pxctoday

» Log in

User Name:

Password:

Not a member yet?
Register Now!

» Find OEM Parts

» Jobs

» wallpapers

Results 1 to 7 of 7
  1. #1
    PWCToday Newbie
    Join Date
    May 2017
    Location
    Gainesville
    Posts
    3

    770 Engine Rebuild

    Hey guys,

    Last summer I had an exhaust stud break off, had to pull the motor and drill it out. In the process I decided I would re-seal the entire motor. I'm just getting around to putting it back together, and the concern was raised that since the crank came out of the crank case (so I could clean, inspect bearing, seals, ect.) that the crank would have to be re-built. Everything is in good shape, nothings burned and basically no wear at all.

    Just wanted some slightly more professional opinions.

    Is rebuilding the crank necessary, or can I just stick it back together as is? Are there any potential problems I might run in to if I just put it back together?

    Also, the forward piston is missing half the piston skirt, which was causing vibration when it was running. It doesn't seem to have caused any damage to the cylinder sleeve or uneven bearing wear. Any suggestion on where i could get a cheap (even used) replacement?

    I'm also having a problem getting the crank shaft off. I was careful not to bend it. I know its suppose to unthread, but dispite putting my manliest manly-ness into it, it won't budge. Does anyone know which was it turns, to make sure I'm not tightening, relative to how the engine sits in the ski?

    Any help would be greatly appreciated,
    Thanks in advance.
    Last edited by blank.stash; 06-01-2017 at 09:11 PM.

  2. #2
    PWCToday Guru
    Join Date
    Oct 2013
    Location
    Ohio
    Posts
    311

    Re: 770 Engine Rebuild

    You should not need to rebuild the crank if the only reason you took it apart was to fix the broken stud.

    However that missing piston skirt could signal an issue. Where did it go? Was it ground up by the crankshaft before it was spit out the exhaust ports? How can you tell there is no bearing wear? If this is the case, you may have damage to the bearings. Are there any gashes in the crankcase where pieces of the skirt may have gotten down there?

    Show us a photo of the broken piston.

    I may have a couple of standard 770 pistons. I will have to check.

    If you are talking about removing the coupler from the back of the engine, it unscrews normally, right hand thread.

    Do yuou have a service manual to follow during reassembly?
    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)

  3. #3
    Frequent Poster Associated98's Avatar
    Join Date
    May 2014
    Location
    Cottage Grove, MN
    Posts
    235

    Re: 770 Engine Rebuild

    If you look in my signature, 6 of those skis got crank up rebuilds. Some for broken pistons, others for melted pistons. Never once did I rebuild a crank. The only time I ever had any crank issues was with my first Daytona 640. Rod bearing exploded. Replaced the crank. Its not worth it to rebuild a crank. You need to press it apart, replace just about everything, and get it ultrasonically balanced. Total for all of this will be somewhere between $600 and a grand. Replacement cranks are found for less than $300 typically. Inspect the crank. Listen to the bearing, feel them spin. Then clean and clean and clean the crank, and just when you think your done, clean it again. You cannot be anal enough with a crank. Re inspect the bearings. Then lube all the bearings with your oil and re install. I have never had an engine fail after rebuilding (knocks on wood...) It all comes down to inspecting and pre lubing.

    As far as the piston, always replace all the pistons at the same time, especially if one is damaged like yours. I would recommend at least honing your cylinders. Install new piston rings on both pistons and seal it up. Pressure test your engine and if it passes your golden. Remember you will need to break in the new rings.
    Last edited by Associated98; 06-01-2017 at 11:20 PM.
    Own:
    99' TS770R
    98' TS1000R
    97' Daytona 1000
    Owned:
    94' Montego (my first) sold
    95' Daytona sold
    95' Daytona parted out
    95' Barracuda sold
    96' Montego sold
    96' Daytona (the one that got away...) sold
    96' Monte Carlo 900 sold
    97' Daytona 1000 clean and beautiful. You will be missed.

  4. #4
    PWCToday Newbie
    Join Date
    May 2017
    Location
    Gainesville
    Posts
    3

    Re: 770 Engine Rebuild

    Hey guys, thanks for responding.

    The previous owner had the engine apart ~3ish years ago because it didn't hold crank case pressure. When i got them he said he broke the piston skirt trying to get the retaining pin out. So the pieces never lived in the crank case. Why he didn't replace it? I don't know, seems kinda silly to me. I wanted to replace it while i had it out.

    No gouges or scratching in the crank case, no metal shavins on the bearing and they are all smooth.

    Do i need to worry about replacing the front or rear crank seal? They're both in good shape and I'd prefer to not if i don't have to.

    I've honed the cylinders, they cleaned up really nice. I had good compress (3 psi separation) before. The walls are smooth and clean.

    I need to measure the bore of the cylinder block, i think they're standard but I'm not sure. I'll take a pic when i get home.

    Thank, i really appreciate it. This has already been really helpful.

  5. #5
    Frequent Poster Associated98's Avatar
    Join Date
    May 2014
    Location
    Cottage Grove, MN
    Posts
    235

    Re: 770 Engine Rebuild

    If you already split the cases just replace them. They slide right over the ends of the crank and are cheap insurance against air leaks. Ive never re-used crank seals and never will.
    Own:
    99' TS770R
    98' TS1000R
    97' Daytona 1000
    Owned:
    94' Montego (my first) sold
    95' Daytona sold
    95' Daytona parted out
    95' Barracuda sold
    96' Montego sold
    96' Daytona (the one that got away...) sold
    96' Monte Carlo 900 sold
    97' Daytona 1000 clean and beautiful. You will be missed.

  6. #6
    PWCToday Newbie
    Join Date
    May 2017
    Location
    Gainesville
    Posts
    3

    Re: 770 Engine Rebuild

    To be able to change the rear crank case seal I have to remove the drive coupler, right? Well sadly she don't wanna budge... I put another coat to mystery oil on it so I'll check back in the morning, but it's not looking too good.

    Would you happen to know what the standard bore on the cylinders are? I'm measuring 83.8 but that doesn't seem right... I think my caliper reading skills are a little rusty.

    Here's a picture of the piston. The side of the skirt with the port(?) in it is what's broken off.
    20170602_190230.jpg

  7. #7
    PWCToday Guru
    Join Date
    Oct 2013
    Location
    Ohio
    Posts
    311

    Re: 770 Engine Rebuild

    When you put this all back together. Make SURE than you get the bearing locating pins and thrust ring back in correctly. They keep the bearings from spinning in the case. If they are in wrong, they can keep the case from pulling together tightly, causing air leaks, or they can come OUT and damage everything inside the engine.
    Last edited by hemmjo; 06-23-2017 at 10:57 AM.
    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)

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