Jump to content

1969 Honda CT90


Recommended Posts

I'd been wanting an old honda motorcycle for a while, so when this showed up on FB marketplace at a price I couldn't say no to I picked it up.  I need another project vehicle like I need a hole in my head, but oh well lol. It's been engine-swapped with a 125cc from a honda 3-wheeler, so should have a bit more get-up-and-go than the stock 90cc.

 

8 hour round-trip to go get it:

 

51261796250_ff36ef176b_b.jpg

 

 

It had been in a barn for a while, and was filthy, so first order of business was to fix that.

 

51261796445_c2cb78fb83_b.jpg

 

51261799260_080fd3bd80_b.jpg

 

 

The reason I got this thing so cheap was that it is in need of a fair bit of work, and had some missing parts. First up was that the rear sprocket and chain were entirely missing. It took a bit for me to be able to go get the bike (darn provincial border closures), so I had ordered a new chain and used sprocket off ebay while I was waiting.

 

51261494484_09aab4fbda_b.jpg

 

51260750866_f6fc44a3c7_b.jpg

 

Much better.

 

51261494019_5b6d2ab22d_b.jpg

 

 

A 'fun' future project is going to be dealing with all the wiring, which has just been unplugged and left dangling. These bikes are 6v and the engine in it now is 12v, so I assume this was just done to prevent blowing all the bulbs and they never got around to wiring in a 12>6v regulator or swapping the bike's stuff for 12v. As it is now the bike should be able to run; the CDI is wired up and there is spark when it's cranked even with no battery.

 

51261798140_5e4ebc5065_b.jpg

 

51260950883_10f8fc0185_b.jpg

 

51260950453_da381f6089_b.jpg

 

 

Speaking of spark, the lead had totally had it, so I replaced with one of the ones that was on my Z when I got it, chopped down to the correct length. The plug isn't in right now because someone stripped the hole and helicoiled it bigger, but the helicoil was coming out and the (larger) threads were pretty messed up. Going to get a m14x1.25 tap and try to fix the threads and use a larger spark plug (stock thread was 12x1.25mm).

 

51260950653_03ddf6282b_b.jpg

 

51260950273_8ac4e6aa95_b.jpg

 

Then there's this interesting setup, I guess the stock bash bar/footpeg mount didn't fit on the larger engine. I'll be making up something a lot nicer for this purpose, as well as incorporating a skidplate etc (these bikes were designed for on/offroad use after all).


51260749491_baf3dc1167_b.jpg

 

 

Some other misc. - One of the exhaust mount studs was broken off, and it was a weird combo mount with the rear shock nut. Welded something workable together:

51260749291_dc0b0e1ffc_b.jpg

 

Spaced it out a bit too as how it was before it had melted the plastic shield a bit:

 

51261492639_eac80b948c_b.jpg

 

 

 

51260022247_253ee0e892_b.jpg

 

Current goal is to get it running/driving, have some fun offroad with it, then fix the wiring, get it registered (I only have a bill of sale currently), and road legal. Oh, and I need to get a motorcycle license haha.

 

 

 

Edited by Noll
  • Like 2
Link to comment
  • Replies 24
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Got the spark plug hole tapped to m14x1.25 with no issues happily. Verified that there is spark, there's definitely fuel getting into the engine (replaced with fresh too although the old gas looked fine), air is a given, but no start even with starting fluid, it wouldn't even pop.

 

Some investigation into why lead to a compression test, which ended up as 30psi. Not good, very not good in fact. I'm hoping it's just stuck rings, have dumped a bunch of ATF down the spark plug hole so we'll see what that does tomorrow. The piston being almost sideways makes it a bit less effective, but here's hoping.

worst-case these are dead easy  and cheap to rebuild, hopefully can run it as-is though.

Link to comment

Ok, engine pulled apart, and culprit found. I think at some point someone ran a spark plug that was too long, and it hit the intake valve before something broke off and bounced around a little.

 

51268007852_c225ca5a89_b.jpg

 

51268749246_338999cb7a_b.jpg

 

 

Thankfully the piston, rings, and cylinder walls both look perfectly fine.

 

51269479654_21299c9733_b.jpg

 

51269480034_b729c85fea_b.jpg

 

 

The valve seats are alright too, the exhaust valve hadn't been seating very well but that seems unrelated.

 

51268934573_01a2e2f73b_b.jpg

 

 

Whatever hit the intake valve dented it hard enough to deform the backside.

