ST90 Restoration Completed

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by HondoMan, Nov 20, 2017.

  1. HondoMan

    HondoMan New Member

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    Hi All, I caught the restoration bug this past July and managed to score a "barn find" 1975 ST90 for my first restoration project. I had not done a restoration previously, but I am a relatively handy and thought I would give it a try. I want to take the opportunity to share my experience for anyone that might be considering a similar project.
    First of all, I now understand that I was very lucky with the ST90 that I purchased. Although really faded and dirty, most of the bike was "there" and in relatively decent shape with little rust. When I made the purchase , the seller also threw in a 1974 CT90 "parts bike". I was not very interested in the CT90, but I came to appreciate that there are a lot of common parts on the Ct90 that I was able to cannabalize for the St90. This saved me a lot of trouble and expense in several cases.
    Once I got the ST90 home, I stripped it, piece by piece, being careful to photograph each part of the bike prior to disassembly and bagging and labeling all of the fasteners and bits and pieces by component. The rear axle was frozen solid into the swing arm and wheel, so I had to take it to a local machine shop to press it out. Prior to taking part to the machine shop I damaged the axle castellated nut while trying to bang the axle out of the swing arm - this was dumb of me, but lesson learned. I also managed to damage the shoulder bolt that attaches the kick stand to the kickstand bracket. I did not know that the shoulder bolt was threaded into the bracket clevis and again tried to bang it out damaging the bolt threads - another novice mistake - fortunately the CT90 kickstand provided me a replacement shoulder bolt.
    Apart from these two incidents, most of the rest of the bike came apart fairly easily with the help of a lot of PB Blaster. Once disassembled I set to cleaning all of the parts. I mainly used scotch-bright, wire brushes and pure household vinegar. I found vinegar to be an excellent cleaning and de-rusting agent. I would drop a batch of parts in vinegar at night and clean them with a wire brush the next day. For the front and rear fender inner surfaces, which were very rusty, I pooled the vinegar in the rusty areas spot by spot, wire brushed them and then primed and painted the cleaned inner surface. The result was very good.
    The handle bar controls on the bike were in very bad shape. I was initially afraid to disassemble them as there are a lot of little bits and tiny springs, but ultimately I had no choice. I was finally able to make one set of fully functioning controls with parts from the ST90 and CT90 handlebar sets (since they are identical). This process included completely disassembling the wire bundles so that I could replace individual damaged wires. The turn signal switch slider was particularly challenging due to its tiny springs and ball bearings. To reinstall it after removal, I ended up having to make an insertion tool from a piece of sheet metal. Using the tool I was able to assemble all of the slider bits and insert the assembly back into the control housing. This required a lot of patience. Once the controls were complete I sprayed painted the finished exterior body's with black low gloss paint.
    I decided to replace the standard ST90 knobby tires with street tires, since I did not intend to do much trail riding. No one makes a 14 inch tubed street tire, so I purchased 14 inch tubeless scooter tires and installed them with a tube inside. Determining the tire sizes was challenging, but I ended up putting a 100/90-14 on the rear and a 80/90-14 on the front. I could probably have gotten away with one size wider on the front.
    For the frame and headlight body paint, I purchased candy topaz orange aerosol paint from Marble Motors on ebay. This was a 200 dollar investment (2 cans base, 3 cans orange, and 1 can clear) but it was absolutely worth it and the paint turned out fantastic. I did find that I could paint the frame with it laying on its side - one half at a time. This really helped to avoid paint runs. Once the paint was done, I let it cure for 3 days and then wet sanded the horn and sides with 2000 grit and then polished it with Meguires Swirl remover 2.0 (#3 cut) . This made for a smooth surface for the "Honda" emblem on the horn. The decal would not have looked good over an unfinished "orange peel" surface.
    The wiring on the bike was a big challenge and also required a lot of patience. I struggled with it for quite a while before finally finding the wiring diagram on the internet. Even with the wiring diagram the wiring was challenging as there were a number of damaged and frayed wires. Also - many of the wire colors had faded and it was difficult to match them to the wiring diagram.
    For the engine, I did the major cleaning with Simple Green and a wire brush and the final clean with acetone. It took several days of on and off work to get the engine looking good. Once clean I repainted the engine side covers in Honda silver cloud and polished the magneto and points covers. Prior to polishing the magneto cover I sprayed the inset "Honda" and "Made in Japan" black and then removed the overspray during the polishing. Very good result. For the cylinder head, I did a light dusting of high temp silver paint. I debated painting the head or leaving it bare - but it was in really poor cosmetic condition.
    The turn signals on the bike were all missing, however there are a lot of replacement Honda signals available on ebay. Honda turn signals are a common part for most all mid-1970's bikes. Make sure to buy 6 volt signals. The 12 volt signals are almost identical, but you cant find the correct wattage bulb for them. Without the correct wattage, the turn signal relay does not function correctly to make the system blink.
    One thing I was not able to find were the turn signal mounts for the handle bars. As an alternate, I installed the turn signals on stems off of the headlight bucket. This is the ST90 "Dax" style and similar installation to the CL200. If and when I can find the right handle bar signal mounts it is an easy move to put them up on the handle bars.
    Dis-assmbly of the rear shocks was also a challenge, as I did not have a spring compressor. In the end I just used 4 vice grips and compressing portions of the spring bit by bit until the spring was short enough that I could screw the end cap off. This was not an elegant solution, but it is a very effective way to get the job done.
    Everything else was pretty straight-forward. I ended up spending right at about 1000 dollars total on parts and paints. I have attached my itemized purchase list along with start to finish photos and the wiring diagram at the following link if anyone is interested.
    There are very useful exploded view diagrams availabe at the following link. These are very handy if you have parts missing from your bike or if you cant recall how to put something back together.

