Topic: How to determine condition of engine, and trans/clutch - 73 cb750

[jabs83]

I just got a '73 CB750. The PO offered it for $50, and I decided to pop on it. It's pretty much a frame with an engine. There's definitely a lot missing, such as the handle bars, controls, levers, battery, wiring harness, oil tank, and sprocket. Some of these parts are in a box I got with the bike.

My question is - in this condition, how do I determine that the engine will spin(not stuck)? I also want to know the same for the clutch/trans - how do i determine that its working without being able to pull a clutch lever? The engine right now should be in neutral(according to PO).

Please help me determine the best way to approach this bike/build. Thanks in advance for responses.

Edit: The kicker is stuck. So any help determining if engine spins will be much appreciated.

[Danno]

to spin the engine kick the kick starter I seriously doubt that the internals of the transmission are bad
if it will roll over with the kickstarter then the next thing to do would be to pull the plugs and do a compression test on it it
is most important that the compression readings are close and 110 or more
could be lower or higher depending on what gauge you have and the length and volume of the hose on it but it is best if they are all fairly close it is a good indicator of consistent wear and not other problems like valves rings etc

[jabs83]

Actually - I forgot to add, that the kicker is stuck. Is there anywhere else i can see if the motor will turn?

[jabs83]

What I would like to try is cranking the motor by hand, but how do I male sure that the bike is in neutral before I do this? As of right now I have references to neutral, as I don't have a clutch lever, nor a sprocket to turn my rear wheel.

Anyone with ideas on how to make sure I'm in neutral before I crank by hand?

[mcpuffett]

if it won't kick over with the kick start it could be frozen?, can you borrow a gear lever that will fit your bike ? that way you can check it is in neutral, you could turn the motor over by using a socket and ratchet on that big alternator bolt you can see in your photo (the one in the centre of the round item bottom of your engine),hope this helps  ;)cheers Mick.

[Rgconner]

What I would like to try is cranking the motor by hand, but how do I male sure that the bike is in neutral before I do this? As of right now I have references to neutral, as I don't have a clutch lever, nor a sprocket to turn my rear wheel.

Anyone with ideas on how to make sure I'm in neutral before I crank by hand?

Put it on the center stand, if has one. No worries about nuetral.

Or

Click it all the way down to first, then one up for neutral. Try and roll it, that will possible only in neutral.

[KingCustomCycles.com]

Again, I will say this with conviction, and certainty, based upon years of experience: 

A COMPRESSION TEST ON AN ENGINE THAT HAS SAT FOR ANY PERIOD OF TIME IS WORTHLESS!

It sounds locked up anyway, so it is a mute point.  Soak the cylinders in ATF and have a go at it in 3-5 days, you may get lucky.

[splitt]

Again, I will say this with conviction, and certainty, based upon years of experience: 

A COMPRESSION TEST ON AN ENGINE THAT HAS SAT FOR ANY PERIOD OF TIME IS WORTHLESS!

It sounds locked up anyway, so it is a mute point.  Soak the cylinders in ATF and have a go at it in 3-5 days, you may get lucky.

After it has soaked, put the transmission in either 4th or 5th gear. Make sure that the rear tire is inflated, then rock the bike back and forth. If you use a wrench on the stator bolt, just make sure that you don't twist the bolt head off. I've had to repair bikes for customers before who have done this.

[jabs83]

Without knowing if the bike is in neutral, how can shift gears or turn the crankshaft bolt... for all i know it could be in second gear? So in my case, where there is no clutch lever - should i be able to manipulate the clutch mechanism by hand, by pulling on the clutch cable, or push on the linkage? Right now the clutch cable, or the linkage won't budge with me manipulating without a lever. I'm assuming I need to pull the clutch in, in order to get it all the way to 5th gear? Let me know if im wrong.

[ekpent]

With all the spark plugs out and no drive chain hooked to the rear wheel the engine will still turn over in gear if it is not locked - froze up.

[jabs83]

With all the spark plugs out and no drive chain hooked to the rear wheel the engine will still turn over in gear if it is not locked - froze up.

Ahh okay - so with the way I have it now(no clutch lever, sprocket, or chain), the engine should turn if the spark plugs are out and it's not locked?

[KingCustomCycles.com]

Abandon all thoughts of the clutch at this time, drop it, forget it, you don't need it.  Good ideas above.

[mrbreeze]

With all the spark plugs out and no drive chain hooked to the rear wheel the engine will still turn over in gear if it is not locked - froze up.

Ahh okay - so with the way I have it now(no clutch lever, sprocket, or chain), the engine should turn if the spark plugs are out and it's not locked?

If it isn't froze up.....it should turn even with the plugs installed. It will just turn easier with them out (you don't have to fight compression). If its froze ....do what King says with the ATF but throw some acetone in with it.Like already said.....it makes no difference what gear its in if the chain is off of the bike. It would be easier to try and free the motor if you had the chain and sprockets on though as you could use the back wheel to move the motor. Lots less leverage with a wrench on the alternator bolt than turning the back wheel. Good luck with it.

[KingCustomCycles.com]

I have used a strap wrench on the stator with a 10' steel cheater bar to free engines.  This develops some serious torque and is best used with the bike strapped to a trailer. 

[mrbreeze]

Sounds like a good idea as opposed to a wrench on the stator bolt.

[jabs83]

Thanks all for the replies. I shot 50/50 acetone and ATF down the cylinders, and will have a go at it after some time.

[jabs83]

So the ATF did the trick. It freed up, and I am able to crank it by hand. I guess I can reasonably assume that the engine will start.

One question though, if someone wouldn't mind answering. I cranked the engine a couple revolutions, and I heard a loud springy click noise. Is it normal to hear such a noise from the engine when turning it? What could the click noise be?

[KingCustomCycles.com]

I have no idea on the noise.  Fire it up and check it out for major leaks, blowby, or mechanical issues.