Broken head bolt and white smoke - Honda CB350

Good day to the good people of DTT,
Just a first time high school age builder here. I rebuilt the engine and damn near the whole bike, so when it finally fired up after 2 years of hard labor I was beyond ecstatic. It actually sounded pretty good, nice and loud w/ the emgo shorties on CL pipes (Believe me—I wish I could afford to replace them with nicer mufflers, and I don't know which dingbat replaced the gorgeous stock mufflers with emgos). Although she sounded good and started with one kick (with a bit of starter fluid), there was white smoke coming out of the right cylinder. This combined with the fact that the corresponding spark plug was slightly glazed black led me to believe I had oil in my cylinders.

I did not replace the valves, as they looked decent and new ones are expensive. So I tried retorqing the head bolt, and it snapped before reaching the appropriate torque spec. And I could not yell any expletives.

Anyways this is me reaching out to the experts—what should I do? Could it be a leaky valve guide? Piston ring issues? how do I get this bolt out? a top end re-rebuild? I was just about to get the bike going, and my soul is now crushed.

This link should take you to a google drive with photos of the bolt and where it went.
https://drive.google.com/drive/folders/10Wzle4sfPQbAB1F4LJNRQ3cwYqcpJVO8?usp=sharing
 

pidjones

Well-Known Member
I suspect with white smoke that you are way rich on that cylinder. Did it smell like gas? For the head bolt, I'm afraid the best way to remove it is going to be by taking the head back off, and if there isn't bolt sticking up then to grab with vice grips you will have to center punch and center drill it with a left-hand bit, which will hopefully grab and screw the broken piece out. Really, if you can't unscrew the broken piece with a pair of vice grips (they make some nice small ones with good gripping jaws) you might be best served by getting someone experienced to show you how it is done. As for me, I learned by screwing up a few times. Save yourself that. And get your torque wrench checked. If it is click-type, you may find that when the barrel hits the spring the first time it is already at the first major division. For instance, on Harbor Freight wrenches, a 3/8 wrench is at 5 ft-lbs when it touches the spring, a 1/2" wrench is at 10 ft-lbs when it hits it.
 
I suspect with white smoke that you are way rich on that cylinder. Did it smell like gas? For the head bolt, I'm afraid the best way to remove it is going to be by taking the head back off, and if there isn't bolt sticking up then to grab with vice grips you will have to center punch and center drill it with a left-hand bit, which will hopefully grab and screw the broken piece out. Really, if you can't unscrew the broken piece with a pair of vice grips (they make some nice small ones with good gripping jaws) you might be best served by getting someone experienced to show you how it is done. As for me, I learned by screwing up a few times. Save yourself that. And get your torque wrench checked. If it is click-type, you may find that when the barrel hits the spring the first time it is already at the first major division. For instance, on Harbor Freight wrenches, a 3/8 wrench is at 5 ft-lbs when it touches the spring, a 1/2" wrench is at 10 ft-lbs when it hits it.
Probably the answer I needed but didn't want to hear. It didn't smell like gas, and I'm pretty sure both carbs have the same jetting, but I'll go through and clean each of 'em again. Is it worth buying new valves/springs since I'm going through the top end again? Much appreciated.
 

pidjones

Well-Known Member
What condition were the valves and springs to start? Have you done a compression check? That might be possible before pulling the head to replace the bolt. (Make sure throttle wide open and no choke for the test.) You will need a new head gasket. Even if jetted the same, float valves can stick and other things can cause flooding. White smoke is unburned gas (getting spark?), or water. Since you are air cooled it isn't water. Oil smoke is usually blue or black. I've also seen chunky grey and brown smoke, but that was from starting a 20 year derelict and blowing critter nests and nut shells out of the exhaust.
Oh, and make sure the replacement head bolt is the correct strength.
 

ex119x

Member
If you pull the cam bearing block off you may be able to get to the broken off bolt. However, it will be very difficult to drill straight and to get a screw extractor in, much less to get the bolt all the way out. That being said and I wouldn't recommend it, it might be possible.
I don't think you have given us enough information about the rest of the issues you have listed. Some smoke on start up of a motor that has been apart doesn't tell much. You said you rebuilt the entire engine, but what did you do? did you bore the cylinders and replace the pistons and rings? Since you didn't replace the valves and springs, did you lap the valves? Did you look at the valve sealing surface and seat? How is the cam chain and tensioners?
 

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