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Discussion Starter #1
Hello. I´m new to this forum and I´m having problems with my CM450 (bobber) from 82 on which I have opened up pipes and cone air filters- no rejetting.. didn't seem necessary coz it was running good then. Anyway, I am also new to everything thats going on inside an engine but I have successfully(I think) put on new clutch plates and springs because I couldn't change from 1st to 2nd gear- When it was driven in 1st gear for a while and gotten warm it was a little better but not great- I could get it carefully into 2nd gear sometimes and then quickly into 3rd..(before it jumped back into neutral) and the rest of the gears worked fine. So now, that I have changed the clutch the problem is exactly the same(money well spent :mad:) I´m guessing that the clutch is not the problem because the issue is the same(?). So I guess my question is- Would there be some CM/CB 450 experts who could give me some ideas what to look at next? Is it the transmission? Compression? Is it wrong oil? I´m using this - Motorolie til Harley SAE 50 5 l Kroon - Motorolie - thansen.dk. Its says its a mineral motor oil for oldies.. I have been soaking the clutch plates for about 15 min. before installing, maybe its not enough? I have adjusted the cable back and forth with no success.
Hope someone can help. Thanx
Klavs
 

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Welcome aboard Klavs
From your description I'm going to say the 1-2 shift fork is probably bent and there may be some damage to the gears, 1st and 2nd.
The oil you are using appears to be 50W oil which is too heavy an oil. 10-40W is used for most riding conditions, 20-50W for high riding temperatures, 90 degrees plus F, not C. Conventional oil is best to use, not synthetic or a syn-blend. But the oil is not the problem.
Do you have the FSM, factory service manual?
 

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Discussion Starter #3
Thank you for the reply! I think maybe(not sure) the problem started when I dropped the bike on its left and hit the gear shifter.. Could it be that the 1-2 shift fork could be damaged that way? I think I have to go the expensive way and take it to the shop. Sounds like something you can't fix if you have no experience with it? Maybe it can be possible with the manual you are talking about?. I only have the Clymer Honda Cb400 Cb450 Cm400 Cm450 Twins Nighthawk (1978-1987) - Service Manual 400. Do you know where to get the other one in pdf?
 

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Dropping the bike doesn't usually do that but it is possible. For tools you would need the basic hand tools plus a torque wrench, hand impact driver and you'll have to make a clutch nut socket, there's a "stickie" for making one. You definitely need the FSM, PM sent about that. If you have time, patience and some mechanical skills we can guide you thru it if you want to attempt it. You will need to remove the engine to turn it upside down. Or you can take it to a shop, be sure to talk with other riders first about the good and bad ones.
 

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Discussion Starter #5
Thanks a lot for help and the PM. Just talked to the shop and its WAY to expensive. I am usually pretty good at figuring out technical stuff, and have plenty of time and little money so I´m gonna try to fix it myself. I´ll get the tools first and get the motor off, it´s gonna take a little time.. Do you think this is what I need? - GEAR SHIFT FORKS 75 HONDA CB400F CB400 CB 400 F FOUR 4 | eBay
 

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Discussion Starter #6
Just found this on the engine CB400NE-3001980. So I gues its a CB400 engine from 1980 right?
 

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Yeah you have a 400 engine, I'm not sure on the engine number but likely it is a 1980. That means you could have a six speed or the 5 speed. Different transmissions mean different parts internally so don't buy anything for it until you know for sure which you have.
A CB400F is a 4 cylinder bike, completely different than the twin so there are few if any interchangeable parts. You'll be looking for the CB/CM 400 engine/trans pieces. I'd suggest new forks rather than used if you can find them.
One other tool I forgot to mention is the rotor puller bolt Flywheel Puller, M20X1.5 R.H. External Thread, Hollow | Motion Pro , you can use any similar bolt to do the same thing or even the oil filter bolt if needed will work.
 

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Discussion Starter #8
Ok I have now removed engine and are about to open it. Is it necessary to remove side parts- clutch, flywheel etc.- to get the bottom case off? And do you have tips how to pry it open? As I understand it´s really hard to get open..
 

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The clutch assembly, rotor/stator and the shift rod all need to be removed to split the case. Be sure all of the bolts are out including the ones in the recessed holes. Using a dead blow hammer or a block of wood against the case hit with a steel hammer start tapping around the seam of the cases. Keep going round and round until you hear a change in the sound, kind of like a hollow sound. In NO case do you ever try the drive something in between the cases to split them, that ruins them.
 

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Discussion Starter #10 (Edited)
Ok, so now I got it open. Ofcourse I made the mistake of putting a screwdriver in between the cases before I got your message.. Maybe it´s ruined. In that case I will buy a new engine and use this one for parts. Anyway I´ll go ahead and take my chances with this one. I have taken some pictures in the area around the shift forks. The left bottom one looks a little bent.. not sure if this is the 1-2 gear? I cannot really get the top gear rod thingy(?) of to reveal those shift forks. Is that needed?
foto 3-1.JPG
foto 1.JPG foto 2-1.JPG foto 2.JPG foto 2a.JPG
 

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You'll need to look at the case mating surfaces to see if they got damaged. Small scratches/dent will usually seal back up with the Honda Bond case sealer.
The gear shaft that won't come out is 5th/6th and since you haven't had a problem there I wouldn't worry about it. You can remove the 8mm bolt that holds the steel plate in place to remove it but it's a real bugger to do and even worse to re-install w/o removing the crankshaft carrier.
The left shift fork in the picture is 1st/2nd gear. Remove the rod and fork. Using a "square" measuring tool place the square on the rod as close to the fork and measure the distance of each fork ear to the square. It may be visually obvious to you.
Need to see closeup pictures of the 2 gears and the slider dogs so we can determine if the gears and/or slider are good or bad.
 

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Discussion Starter #12

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Correct tool. You place one side against the shaft and check the fork tip distance to the other (90 degree) side. Also you are looking for the actual fork to be at 90* to the shaft since it's possible both fork tips bent evenly. The gears and dogs look good.
 

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Discussion Starter #15
Forks look like they are exactly 90 degrees on the shaft
 

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Could be picture angle but the lower right picture it appears the closest fork end is bent inwards. Length and spread of the forks isn't the important part the distance from the tip of the fork to the ruler is. The should be pretty close to the same, a few thousandths' difference is ok, .001"-.004"
 

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Discussion Starter #17
It´s the angle of the picture. I´m not the best photographer.. sorry :) The forks do not appear bent with the naked eye. On the left one(bottom pictures) is 9 mm from both tips to ruler. Is that correct?
 

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There is no published spec, only a spec for the thickness of the fork tips so check that.
In post #12 the picture of the gear. It looks like the bushing is damaged, check that and any other bushings.
 

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Discussion Starter #19
Just measured the fork tip thickness. They are all 5 mm(some a little less) and the manual says "shift fork Claw thickness service limit 5,50 mm". So I guess this could be the problem?
measure.jpg

And is this the bushing you think could be damaged?(actually don´t even know if it is a bushing) What should I look for? To my untrained eye it seems fine..
IMG_1449 copy.jpg
 

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Yeah, that's below spec and may be the source. They need to be replaced.
Notice that the bushing in the gear isn't even? Looks like it's been ground some(dark areas). Could be old oil build up or maybe worn. Lightly polish it with 1500 grit paper and see if it becomes shiny and smooth. I'd inspect all the other bushings in the gears also. This could be caused by using the wrong oil or oil starvation to the shaft. If the bushing is worn it'll allow the gear to twist on the shaft which could cause disengagement.
 
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