Suzuki GT380 Top End Rebuild Project

Discussion in 'Motorcycles' started by alexwlwsn, Dec 2, 2019.

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  1. alexwlwsn

    alexwlwsn Gold Member

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    Dropped off my fresh center cylinder at the shop today so hopefully late this week we'll be hearing the good news that it's finished.

    Also, rolled the old girl out of the shed to take some actual photos.

    IMG_20191228_144141.jpg IMG_20191228_144154.jpg IMG_20191228_144219.jpg IMG_20191228_144226.jpg IMG_20191228_144329.jpg
     
    alexwlwsn, via a mobile device, Dec 28, 2019
    #21
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  2. alexwlwsn

    alexwlwsn Gold Member

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    The weekend of assembly has come! Picked up my cylinders Saturday and spent maybe 2-3hrs on both Saturday and Sunday.

    Saturday I was able to assemble the pistons/rings/rods into their homes on the block. It wasn't nearly the level of effort that a car takes so I was able to pretty quickly.
    IMG_20200104_151358.jpg

    Rings came gapped but I still checked them all. The tolerance is very very tight.

    IMG_20200104_151210.jpg

    Then on went the newly bored and honed cylinder jugs.

    IMG_20200104_153605.jpg

    The nuts at the base likely have a torque spec... but I felt that good n tight worked for this case. I have no idea how a torque wrench would have fit into that area anyway.

    IMG_20200104_161439.jpg

    IMG_20200104_161550.jpg

    IMG_20200105_120524.jpg

    IMG_20200105_124516.jpg

    Once it was all together I attempted to start it, but could only get it to make noise by spraying carb cleaner into the air inlet of the carbs. I'm not sure if it's getting too much fuel, too little, or what. It's getting spark for sure and there's air in the atmosphere so I assume it's an issue with fuel. I guess the next steps are pulling the carbs back out and giving them a better look! I know people say that the GT380 runs best when the carbs are super super clean so an overnight soak in some carb cleaner might be the next step I need to take.

    Here's the little fart I got... Sounds like it's going to be pretty intense once it's actually running right.



    Time to read about carburetors and pull them back apart again!
     
    Last edited: Jan 5, 2020
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  3. alexwlwsn

    alexwlwsn Gold Member

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    Figured out what is likely the cause of my no-start. When turning the motor over I noticed after that initial startup I had, I never got spark again. Looked at the 1 fuse on the entire bike and it was fine, checked over the coils and, well, from the outside they looked okay. Then pulled the points cover off the bike to dig in there. I did a visual inspection to see if they were corroded and they seemed clean enough. Upon further inspection though... the center bolt that rotates the points lobe (don't know the real name) spun freely. It should be attached to the crankshaft by gear so obviously that wasn't right! Spinning it by hand caused the plugs to spark so at least we know we're still getting spark.

    Turns out in 1972 alone they used a plastic gear for this connection, presumably to make the engine quiet (according to other forums) and in 1973 it seems they strengthened it to a nylon one. Still need to research if I can utilize a later 1973 and beyond nylon gear but they seem easy enough to order on eBay.

    Here's the center of the points that is spinning freely:

    screenshot-photos.google.com-2020.01.07-09_00_00.png

    Found a technical service bulletin where they noted the switch from a plastic gear to a nylon gear:
    screenshot-www.ozebook.com-2020.01.07-09_00_54.png

    Replacement part
    screenshot-www.ebay.com-2020.01.07-08_46_01.png

    This adds a few dollars to the overall rebuild but at the end of the day I'm still in it for sub-$500 if I'm doing my math right.
     
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  4. Easter Bunny

    Easter Bunny Professional Engineer Silver Member

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    while i would have done the same thing with regards to bolting the cylinders on for future reference, you can use one of those crows foot socket attachments on your torque wrench, then you have to do some simple math with the overall length to determine what to set the wrench to.
     
