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First freeze, CT90 comes under the knife

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SL350

SL350

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Yepper, the first freeze came through and killed the last of the fall garden. The end of that season coincides with the beginning of another winter overhaul season. The first for my winter of 2014-2015... a 1975 CT-90 K6. I start this past weekend and have overcome the first two stumbles with more to come I'm sure.

Once I had removed the exhaust, drained the oil, and unhooked the points and battery, I started on the carbs. First step is the drain the tank of about 3/4 gallon of gas. This is a year old carb that fits except for the overflow nipple so when I installed it, I sawed it off. That would have been ideal for opening the bowl valve and use it to drain the entire tank.

So I decide to unhook the fuel lines at the fuel filters (2 fuel lines as the petcock on a ct90 is within the carb). Even though these lines are 1 season old, one is pretty stiff. Long story short when I pull the reserve fuel line off the gas filter, the nipple on the gas filter breaks and I can't install the drain hose to the gas can. A finger can hold the gas flow temporarily but I look behind me as see a lawnmower, a dolly and a garage door between me and the 25 degrees outside. By the time I got the bike outside, the garage was so full of fumes, Saturday was over. Lucky for me I did not pick the reserve first and I had already captured most of the gas in the can.

By Sunday 1 pm the garage was livable again. I started to take off the manifold but found the socket could not go over the bolt head because it was too close to the tube to the carby. An open end wrench only stripped it since this bike has NEVER had the bolt removed in 40 years. Eventually I found my vice grips and got it off. (note to self, buy new bolt).

Anyways, this has just started. Don't know if I can join the group at BB in March but they are talking a small bike under 200cc ride. This CT90 was OK for cruising and city errands but at 125 psi, it was well past overhaul time. It was just that I hate fixing something that is working.

Nice treat - the ct90 head can be removed without taking it off the bike. Not sure about the jug.

15200356494_3513c0af9c_o.jpg


Wish I had remembered to wash it first.
 
I was able to remove the head and cylinder without removing the engine. Barrel looks good, head was pretty carboned and the exhaust even more so.

Went online and found out the book says CT90s overhaul to 170psi compression but on the ct90 website, one guy posted that he had done several CTs and never got them out of the 140s. I had measured 125PSI before overhaul so I think I will clean the piston and rings and reuse. The piston and wall measure good so no overbore. Part of me is happy that I can save the expense of a bore but I was hoping for a little more grunt out of this engine, especially going on overpasses from a dead stop at a light.

This is a far as I will go with the head, having removed the rocker arms and all the seals.

15811693216_b3185f3263_o.jpg
 
Waiting for valve stem seals to arrive before handing the head off to the shop and wondering: How would I get that carbon off the head if I did it myself? I already cleaned the carbon off the piston by soaking in MMO and then using a Brillo pad.
 
"How would I get that carbon off the head if I did it myself?" SL350

Small toothbrush sized wire brush or Dremel tool with smallish wire wheel will work just be careful around the spark plug opening.
 
I am too scared to take the valve springs off without the tools. Can't wait for the seals to get here, shipped Thursday.
 
Well this one is almost finished. I never did take it in, just got a brush and cleaned the valves and head of all the carbon. Put it back together and had an oil leak from a seal on an oil passage between the head and cylinder. That has been replaced, valves reset and I am waiting for a camshaft seal that was cracked in the second disassembly. After that, I have to replace the points plate, set timing and gap and then ride.

Trying to get the bike ready for Dos Y Dos TAR ride in Big Bend March 22. Wish some others would sign up and tiddle their way around Big Bend that weekend.

Bought a welding rod box at HF and am mounting it as a tool box on the CT90. Need to find some way to carry a spare tube - thinking about one of those fender bags since the CT90 has a metal front fender.

Oh yea, I found out later that 125 psi compression was actually a good reading for a CT90. So not much hope for more power.
 
Last edited:
SL350 said:
Oh yea, I found out later that 125 psi compression was actually a good reading for a CT90. So not much hope for more power.
Click to expand...

trail 110 engine transplant!!
or the one that has been going around in my head, grom engine and electrics trans plant.
 
The 110 does not fit! The popular upgrade to stay honda is the ATC125m 3 wheeler. Or even more power is the Lifan China engine 140cc engine. That one GOES. But I like mine all Honda and I appreciate the hi-low gear box. You lose that with the engine upgrades.

