has no power and can't go as fast as it used to.

    I went out yesterday and checked some things, checked timing again, it was good. I advanced the cam and retarded the cam 1 pin either way and it was very obvious checking with a square that the original timing was correct.

    I went through the carb again, jets were clear and I assume the vacuum slide is operating as it should.

    Finally I tested the compression (ring gap was within spec before putting the engine together). Manual says 60-90 psi with decompressor operating. I was seeing 180-190 psi. I never took the cam out or messed with the decompressor mechanism so I don't know how that could all of a sudden not be working.

    Anybody have any ideas for me?

  2. #2
    BPS
    BPS is offline
    (Robbie) Veteran Member BPS's Avatar
    Join Date
    May 2018
    Location
    Brady, Texas
    Everything
    Posts
    156
    Member #
    72002
    Liked
    75 times
    I had the same problem on a 500 that I rebuilt that had very low compression due to dust inhalation. The only difference in my case was I had difficulty getting the engine to turn over after it was reassembled where yours was fine until a few days later. In my case the decompressor shaft had worn where is contacts the ball in the camshaft which was making it inoperable. It was like that before the rebuild but had no problems turning over because of the worn cylinder/rings.
    Rangerwhit and pyromedic like this.

  3. #3
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times
    Ahh so maybe the issue was already present, but the lack of compression from the worn rings covered it up?

    I assume you just replaced the cam with a new one?

  4. Remove Advertisements
    PRCForum.com
    Advertisements
     

  5. #4
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times
    Quote Originally Posted by BPS View Post
    I had the same problem on a 500 that I rebuilt that had very low compression due to dust inhalation. The only difference in my case was I had difficulty getting the engine to turn over after it was reassembled where yours was fine until a few days later. In my case the decompressor shaft had worn where is contacts the ball in the camshaft which was making it inoperable. It was like that before the rebuild but had no problems turning over because of the worn cylinder/rings.
    The starter did struggle to turn the engine over, the starter would pause when you turned the key, then it would start cranking. I just figured, freshly honed cylinder and fresh rings....but it would fire right up and seemed to run fine. Would just running premium gas make up for the issue? When we took it for a drive yesterday, it just sounded like it was missing and running poorly. But I guess what is really happening is it's pinging because the high compression.

    Any pointers for checking timing with the motor installed?

  6. #5
    BPS
    BPS is offline
    (Robbie) Veteran Member BPS's Avatar
    Join Date
    May 2018
    Location
    Brady, Texas
    Everything
    Posts
    156
    Member #
    72002
    Liked
    75 times
    Quote Originally Posted by wrench View Post
    The starter did struggle to turn the engine over, the starter would pause when you turned the key, then it would start cranking. I just figured, freshly honed cylinder and fresh rings....but it would fire right up and seemed to run fine. Would just running premium gas make up for the issue? When we took it for a drive yesterday, it just sounded like it was missing and running poorly. But I guess what is really happening is it's pinging because the high compression.

    Any pointers for checking timing with the motor installed?
    The decompressor only does its job on startup. Once the engine starts and rpms increase it retracts and the ball recedes back into the camshaft. On startup the ball pushes the exhaust valve open slightly to lower compression. If it's missing and running poorly that will be a separate problem. Getting that timing gear pointing straight up is kinda difficult with the motor installed because you can't get a good, straight line of sight. If you remove the timing gear and draw two perpendicular lines with a white oil pen it might help.

  7. #6
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times
    Quote Originally Posted by BPS View Post
    The decompressor only does its job on startup. Once the engine starts and rpms increase it retracts and the ball recedes back into the camshaft. On startup the ball pushes the exhaust valve open slightly to lower compression. If it's missing and running poorly that will be a separate problem. Getting that timing gear pointing straight up is kinda difficult with the motor installed because you can't get a good, straight line of sight. If you remove the timing gear and draw two perpendicular lines with a white oil pen it might help.
    Good call on the perpendicular lines.

  8. #7
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times
    So even if the decompressor is not operating correctly, the engine still starts and idles smooth. I have been through the carb twice and it was all clean. I have no idea what else to check. I am about 90% certain the time is correct.

  9. #8
    (Steve) 1000+ Member pyromedic's Avatar
    Join Date
    Apr 2015
    Location
    W. Of Asheville, NC. and N. FL
    Posts
    2,272
    Member #
    25939
    Liked
    1628 times
    Valves adjusted too loosely can cause hard cranking and low power becasue they aren't being lifted as high as they should be.
    2015 Polaris Ranger 570 Full Size XP
    Lock N Ride Polaris Pro Fit Glass Wiper ready Windshield
    Lock N Ride Polaris Pro Fit Glass Rear Window
    Lock N Ride Polaris Pro Fit Poly Roof
    Lock N Ride Polaris Pro Fit Poly Doors with Hinged Windows
    Polaris Windshield Wiper
    Polaris Battery Connection Kit
    Duraclutch
    KFI Front Lower Hitch Receiver
    Pawltector Parking Brake
    Trail Armor Skids
    Odyssey Battery
    SVI Traction Control
    SATV Power Steering
    Badland 3500# Winch
    KFI Winch Mount
    KFI 72" Snow Plow
    Sucool 48w LED back up lights

  10. #9
    1000+ Member Rangerwhit's Avatar
    Join Date
    Feb 2017
    Posts
    1,648
    Member #
    49442
    Liked
    439 times
    Valve lash and/or worn cam?
    2007 Ranger 500 (Carb)

  11. #10
    Starting Member wrench's Avatar
    Join Date
    Jun 2019
    Posts
    20
    Member #
    77199
    Liked
    2 times
    Valve lash is .006" all across the board. I have checked it 2-3 different times. Although I did not check both exhaust valves at the same time as the manual states to do. I am not sure why it matters if you do one or both.

Page 1 of 5 123 ... LastLast

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •