[pitzky]

Don't know if the topic has been discussed before (if yes I wasn't able to find it, sorry!) but now that I'm finally riding my CM400T around I realized it vibrates really a lot...but since I come from a completely different kind of bike (Sporty 883) I don't know if it's normal or if it might be an indication of bad counterbalancing or similar (since I suspect that one of the previous owners put his hands where he should not have)

My observations are:

The bike generally rides at high RPMs, I often find myself at 50-60 km/h feeling the urge to switch to a next gear and realizing that I'm already in 5th gear...but this might be normal, on the Harley I was rarely over 3-4000 RPMs but 4-5000 might be the norm here (correct me if I'm wrong)...also one of the POs has cut out the power chamber which I'll probably replace at some point...

At almost all RPMs the whole bike vibrates A LOT...when idling I can see the front axle jumping up and down (Harley did the same though) but it really gets uncomfortable over 3-4000 RPMs where I can feel my hands and feet getting numb from the vibrations...besides my rearview mirrors getting loose and all that :???::???:

So I guess my question is...is it normal for these engines to vibrate that much or should I start investigating? I never crossed the 100 km/h because it gets almost unbearable over 70-80 km/h even though I realize the bike would have more to offer!

My first guess would be to check the counterbalances, but I guess the engine is also statically balanced? What if the rotor is mounted out of balance or similar?

Right now I'll keep riding it as it is, but I will need to do something soon about it or I'll drop a finger at some point :lol::lol:

Cheers!

 

[dtsmjr8dan]

It sounds, from your description, that you may be running on one cylinder or the balancers are out of sync. Has this engine been out and apart? I mistakenly timed my balancers both on the tc mark and it vibrated like that. Worse vibration than a Harley 74. You mentioned that you are running without the power chamber. Do you have the original air box for the intake? What is your compression like?

 

[pitzky]

The cylinders are both running, I had one misfire at the beginning so I can recognize the difference ? but my mechanic said he suspects the engine has been opened (poor work according to him)...hence my suspect about the balancers which I'll probably have to figure out how to set properly
As for the intake, I'm running with the original airbox so far but I was considering giving it a try with some conical filters and proper rejetting, even though I think it's running slightly rich at the moment...the compression was tested by the mechanic and was excellent according to him, reaching 13 bar, does that make sense?

Cheers!

 

[longdistancerider]

This sounds like the balancers are out of time, fairly easy to get them timed wrong. Dan's missed, I've missed and I'm sure there are others. These engine are designed to be running higher rpm than HD ever thought of. Power doesn't really happen until 4500 and higher. At 60 khm, 37 mph, you should be in third gear (maybe 4th) not 5th.

 

[pitzky]

Okay, I guess I know what I'll have to do this weekend...or as soon as I can in any case...and then probably I'll discover the real potential of the bike...I mean, I'm no race driver and I'll never be...but still I was expecting some different power output...after all my harley had 53 hp over 900 ccm and this should be just short of 40 over 400 ccm and a bike that weighs a fraction, so I know the engines should behave much differently ?
I guess I'll have to keep posting for help once I get started on the task, but first I'll start reading like crazy
Any bids about restoring the power chamber and changing the intake? I'm not really looking for more power, but will the engine benefit from more air?
Cheers!!

 

[dtsmjr8dan]

This sounds like the balancers are out of time, fairly easy to get them timed wrong. Dan's missed, I've missed and I'm sure there are others. These engine are designed to be running higher rpm than HD ever thought of. Power doesn't really happen until 4500 and higher. At 60 khm, 37 mph, you should be in third gear (maybe 4th) not 5th.

I often red line my 400 when the others crank theirs up. After riding bikes with a maximum rpm of under 6000, it took me some time to adjust my ears to the higher rpm's that these engines easily run. I have to rely on the tach at times while riding with the larger, noisier, heavier bikes. These little bikes easily keep the pace of the larger ones , to the surprise of many of them. Shifting from 4th to 5th at 60 isn't pushing the engine at all. (actually feels about right for entering a highway)

 

[pitzky]

Wow...okay I guess it will be a huge adjustment for me then! More than 4000 sounds already weird! But maybe once the balancer is right it will also feel different ?

 

[dtsmjr8dan]

These bikes don't have the torque of the larger displacement bikes, but, they put out 43 HP/ 400 cc compared to the Sportster's 60 HP/ 1200 cc. These weigh @ 400 lbs and the Sportster weighs @ 560 lbs. (that makes them the same power/weight ratio of .9) . You will be surprised at how they perform.

