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Discussion Starter · #1 ·
I picked up a 1980 CB400T Hawk last weekend for a very low price. It was extremely cheap since it came complete with an engine knock :)

Before opening it up I wanted to ask your opinion of the knocking. I've never worked on the bottom end of an engine before so I could use everyones expertise. I used a screwdriver to try and pinpoint the sound and it seems to be coming from the right side and it possibly sounded like it came from the clutch area. I'm not real experienced so I could be completely wrong. Could it be something as simple as the balancer or carbs out of sync? (just wishful thinking :) )

I took the right side cover off to have a look at the clutch and visually it looks fine. All the teeth look good. The basket and the gear behind it do move when push on them though, meaning you can wiggle them. Is this normal? Is there anything clutch related that I can look at to see if the problem is there, before opening up the engine? When I drained the oil it looked great, no metal bits to be seen. Inside the clutch cover was clean as well.

Besides the knock the bike starts perfectly and runs good. No problems in any gears. The noise is more apparent while the bike is sitting still, once moving its less noticeable. This could just be because more road noise is masking it however.

Not sure if it's related or not, but there is quite a bit of free play in the shift lever. You can wiggle it up and down about an inch. My Kawasaki, in comparison, doesn't really have any free play. The lever is tight on the shaft.

I've attached a short video clip of the sound and a few pics of the clutch. Please ignore the smoke coming from the headers, this is just some stuff the seller put on the bike to prevent it from rusting.









Thanks
 

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I'm not at all familiar with that motor, but certain mechanical things are generally the same. The clutch basket shouldn't have any lateral movement at all and probably shouldn't have any axial movement, although a very small amount probably wouldn't cause any problem (worn thrust bearings). If the bearing supporting the clutch shaft has lateral play, that could certainly result in a knocking sound - indeed, I'd say it probably would. I've never encountered bearing play with a roller bearing crank (worn rollers usually make a rumbling sound, but on a crank? I don't know...), which you probably have, but with shell bearings the mains knock under load and the rod bearings knock on the overrun. Pistons loose in the cylinder make a sort of hollow sounding knock (sometimes you can hear this sound when you start up a motor on a cold day - the pistons are normally a little loose 'til they warm up some) and worn wrist pin bearings make a sort of hammering sound much more pronounced at highway speed.
 

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Discussion Starter · #3 ·
Thanks KERRY for the explanation of the different types of internal sounds, great info.

I took a closer look at the parts underneath the right side cover. You can wiggle the big gear that is attached to the basket (collectively called the clutch outer housing I believe) independent of the basket itself. Is this normal? I'm not experienced with clutches but I thought they were basically one piece and they should move as one. Also, the two sprockets to the right of the clutch have movement in them (sorry don't know their names, for the oil pump I believe). The top one has quite a bit actually. You can move it in and out at least 2-3mm. Is this normal? Seems like a lot of movement to me. Wondering if its missing a washer or spacer. Looking at the following diagram, it appears that part #11 is missing which is most likely leading to the movement. I haven't disassembled to take a look yet.



I've attached a pic showing the parts that have movement. Do you think turning the engine manually via the left hand alternator rotor bolt would help any to identify the problem?



Thanks again
 

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Gears on splined shafts can sometimes move in and out; gears on tapered keyed shafts can move only if the shaft moves. It probably doesn't matter that the gear and chainwheels on the right can move in and out, although by the time you're getting to 3mm that seems a bit much. I don't know how your clutch disengagement works (never been inside that bike - looks interesting) but the clutch basket probably shouldn't have more than a very tiny in/out movement if any at all. A little rotational play is probably no problem, there's usually a little gear lash. Lateral play is very not good. Remember: I'm talking here about a motor with which I have no experience at all. Incidentally: Very nice photos.
 

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Discussion Starter · #5 ·
This is my first time inside the bottom part of an engine so I would love some input here to help me diagnose where this knock may be possibly coming from.

I was able to remove the clutch. To my untrained eyes, everything with the clutch looks good. The basket looks fine, no cracks or anything. The gear is attached to the basked too, none of the fasteners were broken or missing. Is there anything else I should look for with the clutch? What about the springs, could weak springs cause any kind of knock?

