Broken head bolt and white smoke - Honda CB350

[thedukefrank]

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]

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.

 

[thedukefrank]

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]

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]

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?

 

[thedukefrank]

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?

I got the bolt off easily. Luckily it poked out enough to tap with a flathead and a hammer. I rebuilt the bottom and tope end, but I think my younger self did a pretty crappy job. If you check that google drive link from the original post, (https://drive.google.com/drive/folders/10Wzle4sfPQbAB1F4LJNRQ3cwYqcpJVO8?usp=sharing) I attached some images of the pistons and cylinder head. I ignored those scratches when I had little to no engine knowledge, but now I'm pretty sure they're a problem. Should I replace the head entirely? I'm assuming those scratches gotta be causing some sort of compression issue (I haven't done a test yet).

I didn't replace or lap the valves, just left them in there since I didn't have the tools.

Also notice the wet looking (oil I assume) pistons. Does that signify a piton ring leak? They are new but I (again stupidly) didn't hone the cylinder walls.

The cam chain assembly is in pretty good condition.

Thanks for the help. Hopefully my past mistakes haven't messed up the engine too bad. I've gotten my grubby hands on a bit more cash thanks to some woodworking jobs (something I'm not a complete idiot about) and am finally willing and able to spend the necessary money on necessary parts.

 

[teazer]

I wouldn't worry too much about the smoke. Sure it shouldn't be smoking, but could be a whole host of things and at this stage, get it running and work out the kinks as you go along.

That head damage looks from here like a broken ring, but we don't see matching marks on the piston, and if that's the case, someone fitted a replacement piston. If you want the motor to be "done right". you need to pull the barrels and measure pistons and bores to determine if it needs a rebore and larger pistons, but that's expensive. Likewise, the valves should be pulled and valves and seats cut or at least lapped to seat better and the valve guide seals can be replaced while you are in there.

If the head is still off and your budget is really tight, I'd recommend getting a cheap ebay valve spring compressor and lap the valves and fit new seals and then run it for now and do pistons when the budget allows.

BTW, the spark plugs we can see in the shots of the head, were they just screwed in a few threads or all the way in those shots? What plugs are they?

 

[thedukefrank]

I wouldn't worry too much about the smoke. Sure it shouldn't be smoking, but could be a whole host of things and at this stage, get it running and work out the kinks as you go along.

That head damage looks from here like a broken ring, but we don't see matching marks on the piston, and if that's the case, someone fitted a replacement piston. If you want the motor to be "done right". you need to pull the barrels and measure pistons and bores to determine if it needs a rebore and larger pistons, but that's expensive. Likewise, the valves should be pulled and valves and seats cut or at least lapped to seat better and the valve guide seals can be replaced while you are in there.

If the head is still off and your budget is really tight, I'd recommend getting a cheap ebay valve spring compressor and lap the valves and fit new seals and then run it for now and do pistons when the budget allows.

BTW, the spark plugs we can see in the shots of the head, were they just screwed in a few threads or all the way in those shots? What plugs are they?

That sounds like a good plan of action for the valves.
There were scratch marks on the old pistons, I was the one who replaced them, but stupidly didn't hone the cylinder walls. I'm going to check the bores and see how it is. Hopefully a rebore isn't necessary.

You think those deep scratches are okay? I think I found a 1971 head in decent shape(will that fit a 73 engine?) that's not stupidly priced.

 

[teazer]

That head is a mess but should be fine to run as long as there are no big high spots to cause problems.

Before you even pull the valves though, turn teh head upside down and pour kerosene or a alcohol into thr combustion chambers and watch all 4 ports to see where it leaks through. If it doesn't leak at all, you could probably just fit and forget for now.