free up piston rings?

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skiri251

skiri251

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I just picked up '69 Honda Trail CT90. Went through carb, valves, ignition timing. Compression is 138PSI. The manual says it should be around 171PSI. This bike got only 6000 miles on it but hasn't been ridden for more than 20 years. I read somewhere that piston rings can stick to the piston and causes low compression. Is it likely? If so, is there a way to free them up without tearing into? Seafoam in the crank case, gas tank? Diesel fuel?
 
Yes it is highly likely. A little runtime will free them. Some ATF in the fuel and oil will help speed the process a little and clean up the internals nicely.
 
slabghost":u4npm6g6 said:
Yes it is highly likely. A little runtime will free them. Some ATF in the fuel and oil will help speed the process a little and clean up the internals nicely.
Click to expand...

Thanks.
How much ATF in the oil? The oil capacity is 0.9 litter. Should I drain the oil after a while or keep going?
 
Running it on the thinned oil isn't good for a long time and especially not under hard use.
It's generally recommended to use 1 quart trans fluid to our 3.8 quart GW so that's roughly 25% mix.
I'd run it easy on this mix no more than 50 miles.
 
About 20% capacity won't hurt in oil for normal riding. I wouldn't push it in race mode or near redline. Once they are free and the compression is right I'd change oil and filter to remove any junk the ATF cleaned off. I substitute 1 quart of oil in the car every other oil change (5qt capacity). 3000 miles to next oil change.I've never had a problem.
 
skiri251":2l9f83fc said:
It's kinda difficult to ride this tiny bike w/o pushing it.....
Click to expand...

That was my first thought being a 90cc unless your like a small 9 year old, lol.
Besides, how much and how often can you ride a little bike like that anyway.

Over a span of a couple weeks starting it and letting it run for a 1/2 hour or so every couple days with a few revs occasionally might be enough.
It's air cooled so put a fan in front of it.
 
skiri251":2a6i0b20 said:
Thank you both.

It's kinda difficult to ride this tiny bike w/o pushing it but I will try.
Click to expand...
In that case I'd use 4-5 oz of ATF in the oil and run it. The ATF in the fuel will help free the rings while running. Adding ATF to the fuel will not reduce the anount of 2 stroke oil needed BTW. It will smoke more but it will do the intended job.
 
My thought is being 2 stroke it would already be lubricating the rings so ATF might not do any good but since ATF is a good cleaner it's worth a shot.
2 strokes are so easy to re-ring if it doesn't help.
 
Unfortunately it's a 4 stroke. After all, it's a Honda who tried to win World GP with 4 stroke.
Yesterday I took her to my usual local mini twisties. Up hill, WOT in 2nd gear and managed 20MPH. LOL,
Down hill and on level ground, it can do 40~45MPH but up hill is agonizing.
Too scary to ride in a city traffic so I will let it idle in my drive way as Dan suggested.
 
HMMM single ohc motor... nope gotta be 4 stroke,,,

Honda Trail 90 CT90K1

Colors:
Scarlet Red
Yellow
They were accented with a gray plastic shroud.
The exhaust system and heat shield were chrome.
The seat was a solo seat with chrome trim.
The chrome luggage rack behind the seat was standard equipment.
The fuel tank had no decal, but the down tube reads "HONDA".
The transmission was an 8-speed dual range.
The front suspension used telescopic fork tubes.
The engine was a 89cc OHC single cylinder with an automatic clutch.
The serial number began CT90-200001.
 

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Yes. That's her. She is yellow.
I am going to ride her on fire trails and OHVA with my son aboard Z50R.

The engine is super-easy to access so I may try over boring it later. (I guess I'd better get a 2 stroke motocrosser instead.)
 
skiri251":14awzr1j said:
Unfortunately it's a 4 stroke. After all, it's a Honda who tried to win World GP with 4 stroke.
Yesterday I took her to my usual local mini twisties. Up hill, WOT in 2nd gear and managed 20MPH. LOL,
Down hill and on level ground, it can do 40~45MPH but up hill is agonizing.
Too scary to ride in a city traffic so I will let it idle in my drive way as Dan suggested.
Click to expand...
If I recall, these where really not geared to do anything on the black top, but put
them on the trails and dirt roads they done very very well. :good: They worked well
back in the day, and it will do you a good job for what your going to use it for. :yes:
 

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