1969 Honda CT90 | GTAMotorcycle.com

1969 Honda CT90

tricky

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Santa was kind to me this year. My uncle has one lying around that he is giving me.

Apparently carbs need cleaning, and something needs replacing... maybe timing chain... I'll have to ask him again.

Will be picking up in the coming weeks, I assume.

Looking to slam & stretch her and get a 190 rear on it. Just playing. Gonna be keeping it as close to original as possible, with a little light restoration if needed (still haven't seen it in person).

Apparently it has 6900 km on it (AKA it's showroom fresh)

Anyone here have info or experience on these things?

EDIT: Added images from near the start of the project. This is after I got the bike and removed the engine.




 
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bitzz

Well-known member
You want to talk to Johnny Bent, of Bent Bikes fame.
He has a couple of those and a parts stash.
905 273 3717 Friday or Saturday
 

theraymondguy

Well-known member
Santa was kind to me this year. My uncle has one lying around that he is giving me.

Apparently carbs need cleaning, and something needs replacing... maybe timing chain... I'll have to ask him again.

Will be picking up in the coming weeks, I assume.

Looking to slam & stretch her and get a 190 rear on it. Just playing. Gonna be keeping it as close to original as possible, with a little light restoration if needed (still haven't seen it in person).

Apparently it has 6900 km on it (AKA it's showroom fresh)

Anyone here have info or experience on these things?

http://ct90-ct110.com/1969454545Trail45904539K1.html

Pretty well covers it.

5-6HP maybe, 4 speed semi auto with 2 ranges. Can run 117cc bore kit (double stock HP), CA200 clutch components will convert it to manual shift.
 

tricky

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Thanks for all the info. I did end up ordering some stuff from DrATV, but it took a month or more to get here so I might look for a new supplier if I'm in a pinch.

This is moving along at a snails pace, FYI.

The bike does have low KM, but it's a bit rough around the edges. I've transitioned from "getting it to run," leaning now more towards total restomod, more emphasis on the "resto," light on the "mod"...

Bike's sitting at my parents, I wont be able to work on it until they move. Long story. But I did rip the engine out and bring it to my condo.

My plan was to change the timing chain and clean the carb. That is what I was told needed to be done. It ended up devolving into a total rebuild from the bottom up. Two reasons for this: the guy who went into the engine before me did a pretty rough job, stripping all kinds of screw heads, making ill-fitting gaskets and generally annoying me, so I want to redo it right.. Second reason is so I can learn something

I have the engine at its most basic now, all apart and awaiting cleaning, stripping & painting.

My question is, I have split the crankcase. Both sides need a good cleaning, but I am worried about introducing dirt into the bearings, an example shown in the last picture. Any advice? Or should I get to scrubbing and stripping the paint, and replace the bearings after... yes I am new to all of this.

And yes, the benefit of having no roommate is you can use your kitchen to clean engine parts :lol:








 

thirstforspeed

Well-known member
my advice: once the cases are open you might as well go all out and replace as much as you can. (thats also why i didnt open the cases on the CB550 build).

its probably gonna be cheaper/easier to just do it all once, that way you know the age of all the stuff in there and will most likely not have to replace them again soon.
if you don't, then murphy's law says that the bearing will fail as soon as you get 500m down the road the first time you take it out after its together.
 

tricky

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my advice: once the cases are open you might as well go all out and replace as much as you can. (thats also why i didnt open the cases on the CB550 build).

its probably gonna be cheaper/easier to just do it all once, that way you know the age of all the stuff in there and will most likely not have to replace them again soon.
if you don't, then murphy's law says that the bearing will fail as soon as you get 500m down the road the first time you take it out after its together.
That sounds about right to me... I just spent an hour or so cleaning the clutch and stator covers and they still have a long way to go. I couldn't protect the bearings through that process so I guess out they'll come

I love following your build BTW :thumbup:


5-6HP maybe, 4 speed semi auto with 2 ranges. Can run 117cc bore kit (double stock HP), CA200 clutch components will convert it to manual shift.
You are referring to the 50caliberracing conversion? That'd go on the 90?? I'd be worried about cooling, but now you are giving me notions

I know DrATV does the 100 or 104 cc conversion, I was thinking of getting the 104 done to my cylinder, and they'll paint it and supply the new piston and rings all in one go
 

theraymondguy

Well-known member
That sounds about right to me... I just spent an hour or so cleaning the clutch and stator covers and they still have a long way to go. I couldn't protect the bearings through that process so I guess out they'll come

I love following your build BTW :thumbup:

You are referring to the 50caliberracing conversion? That'd go on the 90?? I'd be worried about cooling, but now you are giving me notions

I know DrATV does the 100 or 104 cc conversion, I was thinking of getting the 104 done to my cylinder, and they'll paint it and supply the new piston and rings all in one go
You can wash the bearings out with degreaser, kerosene or diesel fuel if you wish to reuse them. Just do a thorough job.

