1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Help GSF250 GJ74A Low Compression/Rebuild the top-end HELP

Discussion in 'Suzuki 250cc In-line 4's' started by Alec, Oct 17, 2018.

  1. Alec

    Alec Active Member

    Messages:
    3
    Likes Received:
    1
    Trophy Points:
    173
    Joined:
    Mar 2, 2015
    Gender:
    Male
    Location:
    Glenelg SA
    My Bike:
    Suzuki Bandit Slingshot GSF250 92
    Suzuki Bandit GSF250N 1992

    Hey Guys,

    I have done a compression test on my bandit... The "dry" results are...
    1=100psi,
    2=110psi,
    3=110psi,
    4=105psi,

    I have not done a wet test. Although not expecting it to be within spec wet...

    According to http://www1.synapse.ne.jp/s-hara/bandit/ban-spece.html SPECS

    Compression Ratio: 12.5:1 kg/cm2 (177.791791 PSI)
    Compression pressure: 11.5-13.5 kg/cm2 (163.5684 - 192.0151PSI)

    -------------------------------------------------

    I am considering a Rebuild of the top end.

    This would include:
    - Honing the cylinders,
    - Lapping and re-seating the Valves
    - New piston rings.
    - Valve Clearances with possibly a few new Shims

    I have made a list of:
    Pistons
    Piston rings
    Shims
    Valves
    Springs
    Gaskets
    Piston Ring Compressor tool
    Valve Stem oil seals
    Total $342.78 (from Aliexpress)

    &

    Been quoted $440 labour for top-end: hone, seat and clearances with ultrasonic bath. (which means i would just have to replace piston heads, fit the rings and lube then close up.


    Questions I have are:

    1. Should I replace all the parts for the rebuild or reuse some?
    2. Should I do the work myself or take it to a shop? (I can get the tools for honing and lapping
    valves plus + many online video).
    3. Are larger piston rings required or just standard?
    4. Is there a checklist for rebuilding a top-end?
    5. Going to this extent should I also dissemble bottom end case?
    6. Are aftermarket valves and cylinder heads/rings any good?
    7. Would I have to replace the valve springs and oil seals.
    8. Do i have to dumb the oil and coolant in the process.

    I’m sure there are plenty more questions...

    I am just trying to understand the length and depth of the project before embarking on it... and whether it would be worth my while considering, it is an old bike and these commonly had the Odometer turned back.

    Any experienced or trained guidance would be very much appreciated.

    Thank you /Cheers
     
    • Like Like x 1
  2. Andych

    Andych Well-Known Member Premium Member

    Messages:
    2,259
    Likes Received:
    1,344
    Trophy Points:
    798
    Joined:
    Oct 6, 2016
    Gender:
    Male
    Location:
    Sydney
    My Bike:
    1987 Yamaha SRX250, Honda 1975 CB400F, Honda 1974 CB250 G5 ?
    You would be best served to pull the bike down fist to survey what needs to be done and take a lot of measurements etc.
    While dong some de-coke work on the head and re-lapping valve (dependant on condition) should be done you really shouldnt go buying new rings, pistons etc until such time as you know the real condition of what you have.
    Unless your pistons are excessively worn or have bits missing you may not need to replace them.. and if all you are doing is lightly honing the bores.. you shouldnt need oversize rings.. if the bores are within specs.. standard rings will be fine. You will still need to check end gaps though.
    You will get a lot more info on the condition of your engine by doing (or having done) a leak-down test.. that will tell you where the biggest issue is.
    Good luck with it all.
     
  3. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    I would be checking the valve clearances against specification first.
     
  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

    Messages:
    3,412
    Likes Received:
    1,948
    Trophy Points:
    898
    Joined:
    Jun 18, 2016
    Gender:
    Male
    Occupation:
    Panel Beater, Spray Painter, Custom Fabricator
    Location:
    Adelaide, South Australia
    My Bike:
    Yamaha's, 1990 FZR250R 3LN3 , 1986 XT250TS 57R , 1984 IT200L 43G
    Welcome to the forum,
    It's good to have another SA member here.