 

[longdistancerider]

Wow...okay I guess it will be a huge adjustment for me then! More than 4000 sounds already weird! But maybe once the balancer is right it will also feel different ?

Wait until you hit 9500 rpm, redline, for the real sound.

 

[ancientdad]

More than 4000 sounds already weird!

Here's a preview... it's a little higher (10,500 or so) but you'll get the idea

 

[longdistancerider]

As they say "sing it to me baby" and these really do start singing

 

[Bill H]

Working on my second cb400a I set the crank mark 180 degrees out on the balancers. When I started the motor and ran it up then let off it the bike danced backwards on the center stand.

I had to drop the motor and tear it down again to reset it. Hard lesson to learn. At least you didnt do it to yourself. I agree that the problem is in the balancers . Pick up a FSM and with the help of the forum you will be riding in no time. Look at the bright side you will get to see what the rest of your motor looks like.

Bill

 

[pitzky]

Working on my second cb400a I set the crank mark 180 degrees out on the balancers. When I started the motor and ran it up then let off it the bike danced backwards on the center stand.

I had to drop the motor and tear it down again to reset it. Hard lesson to learn. At least you didnt do it to yourself. I agree that the problem is in the balancers . Pick up a FSM and with the help of the forum you will be riding in no time. Look at the bright side you will get to see what the rest of your motor looks like.

Bill

Yeah I just went through the balancer section of the FSM...I have to admit I was hoping in some solution that did not involve stripping down the whole engine, but looks like that's the only way...Is there no way to do "fine" adjustments that might help me get through whatever is left of the summer so I can wait for the winter to split the crankcase? I kinda really don't want to do it now where the sun still shines if I can avoid it / postpone it...especially since it seems just "a bit" off (not jumping from the center stand as you mentioned :-D)

I was anyway thinking of stripping down the engine in the winter to discover the rest of the motor, clean it and repaint it (leaky carbs and oil gaskets destroyed my new paint job on the engine :lol...but yeah...in the winter...:-D

Any thoughts on that?

Cheers!!

 

[dtsmjr8dan]

You can have it out and split in an afternoon. Take your time. Re-time the balancers and stick it back in the frame the next afternoon. You'll be glad you did.

Here's what you'll probably see. (note: align front with 'tc' and rear with 'th' line)

https://www.hondatwins.net/forums/1-project-logs/75985-79-cm400-rings-balancers.html

 

[pitzky]

Yeah I saw your post, very informative! And thanks to you I'll be extra careful with front and rear...before starting...any tip as to what I'll need? Of course new oil for when I reassemble it, some special sealing agent for the two halves of the carter? Would it make sense to just look for some solid 450 balancers as many of you did before even opening? I'd prefer to be as prepared as I can ?

Cheers and thank you all for the comments ?

 

[dtsmjr8dan]

If you can find some solid 450 balancers at a reasonable cost, that would definitely be a good improvement. As for anything special, you will need a tube of 'Hondabond" (Made by Threebond and also called Yamabond, etc) to seal the case halves, a clutch nut tool (there's a thread on here to make your own), and a 20mm X 1.5 pitch bolt to act as a puller for the rotor. Follow the manual and you can't go wrong (but, being in a hurry, I did...lol). If you encounter any trouble along the way , you know where to get the answers....lol

 

[longdistancerider]

Get an earlyish start and working diligently this can be done same day. Hardest part is usually dropping and lifting the engine out/into the frame so if you have access to a lift jack that helps
View attachment 263524

 

[pitzky]

Okay, then I guess I'll get the Hondabond and explore the possibility of getting new balancers...and I'll look into the clutch nut and the rotor puller...do I have to disassemble the cylinder or can I just turn the whole engine upside down and let the pistons rest in peace? (All the gaskets have just been changed there :lol
As for removing the engine I did it once for painting it, not having the frame underneath it's almost a piece of cake compared to the sporty ?

I'll keep you posted whenever I get to start the job ?

 

[80cb400t]

I haven't done it yet myself but the answer to that question is always yes, the top end can remain assembled while you split the cases.

 

[pitzky]

I browsed through ebay and found these:

https://m.ebay.ie/itm/1981-Honda-CM...weighted-gears-shaft-/292313413192?nav=SEARCH

Looks like they're solid, even though they come from a 81 CM400, @dtsmjr8dan you observed the same when you changed yours right? Seems the 81 came with the solid ones then...I guess I'll buy them so I get that part sorted out

Cheers!