Sounds like you're running on only one cylinder. If can touch either of your headers without losing skin after running, that's the side that's not firing.

 

You letting the bike warm up a bit before jamming on it? What's the compression?

 

Welcome to HondaTwins. This is a very helpful place. I would start with the basics, tune up,oil change and ect. Here is a link to a list of things to do. Some of this is safety related. If you do it all you will have a like new bike. Sounds like you should focus on the engine.

Checklist for the new to you old bike.

Here is a sequence to follow for a tune up.

 

And James is the first one in with real help Sorry - man. Anyway, welcome to the forum. We'll help you fix it.

 

Have the carbs been sync'd and mixtures set after that is done?
Compression? Valve adjustment?
Where you attempting to ride it w/o the air box boots in place?

 

I appreciate the link James, I have done a couple of those basics already, but there is obviously more to be done.

I was only letting the engine warm up for a few minutes before pushing the throttle.

The only compression testers I can find don't fit. So I went ahead and rented one, and just firmly pressed it against the spark plug openings to at least make sure the engine was alright. Looks like the right piston moves, but the left does not. This was also indicated by a clean spark plug on the left. So what now? Did I get screwed over?

 

the left piston doesn't move? With no abnormal noises? I would look down in the spark plug hole or put a dowel in the spark plug hole and turn the engine over, in the normal rotation direction, by hand and see if the piston is actually not moving or just no compression.

 

By the way you can't just firmly press the compression gauge onto the engine and expect a good reading. You need to screw/thread it into the spark plug hole.
If you are still not getting any compression at all from the left cylinder then I suspect one of two things.

1. Your rings are bad, either they are broken or somehow have aligned themselves on all the gaps.
2. Your piston is toast. Could be that there is a hole in the piston.

 

Yeah, I'd suspect a holed piston or broken valve before I thought that the piston wasn't moving - the thing that is attached to the bottom of the piston is unlikely to be silent if that is the case, lol. Although... When I test-rode my motorcycle, I got it going faster than 35 MPH and it was only firing on one cylinder (zero heat in left header pipe). So I would not be terribly surprised if there were multiple issues at work here. For example, put it in neutral on the center stand and see if the rear wheel spins freely or if the rear brake is sticking. If it isn't, have someone lift the front end and try to spin the front wheel. Check pressures in tires to make sure they are not underinflated. Stuff like that.

I wouldn't expect it to easily exceed 35 MPH on one cylinder, lol (or really go that much faster), but if everything else is a-okay, I'd think you'd have at least 15 or 20 more MPH (on a flat road, with a long run-up, et cetera). But that's just my uneducated guess.

Regards,

 

I understand that I won't have an accurate reading by merely pressing the compression tester against the engine, but when I can get 120 psi on the right and 0 on the left, I feel that is pretty telling.

No unusual engine noises, and both the right and left headers do get very hot. As far as figuring out whether it's just a lack of compression or the piston just not moving, if I look down the spark plug hole on the right, the piston is very obviously moving, where as on the left, I can see part of it and it stays stationary.

As a side note, it turns out the bike had the wrong spark plugs (the electrodes where much smaller than they should have been). I replaced them with the proper plugs and the bike now at least gets up to about 45mph.

 

+1 on using a screw in type compression gauge. It's a 12mm adapter that's needed.
Get a solid reading using that and report.
Proper compression test is both plugs out, choke in the OFF position, throttle held wide OPEN. Crank until the gauge stops rising, usually @10 revolutions.

 

If the left piston is not moving, STOP RUNNING IT!

 

So it looks like I was mistaken. The piston is moving, there is just no compression. I can't give a completely accurate psi, because I can't find the proper adapter for the compression tester. I tried to rig a rubber stopper but the best I could get was 90 psi on the right, but still 0 on the left. Looks like the next step will be to take the top of the engine off and take a look at the rings/piston. Will I need to remove the engine completely to do this?

 

I don't think you'll need to remove the engine from the frame to rebuild the top end on this model

Section 05 Engine Removal and Installation


EDIT - actually look at this one
http://www.mediafire.com/download/i9agz248g3g8mpo/Section+06+Cylinder+Head+and+Valve.pdf

 

You can remove the head and cylinder in frame. My concern here is that given there's damage of some sort to one cylinder what's the bottom end look like.
Do you have the FSM?

 

You can always bump a bit of oil in the plug hole and rerun the compression test. Since your gauge doesn't screw in you might want to stuff a towel around it too, but it may help determine piston or valves.

 

Check to see if a valve is stuck open. Might just be jammed or bent for 0 compression, or a hole in the piston. Rings would have some compression just low.