 

51269775790_979f97c7b7_b.jpg

 

 

Super high-tech homemade valve spring compressor setup, and the current state of things:

 

51268934868_a05c232741_b.jpg

 

51268933978_a6ac9ef863_b.jpg

 

 

Also realized this engine is actually out of an ATC110, which mean an even simpler wiring diagram to deal with which is nice. The entire atc harness is stuffed into the ct90 right now, should be able to use most of it as-is with some shortening of wires. it's set up to have 2 different main alternator outputs, the black/red to the coil and CDI, and yellow to the lights. I'm sure I can work out a way to make the yellow work for both the lights as well as a voltage regulator of some sort + a battery if I decide to not just keep the battery-less setup. Undecided though, we'll see what route I take.

 

51269480054_631e4b8f9b_b.jpg

Edited by Noll
  • Like 2
Link to comment
7 minutes ago, ]2eDeYe said:

Awesome! I learned to ride on one of these on my uncles farm.  

I am rebuilding an old Yamaha version of one of these that me and my brother rode as kids. 😄

 

4 minutes ago, ]2eDeYe said:

There is a guy on youtube that rides one all over. He modified it with a bigger engine and an mx frontend. 

 

 

 

 

Nice! They (and other similar bikes) are pretty neat, it's not going to be fast but should be a good time.

 

Oh yeah, C90Adventures is how I found out about the c/ct bikes to begin with as it happens. Hopefully he's able to resume his trip soon, the videos are awesome.

Edited by Noll
  • Like 1
Link to comment

Ok, A bunch of looking at the engine harness and frame harness diagrams later, I'm pretty sure I've photoshopped  a combined harness that will work. if I can find a dual pole (separated) keyed ignition switch I'll run the lighting/horn circuit through that so it only works with key on. I don't want to run the coil power and light power wires through the same contacts, defeats the point of them being separate and might break things.

 

51272231625_d5e4de47df_b.jpg

Edited by Noll
  • Like 1
Link to comment
10 hours ago, Lockleaf said:

If cant find a switch like you want, couldn't you use the key to trigger a relay to power up the two circuits independently?

 

That's a good idea! I just bought a 4-wire ignition switch from a 90's honda ATV that I think SHOULD work, but that's a great backup plan if it doesn't. Should arrive tomorrow.

 

-------------------------------

 

Got some stuff done on the bike today. 1st up, the exhaust had a pretty considerable split and nearby pinhole. Instead of trying to weld it up and blowing holes in the thin metal I welded a patch over everything.

 

51275262241_6950bd72e1_b.jpg

 

51274514037_fa0a3c9190_b.jpg

 

Next up, the foot pegs/kickstand. The setup on the bike when I got it was a bit sketchy to say the least, way heavier than it needed to be, a big catch point for rocks, tree limbs, etc and looked like stevie wonder did the welds.

 

51276285640_15628f5d52_b.jpg

 

 

Made a mounting plate:

 

51275432008_fc6d546b75_b.jpg

 

 

Welded the (cleaned-up) pegs on, and welded a bit of square tubing between the cut-off sections.

 

51274513497_e6a6501f0f_b.jpg

 

 

Welded some bar stock on top to give it even more strength, and cleaned stuff up.

 

51275991144_250c058d08_b.jpg

 

51275261076_46d42ace0e_b.jpg

 

Did my best to bend the pegs int some sort of evenness as they were bent in 4 different directions, they're more even than they look here.

 

51274512967_5ff2679a15_b.jpg

 

 

And on the bike. Happy with how it turned out! Will get some paint of course, just need to decide if I want to integrate the skidplate I'll be making into it or have that be a separate bolt-on piece.

 

51276284550_24ede56551_b.jpg

Edited by Noll
  • Like 2
Link to comment

Got some more done today. With the homemade wiring diagram in hand, I cleaned up the bike's harness to match, as well as adding in the ignition key switch etc.

 

51283705561_a1b01f1ca6_b.jpg

 

51284428939_28e1d3d7f3_b.jpg

 

Pretty happy with the result. My bike's missing the cover that would normally hide the harness running along the tube here, but it doesn't look terrible IMO. I'll also be 3d-printing a cover for the back of the hole the ignition switch goes in.

 

The light wiring is still left unplugged for now though, want to get the bike running first and will need to do something about the 6v headlight before I can plug any of the lights in (the headlight's load stops all the other bulbs from blowing with this battery-less system). I have an old 7" H4 light with a smashed lense lying around, I might cut the base out of that and epoxy it to the back of the 6v light (which is currently a sealed beam) to allow me to use conventional bulbs. If I can find a 35/35w H4 bulb (the same as stock for the atv the engine came out of) I see no reason this wouldn't work fine.

