Topic: 1975 CB125 - little aluminum flakes coming out of the crankcase vent w/oily mist

[sangyo soichiro]

Okay, it's not a SOHC4, but this is a general question that could apply to all engines I suppose.

I have a 1975 CB125 single cylinder.  I'm still in the process of working all the bugs out of it and getting it to run properly.  Yesterday I solved one problem of a fuel flow issue, but only to encounter yet another problem.

As I was taking it for a test ride, my pant leg got coated with an oily mist coming from the crankcase vent tube.  When I looked at my pant leg, I noticed a million little shiny pieces of metal.  I have a really strong magnet and tried to see if they were steel or something else, and they didn't respond to the magnet, so I figure they're aluminum or something like that.

Needless to say, I'm going to have to tear the engine completely apart to see what's going on, but do any of you have an idea of what I can expect to see inside there?

Thanks in advance.

[mrrch]

The simplest thing would be worn out aluminum clutch plates but you are going have to dig into it further (start at the clutch cover)
Is the oil overfilled? causing it to pump out the breather.

[sangyo soichiro]

Thanks mrrch, I hadn't thought of the clutch plates.  I thought maybe the piston was scoring the cylinder. 

The oil coming out the breather is a mystery to me, because as best I can tell, it has just the right amount of oil (one quart, and also reads right on the dipstick).  But it definitely is spitting oil way more than it should.

Another thing I failed to mention is that it doesn't run quite right.  It will die if I try to let it idle, and I wasn't sure if that was a carb problem or something else.  Kind of hard to set the idle though if it's due to something else.

WIll definitely start at the clutch cover though, and see if that's it.  Thanks for the tip, mrrch!

[CycleRanger]

Check the cam chain tension. I'd suspect the chain has stretched and is rubbing on the tunnel.

[crazypj]

I think it was only the MX bikes that got alloy clutch plates?
 CB125 did have cam bearing issues but you would also need piston/ring problems to be blowing oil out of breather.
 You did check oil with bike completely upright (stand legs are often bent and bike tilts to left)
 You didn't screw dipstick down to check level?
 I think you need some engine work to find out whats wrong.
 Simple little single cylinder motor only takes a couple of hours to remove and completely strip, takes longer to clean the old gaskets off mating surfaces than the actual strip/re-build process (I know it's part of the process but you get my meaning  )

[Don R]

If you have access to a compression tester you might check it. Cam chain tensioner sounds likely.

[sangyo soichiro]

Cam chain tensioner is another thing I hadn't thought of.  Thanks again guys.

Crazypj, I had the bike in the center stand and didn't screw in the dipstick when checking.  I'll check the cam bearings too.

Don, I do have a compression tester, and I'll see what it does with that.

Looks like I'll have to tear it apart regardless of the problem in order to clean out all the little chips.  It's nice though to know in advance what to look for.

Thanks again guys.

[Eydugstr]

You also might want to clean out the oil sludge trap (underneath the right side engine cover, held in place by three concave screws) and the oil filter screen underneath, can imagine they're pretty nasty, too.

[sangyo soichiro]

Will do, Eydugstr.  Thanks for the info!

[crazypj]

I've never had a problem with the cam chain or tensioner on the CB125/185/200 (or even the 100cc variant)
Chain can be loose though if itwas never adjusted or not adjusted correctly
That tends to wear the sides of the cylinder and head which hopefully is all you have wrong with it.
 The centrifugal filter works pretty damn good at removing particles before they hit the big end, the higher the rpm, the better it works 

[sangyo soichiro]

Check the cam chain tension. I'd suspect the chain has stretched and is rubbing on the tunnel.

Bingo. 
That was the cause of the aluminum flakes.  Seems the PO never adjusted the tensioner.  And I failed to check it myself.   

...but you would also need piston/ring problems to be blowing oil out of breather.

Double bingo. 
The top 2 rings were not only broke, but shattered.
Unfortunately, Honda doesn't make the standard rings for the 1975 125 anymore.  They still sell the 1.0 over, but I didn't really want to have to have it bored and buy the corresponding piston.  The girlfriend (my personal parts finder  ) found some standard rings on ebay, so I hope they work.  Still waiting on them in the mail.