    https://www.cmsnl.com/honda-st90_model738/partslist/

    My total time for the restoration project was 3 months. I usually spent at least an hour or so every day doing something or other on the bike.

    My final challenge was getting the engine to run after its 30 year nap. Although in generally good apparent condition, the motor was very stubborn to wake up and seemed to have very low compression. I was just about to tear the head and cylinder down when I read a note on a blog about injecting a bit of motor oil into the cylinder (through spark plug hole) to boost the compression.This worked like magic and the motor immediately had noticeably higher compression and popped right off after a few kicks. Great tip to keep in mind.

    Thanks to the Lil Honda members that provided advice to me along the way! Also, I highly recommend DrAtv for parts. Everything that I purchased from them was exactly right, delivered quickly and reasonably priced.

    The following link has a selection of photos that I took along the way.

    https://www.flickr.com/gp/140778798@N04/Y3Li41

    Purchased Items:

    Item Cost ($)
    Barn Find Bike 300
    Air Filter Box Assy 70
    Rear Inner tube 15
    Front Inner tube 15
    Spoke 14
    Key 10
    Carburetor 50
    Wheel Bearings 20
    Various Paints/Primer 100
    Wheel Sprocket Studs 20
    Front Tire (Street) 50
    Handlebar Grips 8
    Frame Grommet 7
    Decal Set 50
    Topaz Orange Paint 180
    Fork Oil 10
    Chain 16
    Battery 10
    Clutch Cover Gasket 8
    Turn Signals and bulbs 60
    Seat with Pan 110
    Back Tire (Street) 55
    Brake Cable 15
    Speedometer Cable 20
    Headlight 48
    Throttle cable 20
    Mirrors 26

    Total : 1307
     
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  3. b52bombardier1

    b52bombardier1 Well-Known Member

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    Hello Eric,

    Very . . . . very nicely done and you should be very proud. It appears that you got lucky on the two hardest parts of any ST90 restoration. 1 - those rear turn signal mounts on the tool box were not torn and shredded beyond hope of use or repair. And 2 - you appear to have a functional speedometer cable . . . very hard to find. Run a followed search on Ebay and the original turn signal mounts will eventually show up. The third hardest thing to find that you might never want is a luggage rack for behind the seat. "Triple-A" made the best one back in the day, IMHO and both of my ST90 bikes and my CL100 all have a Triple-A rack. In fact, you can widen your search a little because the same CL100 rack from that company fits an ST90. In any case, make sure you get the two support pieces for this rack because its useless without them but I could fab you up a set if you needed them.

    I also had no trouble with that black handlebar switchgear on either side but it is also tough to find. Fortunately, your micro surgery with the CT90 stuff was sufficient to get yours going again. And a same or nearly the same year CT90 wiring diagram works well. Only the wire lengths are different, AFAICT.

    A lot of people don't like that topaz bike color but I love it for the reminder of some almost forgotten kind of candy I used to get as a kid that was the same color. I'm gettin' homesick just thinking about that candy . . .

    But again, nice job and thanks for keeping another ST90 out of the smelter.

    Rick
     
    #2 b52bombardier1, Nov 20, 2017
    Last edited: Nov 20, 2017
  4. red69

    red69 Well-Known Member

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    Nice work. Eric. I love seeing bikes come back from the dead. Nice color choice.