Only power problem that I get is going over I30 where I stop at a stoplight and have to climb over the overpass from a dead stop. It'll do it but it really makes the guys behind you a little steamed.
 
the 110 don't fit????? how? I thought the only difference was bore and stroke.
 
Oh I think I misspoke, it probably does bolt right in. There are other issues like the 12v (a positive) but needing wiring changes. Some 110s were without hi-lo and that is a real put off. I guess I was never interested in an upgrade for 89cc to 105cc as being worth the trouble. The Lifan 140s though, they are significantly more power.

Most of the time if I want to go faster I just take the SL350.
 
1980 didn't have the dual range but Honda quickly figured out their mistake and put it back on. 80-81 has half wave charging system later has full wave higher output charging system.

the lifan engines over 125cc can have issues with busting the bottom end, they didn't reinforce the bearing bosses in the case and they can crack and fail.

my first bike was a trail 110 and I rode the wheels off that bike and it was not a easy job to do!
 
doing some digging, the extra 20cc is only good for half a horse at best, a well tuned 90 often being a bit faster. benefits of the 110 being CDI ignition and much better charging system (82 and later)
 
focus frenzy said:
1
the lifan engines over 125cc can have issues with busting the bottom end, they didn't reinforce the bearing bosses in the case and they can crack and fail.
Click to expand...

I only recently have heard this about the Lifan engines. There are guys who put tons of miles on them without problems. Wondering how much this really is an issue.

These little CT90s and CT110s really can withstand an incredible amount of abuse. I know too many stories of cross country and cross world stories like DOT.

I am going to ride Big Bend on this one in March.
 
SL350 said:
I only recently have heard this about the Lifan engines. There are guys who put tons of miles on them without problems. Wondering how much this really is an issue.

These little CT90s and CT110s really can withstand an incredible amount of abuse. I know too many stories of cross country and cross world stories like DOT.

I am going to ride Big Bend on this one in March.
Click to expand...

Looks like You are staying busy!

and....Friends don't let friends put Lifans on their classic Hondas!:doh:
 
Most guys who buy vintage want vintage. Even when hot rodding the purists want vintage hi performance products. I guess for me it is when I see a guy taking a hacksaw to a bike that will never be made again to make it a "bobber". Some do look cool but you just can't UNDO it. The lifan engine upgrades... they can be taken off just as easily as they were bolted on.
 
focus frenzy said:
why not? looks like honda is using them now (grom engine)
Click to expand...

Speaking from personal experience, I am not a fan of the Lifan line.
A good friend of mine bought out a small local shop.
I went along to help Him sort and move the inventory to His shop.
The loft of the shop was full of Lifan motors, all of them looking new, but all of them had catastrophic failures (that We actually examined)
Broken rods and cranks, spun bearings, bad castings, etc.
There were probably 150 motors in the loft. He told Me I could have them if I wanted, so I stripped the fastners and some covers and castings, and scrapped the rest.
Externally, the were almost identical to the Honda motor, but apparently the Chinese are lacking in the metallurgical sciences at this point. The Quality control boys must have been asleep on the job. Every day.
 
SL350 said:
Most guys who buy vintage want vintage. Even when hot rodding the purists want vintage hi performance products. I guess for me it is when I see a guy taking a hacksaw to a bike that will never be made again to make it a "bobber". Some do look cool but you just can't UNDO it. The lifan engine upgrades... they can be taken off just as easily as they were bolted on.
Click to expand...

Yes yes yes. Taking a vintage bike and butchering it is wacky to me. I also have to admit a few look cool but most uncomfortable and only good cruising around town with the cardboard thick seat. Saw a SR500 Yamaha that someone went to town on. Sad to take a rare bike and make it worth less.
 
This CT90 is ready. Drove it about an hour today and she ran just fine. Not a drop of oil leaked, as it should be. I tolerate some oil loss on some bikes but where I take this little guy I don't want to spoil any water or critter. She is a tight ship!

Took it to power line right of way and bounced up and down. One thing I can't do is ride the pegs for any length of time. As I stand up, I leave the bars so I have to hunch over and bend knees way too much. CT90s may be off-road bikes but they are for riding on the seat.
 
You could put a ape hanger bar on it so you are more comfortable standing ?
 
why no pics?!?!?! im a mini trail nut
 
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