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  5. alexwlwsn

    alexwlwsn Gold Member

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    Yeah I saw that as an option but that would've been real annoying to calculate. It is also real tight between those cylinders and man I wasn't about to go buy a new torque wrench to get a $200 bike's motors torque'd to perfect spec.
     
  6. Al3xRats

    Al3xRats Silver Member

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    Following because friends


    Sent from my iPhone using Tapatalk
     
    Al3xRats, via a mobile device, Jan 8, 2020
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  7. alexwlwsn

    alexwlwsn Gold Member

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    Oh hello other Alex
     
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  8. alexwlwsn

    alexwlwsn Gold Member

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    Ordered the new points timing gear and appropriate oil seal today and they should be here in 2 or so days. Our grand total has exceeded $500 but I didn't really have a strict budget for this bike as that's still silly cheap. Most people pay more than this in riding gear alone for their bikes.

    screenshot-docs.google.com-2020.01.10-09_40_23.png
     
  9. alexwlwsn

    alexwlwsn Gold Member

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    Started disassembly for when my new points gear arrives.

    IMG_20200112_114107.jpg

    Points gear lines up with that straight cut gear you see to the right. It has a dot on it and there is a corresponding arrow marker on the block. Once that is lined up it's apparently easy to set the timing of the motor??? We will see! There doesn't seem to be a 1, 2, 3, 4, etc. step by step so here's to learning.
    IMG_20200112_115023.jpg

    Chunks of gear from the crankcase:
    IMG_20200112_115314.jpg

    Edit. Looks like the 1973 and on gear is keyway'd and mine has odd notches that fit into corresponding tabs on the shaft. This will be interesting to attempt to fit.
     
    Last edited: Jan 13, 2020
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  10. alexwlwsn

    alexwlwsn Gold Member

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    And the new points gear is in!

    IMG_20200114_193648.jpg

    Went in without a hitch, it was just keyway'd and held in by a washer, lock washer, and a nut. Now I'll be utilizing a "no dial gauge" timing method that seems to be popular on forums. Apparently these motors are pretty forgiving on the timing so for stock engines, you are generally good to go so long as you get it close.

    Screen Shot 2020-01-14 at 8.34.07 PM.png

    Useful references I'll need later:
    http://www.suzuki2strokes.com/forum/viewtopic.php?p=118282
    http://www.suzuki2strokes.com/forum/viewtopic.php?p=114633
    http://www.suzuki2strokes.com/forum/viewtopic.php?p=103194
     
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  11. alexwlwsn

    alexwlwsn Gold Member

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    Sorry to blow up my own thread. After research though I might as well either a) purchase a dial gauge or b) stick a screwdriver or similar cylindrical object into the cylinder in order to measure where the cylinder is. It seems I just need the cyl 1 point to close the circuit around 2-2.5mm before TDC which might actually be possible with a homemade tool. If the home remedy fails, I can stick this sucker to my frame and I'll end the day with a usable tool anyway...

    screenshot-www.amazon.com-2020.01.15-11_26_31.png

    Ign timing spec seems to leave me a good bit of wiggle room:

    screenshot-drive.google.com-2020.01.15-11_48_14.png

    Along with that, I need to set the points gap to about 0.016" which won't be an issue using feeler gauges.

    So, for tonight I'll likely do the following:
    1. get the engine close to time (using marks on the crankcase) and reassemble the right side of the engine case
    2. reattach the points plate
    3. measure the points gap and adjust as needed
    4. check the time
    5. stick something in the right cylinder and see if I can accurately measure 2mm before TDC
     
    Last edited: Jan 15, 2020
  12. alexwlwsn

    alexwlwsn Gold Member

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    Update! Had a long weekend and got a lot of wrenching done on the bike. I've cleaned the carbs, set the float height correctly, cleaned the points, set the point gaps, set the timing (got real close without the dial gauge), and assembled everything.