    Service limit for compression is 8.05kg/cm2 (114 psi) so you are only just under that
    You could try running some Threebond Super Engine Conditioner through it and see if it improve's at all.
    Repco at Somerton Park (just up the road from you) sell it for around $14 a can (it's kept behind the counter) so you'll have to ask for it.
    And as suggested above check your valve clearance's, it might be giving you slightly less compression due to carbon build up from tight clearance's etc
     
  5. Wozza

    Wozza Active Member

    Messages:
    361
    Likes Received:
    190
    Trophy Points:
    148
    Joined:
    Mar 21, 2017
    Gender:
    Male
    Location:
    South Australia
    My Bike:
    GB250
    +3 for valve clearance with the crap fuel(91) we run here in aus, valve seat regression is pretty common on mid to high k bikes
     
  6. Alec

    Alec Active Member

    Messages:
    3
    Likes Received:
    1
    Trophy Points:
    173
    Joined:
    Mar 2, 2015
    Gender:
    Male
    Location:
    Glenelg SA
    My Bike:
    Suzuki Bandit Slingshot GSF250 92
    Hey Again guys,

    I still ain't got her going yet. I found the ignition coils had bad resistance, So have ordered aftermarket coils. Currently..

    LS PRI 4.4 & SND 1407k
    RS PRI 4.4 & SND 1367K

    I can't remember if you need to dump coolant when doing valve clearances? I guess the best thing to do is them first before fitting new ignition coils or re-jetting and checking bowl levels.

    I fitted new o rings, needle jet, jet needle and changed size some jets from a kit; aliexpress styles. turns out it was the kit for the 50ccX4 model not 45ccX4. main jet being 15 not 10.5 from memory. Also having different slides diaphragms with two holes in them not just one. She fired up and was running differently. better i believe however once hot died. Which lead to me changing back alot back to stock. I now suspect it may have been the coils which caused heat die?? anyway the saga continues.

    thanks for your help

    XD
     
  7. AndrewStockham

    AndrewStockham Member

    Messages:
    8
    Likes Received:
    3
    Trophy Points:
    13
    Joined:
    Mar 19, 2019
    Gender:
    Male
    Location:
    Australia
    My Bike:
    95 GSX250F (project) and 2015 MT07-HO
    Hey Guys,
    First time poster, i am in a similar boat with low compression. it starts but obviously has no power and revs hang for a little bit before returning to idle
    I have a 95 Across that i have been restoring and I'm scratching my head at the moment. It has 50PSI compression across all four cylinders, hot, cold, wet or dry the compression stays the same. Below is all the things i have changed/checked:
    • New timing chain
    • Valve clearances good
    • lapped intake and exhaust valves,
    • new standard sized pistons
    • honed bores (measured by professional and within in limits)
    • pistons inspected within limits
    • new head gasket
    The timing is spot on in relation to the service manual. I have vacuum/carby balancing gauges connect it and it indicates late valve timing. my current thinking is what if i advanced the inlet cam by one tooth and see if that improves compression? how close is the valves to pistons? Is there a a large risk of the two coming into contact with just a single tooth of difference?

    Can someone please help me look for something i haven't done yet? Do i push it out side and set it on fire or take it to a mechanic and have them sort it out?
     
  8. Andych

    Andych Well-Known Member Premium Member

    Messages:
    2,259
    Likes Received:
    1,344
    Trophy Points:
    798
    Joined:
    Oct 6, 2016
    Gender:
    Male
    Location:
    Sydney
    My Bike:
    1987 Yamaha SRX250, Honda 1975 CB400F, Honda 1974 CB250 G5 ?
    Best to start your own Thread... then I am sure there will be plenty of assistance given.
     
  9. AndrewStockham

    AndrewStockham Member

    Messages:
    8
    Likes Received:
    3
    Trophy Points:
    13
    Joined:
    Mar 19, 2019
    Gender:
    Male
    Location:
    Australia
    My Bike:
    95 GSX250F (project) and 2015 MT07-HO
    • Like Like x 2

Share This Page