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Thread: Squish clearence

  1. #1
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
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    51

    Squish clearence

    I have a old suzuki project. Its a 73 gt 185. Factory specs are 49mm x 49mm bore and stroke. 7.0:1 compression made 21hp. I have 1mm OS pistions (twin cylinder two stroke) which would make 50mm x 49mm. Can I safely increase to the compression to say 10:1? I have measured the new oem gaskets base is .55mm head gasket measures 1.19mm. I measure and old heas gasket it was 1.00mm. I have asked around looking for some help. I know its not a 3 wheeler, so if theres a problem i will gladly remove. I know some of you guys on here are the best at this kind of information.

  2. #2
    Join Date
    Jul 2018
    Location
    TN
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    1,066
    Increasing compression can have the opposite effect on a two stroke. You gain power in a 4 stroke but you start losing power in a two stroke unless port size and port timing as well as the exhaust all work together. Not saying you can't do what you ask, just saying with 2 cycle, there's a law of diminishing return up to the point where you lose too much power on the compression stroke. Sounds crazy but I learned this tinkering with chainsaws and it's a fact.
    Nice thing about playing with head gaskets though, you can always put them back easily.

    Sorry I can't help you more specifically. Good luck.
    I was born and raised on Venus & I may be here a while.....

  3. #3
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
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    51
    Thats why im here. Lol It just seemed really low for compression. I was thinking if i could in theory get 9 more hp out of 3 more points? Im getting ready to put it back together. I thought I would ask. Be hard trying to find a diffrent size head gasket. I was planning on changing the base gaskets. I know that would change the port timing a lil. Just wanted some advice. Head would be easy to mill with 90 plug hole.

  4. #4
    Join Date
    Apr 2011
    Location
    Mexico
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    8,925
    Rather than get radical and make a mess as Gabriel eluded to I'd just mill 0.030" off the head, clean any casting slag at the base of the transfers and raise the exhaust port 1mm. You don't want high compression on that engine as it will probably kill your over-rev and make it feel peaky.

    Take a good look around the header flange of your pipe, some of the old stuff had messy welds in that area that could be smoothed out for a small gain.

    Make sure to pressure test the engine when you get it buttoned up
    It sucks to get old

  5. #5
    Join Date
    May 2006
    Location
    Not here
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    4,728
    There's a few of us GT fans here.

    Somebody else has a GT185 and my first street bike was a GT380. Sounded like a moped but was a quick little bike. Fun to ride and very reliable

    Hopefully Brendon or Knappy or somebody will chime in.

    Sent from my Z958 using Tapatalk

  6. #6
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
    --
    51
    Thank you all for the feed back. It ran pretty good before I took it apart ( only reason im fixing it ). The oil/premix pump wasnt working. I had premix in the tank 32:1. That pump feeds the main bearings and cylinders. I was worried about it running lean with the premix in the tank and no oil going to the main bearings. Took it apart and the oil pump shaft( teeth chewed) and kickstarter gear with the worm gear was broken in two pieces. Didnt see any other damage. I still not sure what caused it? Maybe the motor was siezed before i got it and they kicked the heck out of it and broke it. Or that oil pump locked up somehow but it seems to work by hand just fine. Not sure but i did read some problems out of dip sticks hitting something on the clutch side, mine hase already been removed with a regular plug and no threads in the case. Fits pretty good actually. It really didnt need a bore job had some shinny spots on the pistons and cyl walls with no scaring. It was like 60 bucks for new rings or 130 bucks for new pistons and rings. I didnt want to get radical with it. I just thought maybe a simple bump in compression might help out some. If i have to do all that ill prob just leave it alone. Unless you think milling the head .030 over would help. I cant get that done the same time I drop my cylinders off in a few days. But I really dont want to change the port timming. I have never done that before. I could definately prob clean and smooth the exhaust ports up. Esp if I can find a good you tube video. Lol
    Last edited by wildcatfan; 08-25-2018 at 11:33 AM. Reason: Forgot something

  7. #7
    Join Date
    May 2015
    Location
    San Diego, CA
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    1,606
    Suzuki2strokes.com is a good resource.

    I agree nearly word for word with El Camexicans post.....you don't want 10.1. 2 strokes are finicky with changes to the internals. Even cleaning the ports (smoothing) things out can alter riding characteristics. That is a nice little classic machine you have there. I personally wouldn't do anything that could potentially harm the street ability / characteristics of the bike.