Track down a good sized sharpening stone (like old man on the porch, sharpening his favourite knife style sharpening stone), use it to remove the ragged bits of hardened gasket your razor blade can't remove without digging into the metal.

117cc high compression can be had but its a good amount of fuss, and now with the Dollar in the toilet... costly. If you're just looking to freshen it up, a set of rings and a hone will do. With the 17" wheels the CT90 does OK, it'll hold 45 MPH with an adult - less with a head wind.

The CT90 is a dead ringer for the ATC 90/110/125 - I had a sidebar with a chap I know, perhaps a crank and top end swap would be more direct... though would remain at 9.4:1 compression...

Maybe just get it reliable, then fiddle with it? Swapping in a new cam chain can't hurt (usually you can gauge the state of the chain based on the wear of the cam sprocket), though there's little to be gained from a performance perspective unless it was really whipped. Points adjustment (0.016") plays a major role along with a cleaned carburetor, and lets not forget valve lash.
 

tricky

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Maybe just get it reliable, then fiddle with it? Swapping in a new cam chain can't hurt (usually you can gauge the state of the chain based on the wear of the cam sprocket), though there's little to be gained from a performance perspective unless it was really whipped. Points adjustment (0.016") plays a major role along with a cleaned carburetor, and lets not forget valve lash.
Exactly. I'm leaning towards the DrATV big bore just so I can get the cylinder cleaned up and grab a few extra hp. The rest I'll stick with stock until its up and running and I'll take it from there

Cam chain wasn't meant as a performance increase at all, last guy said it was knackered and so I got a new chain and sprockets cause they're fairly inexpensive

A while ago I toyed with the idea of an ATC125 but then I lose the low-range I think... then I thought about putting the 125 jug and head on a 110 crankcase but that's getting a little out-of-hand. Maybe down the road. Lots of time for that later.
 

boyoboy

Well-known member
my advice: once the cases are open you might as well go all out and replace as much as you can. (thats also why i didnt open the cases on the CB550 build).

its probably gonna be cheaper/easier to just do it all once, that way you know the age of all the stuff in there and will most likely not have to replace them again soon.
if you don't, then murphy's law says that the bearing will fail as soon as you get 500m down the road the first time you take it out after its together.
+1...
 

boyoboy

Well-known member
You can wash the bearings out with degreaser, kerosene or diesel fuel if you wish to reuse them. Just do a thorough job.

Track down a good sized sharpening stone (like old man on the porch, sharpening his favourite knife style sharpening stone), use it to remove the ragged bits of hardened gasket your razor blade can't remove without digging into the metal.

117cc high compression can be had but its a good amount of fuss, and now with the Dollar in the toilet... costly. If you're just looking to freshen it up, a set of rings and a hone will do. With the 17" wheels the CT90 does OK, it'll hold 45 MPH with an adult - less with a head wind.

The CT90 is a dead ringer for the ATC 90/110/125 - I had a sidebar with a chap I know, perhaps a crank and top end swap would be more direct... though would remain at 9.4:1 compression...

Maybe just get it reliable, then fiddle with it? Swapping in a new cam chain can't hurt (usually you can gauge the state of the chain based on the wear of the cam sprocket), though there's little to be gained from a performance perspective unless it was really whipped. Points adjustment (0.016") plays a major role along with a cleaned carburetor, and lets not forget valve lash.
umm are you saying to use a grinder on flat mating surfaces? with an old man on the porch grinder (whatever that is). not sure i am following/understanding you on this.

you check camchains by measuring stretch over a specified number of links - numbers should be listed in shop manual under specs
 
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Joe Bass

*probably eating right now*
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@tricky , not sure but iirc @ecozslak (sp?) has some experience with them

Sent from my custom purple Joe Bass mobile device using Tapatalk
 

tricky

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It's been a while, but I'm back at it now.

The engine is almost done, bottom end is mostly together, I'm just waiting on some piston rings to close it up. There was a fair bit of :confused: with the top end, the piston is Honda and unmarked, but 0.72mm (0.028") over stock it seems. Tolerance between the bore and cylinder is still in spec though (to the best of my measuring ability) and so is the taper, so I'll check the gap on the new rings (which are +0.75mm??) and with luck we'll be good.

