Help with engine knock/ overheating??

[youngwolf]

Bike: 1972 Honda CB750 K2

This bike apparently hasn't touched asphalt for 15 years before I acquired it. Mostly garage stored. Wouldn't start at the guy's shop but would turn over. Brought it home and cleaned the carbs and the gas tank thoroughly. Started up first try and drove well. Ran a little rich but nothing crazy. I noticed a slight engine knocking/ tick and decided to do some research. Initially thought that the three bolts holding the flywheel in the crank case might be loose but it turns out that the older models of this bike don't have those bolts. Next I tried loosening the cam chain tensioner and the noise didn't stop but it did change. Seems to at least partially go away at higher RPM's. I am going to try tightening the tensioner this time and see if that helps, but wanted to get some advice first. Here's a video of the noise:

https://www.youtube.com/watch?v=1-bnhTuL0ws&feature=youtu.be

Let me know what you think / possible solutions.

My 2nd problem is that the engine seems to be running hot or easily overheating. I don't know if it's a coincidence or not but I didn't notice anything until I started messing with the air mixture screws on the carbs to try and lean out the mixture. Rode it to work fine and then rode it to lunch, when I got back from lunch there was a little smoke coming from the engine slits on the left side of the top end. When it cooled down I noticed some oil residue on the slits where it was smoking, not a lot though. There was also smoke coming from the air release of the oil reservoir. A lot more seemed to be coming from the reservoir than the actual engine. Do I need a higher temp oil or is this a major engine issue? I should also note that the day this happened it was about 105 degrees out. Rode it this morning when it was only 90 degrees and some smoke still came out of the air release on the reservoir after a little ride around the neighborhood. Also smokes if it idles for a while, even in shade. It hasn't smoked or leaked any oil from the top end since that one time but I'm still worried. Please let me know what you think.

 

[dirtdigger]

Could be cam tensioner roller wheals are hard and started to chunk, some of it is normal primary chain noise. Check/adjusted valves? Sync the carbs? adjust points/timing/dwell? Compression check to see if the motor is in good shape?

If you got a lot of blowby coming out the vent means you have combustion leakage past the rings...you could easily have stuck or broken rings after sitting that long and not knowing the history.

Air cooled engines will run hotter then water cooled. How do you know it is running hot? Letting the bike sit and idle will overheat and kill the motor faster then anything, never sit more then a couple of minutes without moving, no airflow, no cooling.

Early head gaskets had issues with oil weeping, newer honda gasket helped many times but the biggest issue was the weak oem cylinder studs that would stretch over time and reduce the clamping load on the head gasket. The worst ones happend when people over heated the engines alot by doing a lot of idle time and a lot of stop and go traffic.

 

[youngwolf]

So I went ahead and tightened the cam chain tensioner all the way and the knocking completely disappeared from the top end. Still a little noise at idle that sounds like it's coming from the crank case but I basically have to put my ear down next to it to hear it. Even that noise completely disappears when I hold in the clutch. I know that these old bikes make a lot of noise even when they are running well but it sounds more like a sewing machine now and not a jackhammer, so I'm assuming that's good.

Basically I just assumed the engine was running hot because of how hot the oil in the reservoir was after such a short ride. I'm going to do a full oil change and see if that helps any. Should I be using regular 10W-30 motorcycle oil or is there a high-temp oil I should be using?

 

[dirtdigger]

10-40 is the recommended oil weight unless you are in a very hot climate, 10-30 is way too thin. Are you actually measuring the oil temperature?

What do you mean tightened the tensioner all the way? The tensioner is spring loaded, if you over tighten it by pushing on the plunger through the end you Will ruin the tensioner wheels and ruin and probably break the timing chain. If it is noisy under normal spring tension you have issues inside. The primary chains make noise as does some gear noise at idle, when you pull the clutch in you take the load off the primary chains and stop the trans gears from rotating.

 

[youngwolf]

Update: as far as the cam chain tensioner goes when I say I tightened it all the way I just mean I lightly seated it and then backed it out about 1/8 turn. I've rode at least 50 miles since then and all has been well with that.

So for the overheating, I just assumed that it was overheating because of the blow-by and the weeping on the head. I have not been measuring oil temp but I did a full oil change including filter and used 10W-40 Mobil 1 full synthetic. Little to no weeping since the first incident and no more blow-by. I stop after long periods of riding and check everything over, and so far it's been doing much better. It was 110 degrees Fahrenheit for a couple days last week and that's when the "overheating" incident happened. It has been low to mid 90's for the past few days and the bike is running great. Could the extra 10-15 degrees have affected it that much or am I just misdiagnosing it?

Last thing: after the oil change, clutch is super sticky and harder to shift. Does oil flow through the clutch case, and if so, should I have pre-lubed it after the oil change?

 

[dirtdigger]

Im still not understanding you cam chain adjustment, the 750 is spring loaded with a lockdown bolt, there is nothing to seat or back out. You loosen the lock down bolt, the spring tensions the chain and you tighten the lockdown bolt back down. Unless it has an aftermarket manual chain adjuster. If it is stock it sounds like you are not doing the adjustment correctly.

Is this motorcycle specific full synthetic? You should have gone with conventional non synthetic motorcycle oil. Synthetic oils very well can cause clutch issues. It will probably start causing starter clutch slipping issues in the near future.

 

[amc49]

X2 the last post, OP is not doing something correctly in the tensioner adjusting. You most certainly don't leave anything 'backed off', the engine can whip the chain backwards to tear parts up at a hard decel with a loose tensioner tensioning by spring alone. The spring sets it ONLY then you tighten at that set spot. Tensioner is then firmly locked in that place until the next adjust.

X2 on the possibly too slippery oil too.