CB350 - Noises while setting timing

[hatchb4ck]

Okay, I'm a bit worried about asking this question for fear of what the answers might be. But, perhaps I am just being paranoid that something is mechanical wrong inside my engine.

Here goes. When you turn the engine over while setting the timing on a CB350 how much valve train noise should be heard? I noticed tonight while working on my timing (points are pitted so I'll be running to the parts store to get a file to dress them with) that there were distinct pops coming from the engine/valve train while turning the engine by hand. These happen at certain points in the revolution consistently, normally as I come to the double marks before the LF and F timing marks during the counter clockwise rotation. The engine wants to turn over under it's own pressure as it passes these points.

This is a new-to-me motorcycle and it has been running well, a bit noisy when running, but nothing too excessive in my opinion. I've adjusted the valves and they only required minor changes to bring them into spec.

Once I get the timing set, I'll be warming the engine up and testing the compression.

To all the learned DTT'ers out there, does this sound normal?

Thanks in advance for any comments posted....

Joe

 

[SONICJK]

Hmmm,
doesnt sound "normal" per se...
Adjust your valve clearances and see if it continues.
Perhaps your valves are kissing your pistons?

 

[hatchb4ck]

@SONICJK - I've double and triple checked the valve clearances...they are as close as I can get them.

I didn't feel any great amount of play or tightness in the adjusting screws.

I've turned the engine over by hand with my fingers resting on each of the rocker arms and none feel like the are the source of the noise. Is there a way, externally, to check if the valve is "kissing" the piston? I'd suspect not, but thought I'd ask.

 

[HerrDeacon]

Sounds normal to me, its just the valves opening and closing and the piston moving up and down. The engine running past the marks is normal on a 350 as well, bit of a pain but nothing to worry about.

 

[DrJ]

That may be the camchain tension not being set correctly.

 

[hatchb4ck]

@DrJ - I've run through the cam chain tightening procedure a couple of times as well. HerrDeacon may be right, I could be chasing my tail a bit.

If it might help, I'll record a video of turning the engine over and the sound it's making.

After that I'm going to get the points/timing done, fire it up and see from there.

I plan to tear the bike down over the winter to clean, repaint, rewire, and slightly modify it. No time like the present to start collecting the parts to rebuild the engine. Or maybe find a spare engine.

Thanks Drj and HerrDeacon for your comments.

 

[djelliott]

Sounds totally normal for a CB350. You always hear the "chug" on the compression stroke and the little "bup" as the valves close. If you yank your spark plugs it will move around a bit easier.

 

[Sonreir]

Honda 350 and 360 have some of the loudest valve trains I know. They're just weird that way.

 

[hatchb4ck]

Okay...I've posted up a video on youtube which shows me manually turning over the engine and the sound can be heard. Although it can be heard twice earlier in the video, the one at 33 seconds is the best example. The only way to describe it is a pop or solid click sound.

Give it a listen.

http://youtu.be/ICZNOBySEPY


Thanks everyone!

 

[DrJ]

I still say it's the camchain.

 

[djelliott]

Is your cam chain tensioner not locked down? Sounds like its bouncing back.

 

[hatchb4ck]

@djelliott - I can't see inside the housing, but the bolt feels like it is tightening down on it.

I wonder if it isn't taking up the slack when I loosen the set bolt, like it is stuck and the spring isn't pushing it out.

I guess I can pull it and make sure that it is moving freely and that the wheels on tensioner arm aren't chewed. The latter being likely given the vintage of the engine.

It's acceptable to cut your own gasket for that, isn't it?

Thanks for your thoughts.

Joe

 

[djelliott]

Oh yea. A custom gasket would be fine there.

 

[hatchb4ck]

I pulled the cam chain tensioner and took a peek at the upper wheel. Although not perfect, it shows some wear, it still moves freely and isn't all chewed. The tensioner piston and spring moved freely. I re-installed it and adjusted it per the manual.

I took a bit more time to really listen and feel the different components in the valve train as I rotated the engine. The clicking/popping alternates from side to side as each piston rolls through the 4-stroke cycle. Could this be play in the rocker arm adjuster shafts?

The only way to know is to take off the rocker cover and run it through the cycle to see what might be moving.

 

[hatchb4ck]

@djelliott or any of the other cb/cl350 owners out there.

Would one of you be willing to record the sound your engine makes while you rotate it during a valve adjustment? Or atleast listen closely to it and mention if you hear any popping/clicking in the valve train during the rotation.

Thanks for all the suggestions so far.

Joe

 

[SONICJK]

Mine does not make any popping noises like yours. Just the lug and slide noises of the piston moving.

 

[djelliott]

Mine does not make any popping noises like yours. Just the lug and slide noises of the piston moving.

Same here. Sorry. Wish I had a better answer.

 

[hatchb4ck]

SONICJK and djelliott, thanks to both of you for your help.

At this point, there really isn't much I can do except open up the valve train.

I'll try to pick up a second engine for parts.

If I find anything interesting in the cam/rocker area, I'll post up the pics.

Thanks again!

Joe

 

[hatchb4ck]

Good and not so good news, identified the problem.

It was the cam chain tensioner, and excess slack in the cam chain causing the noise. A friend came over today with two additional engines for comparison. One has a perfect cam chain wheel (absolutely no wear on the wheel at all). I bought the engine for parts to rebuild mine with. We were able to reproduce the sound by removing the plunger/spring/housing and turning the engine over. I was also able to get rid of the sound on my engine by holding the tensioner in with my fingers and turning the engine over.

So, that raises the question of why I can't get the tensioner on mine to tighten up enough to get rid of the play using the plunger/spring. I must be misunderstanding the procedure. Here are my thoughts on what is happening.

According to the procedure in the Clymer manual, you turn the engine over until the intake valve on the left cylinder is fully open (arm all the way down, pushing the valve open), then starts to close again. From there, continue turning until the LT mark is reached which is TDC on the compression stroke for the left cylinder. Then, loosen the lock nut and retaining bolt allowing the spring to push the plunger out applying tension to the chain via the tensioner. Straight forward enough.

Where I'm running into a question is prior to reaching the LT mark, the force of pulling on the wrench to turn the motor over changes to one where you have to hold back on it to stop it at the LT mark (also the point where the click/pop sound occurs). This change is due to the action of the valve train and valve springs. So, if the force of pulling the crank around (pulling on the cam too) changes to one where the crank is being pulled by the cam chain, wouldn't the tension on the chain change from the front of the engine to the back of the engine? And if so, how would the tensioner be able to take up the slack which is now at the front portion of the chain running to down to the crank.

Think of a bicycle with a coaster brake. You pedal forward, the top of the chain is tight and the bottom has a bit of slack. Now, rotate the pedal backwards to apply the brake, the top becomes slack while the bottom tightens up. When the action of the valve train begins to pull the crank over, it tightens up the back side of the chain.

Am I missing something in the procedure? Is there something wrong with the Clymer procedure? Is lining up the LT mark not a strict requirement rather you just need to make sure it is at TDC on the compression stroke, then turn it a bit more to tension the front of the chain again?

What do you guys think? Am I way off on what I am thinking with the different tensioning of the chain or am I doing something wrong?

 

[hatchb4ck]

For some reference shots of the two chain tensioners.

Here is the current one:

Here is the one in the engine I just bought from my friend:

That second one is in perfect shape, not a mark on it.

So, now to tear down the parts engine and get the parts out of it and order a top end gasket set.