 

Well I think I found the problem.

https://imgur.com/a/BQjmz

Which begs the question, where are the part of the valve and bolt that are supposed to be there? Looks like I'll have to learn how to take this thing apart.

 

Well, those screws don't just go walking off... I don't think you need to tear down any further.
That on the intake side?

Part#90012-414-000
Nut has a separate #

http://www.cmsnl.com/honda-cb450sc-nighthawk-450-1983-d-usa_model7220/partslist/E++04.html#results

Edit: looked again. It's the left exhaust.

 

Just posting for comic relief and hopefully motivational. One of my favorite rides tops out at 38.5, so you can't let this beat you!

 

OK, so the valve adjuster screw and lock nut are somewhere inside. Look carefully in and around the valve spring area to see if you can locate them, use a magnet probe. If not then they've already fallen into the sump area where they will sit forever until the engine is taken apart. Normally this would be of concern but this engine has been run this way which means they fell through without getting lodged in on of the 2 chains. The pickup screen will prevent them from leaving the sump, you may get lucky and they'll flush out during an oil change (unlikely)
So order a screw and nut from Honda, adjust the valves and sort out any other issues that arise.

 

I was able to find the two components with a magnet! The nut was sitting underneath the opposite (right) exhaust valve and the screw was down in a crevice in the front of the cam chain. I did my best to reassemble and adjust the valves following this video:

However, on my bike the tappet gauges would only slide in-between like he showed in the video on my left intake valves. The rest of the valves (on both sides) would move up and down with the screw. I just tried to eyeball it and get them all looking like the left intake valves. I reassembled everything, and now there is a high pitch tap/knock on the left side that wasn't there before:

Haven't ridden it for fear of messing something up.

Also, thank you fendersrule for the comic relief. I'm doing my best!

 

You got a second chance at this and you should try and get it right and not eyeball or shortcut it.
Do you have the service manual?
Did you run through the entire checklist of the new to you bike?

http://www.hondatwins.net/forums/62-engine-discussion/44871-topping-out-35-mph.html#post355986

 

Not trying to take anything for granted doode, that's why I keep coming back here. My bike is sitting outside in an apartment parking lot, so I have to reassemble every night after I finish doing something on it. I figured I'd at least hear what it sounds like, but like I said, I didn't ride it for fear of messing it up. Not trying to take shortcuts, but I'm also kind of flying by the seat of my pants here, and don't know why I can't do the valve adjustment properly.

I have multiple service manuals, diagrams, walkthroughs, etc, and I cross reference everything before I so much as adjust the torque on a screw. I have not made it all the way through the entire check list, but I've hit the majority of the major ones. Doing what I can while going to school full time and working full time in another city.

 

OK, several problems with that video. Never use an adjustable wrench, it's a 10mm and use the box end not the open end. Feeler gauges go in from the side so they remain flat instead of bending over the edge of the head giving a false read. Tighten the lock nt while holding the screw in place with the screwdriver. Engine has the be rotated again before the other side is adjusted.
So, now that it's hot you have to wait 2-4 hours to cool completely.
Set the engine to the T mark, TDC. Look at the end of the cam and notice the notch? Facing down means the left side valves can be adjusted, up means the right side.
Loosen the lock nut 1/2 turn, insert the feeler gauge from the side so it remains flat against the top of the valve stem. Adjust the screw so the feeler gauge won't pull out, if you use your finger tips on the screwdriver you'll feel when it stops turning easily and that's the same time the feeler gauge becomes locked in place. Not holding the adjuster screw in place with the screwdriver so the adjustment doesn't change tighten the lock nut, spec is @10 ft lbs, securely. The feeler gauge at this point should have a slight drag on it when you pull it out. If it pulls easily w/o drag it's loose and if you have to tug it's tight. Re do as needed.
Now that you've adjusted one side turn the rotor one full revolution to the T mark again and you'll notice the cam notch has moved 180* meaning the other side can be adjusted.

 

Thank you everyone for the help, I really do appreciate it.

Longsistancerider, those instructions were spot on, doing that I was able to adjust all of the valves properly with the exception of the problem left exhaust. If I unscrew the adjuster screw all the way, the valve just follows until it reaches the arm. Is this an issue with one of the springs on that valve?

Also, I received an adapter in the mail today for the compression tester, and I was able to take a proper measurement:

Before valve adjustment
Right - 120 psi; Left - 0

After
Right - 135; Left - 0

And then there is still the tapping. Here is a longer video:

Another thing that's been going on is the engine seems to have oil on it all the time on both sides, but more so on the left (but maybe that's just because it's leaning that way?). Here are some pictures taken after it's been sitting in 70-80 degree weather all day:
https://imgur.com/a/zVm4n

I'm assuming this indicates a crack or bad gasket?