 

One upside to the lack of battery with this config means that I can at some point get some wrenches etc and make a little tool roll specifically for the bike stored where the battery would have gone. Handy for when doing a road trip etc.

 

Yesterday I went to our DMV equivalent and got the bike actually registered in my name. Despite not having ownership papers this was relatively straightforward, bill of sale from the guy I got it from and a sworn affidavit I wrote up explaining why I thought I was the rightful owner and away I went. it did take a bit of time though as they had to call head office due to the vin # being one digit shorter than the minimum their system would accept lol. I would have thought there would have been some sort of override for older pre-standardized-vin-length vehicles, but I guess not. They did something in the end that worked though, and I now have ownership paperwork in my name 🙂 .

 

Pretty much just waiting on parts now, not sure if there's anything else I can really do in the meantime.

Edited by Noll
  • Like 1
Link to comment

Well, new tires ended up showing up today (wasn't expecting them till next week at the earliest), so got them swapped on. Was more of a hassle than it should have been, but got them done in the end with no leaks in the tubes.

 

51285957136_e1d536f953_b.jpg

 

51285956876_c6e30e0dac_b.jpg

  • Like 2
Link to comment
2 hours ago, ]2eDeYe said:

3d printing is awesome. 😄

 

It really is. Super nice to be able to grab some dimensions off something, do some CAD design, kick off a print, and have a completed part a few hours later. This will have some more printed parts on it as time goes on I'm sure, and the Z definitely will too in the interior etc.

  • Like 1
Link to comment

Got a lot done the past couple of days, but didn't take many pics. Had my 2nd vaccine shot yesterday and was/am feeling like death, so was just getting stuff done as opposed to doing photos.

 

New valves showed up yesterday, so got them all lapped and installed with springs etc.

 

51297481663_60155c5b50_b.jpg

 

51298316180_0afabbd4bf_b.jpg

 

Did a water leakdown test overnight, perfect seal. Spent a few hours today putting everything back together, doing timing, valve lash, etc etc etc.  Happily over 120psi (pic was before I got it up to the final value); heck of a lot better than the 30 it was at before.

 

51298416770_cb2e8d3705_b.jpg

 

51298316540_d89a85803f_b.jpg

 

It fired right up with starter fluid down the intake, but there's absolutely nothing when trying to just let the carb do its thing which isn't super surprising. The bike sat for quite a while in a barn before I got it, so probably just old gas gumming things up. Will tear down the carb tomorrow if time allows, that should be the final hurdle to making it drivable.

 

Then just need my new brake levers to show up, adjust the rear brakes, and figure out what I'm doing for a headlight (pretty sure this engine is 12v and I have a 6v sealed-beam installed at the moment).

 

Also had a lawnmower air filter and a bunch of 1.5" radiator hose arrive, going to make my own airbox setup instead of spending 150-200+USD on used oem parts.

 

 

Edited by Noll
  • Like 1
Link to comment
  • 3 weeks later...

Happily the carb is there in in great working order, want to make an airbox to keep the low-pressure intake stuff and allow me to have the intake up high as it is stock for water crossings etc.

 

-------------------------------------

 

Dropped off from posting in this thread for a little bit. Just after my last post I got the carb cleaned and working well, and drove the bike up and down the driveway. Pulled the plug to check how it looked, and this finished off what was lest of the threads in the head 😞 . needless to say this was a bit disheartening, but after a week or so I got the head to a machine shop that was able to put in a thread insert despite the hole having already previously been drilled/tapped larger.

 

51333392539_ec46c813cc_b.jpg

 

I then threw the engine back together for the second time, and was able to properly ride it  for the first time! Oddly it runs clean when cold but was smoking a ton after it warmed up - rings/cylinder looked good, brand new valve stem seals, etc and the fact that it doesn't happen when cold is rather odd IMO. I have a hunch that a bunch of the ATF I dumped into the cylinder back when i was figuring out the cause of no compression is in the exhaust and burning off once the exhaust gets hot. Going to try to run the bike without the muffler (just the up-pipe) and see if that makes a difference, would make sense that there was atf in the miffler baffles if so.

 

Beyond that, if anyone has suggestions as to what could cause this I'm all ears, seems like wayyyyy too much to be condensation burning off lol.

