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So terrible day. It started as a great one; all I needed to do was to add oil, button up some wiring, add gas, and finally start up and go for a test ride. WRONG.

While going through the normal motions of starting a bike that hasn't been started in several months, after a "restore to life" on my 1972 CB450. Took a lot of kicks to get it to begin to sounds like it was about to start, alot of starter button as well, instead of draining my battery, I was kicking it to try and get the fire up. I was getting the normal sounds, could hear the exhaust trying to bring it to life on each kick.

Then, nothing... all of the, what I'm guessing is compression, was gone, no sound from the exhaust, no pressure when hitting the kickstarter. I mean, I can feel the spring pressure, and hear gears turning, but thats all, there is no give of air through the engine. When I try to use the starter button, same thing... nothing from the exhaust. This happened right when it began to come to life 2 times, where the engine started to catch and rumble, then this happened.


Any ideas on what the heck this could be? And now I gotta start from scratch again on this bike. Sigh, super frustrating, I thought today would be the day I could actually take it on it's first spin. It's started before, several months ago, after I purchased it and put in a PAMCO, coils, basic usuals. Now, after doing a whole brat/cafe thing, and getting to the end, now this.

Like I said, it makes an interesting clicking of gears sound, and I also tried to start it while in gear with the starter, and the rear wheel does turn when doing so... but still not grumble from the engine... any ideas? COuld it be the cam chain? How would I know?

Thanks in advance.
 

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Pull the spark plugs out and put your finger on the holes one side at a time to check for compression in each cylinder while slowly pushing down on the kick starter. Make sure the kill switch is turned off so you don't get shocked by the spark plug lead. If you get a blast of air from the holes then I think the cam chain has not broken.
 

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Pull the spark plugs out and put your finger on the holes one side at a time to check for compression in each cylinder while slowly pushing down on the kick starter. Make sure the kill switch is turned off so you don't get shocked by the spark plug lead. If you get a blast of air from the holes then I think the cam chain has not broken.
No luck. So pulled a plug, literally no pressure coming out. Only can hear the turning of gears when hitting the kickstarter, or starter button. And clicking.
 

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No luck. So pulled a plug, literally no pressure coming out. Only can hear the turning of gears when hitting the kickstarter, or starter button. And clicking.
Pull the valve covers and alternator cover and turn the crank with a wrench, see if the cams are moving
 

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Pull the exhaust cam cover off, (8 bolts) on the front of the engine and observe the cam sprocket to see if the chain is still intact or if it has slid down into the case indicating it is broken.

Rotate the crankshaft CCW slowly, using the 14mm crank bolt on the left side of the engine behind the round plate with 3 screws and see what the chain is doing and whether the cam is moving in tandem with the crankshaft. Do this slowly, some Hondas are "Interference" motors and if the timing chain breaks you may kiss the pistons with the valves and you don't want to do further harm if that is the case.

If the chain is broken, the motor must be pulled for repair.
 

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Pull the valve covers and alternator cover and turn the crank with a wrench, see if the cams are moving
You beat me to it Tom, LOL
 

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Let me amend what I said about the need to pull the motor if the cam chain is broken. It MIGHT need to be pulled. I did repair my old 550-4 when the chain broke at 5000 miles on I-95 at 3:30 in the morning. I pushed that thing 3 miles and arrived home at 6:30. This incident was the basis for my User name on this forum.

It might be possible to fish the chain out of the crankcase and if the master link or broken link comes with it you might be able to connect a new chain to the old one and feed it through and around the cams and tensioner and restake a new master link completing the repair. It sounds like it might have broken, (if this is the case) while you were trying to start it and maybe caused no damage. If the link broke and fell into the crankcase then it might be pulled out with a magnet, but would be difficult.

I know this is not what you want to hear, but rest assured, many on this forum have experienced a failure which required a teardown and rebuild of their motors.
 