    Bob
     
  5. kirrbby

    kirrbby Well-Known Member

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    That is a GREAT lookin bike. Nice job.
     
  6. Enginedoctor

    Enginedoctor Well-Known Member

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    Yeah very nice. Such an oddball bike... and only 2 parts to paint body color... for what you're into it, that thing is astounding. I respoked a rear wheel a while back from an st90 and went through an eBay Thai guy to get the sets of spokes. I didn't want to shell out the money for a set one by one from Honda.... anyways great work I bet it corners like a dream on the road with those tires....
     
  7. Shamrockwill

    Shamrockwill Member

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    Great job and thanks for the detailed account. I am slowly restoring a 1974 ST90 myself. What kind of paint did you use on the exhaust heat shield and how did you get the emblem off and back on?
     
  8. HondoMan

    HondoMan New Member

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    I used a high temp primer and finished it with Krylon High Heat spray paint. This is basically the same thing you would use to repaint a bbq grill. I did not remove the emblem, just carefully masked around it. One piece of advice - be sure to sand the primer well prior to the Krylon so you get as nice of a gloss finish as possible.
     
  9. Shamrockwill

    Shamrockwill Member

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    Thanks. I'm planning on using BBQ paint for the exhaust but didn't know it could be made to come out glossy enough for the heat shield.
     
    #8 Shamrockwill, Jan 14, 2018
    Last edited: Jan 17, 2018
  10. Shamrockwill

    Shamrockwill Member

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    Got another question for you HondoMan. When I was disassembling my ST90 there was Hondabond or the equivalent holding some of the grommets to the frame. Problem is I can't remember which one's. I only remember it being on the air cleaner gasket and some frame grommets. Did you use any? Are there some grommets that need it and some that don't?
     
  11. b52bombardier1

    b52bombardier1 Well-Known Member

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    I did not need Hondabond on any of the grommets on my two ST90 bikes and Honda did not need it at the factory. I guess I was lucky here because the rubber edges of my frame and air cleaner grommets were still in good enough condition to not any additional "stickem'" for mounting them.

    Rick
     
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  12. Shamrockwill

    Shamrockwill Member

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    After looking closely at all my leftover rubber parts it appears that it wasn't the grommets but rather the carb to air box boot and the air box to frame boot as they are what have some leftover Hondabond on them. But If Honda didn't use any at the factory I don't see why I need to. I guess that means I'm not the first one to take this bike apart. Thanks Rick! Hopefully mine turns out as nice as this great ST90 revival by Hondoman.
     
    #11 Shamrockwill, Feb 12, 2018 at 1:51 AM
    Last edited: Feb 12, 2018 at 3:10 AM
  13. kirrbby

    kirrbby Well-Known Member

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    If you start reading in this thread, around post #98, there is some info about gluing the carb boots. Weatherstripping glue is recommended.
    https://lilhonda.com/index.php?threads/tuning-time.19262/page-5
     
  14. Shamrockwill

    Shamrockwill Member

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    Thanks Kirrbby. Is there a reason 3m weather stripping is preferable to ThreeBond 1184 or the other liquid gaskets?
     
  15. allenp42

    allenp42 Active Member

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    Attached Files:

    #14 allenp42, Feb 12, 2018 at 11:17 PM
    Last edited: Feb 12, 2018 at 11:39 PM
  16. kirrbby

    kirrbby Well-Known Member

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    I"m thinking there is probably a reason for using the WS adhesive, but I really don't know. Maybe someone will chime in about that. The stuff Allen pictured is what I remember seeing before, for this application. But I'm not familiar with it, or it's characteristics.
     
  17. Cleato904

    Cleato904 Member

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    The reason one would use WS adhesive is to completely seal the air
    boot(s) to the ducts or air box. It helps to prevent accidental water or fine dust from getting into the engine through small cracks. Honda does use WS adhesive on all '80(s) to present bikes, atvs on the carb intake boot at the airbox to form a water tight seal. I use Honda grip glue which is WS adhesive to reseal the boots to the air box numerous times without any failures.
     
  18. Shamrockwill

    Shamrockwill Member

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    I'm clear on the reasoning behind sealing the boot but I'm wondering if ThreeBond 1184 (same as HondaBond) would work just as good as 3M weatherstripping for this application? Mainly because I already have a tube of ThreeBond 1184
    -Will
     
    #17 Shamrockwill, Feb 14, 2018 at 8:37 PM
    Last edited: Feb 15, 2018 at 2:53 AM
  19. Cleato904

    Cleato904 Member

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    It'll be fine to use, Honda bond and ThreeBond are both playable when dried and will flex with the boot and not flake off.
     
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