The reason I don't just go up to 1.0mm over bore with a new piston is I have been leaning more and more towards throwing in a Lifan 140 or 150, but I want to get it up and running with the original engine first to prove to myself that I can. Though that seems more a pain-in-the-ass now because I found the exhaust is blown (last picture), after taking off the heat shield

I've taken everything else down to the screws, everything red in the following pictures should be blasted and painted. Originally I wanted to paint it myself as a learning experience, but this seems beyond my
capabilities now so I'm gonna shop around

I have new stiffer forks and rear shocks, and some other goodies ready to go on, so once the metal is painted I can start putting it back together :D










 

TK4

Well-known member
"The piston is Honda and unmarked, but 0.72mm (0.028") over stock it seems."
Its likely 0.75 mm oversize, that's how Honda does things.
On the underside of the piston there should be a number stamped, that will tell you what model it was originally used in if someone has already rebored and swapped it out.
 

tricky

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"The piston is Honda and unmarked, but 0.72mm (0.028") over stock it seems."
Its likely 0.75 mm oversize, that's how Honda does things.
On the underside of the piston there should be a number stamped, that will tell you what model it was originally used in if someone has already rebored and swapped it out.
That's why I went for the +0.75 rings. That 50.72 mm measurement was at the skirt, 90 degrees to the pin. About 10 mm up from the skirt it was 50.68 mm

I was told they are usually marked if they are oversize, but this one doesn't seem to be. One on side, near the pin, it says "HONDA," and on the opposite side it says "CS90" and something tough to make out, mabye "11/6" (in picture). No other markings I can make out

No surprise really its a CS90 piston, I assume those engines are the same, just without the sub transmission

 

PrivatePilot

Ironus Butticus
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Do NOT use anything abrasive on metal mating surfaces...even a few thou ground off in the wrong spot trying to remove a gasket may result in a failure to ever be able to reseal things properly again.

3M makes some magic tools for this. https://www.amazon.com/Scotch-Brite-07528-Quick-Change-Attachment-Aluminum/dp/B000FW4LDU

I've used this on a few diesel engine rebuilds and they are like freakin magic - put in in your drill and it wipes away old gasket and crud like a steel wheel, but it doesn't harm the metal whatsoever.

I'm sure they can be found cheaper, that was just the first link I could pull up quickly.
 

tricky

Well-known member
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Do NOT use anything abrasive on metal mating surfaces...even a few thou ground off in the wrong spot trying to remove a gasket may result in a failure to ever be able to reseal things properly again.

3M makes some magic tools for this. https://www.amazon.com/Scotch-Brite-07528-Quick-Change-Attachment-Aluminum/dp/B000FW4LDU

I've used this on a few diesel engine rebuilds and they are like freakin magic - put in in your drill and it wipes away old gasket and crud like a steel wheel, but it doesn't harm the metal whatsoever.

I'm sure they can be found cheaper, that was just the first link I could pull up quickly.

Interesting... I've never heard of those. The reviews look good, I'll definitely pick some up.

I have an assortment of plastic scrapers that I've been using to date, and good quality razor blades for the fine stuff. But that looks like it could be a better alternative, thanks!
 

PrivatePilot

Ironus Butticus
Site Supporter
I've used scrapers, razors, chemical strippers etc etc on old gaskets and adhesives - once you've used one of these wheel doodads you'll never go back.
 

tricky

Well-known member
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I would like to give more pictures, but most of the parts are out for powder coat with Mike at Brightside Customs

In the mean time, I'm scrubbing wheels....... yayy....... The chrome has held up real well over 47 years though, only a few rust spots here and there, but I won't worry about those now.




The engine is a bit more of a tragic tale. I was finally done (or so I thought) after dragging my feet for a year. I put the head back on and went to torque down the bolts and one of the cylinder studs wasn't staying in place.

When I stripped down the engine the first time, that stud was rusted in real well. I had to bring it to a friend at his shop, and he had to spend hours getting that thing out. I remember him saying something like the engine took a part of his soul. Well I guess those threads were damaged enough even after he tended to them that the cylinder stud doesn't want to stay in place, and I am not comfortable torquing it down any further cause it feels like bad things will happen.

I guess I'll have to get a helicoil or something put in there... which means tearing the engine down again. Good thing is, I can probably tear it down in less than an hour now. It's all clean and shiny and I replaced all the fasteners with stainless steel socket cap screws. Nothing like the first disassembly, which took me forever and left my extractor set abused.

I'm not too bothered about doing this, it'll give me a chance to change the crank bearings, which I shied away from doing the first time. I guess if I'm gonna do something, might as well go all out?


The colour scheme that Mike's doing with the powder is something similar to this:


And for the purists, I'm not making any other permanent mods so with a respray it can be brought back to stock.
 

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