Results 1 to 4 of 4
  1. #1

    Compression on Seadoo 717 with new top end

    I've got a 1996 Seadoo 717 SPX. I put a new top end in it and a used crank because the ski sat for a while with water in it. It's a SBT top end with the standard bore. I mixed the gas and oil at 50/1 and left the oil injection on as well. I completed the rebuild and decided to place the ski in the water and test it out. It ran fair for a couple of minutes, but then does nothing but foul plugs. I brought it back home and tested compression. 150 on the PTO side and 115 on the Mag side. Sorry I did not test compression before running it all together.

    So I decided to take the head off to see whats going on. Everything still looked good. Rings, cylinder sleeves, gaskets and pistons. I put the head back on and now both holes are at 120!! And yes I did re torque the bolts to 18 ft lbs. Please note that I used the same gaskets as less than 30 minutes was on them.

    Can anyone explain whats going on with the ski? When it was all tore apart I did clean the carbs. Well, just what I could service without buying a rebuild kit, so just the jets and needle/seats.

    Can someone please tell me what my next step should be? I am going to get another compression tester from Oreilys tomorrow to rule that out. But should I just drain the gas/oil mixture and run straight gas so it stops fouling plugs? I always thought this was best practice to help seat the rings. I thought twins should both have 150 ish for PSI. Any advice will help!

    Thanks,


  2. #2
    150 psi is normal compression.. And you should not reuse paper or metal gaskets (o-rings can be re-used).. 50/1 premix with oil injection should not foul plugs within a couple of minutes..

    You purchased a used crank, thus it has used crank seals.. And you have no idea of the orginial engines condition or issues..

    The engine compression can be effected by leaking gaskets, leaking seals, leaking rotary valve or leaking past the rings..

    Pressure test your engine and the rotary valve oil chamber..

    Remove Cylinders - Inspect pistons, rings, cylinders walls and check Piston to Cylinder clearance and install new gaskets..

    Inspect rotary valve cover clearance..

  3. #3
    My first problem was a crappy compression tester. I got a new one and both holes register at 130's. Ski runs great after I cleaned the fuel filters inside the carbs. It's probably a good idea to change the fuel lines all together, but for now cleaning the carbs fixed my problem.

  4. #4
    Tool Bag water worx's Avatar
    Join Date
    Aug 2006
    Location
    Sunny Fla
    Posts
    1,925
    +1
    66
    Quote Originally Posted by KYHI View Post
    150 psi is normal compression.. And you should not reuse paper or metal gaskets (o-rings can be re-used).. 50/1 premix with oil injection should not foul plugs within a couple of minutes..

    You purchased a used crank, thus it has used crank seals.. And you have no idea of the orginial engines condition or issues..

    The engine compression can be effected by leaking gaskets, leaking seals, leaking rotary valve or leaking past the rings..

    Pressure test your engine and the rotary valve oil chamber..

    Remove Cylinders - Inspect pistons, rings, cylinders walls and check Piston to Cylinder clearance and install new gaskets..

    Inspect rotary valve cover clearance..
    So your over here now talking about chit you know NOTHING about !!!

    The 720 does not have any metal or paper head gaskets.

    Here is a piece of advice before telling someone else how to fix things......You should know what you are talking about & I dont mean reading from a manual.

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. FS - Parts Seadoo 787, new top-end, less than 10hrs since pro-x pistons installed
    By vspec1 in forum Sea Doo Classifieds
    Replies: 0
    Last Post: 05-23-2016, 09:08 PM
  2. New top end in 1996' 780 SLT with engine in the hull?
    By Todd36 in forum Polaris PWC Performance
    Replies: 2
    Last Post: 05-03-2014, 06:30 PM
  3. Seadoo 787 New top end, BURNING THROUGH OIL !
    By topfli8979 in forum 2-Stroke Performance
    Replies: 7
    Last Post: 07-07-2013, 01:29 PM
  4. 99 gp800 new top end with a problem
    By silvercrxsir in forum Yamaha PWC Performance (2-stroke)
    Replies: 5
    Last Post: 04-18-2012, 04:20 PM
  5. new to doo looking @ 05 with new top end
    By firehawk in forum 4-Tec Performance
    Replies: 0
    Last Post: 04-16-2008, 08:58 PM

Posting Permissions

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