[crazypj]

500f rings fit, 56mm bore

[CycleRanger]

Bingo. 

Double bingo. 

Glad we could help.  Thanks for the follow up, let us know how it goes!

[sangyo soichiro]

500f rings fit, 56mm bore

You just made my day!  Thanks for the tip!

[crazypj]

See if you can find a CB250 piston, at least you'll have a high compression CB125 (may be too high?)

[sangyo soichiro]

See if you can find a CB250 piston, at least you'll have a high compression CB125 (may be too high?)

I'll keep my eye out for one!  I don't want to make this into a race bike, but I would like to get it to go up to 70 mph or a little more (just for a little more wiggle room on the highway).  Once again, thanks for the tip! 

I wonder if I can put on a smaller rear sprocket and get to go 70 or more, with little hinderance on the low end riding...?

[crazypj]

You need a bigger carburetor to go faster
I used to use the left carb off Suzuki GT250 as they were available real cheap 30+ yrs ago.
Had an XL125 clocking 90mph with it

[sangyo soichiro]

You need a bigger carburetor to go faster
I used to use the left carb off Suzuki GT250 as they were available real cheap 30+ yrs ago.
Had an XL125 clocking 90mph with it

Wow!  90 would be great!  Now I'll have to keep an eye out for a bigger carb too.   

[Flying J]

I changed the gears on both my 125s to get a little more top speed. I went with a .50 over on my rebuild. I also have a bigbore piston kit that i thought i was going to use but didnt if you are interested in that. Have you rebuilt the carbs? Every 125 carb i rebuilt had leaky floats. Just something to check.

[crazypj]

Yep, practice on a 125, then get a 500 or 550 and do everything 4 times 

[Flying J]

Yeah i like single cylinders. 1 piston at $25 is not so bad. But when your running a 4 cylinder everything quadruples! Your $25 piston and $40 cylinder bore just became $100 for pistons and $160 for a bore! I never want to rebuild a CBX

[crazypj]

Yeah i like single cylinders. 1 piston at $25 is not so bad. But when your running a 4 cylinder everything quadruples! Your $25 piston and $40 cylinder bore just became $100 for pistons and $160 for a bore! I never want to rebuild a CBX

LOL

[sangyo soichiro]

I changed the gears on both my 125s to get a little more top speed. I went with a .50 over on my rebuild. I also have a bigbore piston kit that i thought i was going to use but didnt if you are interested in that. Have you rebuilt the carbs? Every 125 carb i rebuilt had leaky floats. Just something to check.

Thanks for the info.  I cleaned the carb but that's about all I did with it.  I'll have to inspect the floats better next time I have it apart.

About the big bore kit; what is the bore diameter of it?  And does the new piston increase the compression ratio?  I wasn't planning on boring it out, but it's something I might consider.

But what really piqued my interest is your mention of changing the gears for a higher top end speed.  I do have a spare 750 engine to scavenge parts from.  Without having it in front of me, do you by any chance know if I can use any of those gears for the final drive of the 125?  Or I also have a spare 125 engine I can use the gears from, will any of those work?  Like I said, I don't have the stuff in front of me, so I can't check it for myself at the moment.  If none of those will work, mind if I ask what you used for the final gears and where you got them?

[Flying J]

I think on my blue 125 i bumped the front gear from a 15 tooth to a 17.\

The big bore kit im not sure how big it is ill have to check but i think its a 58mm. Not sure on the compression either.

Here are a few pages to give you an idea on big bore options.
http://hondacg125.awardspace.com/how_to_increase_engine_size.htm
http://www.powroll.com/P_HONDA_VINTAGE_100-125.htm

you can spend as much as you want on these little motors. But in the end its still a tiny motor.

[sangyo soichiro]

I think on my blue 175 i bumped the front gear from a 15 tooth to a 17.\

Ah... ha ha, for some reason I was thinking internal gears when you mentioned "gears".  Yeah, I had been thinking sprockets at first.   

Thanks for the info on the big bore stuff.