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Thread: 750/850 hybrid pistons search

  1. #1
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    Default 750/850 hybrid pistons search

    I am building a Suzuki GS750E with GS850G cilinder block and head.
    The cylinders fit the casings after some persuasion.
    I expected to buy some nice forged pistons but all i can find are the 69mm Wiseco´s for the 750 block.
    Then I saw a set of 71 mm GS1000 MTC Pistons at SPS. (no affiliations)
    It looks the same and the wrist pin should be 18mm for both.
    My biggest concern is if the compression ratio and the squish zone would be okay.
    I am shure someone has tried fitting 1000 pistons in a 850.
    Any good experiences ?
    Under no circumstances should both hands be removed from handlebars.
    (1977 owners manual)

  2. #2
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    I'd ask Nick at SPS first as he should know what fits off the shelf.
    Regardless of that though if the pistons fit the rods and the liners will bore to take the 71mm pistons the rest can be sorted using block spacers or a skim depending which way the pin to crown height differs, if at all ..
    Squish needs to be no less than 1mm.
    All relatively basic stuff when putting together a build motor..
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  3. #3
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    Thanks Zed,

    Just what i needed to know !
    The bore is no issue, the liners can easily take 2mm. more. (69mm original)
    I will contact Nick when he´s back.
    Under no circumstances should both hands be removed from handlebars.
    (1977 owners manual)

  4. #4
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    77-79 GS75 and all GS850 uses 16mm wrist pins and the GS1000 uses 18mm wrist pins. The 69mm Wiseco pistons should drop into the GS 850 block with just a light hone job.
    Last edited by TeamDar; 05-13-2021 at 11:49 AM.

  5. #5
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    Ah, my mistake; thanks for the warning.
    I have 2 cilinder blocks with the first overbore (0.50) so no 69mm Wiseco´s for me...
    Under no circumstances should both hands be removed from handlebars.
    (1977 owners manual)

  6. #6
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    He is absolutely correct, the pins are larger on the 1000.
    You need what I have 7 of, old MTC 72 mm GS850 pistons... Mine are not for sale, however! I thought I had bought the last set. Then due to a machine shop screwing up my valve job, I had severe detonation on one or two cylinders and destroyed one piston. Then another guy had come along and after reading of my pistons, contacted MTC and they ended up digging up another set. He held on to them and did nothing with them and then sold them to me after he lost interest...

    The best I could do for you is send you the blown up piston if you were interested in having JE Pistons or Carillo Rods / CP Pistons copy it and make you a custom batch.

    I'll eventually be building up another 920cc GS750 engine with this other set, and using the best 2 of 3 remaining pistons from the 1st set to build a 489cc GS400 using GS450, 850, or 1000 sleeves in GS425 cylinders and a ported GS425 head...

    I f'd up my shift forks in my current GS750 engine slightly, but it runs AWESOME with 850 cylinders pistons and cams, but if it gets harder and harder to downshift into 2nd & 1st (&3rd?), I may throw together the 920cc ported head Yoshimura Stage 1 cams VM29 smoothbore carbs top end... it'll once again likely be the fastest GS750 around..
    I already give my Ninja 750 / ZRX1100 / ZRX1200 buddies a real run for it with them trying to catch up to me in the twisties of Appalachian Southeastern Ohio and West Virginia on my old air cooled "dinosaur," and its plenty fast with this setup... Honestly I scratched my head when these guys on newer more advanced and larger displacement bikes shake their head when looking at my bike while commenting on how fast it is...lol! Maybe it's because I'm not afraid to rev it to the moon? I'm also severely addicted to high speed cornering on really twisty pavement in the remote Appalachian hills... Focus & practice goes a long way with that kind of drive

    Despite the current setup's pleasing performance, I have the Yosh cams, VM29 smoothbores, ported head, and 920 pistons/cylinder ready to go...just need to get Pearson Racing to weld up a crankshaft for me for extra strength & insurance against blowing it up...and I'll have the ultimate 8V GS750!
    Last edited by Chuck78; 05-25-2021 at 09:40 PM.

    '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

  7. #7
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    Hi Chuck,

    Thanks for the offer.
    I am gonna pass cause i don´t want to go over 71mm.
    Maybe i just use my old 750 bank and go for the Wiseco´s.
    I have a 850 cv head and vm 28mm. carbs so that should give it some flow.
    First thing will be welding the crank and put the cases together with new seals and cam chain.
    Sounds great driving around the twisting mountain roads.
    in Holland we use the twisting dike roads following the rivers and fields, no mountains in the low lands ;-)
    Under no circumstances should both hands be removed from handlebars.
    (1977 owners manual)

  8. #8
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    You can get Cruizin Image pistons for 1mm GS850 oversize, they are basically a near exact OEM piston copy, 870cc.

    Why don't you want to go over 71mm? I successfully ran 72mm in 850 cylinders for years until a bad valve job (car machine shop inexperience) wrecked one cylinder. Thicker walls left on 72mm vs Wiseco 60mm bored into 750 sleeves...
    850 +1.0mm pistons = 870cc FYI, nice grunt added.

    '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
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    Well, Cruisin image sells a set for 150 $ compared to 440 $ for a original 1mm oversize set.
    Not that the original set is available but the huge difference made me suspicious.
    There are no long term reviews, it seems to good to be true and cheap is often expensive.
    I might be wrong but i don't want to take any chances.
    Under no circumstances should both hands be removed from handlebars.
    (1977 owners manual)

  10. #10
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    Location
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    Aside from the alleged GS650 740cc big bore pistons, the other pistons that Cruizin Image sells as big bore kits are hugely popular amongst the Honda crowd, with greater reviews for reliability, quality, etc
    I have a set of 70 mm GS 850 Pistons from them new in box still, and they appear identical to OEM, which goes along with what a lot of other people across the internet in various makes of vintage Japanese bike forums have said as well.

    '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

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