I then removed the external shift mechanism. All the bearings there looked and moved nicely. Do these parts look like they are installed correctly? This is before I disassembled so I'm just wondering if the previous owner installed it right.



One thing I noticed is that both the output shaft (#1 in the pic below) and the gearshift drum (#2 below) had some free play. Is this normal with the engine in gear? I have no idea, and so I thought I'd mention it in case it could be leading to the knock. The gearshift drum has about a quarter turn of free play, whereas the output shaft has about five degrees. Does the gearshift drum move or try to move (i.e. pressure against it) when the engine is running? If this amount of free play is not normal, what could be causing it?



Also, I noticed a few pieces of hard red stuff. Almost like glass, but I'm thinking its red loctite.



Thanks for listening.
 

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Discussion Starter · #6 ·
Just out reinstalling the shift mechanism and noticed looking at the pictures, that the little wheel at the end of the detent arm wasn't riding on the edge of the cam plate. You can see it in the picture below (red arrow pointing to it). This doesn't look right to me, shouldn't the wheel be riding right on the edge of the plate? When I reinstalled it I set it up to do this. Wondering if the previous owner installed it incorrectly or if the bolt loosened up and the arm slipped.

Can someone confirm that this is correct?

Here is the pic of how it was when I opened it up.

 

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You are correct. The little wheel should be riding right on the edge of the star wheel.

I had a Honda CM185 Twinstar that did the same thing. I have no idea how it got that way, but I put it all back together and had no further problems. Probably the bolt backed loose somehow...
 

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Discussion Starter · #8 ·
kirkn said:
You are correct. The little wheel should be riding right on the edge of the star wheel.

I had a Honda CM185 Twinstar that did the same thing. I have no idea how it got that way, but I put it all back together and had no further problems. Probably the bolt backed loose somehow...
Thank you for the confirmation kirkn.

Now since I've taken the clutch cover off I've found two things wrong in there (missing washer and incorrect detent arm/wheel setup). Still don't think I've found the cause of the knock though :cry:

Once I get the washer I'll put it all back together and see how it sounds. If it's still there, I may need to open it up. :(
 

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Discussion Starter · #9 ·
Re: 1980 CB400T - Engine Knock - Updated Video

I adjusted the balancer chain with the hope that this was the cause. No such luck. Put it all back together, started it up and the knock is still there. :(

While it was running I used a screwdriver again to help pinpoint the noise. I could hear it best when the screwdriver was at the top of the clutch cover. So, I took the right side off again and then spun the rear tire with the engine in gear. You could really hear the noise then. First thought it was the clutch rattling so I took that off and it was still there. Sounds likes its coming from the output shaft that the clutch sits on. I've included two videos: one with the clutch on and one without. The one with the clutch on shows some movement when it slows to a stop, not sure if its relevant or not.






I now know at least that I'll have to open it up. Any ideas on what may be causing this? I'm totally new to transmissions so any insight on what to check would be greatly appreciated.

Thanks.
 

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Just a couple thoughts without much analysis of your description: a slightly bent gear shaft will cause a knock (seems impossible, but I bent one many years ago, BSA Victor. Very loud knock). Another possibility: a small particle of foreign material embedded in the valley between gear teeth. You might mark the clutch, maybe the other gear to see if the knock occurs at the same point in each revolution. A friend had this happen on his MGB, chip from a synchronizer clutch lodged in first gear.
 

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It appears to me you are missing a thrust washer (goes against the layshaft bearing before the clutch hub goes on).. And be SURE the domed washer fits with the "Outside" marking facing out when you reinstall it in the hub (under the "special" hub nut)...Either of these could be the cause of the freeplay you seem to have...... You are also missing a bolt on the shift drum plate...These should be slaked in place and have locktite used......(That's what those red chunks were...excessive locktite)
The drum stopper-arm bolt needs a washer as well.... Missing parts cause problems...
 

