1972 cb450 meltdown

C

Crunchybeard

Active Member
Hey guys. first off im new to this forum, but have been to this forum alot and really love all the info and everything about it....so now my problem

I am working on a 1972 cb450 that i bought from a guy who had it sitting around his shed. He said it was working a month before i bought it, but when i teared into it, the starter clutch had been abused (physically), the starter motor was broken internally, and the pistion rings were...well werent rings. so after wiring the bike and finishing everything that doesnt have to do with the engine i finllay go to work on my engine. i clean and polish the piston heads, get new rings, new starter motor, new starter solenoid, new starter clutch, new clutch plates, new cam chain, new plugs, and ive completely rebuilt the carbs with new screws. now i wouldnt consider myself a beginner when it comes to motorcycles, but the problem im having has had me stumped for three months! Ive been scouring the web and forums like Indiana Jones and still havent found my answer....okay that may be an exaggeration, but u know what i mean.

I got a little antsy and decided to try and kick my bike to life.......okay i no i probably should have adjusted the valve clearance, set ignition timing, and set points, but i just couldnt wait I NEEDED TO HEAR MY BABY BREATH!! to my surprise when i kicked it, it fired for a split second, so i kicked again and same thing. then i kicked it one more time and i hear a loud bang and now my kicker only goes half way down and stops. I no the kicker only activates the crank when its half way, but it doesnt even budge after the halfway mark. So i go and try the starter, it engages the crank, but the engine gives a loud bang and stops. so i take off both right and left covers to see the problem. clutch is fine, clutch bolts are torqued correctly, the little "critical" ball is in the right place, and i adjusted the clutch around 150 times. The gear that connects to the starter clutch and the starter motor is in place and connected properly and theres proper voltage getting to the starter motor. Now im having trouble with my clutch. When i pull the lever the kicker becomes free, but when i put it in gear and pull the lever, nothing disengages! im wondering if i broke a clip inside the motor or something may be jammed in my tranny (my transmission not that guy at work). any help would be greatly appreciated. Im trying not to tear into the motor case because i dont really have experience doing that, but if i really truly have to then ill do it on thanksgiving break. right now my almost completed bike is in parts and looks as if i just bought it...THIS SUCKS!!!
 
Sounds like the kick won't go any further because the ENGINE won't turn, not because there's something wrong with the clutch...

Throw a wrench on the crank and see if the engine will still turn.

Perhaps cams were not timed properly and you've got valves hitting pistons.
 
Thanks for the reply. I tried that saturday and the crank only turns half of what it should. it stops around mid turn on second revolution.
 
450 engines are full of little bitty parts and anyone of them meeting something they aren't supposed to will cause them to lock up.

You have something that is stopping the crank from turning sounds like, either you've dropped a valve into a piston or your cam chain broke and you hit a valve with a piston. Could be that one of the rollers on the cam chain broke and fell into the crank locking it there. Could be that you have a piston seized or in the rare weird case a rag where it shouldn't be. I've seen it, almost done it myself.

The CLUTCH sounds like it is working fine since you can pull it in and kick the kicker. The kick starter shaft/gear engages at transmission so pulling clutch unlocks the trans, its a safety feature. The loud bang when the starter is engaged is just that, the starter clutch going BANG once it locks into the crank.

All in I'd say your issue is between the piston and the head some where. Time to pull an engine and take it apart and be prepared for broken parts. ALL valves must be removed if any are suspected to be bent or one is broken. 450 valves are very soft and will bend if given any chance.

AS always when it comes to early Honda twins I suggest going to and digging through the forums at Hondatwins.net. I've learned a lot from over there myself and I'm a member over there too.
 
Yes, you have things hitting stuff internally that shouldn't, it sounds like.

That means bent valves, if that's the case. Pull the plugs, shine a light in the plug hole, you can see if valves are hitting the pistons.
 
this is awesome! thx for the replies. I pulled the plugs already and looked inside, the pistons are moving correclty and there doesnt seem to be any debris from broken parts on them. i checked the cam chain and its fine, but i have checked the valves! i didnt even think of that!!!! i havent checked the rollers either!!! YYYAAAHHHOOO! finally some new info and a lead to bringing a new bike into the world! thx for everything, ill check all this tonight and post what i find.

frogman could u explain what u mean by rag where it shouldnt be? do u mean literally a rag like a wash rag?
 
What I'm saying, is shine the light in both plugs, attempt to turn the engine over with a wrench. When it will no longer turn, check to see if one of the valves is hitting a piston.

When you reassembled the top end, did you have the cam marks aligned properly witht he markings on the head while the crank was in proper position?
 
gotcha. i will definetly check that tonight. i hope thats the case cause i dont want to tear the engine apart. thx for the replies
 
Cam chain timing is outlined in the shop manual with pictures. Its actually one of the hardest parts of a rebuild because the cams are going to want to turn as you are connecting the chain and you can get the marks OFF. Sometimes the marks on the cams are misunderstood for the right/wrong ones. You can check that by pulling the cam shaft covers and watching the cams work as you spin the engine. Can also check for proper actuation of valves that way.

As for the rag, I've found shop rags in engines that somehow got left in them during assembly. Matter of fact my 360 looked like it had a dog or something hairy left in it because of the amount of fur I found in it. :o
 
I'm gonna recomend that you look this thread over as well.. guy goes through the entire valve train of a 450. Shows what the marks look like.

http://www.hondatwins.net/forum/viewtopic.php?f=5&t=12231
 
lmao. okay so ill check the manual and see if i did the cam chain timing correctly or not...more than likely i did it wrong cause i pretty much slapped it together. thx for the replies!
 
Yeah, if you did not set cam position properly to each other and crank position, you bent something. It will have to come apart. You'll have to check for whats bent, whats broken, and rebuild.
 
....people are looking at me and wondering why i started crying...how to explain... :'(

do u think i could take the valve out of the top without taking the engine out of the frame (assuming its a bent valve)?
 
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