Page 1 of 3 123 LastLast
Results 1 to 10 of 23

Thread: '81 GS650G: Aftermarket oversize pistons hit head

  1. #1
    Join Date
    May 2018
    Location
    Vancouver, BC
    Posts
    27

    Default '81 GS650G: Aftermarket oversize pistons hit head

    Hello everyone,

    After a long abstinence here I'm looking for some knowledge and advise.
    I bought a cheap GS650G, lots of issues, came very close to quit, but actually made it my pandemic project and learning experience (along with toooo many $$$ spent, but hey, gained a lot of experience!)

    Here I was looking for oversize pistons...
    Here I was about to quit...

    Sooo a pandemic and gazillion years later here I am. Absolut total rebuild of the engine: balanced and polished crankshaft, all!! new bearings and gaskets, complete rebuild of the head, machined cylinders for oversize pistons and... the infamous cruzinimage 740ccm bigbore kit.

    Last weekend I finally wanted to put it all together and that's where i ran into issues where I'm looking for advices.

    Turns out the shape of the cruzinimage pistons are significantly different than the original ones. And thats where they hit the head. Here are some pictures to give you some idea. I probably need to clear around 5mm until the piston won't hit the head anymore....
    Collage.jpg

    Soooooo, what should/can I do???
    Vancouver, BC
    Suzuki GS 650G '81

  2. #2
    Join Date
    Oct 2020
    Location
    North Lincolnshire - UK .
    Posts
    143

    Default

    That's certainly not right .
    Depending on crown thickness you may be able to machine enough off to get the correct clearance and compression ratio or space the block but at a guess i'd say they sent you the wrong pistons.
    Last edited by zed1015; 05-13-2021 at 05:22 PM.
    Mikuni Viton Choke Plunger Seat Renewal.
    VITON Choke plunger seals .KAWASAKI Z1,Z900,Z650,Z1000,Z1R,SUZUKI GS1000,GSXR,RF | eBay

    Air Corrector Jets for Mikuni VM 24, 26 and 28mm carbs .

    https://www.ebay.co.uk/itm/254380193...84.m1555.l2649




  3. #3
    Join Date
    Jun 2008
    Location
    New Buffalo, Michigan 49117
    Posts
    5,718

    Default

    IOM: Those are so out sized, they could never be machined to fit.
    "Only fe' collected the old way, has any value." from His Majesty O'Keefe (1954 film)
    1982 GS1100G- road bike, body, seat and suspension modded
    1990 GSX750F-(1127cc '92 GSXR engine) track bike, much re-engineered
    1987 Honda CBR600F Hurricane; hooligan bike, restored

  4. #4
    Nessism's Avatar
    Nessism is offline Forum LongTimer GSResource Superstar
    Past Site Supporter
    Super Site Supporter
    Join Date
    Mar 2006
    Location
    Torrance, CA
    Posts
    33,710

    Default

    Are you sure the pistons are hitting the head? Could the valves be mistimed causing them to hit the pistons? If it's the pistons you might want to put some clay on the piston top so you can figure out where it's hitting.

  5. #5
    Join Date
    May 2018
    Location
    Vancouver, BC
    Posts
    27

    Default

    Thank you so far for your feedback.

    Quote Originally Posted by zed1015 View Post
    That's certainly not right .
    Depending on crown thickness you may be able to machine enough off to get the correct clearance and compression ratio or space the block but at a guess i'd say they sent you the wrong pistons.
    I'm not sure if I want to alter the pistons. Taking stuff off sounds kind of wrong.
    Unfortunately I bought these pistons a while ago. I will contact cruzinimage and see what they say.


    Quote Originally Posted by Buffalo Bill View Post
    IOM: Those are so out sized, they could never be machined to fit.
    Yes, I agree.

    Quote Originally Posted by Nessism View Post
    Are you sure the pistons are hitting the head? Could the valves be mistimed causing them to hit the pistons? If it's the pistons you might want to put some clay on the piston top so you can figure out where it's hitting.
    I'm 110% sure the pistons are hitting the head. I have not yet put in the cams therefor all the valves are fully in.
    Also no clay needed, the head leaves some tiny scratches on the piston. The problem is the big dome shaped "crown" of the pistons.

    https://www.thegsresources.com/_foru...38#post2603938 This post shows the difference where it becomes obvious.
    Vancouver, BC
    Suzuki GS 650G '81

  6. #6
    Join Date
    May 2008
    Location
    Brisbane, Queensland, Australia
    Posts
    1,470

    Default

    We had a GS drag race guy who worked in our shop and he would often cut a spacer base gasket out of aluminium road sign material to lower compression for turbo applications.

    Could be worth a try if you don't want to relieve the head or machine the pistons straight up.
    Current:
    Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha )

    Past:
    VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
    And a bunch of other crap Yamahas....

  7. #7
    Join Date
    Aug 2012
    Location
    Columbus, Ohio
    Posts
    3,601

    Default



    Quote Originally Posted by Berti View Post
    Well, I bought these pistons and this is the result...

    https://www.thegsresources.com/_foru...23#post2651323
    Awww man that SUCKS! They basically sold you a hemi head's domed piston, nearly identical to the stock 77-79 GS750 piston...
    I would DEFINITELY be contacting them to complain, at least so they pull them and don't screw over anyone else... Unless perhaps they actually did mix up and send you GS750 65mm stock hemi pistons vs big bore GS650 65mm closed chamber head pistons...
    MAJOR BUMMER...
    But... an 80+ 8v GS550 head may potentially work on that piston with minor dome machining around the perimeter. There's no way you could machine that big hemi dome down to the 650 dome shape/size, you'd cut through to the back side...

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  8. #8
    Join Date
    Aug 2012
    Location
    Columbus, Ohio
    Posts
    3,601

    Default

    So this isn't just a "stock photo" of a similar item... The dome design differences here is very plain to see, & CLEARLY will not work with the head designed to be used with the 650 piston...


    vs
    Last edited by Chuck78; 05-14-2021 at 12:43 AM.

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  9. #9
    Join Date
    Aug 2012
    Location
    Columbus, Ohio
    Posts
    3,601

    Default

    Berti, do you have a good accurate set of calipers to measure the piston skirts on those?
    You might be able to drop in a set of these Wiseco 740 pistons into those bores. I "might" possibly be conviced to sell one of my 2 spare sets. I was holding onto one for a friend who didn't have the $ to buy a set at the time, & has since had 2 kids and hasn't gotten around to putting the 650 top end on his 550... he's too busy with his kids, wife, job, PE175 Suzuki, & GS450E...

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  10. #10
    Join Date
    May 2018
    Location
    Vancouver, BC
    Posts
    27

    Default

    No, it's not a stock photo and the actually image. I sent cruzinimage an email explaining the situation. Let's see how they react. I'm not really happy with them.

    Now that my cylinder is already bored oversize I don't have too many options here.

    I don't actually want to go the road with extensive altering head/piston or even heads from different bikes. Just frustrated at the situation.

    If you let me know what exact measurements you need, I have ways to precisely measure!
    Vancouver, BC
    Suzuki GS 650G '81

Posting Permissions

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