Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.
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Thread: Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.

  1. #1
    Junior Member BenHume's Avatar
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    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.

    Title says it all. Previous owner mentioned that he replaced something in the transmission, (i texted him so maybe he'll let me know what he did) and I have the bike running well but have found that after warmed up, the bike has trouble staying in second and will pop into neutral or even once it popped into first. If i manage to get it into third it stays there and will shift up the whole way and then back down. I did a cold drain when I first got the bike because I had to install a pin on the clutch lever (that the PO removed to replace a spring) and then put that same oil (was perfectly clean) back in the bike. after putting a bout 30 miles on it and noticing the shifting issues I figured he must have messed something up and drained the oil and removed the right engine cover. I found lots of sparkles in the oil, but from the standpoint of a noob the tranny looks nice and intact. The first 20 miles I put on the bike I experienced no problems, it shifted like a dream. Any ideas before I start tearing it apart? I have the shop manual and have worked on most parts of a motorcycle besides the tranny so this is sorta new to me. - Ben

    When I shift down to first, It feels like a nice snappy click, and the same back to neutral. Shifting up to second however, and there is not satisfying click at all, but the neutral light will go off. I watched the stopper plate rotate as I reached around and shifted, and when shifting to second, the bottom shifter arm doesnt appear to contact the little pins on the shifter drum. I will remove the clutch basket and try to get a look at the drum and everything.

    PS: Its a 1982 cm250c
    Last edited by BenHume; 03-18-2019 at 10:49 PM.
    1981 Honda CM400C

  2. #2
    Super Moderator J-T's Avatar
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    Let us know what you find there. Pictures will help.
    JT
    81 CM400T Under re-construction
    82 GL500

  3. #3
    Senior Member drydreamer's Avatar
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    Hi Ben, you have a manual and know of cmsnl for the very helpful exploded views. Research research research prior to "going in".

    You have the clutch peg spanner and a flywheel extrator bolt, being the only 2 "normal" special tools needed for these engines.

    Once the clutch basket is off you will see better the outer gear selection components, and, notice the gear selector cross shaft and sprung loaded "hook" can be removed.

    If its jumping out of gear, which is seems to do, then suspect the dogs ( all that "glitter" probably ) will be worn. They are ever so slightly dovetailed, but probably not now.

    Engine out but you don't have top take the cylinder head off to work on the transmission thank god as the 4 inner head bolts can be very problematic. They are crutial.

    Before you go in to deep and with the engine still being capable of running, I would remove the clutch cover and drum cover and drum and clean. I would also flush out all the crap that is inside the engine to include the kick start oil trough and sump floor.

    Whilst the clutch cover is off access the balance chain and its adjustment, also the cam chain.

    You say the engine has been apart before, what color is the sealer between the upper and lower crank case joint and cylinder base gasket ( even the clutch cover gasket for that matter ) ?

    pictures pictures pictures.

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  5. #4
    Junior Member BenHume's Avatar
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    Ok, finally got around to pulling the engine. 1982 CM250 C, as I mentioned above I assume the dogs are worn and that's why I cant shift into second. I have the shop manuals.

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190611_160123.jpg

    Pulling the engine was easier than I thought, and only weighs about 80 pounds so I just lifted it out of there and got it on my bench. I am going to update this as I go through the process. One snag Ive come across so far are the three bolts that hold on the oil pump.
    I have a ryobi impact driver that doesn't seem to have what it takes. they haven't budged and I don't want to strip them. Is it possible I can repair the transmission without even removing these? What do you all suggest... some sort of liquid wrench and a more powerful impact driver?

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190612_001922.jpg

    I don't see any possible way to split the case and access the transmission without removing the whole top end.. luckily I rebuilt the top end of a 1982 CB650 nighthawk so I have all the tools I need to remove valves if need be, lap them, reinstall the pistons into the cylinders etc. Just have to follow the manual and slowly take it apart.

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190612_001928.jpg

    I also assume I'll need to remove the flywheel so I may need to buy a special tool.. haven't looked into it.

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190612_001941.jpg

    Any tips are much appreciated!
    1981 Honda CM400C

  6. #5
    Member Mr. Mike's Avatar
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    Ben,

    Sounds like you’ll be fine with the experience you have.
    With regards to your impact tool. I’d first get a hammer type impact tool and jis bits. But this I learned years ago with stubborn case bolts; first, WD40 the screw heads and wait a bit, then take the proper fitting bit tip and while holding the bit in the screw head, rap it with any medium small hammer a couple of times, then use the impact tool. The shock of hitting it first breaks some holding tension. Using a Phillips head tip on the softer screws will leave you frustrated and will likely distort the screw head, so be careful. And the cases are only aluminum and crack easily using hammer driven impact (this is we’re my inexperience bit me years ago). While the screws are out, and if you buggered any screws, see if there is an aftermarket stainless set available.
    longdistancerider likes this.
    1966 CL77
    1978 CB750K
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  7. #6
    Junior Member BenHume's Avatar
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    Ordered some JIS bits to remove the oil pump, but now Im stuck on removing the rotor. How should I go about holding the rotor still so that I can remove the bolt? Also, whats that threaded hole in the end of the bolt?

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190622_163331.jpg

    I read somewhere online that you can use a penny or something to mesh the gears? I see in the manual a $100 tool that holds the clutch basket still.. would rather not spend that money.

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190622_163338.jpg
    1981 Honda CM400C

  8. #7
    Super Moderator longdistancerider's Avatar
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    The FSM shows the clutch still installed and held with a special tool to lock the crankshaft from turning, this is where you could use a penny between the clutch and crank drive gears to do the same thing. Then the rotor bolt is removed and it comes off.
    Sounds like you need the FSM, PM sent
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
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  9. #8
    Junior Member BenHume's Avatar
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    Update! Ok, So my JIS bits showed up and with some heat, and my impact driver, followed by my impact drill I was able to remove one... one of the oil pump bolts. The bit broke after attempting to remove the other two.. so I dremeled the heads off carefully, removed the oil pump, and unscrewed the remaining threads by hand! crazy.. oh well..

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190626_185225.jpg

    Next, I bought a 16mm 1.5 pitch bolt and got the rotor off. I had to remount the motor temporarily in order to turn the wrench, but it came right off!

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190626_185232.jpg

    I then followed the manual to crack the case, which went perfectly.. and removed the shift drum and transmission... This is where it gets odd.

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190630_224023.jpg

    Engine oil was full of metal sparkles.. grey metal sludge deposits in case.. coupled with the inability to shift fully into third.. worn dogs? I am afraid the whole transmission looks... pristine? what should I be looking for? I thought the wear would be obvious but the "dogs" all look perfect as far as I can tell... any ideas?

    Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190630_224049.jpg Cm250C Won't stay in second, pops to neutral or sometimes first, metal dust in oil.-img_20190630_224036.jpg
    1981 Honda CM400C

  10. #9
    Junior Member BenHume's Avatar
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    One idea.. The owner installed new clutch pads and hadn't rode the bike since he installed them. I then get the bike.. get it running and ride it around.. and find metal dust in the oil. Could this just have been dust from the new clutch pads? what if theres nothing wrong with the transmission at all? I'm really not seeing barely any wear on any part of the transmission... could the higher concentration of dust cause the transmission to lock up? Should I have just flushed the case and added new oil and tried again? oi.. either way it was fun to take this apart and with some new gaskets it'll be easy to put back together...
    1981 Honda CM400C

  11. #10
    Senior Member mike in idaho's Avatar
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    What do the shift forks look like?
    '65 YG1
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    My company car is a Kenworth

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