    Unfortunately, she just won't start! I'm not too bothered by it since it's been between 25 and 34 degrees F so this might just be the wrong season to get a carburated motorcycle running. With carb cleaner sprayed into the carbs at WOT, I get a sputter but that's about it. It's likely the timing could still be off, but even if it was sparking a millimeter or two early/late, I still feel like it should at least start. Soon I'll pick up some starter fluid to really see what's up since carb cleaner probably isn't the best tool for the job. It's also running pod filters rather than the stock airbox so I might honestly need to get a jet kit for it before it ever runs alright anyway. I'd like to at least get it idling though before changing out any physical things in the carbs.

    Anywho, here's a few photos.

    Points plate (showing the left cylinder at ~3mm BTDC in that indicator window):
    IMG_20200118_172012.jpg

    Carb bottom end:
    IMG_20200119_163936.jpg

    Float height set at 24.25mm:
    IMG_20200120_104125.jpg
     
  13. Easter Bunny

    Easter Bunny Professional Engineer Silver Member

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    how did you set the dwell on the points?

    are you positive that the cam timing is correct?

    are there any ground wires that you touched that could be broken or not connected properly?

    did you remember to open the petcock on the fuel tank?

    after the cleaning are you sure that the fuel jets are clear?

    could there be water in the gas?
     
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  14. Db09ms3

    Db09ms3 Silver Member

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    Back in my small block chevy days we would just take a small cup with fuel, open the carb, pour in a splash, and fire it up.
     
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  15. alexwlwsn

    alexwlwsn Gold Member

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    1. points gap set by feeler gauge as per manual/forum recommendations
    2. no cams on a 2 stroke
    3. Points checked with multimeter to verify connectivity and lack of (when they should be open)
    4. yes lol
    5. you can see through them
    6. fresh fuel with stabilizer in it as well

    All good questions! I actually have an idea what might be wrong but I'm going to test my theory tonight and report back soon. Might have to do with the actual physical timing of the engine. I have the points opening 3mm b.t.d.c as per the manual, but there's one last thing I need to look at.
     
  16. alexwlwsn

    alexwlwsn Gold Member

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    My sneaking suspicion was right! So, when first assembled the bike, I used the dot on the timing gear, and lined up the "L" mark on the timing propellor. I noticed that when the L point opened though, the cylinder near my right leg was at TDC and the left cylinder sparked. So, I thought something was weird with the plug wires and simply switched the L and R wires. After much thought, I came to think, maybe someone in the last 40something years had messed with the engine and had it somehow all flipped around. So, that would mean that L = C, C = R, and R = L. Easiest way to test this theory would be to re-pin the actual harness that supplies the coils with power. I did just that, added a little carb cleaner to the carbs, and whadda ya know she fired up first kick.



    So, now we know the timing is at least in the right neighborhood and when it's idling nicely, I can adjust it further.

    I will say though, it hasn't started yet on just gasoline from the carbs. Might be because they were dry when I started it, or something else. Either way, I know now we have spark, obviously, we have air, and now I just need to get the fuel flowing and we should have a running bike! It looks like this Sunday will be 48* and partly cloudy so we have a plan!
     
  17. alexwlwsn

    alexwlwsn Gold Member

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    Just make sure you have a fire extinguisher on hand for that trick
     
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  18. alexwlwsn

    alexwlwsn Gold Member

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    And she's idling! Before last night, I thought I needed to turn my idle air adjustment screw out - as the pod filters allow for more air, so it would need more gas? Turns out I needed to turn them in. ~1 screw inwards from the manual "beginning" setting and she started up!



    The idle is pretty high in this video but afterward, I tightened all the hoses and fittings and it's a little less aggressive and smoother. Now I need to figure out how to get a) timing perfect, b) idle air adjustment correct and even on all 3 cylinders, and c) idle screws set to where it idles around 1100-1500 evenly on all cylinders. I may also replace at least some of the fuel lines as I think the screw clamps are starting to cut into the rubber in a couple of places.

    I can't imagine that'll take too long. I feel like we're at the point now where I can drive it around the block, and very close to being a ridable bike. Can't wait to cruise down the road with a big ole cloud of 2-stroke smokeeeee behind me!
     
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