At what point would you consider a rebuild??
pxctoday

» Log in

User Name:

Password:

Not a member yet?
Register Now!

» Find OEM Parts

» Jobs

» wallpapers

Results 1 to 9 of 9
  1. #1
    PWCToday Newbie GarryG's Avatar
    Join Date
    Mar 2018
    Location
    Mellons Bay, New Zealand
    Posts
    26

    At what point would you consider a rebuild??

    I have a '99 Waverunner XL760. At the moment it runs great and not showing any issues, however 2 years ago the compression was showing 140/150 psi. This was done by a service centre. I borrowed a compression tester from a colleague at work and checked it yesterday (don't know if this has been calibrated), anyway, it is showing 120/130 psi.

    So the question arises....When should I consider a top-end rebuild?

    All feedback appreciated.

    Cheers Garry

  2. #2
    PWCToday.com Is My Home Away From Home JSNate's Avatar
    Join Date
    Apr 2010
    Location
    Michigan
    Age
    55
    Posts
    4,112

    Re: At what point would you consider a rebuild??

    As compression continues to deteriorate, it will take longer to start and performance will suffer. What is most concerning is the disparity between the two cylinders. 10 PSI difference is significant and indicates that one cylinder may have scoring or a damaged ring. A top end is easy to do. Particularity if it does not need a bore. You may be able to get good, even compression with a new set of rings and gaskets.
    Last edited by JSNate; 02-21-2019 at 03:50 PM.

  3. #3
    Top Dog wire4money's Avatar
    Join Date
    Aug 2008
    Location
    Central Oregon
    Age
    45
    Posts
    1,621

    Re: At what point would you consider a rebuild??

    I believe Yamaha staggers compression, so a 10 psi difference is normal. IIRC, the rear is lower. I would not put too much thought into different numbers using different gauges. If it runs good, run it.

  4. #4
    PWCToday Guru
    Join Date
    Oct 2013
    Location
    Ohio
    Posts
    472

    Re: At what point would you consider a rebuild??

    Did you do your compression test with the throttle wide open? if you do it will the throttle closed your numbers may be lower.

    Get one of those little inspection cameras, like used for looking into walls, take a look in the cylinders for damage.
    2, 1998 TS 770 L, restored and running great. (Except for the one with engine that SBT put the WRONG crankshaft bearing into and is now sitting as I collect repair parts)

  5. #5
    PWCToday Newbie GarryG's Avatar
    Join Date
    Mar 2018
    Location
    Mellons Bay, New Zealand
    Posts
    26

    Re: At what point would you consider a rebuild??

    Quote Originally Posted by hemmjo View Post
    Did you do your compression test with the throttle wide open? if you do it will the throttle closed your numbers may be lower.

    Get one of those little inspection cameras, like used for looking into walls, take a look in the cylinders for damage.
    Was just a push on gauge, so didn't have enough hands I just pushed on the top and turned the starter, so no throttle.

  6. #6
    PWCToday Newbie GarryG's Avatar
    Join Date
    Mar 2018
    Location
    Mellons Bay, New Zealand
    Posts
    26

    Re: At what point would you consider a rebuild??

    I have been told that the cmpression is staggered, so not to bothered about the difference.... Might try it again after reading Hemmjo's comments... Cheers

  7. #7
    PWCToday.com Is My Home Away From Home john zigler's Avatar
    Join Date
    Mar 2003
    Location
    wisconsin
    Age
    52
    Posts
    8,692

    Re: At what point would you consider a rebuild??

    If it runs fine, just ride it. I am sure you'll be good for a long time.
    RCJS also doing business as WATCON
    608-743-1305 9am to 5pm CST m-f
    email watcon@watcon.com

    Please visit our web sites

    new parts / products / services www.watcon.com
    used parts www.rockcountyjetski.webs.com
    thank you

    Please check out and like WATCON on Facebook

  8. #8
    Top Dog Benflynn's Avatar
    Join Date
    Aug 2015
    Location
    Birmingham
    Posts
    1,785

    Re: At what point would you consider a rebuild??

    U can take the head off pretty easy and see what's going on down there, anyways you want to rebuild right before or right after it breaks

  9. #9
    PWCToday.com Is My Home Away From Home JSNate's Avatar
    Join Date
    Apr 2010
    Location
    Michigan
    Age
    55
    Posts
    4,112

    Re: At what point would you consider a rebuild??

    Quote Originally Posted by GarryG View Post
    I have been told that the cmpression is staggered, so not to bothered about the difference.... Might try it again after reading Hemmjo's comments... Cheers

    I've done some research regarding some 760 engines Yamaha installed in sit down PWC in that era. And I was surprised to find information on "staggered compression" on some of the 760's built. I could not find information on how it was attained with the engineering/design of the 760. I assume that it most likely comes from the cylinder head squish cut.? But, information did state that a 5 PSI difference is considered "normal" on these engines.

    Any 760 or 701 I've worked on/modified always had even compression. So, I've never witnessed it first hand. I am glad that I came across your thread and learned something I was not aware of. I am currenlty running a ported 760 in one of my AM hulls and with a Pro-Tec head, compression is even at 183 PSI. I have another 760 lined up for my next build and that engine is stock with compression at 150/150 PSI.

    Also, I too have found a difference between brands and quality of gauges that will read lower PSI than a better gauge. If she starts easily and runs strongly, you are probably fine and good to go.

    Good luck and have fun!
    Last edited by JSNate; 02-23-2019 at 11:34 AM.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBadvanced CMPS v4.2.0