    But check out suzuki2strokes.com. It's always nice to learn from others mistakes or success.

  8. #8
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
    --
    51
    I cecked the compression before i tore it down. It was running on and off on two cylinders and the plug was wet and getting fire so i assumed rings on that cylinder. I couldnt use the kickstarter because it was broken inside didnt know that yet for sure. I used the electric starter and forgot to pull that plug off the other cylinder and it fired up on that side. Lol Showed 130lbs running off the other cylinder. I unpluged the plug cap and hit the starter showed 100lbs after a few cranks thats all it would climb to. Checked the side that was running earlier it also had 100lbs. Is that high/low/ borderline? The problem ended up being the plug on that one side even though it looked new. I ended up b6hs plugs in it. One size hotter than oem. Ran just fine but i had to hold the throttle wide open to start but then reved up fine. Thinking i got a charging issue as well and prob a bad battery.

  9. #9
    Join Date
    Apr 2011
    Location
    Mexico
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    8,925
    Regarding your pre-mix VS injector pump, don't worry about getting oil directly to your crankshaft as it still gets there with pre-mix.

    I've always been leery of oil injector pumps. Even as recently as the late 80's I have personal experience with them failing. They are nice on a road bike though, but I don't like the risk factor of a fill light going out, or a mechanical mishap after the warrantee period is up.

    100 psi after repeated cranking with the carbs open sounds low. Are the pistons black below the rings? You'd need to find Suzuki's compression specs, but I would think no less than 120 psi and probably closer to 140 would be the spec. If it really is that low it might be contributing to your cylinders cutting out. Keep in mind that when a 2 stroke revs up and gets "On the pipe" so to speak it raises the cylinder pressure as the pipe acts like a turbo charger when it pulses back into the cylinder.

    Given the other issues you are having with the bike at the moment I would suggest you hold back on any modifications until you get it sorted out in stock form. There is nothing quite as frustrating as chasing a problem at the same time as you are making mods and second guessing yourself as to whether or not the mods are the cause of the problems. I'm the poster child for this sort of stupidity.
    It sucks to get old

  10. #10
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
    --
    51
    Yes, I completely agree with you. Im gonna just leave well enough alone. Get everything lined out. Yes, I did hold the throttle wide open durning the tests. And I can see some black below the rings. Im still kinda nervous about not using that pump at all. But i understand what your saying. It has four crank bearings and 3 seals. Let me see if i can upload a pic of the crank case so you can see. Thanks everyone for your input.

  11. #11
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
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    51

    Heres the bottom end.

    Look like it would oil the mains ok on premix only?
    Attached Thumbnails Attached Thumbnails 20180822_213120.jpg  

  12. #12
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
    --
    51
    You can see that oil seal blocks one bearing on the left cylinder. You would think that seal belongs in the middle.

  13. #13
    Join Date
    May 2006
    Location
    Not here
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    4,728
    I disconnected my injector pump and just carried a bottle of Spectro with me and mixed in the tank on fill ups. I rode it for a couple years like that.This was before the internet and when you took the advice of questionable "experts"

    Although... I did just read this tidbit so it warrants checking into before you take my advice.....looks like I was lucky I didn't melt mine down like that.

    Sent from my Z958 using Tapatalk

    Last edited by ironchop; 08-25-2018 at 10:45 PM.

  14. #14
    Join Date
    Apr 2011
    Location
    Mexico
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    8,925
    That right of center bearing looks like it might have a hard time getting oil from premixed gas, the others would be fine. I guess I’m changing my opinion of the need for an oil pump on that thing, but I’d still toss a little oil in the gas tank to be safe.
    It sucks to get old

  15. #15
    Join Date
    Dec 2016
    Location
    Northeastern Kentucky
    --
    51
    Quote Originally Posted by El Camexican View Post
    That right of center bearing looks like it might have a hard time getting oil from premixed gas, the others would be fine. I guess Im changing my opinion of the need for an oil pump on that thing, but Id still toss a little oil in the gas tank to be safe.
    Yea, I understand what you are saying. I have done the same in past myself, but they were single cylinder KE, KM, yamaha GT. I prob would have ran it anyway but the man i bought it off of warned me it would seize it up with the premix. He seemed pretty knowlegable and pointed the main bearing lines. Idk it looks the same to me about that bearing off center. Prob run the injector and like 70:1 premix?

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