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Discussion Starter · #12 ·
Thanks guys. I'll do some further digging based on your feedback. I'm going to start the process of opening the engine tonight. First time so wish me luck. :D

66Sprint, thanks for pointing out the missing parts. I was already aware of the missing shift drum plate bolt, but thanks for pointing out the others. I've noticed a host of either missing bolts or incorrectly installed bits since taking off the clutch cover. Makes me wonder what kind of mess is inside the engine.

Thanks again for your help.
 

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Discussion Starter · #13 ·
I picked up the alternator puller today and finally got the bottom engine case off. I was sort of hoping the issue would be pretty obvious but unfortunately it isn't. I've checked all the teeth and they appear fine. Although this is my first time seeing a transmission so I may be missing something obvious. There doesn't appear to be anything stuck in between the teeth either.

I rotated the two shafts manually while watching the gears and it appears that the "knock" occurs with every rotation of the shaft that holds the chain sprocket (countershaft?). I get to the same point and I cannot rotate it past this point.

I removed this countershaft for a closer inspection and don't see anything obvious. One thing I did notice though was that there wasn't a locating pin on the end bearing, should there be? Not saying this would be causing the issue but I thought there should be one there to line up the oil port.

I've included a video showing the tranmission and where it stops moving. I can't move it past this point with my fingers but with the engine running I guess it just powered through this sticking point.

Any help or insight would be greatly appreciated. I'm not really sure how best to go about diagnosing the issue. I don't mind picking up another transmission but I'd like to know what's causing this first.

 

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Discussion Starter · #14 ·
Under further investigation I now see a chipped tooth one of the gears. I'm guessing this will be the culprit of the knock. When turning it appears to correspond with the knock when that tooth messes with its sister gear on the main shaft. Just priced it on Bike Bandit and it's $90!!!!! How are these prices compared to going through a Honda dealer? For the price, am I just better off picking up a used transmission off eBay?

Here is a picture:

 

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You can probably find a complete "dead' engine , maybe a whole bike for $100 or so.... Careful disassembly while paying attention may reveal the "missing" or mis-installed parts on yours.....
Plus, you'll have lots of spare parts!..... Win, Win.....

What are those dents in the countershaft bearing outer race?.....That can't be right either....
 

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Discussion Starter · #16 ·
Finding an old engine where I live is not easy. Very hard to get old bike parts around here. There is one place that I can check but it may be a long shot and he's known for very high prices. I'll check though as you never know. If not, I'll have to try my luck with eBay. You'd never find a whole bike for $100 here either. It could be in totally disassembled and in a garbage bag and they'd still want a fortune for it.

Which marks are you referring to (A or B in the below pics). The B marks are there to align the race so that it matches up with the oil port, they should be level with the case. They don't line up in the picture because I just threw it back in for the pic. I'll line it up correctly for final assembly.

 

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I have a complete 79 CB400T2 engine in my garage. Most of the rest of the bike too, missing front end and rear wheel (that's all on my 450 now).
But shipping is a deal-breaker in your case, I think.........
 

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Discussion Starter · #18 ·
Thank you Bill for the offer, but you're right, the shipping would be huge. Getting anything shipped here is a big deterrent, takes forever and costs a lot. Especially heavy objects like that. Appreciate it though.

That brings up another quesiton though. If I just want to buy a used transmission, is there anyway of knowing what other models use the same transmission. Or even one that will fit in this case and work? I know for the same year there were CM400's, is there anyway of knowing whether a transmission from one of these will work? Is there any type of cross reference I could use to verify before buying one?

For example, looking around on eBay there are a number of CB400 transmissions, some saying they are actually from a CM. Others are from different years than my 1980. I don't want to buy one of these (or even a local one) and find out it won't fit. I know there are six speed ones out there, whereas mine is a five speed.

Here is a search of CB400 transmissions on eBay: http://shop.ebay.com/?_from=R40&_tr...=cb400+transmission&_sacat=See-All-Categories
 

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I take it you can't file down anything that exceeds the original tooth contour and run it that way? That's a pretty normal approach with gear sets on machinery. Don't file the hardened tooth faces, just the chipped part.
 

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I think your chipped tooth is first gear countershaft, no??
That part is common to almost all the CB and CM 400, also CX500 and GL500.
The countershaft itself is common to almost all CB/CM400.......
 
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