 

 

 

The other annoying thing is that the rubber seal that's for where the chain travels between the cylinder and head is leaking a decent amount, so I get to tear the head off for the 3RD time to fix it. Whee. bit of RTV silicone applied carefully to both sides where the gasket goes and some aviation gasket sealer on the metal-to-metal mating surfaces should do the trick I hope.

 

51332872208_deda86d51b_b.jpg

 

 

Didn't feel like doing more engine work just yet though, so today I worked on modifying the headlight. cut the sealed beam light assembly out and drilled the hole out larger:

 

51331927352_dd36cd13a9_b.jpg

 

Bought a cheap chinese ATV headlight off amazon for ~20$ CAD or so , and hacked it up till I had just the headlight holder assembly. Epoxied that in place the right way up, and once that cures I'll have a 12v headlight with replacable bulbs instead of the stock 6v sealed beam 🙂 .

 

51332871808_006858151a_b.jpg

 

51333657110_8ba92ab37c_b.jpg

 

  • Like 1
Link to comment

No major progress today, but I did run the bike for 20 minutes with no muffler, and confirmed that there is no smoke at all under any amount of throttle. Has to be ATF (or oil I guess) in the muffler baffles then, guess I just need to ride it long enough for it to burn off.

 

Gratuitous motorcycle pic just because.

 

51335337908_ef7515c5e4_b.jpg

  • Like 2
Link to comment

Bunch of welding jobs done today. First up, the exhaust was3 different bits only slip-fit together (some previous owner doing a DIY job to make the exhaust work with the ATC engine) and leaked like a sieve, so I tacked everything, removed it, and welded it up. Exhaust is still a slip-fit into the muffler but has gaskets etc there to stop it leaking.

 

51350091832_7f585d08e9_b.jpg

 

51350090352_4a50025a5f_b.jpg

 


Next up, got the rear brakes working. Stock the bike would have had a foot brake pedal for the rear in addition to the hand lever, but that and the center stand are MIA. The way the linkage works, without something holding the rod that goes to the foot lever in place the brakes don't work when you use the hand brake, so I made a little tab and welded it on the frame to do so. I want to get a foot brake setup eventually, won't be hard to remove the tab and give it a lick of paint when that happens.

 

51350822886_55d362f0de_b.jpg

 


lastly, the bike had a skidplate/bash guard from stock and that is also missing. I could buy an OEM one but they're not super beefy and I don't know if it would work with the engine swap anyway, so I started making my own.

 

cut up some square tube and welded in some captive nuts, then welded to the footpeg mount. Don't mind the crap welds, welding upside down sucks - i'll pull it off and finish weld/paint later. Didn't want the skidplate being welded directly to the peg mount as taking it off would involve removing the side-stand and it's  a pain to keep the bike upright if so.

 

51351840865_f7e03c0334_b.jpg

 

 

Bent up some steel rod I had lying around, and mocked up. the underside of the engine will of course get a beefy skidplate etc, not sure yet if I'll have a hole for oil drain or have the skidplate be removed for that.

 

51351049378_4bd094acd1_b.jpg

 

51351049078_b86180a479_b.jpg

 

51351562369_f39f3daeb2_b.jpg

 

I'll finish that the next time I work on the bike. At this point it's skidplate, air intake box, and wait on the voltage controller to arrive and it should be ready to get made road legal!

  • Like 2
Link to comment
On 7/24/2021 at 2:33 PM, Noll said:

Happily the carb is there in in great working order, want to make an airbox to keep the low-pressure intake stuff and allow me to have the intake up high as it is stock for water crossings etc.

 

-------------------------------------

 

Dropped off from posting in this thread for a little bit. Just after my last post I got the carb cleaned and working well, and drove the bike up and down the driveway. Pulled the plug to check how it looked, and this finished off what was lest of the threads in the head 😞 . needless to say this was a bit disheartening, but after a week or so I got the head to a machine shop that was able to put in a thread insert despite the hole having already previously been drilled/tapped larger.

 

51333392539_ec46c813cc_b.jpg

 

I then threw the engine back together for the second time, and was able to properly ride it  for the first time! Oddly it runs clean when cold but was smoking a ton after it warmed up - rings/cylinder looked good, brand new valve stem seals, etc and the fact that it doesn't happen when cold is rather odd IMO. I have a hunch that a bunch of the ATF I dumped into the cylinder back when i was figuring out the cause of no compression is in the exhaust and burning off once the exhaust gets hot. Going to try to run the bike without the muffler (just the up-pipe) and see if that makes a difference, would make sense that there was atf in the miffler baffles if so.