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Discussion Starter #9
Let me amend what I said about the need to pull the motor if the cam chain is broken. It MIGHT need to be pulled. I did repair my old 550-4 when the chain broke at 5000 miles on I-95 at 3:30 in the morning. I pushed that thing 3 miles and arrived home at 6:30. This incident was the basis for my User name on this forum.

It might be possible to fish the chain out of the crankcase and if the master link or broken link comes with it you might be able to connect a new chain to the old one and feed it through and around the cams and tensioner and restake a new master link completing the repair. It sounds like it might have broken, (if this is the case) while you were trying to start it and maybe caused no damage. If the link broke and fell into the crankcase then it might be pulled out with a magnet, but would be difficult.

I know this is not what you want to hear, but rest assured, many on this forum have experienced a failure which required a teardown and rebuild of their motors.
****, **** ****.. I literally was celebrating today because I'd finally get to do a test ride. This is my first bike, first build, first actual ride on the dang thing.

Ok, so could this have been caused by a tensioner that was too tight? I adjusted the tensioner a few days ago, (well so I thought). I'll get into the cam covers, probably tmrw and see what I can find. Maybe tonight. Dammit!
 

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We have all been there. Do not allow this to discourage you. These old bikes can try our patience sometimes, but in the end it is worth the hassle.
 

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Only thing I can think of that would produce an abrupt loss of compression is a broken timing chain and it is holidng a valve open on both cylinders.
 

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We have all been there. Do not allow this to discourage you. These old bikes can try our patience sometimes, but in the end it is worth the hassle.
Thanks, I know I'll get through it, if anything, gives me an excuse to continue to tinker on it. So, I pulled the cam cover on the exhaust side, chain is still there, I haven't tried turning anything, just opened and can see that it's there, tried to budge it by hand to see if there'd be any response, but couldn't but also not sure if I should be able to turn it by hand.
 

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I'm confused on what I should be doing next. Pulling the chain off? Rotating the kickstarter? Rotate the crankshaft? I guess I'm unsure what I'm looking for, and then what with the findings? Thanks all for all the help so far.
 

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I'm jumping in here with some quick questions.
Did you personally ever run it, or check compression before today?
What's your valve clearance at? I don't know the 70s 450, but are you able to confirm your cam timing is good and valves are within spec?
 

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I'm jumping in here with some quick questions.
Did you personally ever run it, or check compression before today?
What's your valve clearance at? I don't know the 70s 450, but are you able to confirm your cam timing is good and valves are within spec?
When I purchased it did not run, however, compression was good, just needed coils, timing, and carb rebuild to get it going. Once I got it running, I did not ride, as tires were cracked. So I began on all of the other things, lights, controls, new wiring, bars, seat, paint, gaskets, crankcase covers, cables, etc. With everything else completed, and after buttoning up wiring, this is the first time I've tried starting it again, and then this. The clutch probably needs more adjustment, but could this cause these issues?

For the timing, I installed a PAMCO electronic timing ignition, which made it fire up instantly several months ago, before I tore the bike down. (not engine rebuild, mind you).
Not sure of the clearance.
 

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Remove your air filter and put your hand over the throat of the carb. Try and start it and see of you feel suction from the non compression side.
 

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Remove your air filter and put your hand over the throat of the carb. Try and start it and see of you feel suction from the non compression side.
Non compression side? Not sure if I follow. With me trying to start it, can't this increase or bring probability of more damage?
 

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It's totally possible.
I'll send you a p

Edit: sorry, just reread the first post... Didn't realize you lost compression while trying to start it. If it were me, I'd immediately check calve clearance and cam timing. You're right, don't try and run the engine.


Non compression side? Not sure if I follow. With me trying to start it, can't this increase or bring probability of more damage?
 

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I kind of doubt the cam chain is broken- despite their flimsy appearance they are incredibly tough.
I've worked on 450's for 50 years, have seen hundreds of them, and I've never seen a broken cam chain.
I've seen them get loose, flop around and cause incredible damage, but never a broken one.
If one was to break, it would get all wadded up at the bottom of the crankshaft and prevent it from turning over at all......
 
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