Results 1 to 6 of 6
  1. #1
    silvercrxsir's Avatar
    Join Date
    Sep 2011
    Location
    ocala,fl
    Posts
    334
    +1
    8

    99 gp800 "loud" engine or am i overreacting

    Just rebuilt my whole top end and carve last month and had it out on the lake to break it in ran great but ended up having a lean condition in the front cyl and scored up the front cyl it went from 150 psi down to 120 so I had a machine shop hone the cylinder and ordered a new piston and crank seals and wrist pin bearing split the cases resealed it up and leakdown tested it and when I run it at idle its still loud has like a rattling kinda light knocking noise even though all the bearings seemed to be ok and smooth and if u rev it up it goes right away it idled smooth and has lots of power I did the trick where you put a long metal bar against your ear and place it all around on the motor to try to pinpoint it but no luck it sounds like its and coming through the carbs I'm running 93 octane 24:1 yamalube for the break-in I know my compression is around 30 psi higher than stock could this just be the reeds and the higher compression accountable for all this noise the motor was rebuilt with a complete top end kit from sbt with resleeved jugs I never dealt with them before so I don't know how well their machine work and fitting is I live in ocala flag so if there is anyone in the area that has more of an idea I can show it


  2. #2
    Is it possible that the bore was honed out for the new piston with too much clearance and it could be the piston knocking/rocking in the bore..? If it is, u have to be carefull that it doesn't nip up on a port. But hopefully it's not this.. I. Seen this alot in car/truck motors.

  3. #3
    silvercrxsir's Avatar
    Join Date
    Sep 2011
    Location
    ocala,fl
    Posts
    334
    +1
    8
    It's hard to say cause the machine shop lightly honed it and with the new piston and rings and its back up to 150 psi there's still some scoring in the cylinder but nothing major and I just pulled the cylinder again to inspect the new piston and noticed some light scoring marks on the new piston I'm wondering if this is caused by sbt sizing the pistons and cylinders incorrectly I tried to warranty the first time it happened but the lady there insisted it was caused by a lean condition even though everything had good lubrication and on this time around the motor has only run for less than 20 min all together at idle speed and the plugs were pulled twice to ensure fuel delivery my only other option seems to be to pull the pistons and jugs again and have a good machine shop inspect the sizing of the piston and bores this has to be in the top end somewhere since the lower rod bearings seem good and have no up or down play

  4. #4
    i think gettin them re checked will be the best thin to do.. then theres no "guessing" at least u have them appart partially.

    they may have sent u a std bore piston but u might have .25 or .5 over sized bores?

  5. #5
    silvercrxsir's Avatar
    Join Date
    Sep 2011
    Location
    ocala,fl
    Posts
    334
    +1
    8
    The pistons have .009" of clearance the book says .0035-.0045" and sbt recommend .005" so I have too much clearance hopefully the birth lady working there will.warranty this

  6. #6
    im glad we got it b4 it did any damage keep us posted

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. WTB - Parts Wanted. 99 SLH 700 engine or crank
    By bad brad 22 in forum Polaris Classifieds
    Replies: 0
    Last Post: 07-18-2014, 12:35 AM
  2. 2-Stroke '99 GP800 Engine rebuild
    By 99waverunner in forum Yamaha Projects & Build Threads
    Replies: 10
    Last Post: 02-21-2014, 01:39 PM
  3. 99 gp800 engine blown
    By bigtall in forum Yamaha Open Discussion
    Replies: 3
    Last Post: 09-06-2011, 03:22 PM
  4. 99 GP800 Seat Cover or new seat? Knife slash...
    By neowind in forum Yamaha PWC Performance (2-stroke)
    Replies: 1
    Last Post: 08-15-2009, 04:27 PM
  5. Hi temp warn, engine or ? bubbling
    By Hecyan in forum 4-Tec Performance
    Replies: 1
    Last Post: 06-26-2006, 06:09 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
  •