 

Beyond that, if anyone has suggestions as to what could cause this I'm all ears, seems like wayyyyy too much to be condensation burning off lol.

 

 

 

The other annoying thing is that the rubber seal that's for where the chain travels between the cylinder and head is leaking a decent amount, so I get to tear the head off for the 3RD time to fix it. Whee. bit of RTV silicone applied carefully to both sides where the gasket goes and some aviation gasket sealer on the metal-to-metal mating surfaces should do the trick I hope.

 

51332872208_deda86d51b_b.jpg

 

 

Didn't feel like doing more engine work just yet though, so today I worked on modifying the headlight. cut the sealed beam light assembly out and drilled the hole out larger:

 

51331927352_dd36cd13a9_b.jpg

 

Bought a cheap chinese ATV headlight off amazon for ~20$ CAD or so , and hacked it up till I had just the headlight holder assembly. Epoxied that in place the right way up, and once that cures I'll have a 12v headlight with replacable bulbs instead of the stock 6v sealed beam 🙂 .

 

51332871808_006858151a_b.jpg

 

51333657110_8ba92ab37c_b.jpg

 

 

 

Great simple mod. 🙂

 

  • Like 1
Link to comment
19 hours ago, ]2eDeYe said:

 

 

Great simple mod. 🙂

 

 

Thanks! Cheaper than buying an aftermarket headlight, and a lot faster than waiting on shipping from thailand etc 🙂 .

 

--------------------------

 

Got the skidplate all built and painted today, pretty happy with how it turned out. 4mm steel plate and solid rod, so it should be able to take quite the hit without bending.

 

51353619703_9964a1a375_b.jpg

 

51353619353_4d57af9e57_b.jpg

 

51353619158_3baed70266_b.jpg

 

51353618908_068a65e6a8_b.jpg

  • Like 2
Link to comment
23 hours ago, ]2eDeYe said:

It'll look great with some scratches on it. 


Will definitely match the rest of the bike's paint better that way lol.

 

Had another test ride today, pretty sure i burned out the last of the ATF in the exhaust finally and also scuffeds the skidplate slightly lol.

 

51356688255_33f4b8ab3e_b.jpg

 

 

The voltage regulator (silver box below the cdi) arrived so got that wired up - nothing to it really, one to ground and one to the main power lead for the lights. It's set to max out at 13.7 or .8 volts stock, but I could adjust it higher or lower if I want.

 

51355670281_b17b2d0417_b.jpg

 

 

side mirrors arrived too, so got them on. This thing is looking pretty good if I do say so myself! All that's left now is to make an airbox, and then it can go get safety'd .

 

51354928957_29dccb4393_b.jpg

 

 

 

  • Like 2
Link to comment
  • 4 months later...

Haven't updated this thread in a while, but have been tinkering away on the bike.

Rewired all of the brake light circuit so it all works, did a LED headlight conversion, and purchased a CT200 (the bike before the ct90) center stand and boot brake pedal and modified it to work on the 90 (the 200 assembly was FAR cheaper on ebay than 90 specific stuff and it only required me to lengthen the legs of the stand and some other misc.).


Finally got around to pulling the head off again the other day to diagnose/fix the oil leak that the bike has had for a while now. Can you spot the issue lol?

 

51767393784_33e2beffd6_b.jpg[/url]

 

Somehow the headgasket dropped down a bit last time the head was installed, whoops. These CTs are unkillable though, other than the oil leak (HG sandwiched between head and barrel let oil leak from the chain passage) the bike ran perfectly, started first time, etc. if it wasn't for the oil leak I'd never have pulled it apart.

 

51766750686_b780bfb36e_b.jpg

 

Happily i had a new one from the gasket set I ordered when I pulled the head off the first time. I didn't use it then as the OD was slightly too large for some reason, but 5 minutes with a file and scotchbrite pad on the copper gasket fixed that right up.

 

51766997188_94a5a04b43_b.jpg

 

 

While it was off, I added a horizontal brace piece to the tube uprights of the skidplate, should make it more resilient to smacking something from below and then bending these outwards.

 

51767393369_982718e173_b.jpg

 

 

And with that it's pretty much ready to go get a safety inspection and license plates whenever I get around to that (probably spring).

 

51765923307_8d83b72285_b.jpg

 

Rolled it outside this evening to have a look at the effectiveness of the LED headlight:

51766996728_799357c89b_b.jpg

 

51766749761_2b17b4d3e0_b.jpg

 

51765922662_f7181ac971_b.jpg

  • Like 2
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.