Topic: '75 CB750 click/tap noise when turning over

[Dunk]

This bike has had a tapping at idle since I got it. It runs great, valve and cam chain adjusted several times. No clearances are opening or or drastically changing, it has been pretty close to spot on every time I've checked. Carbs have been synced, float level set, etc. I knew it would be an issue I'd have to address at some point, and here I am now that the last time I rode it the noise seemed to have gotten worse. Note that the oddity is when I have run the bike very hard and it gets hot the noise will often go away at idle, though normally easy riding it is always present at idle. After letting the bike sit for nearly a year, working on some dual sport projects while riding my other CB750, it's finally time to get into it.

I'm getting ready to pull the engine so I can have a look at the top end at least, and dig as far as I need to. Since the basics don't seem to have made a difference it'll need to come out unless I'm overlooking something. Before I spoil the pot with my guesses please have a listen and let me know your thoughts on what you think it may be or where I should be looking.

[ekpent]

I can hear a tinkling type of sound. Have you ever had it apart in the past as I see some allen bolts on it. Hard to tell much from the video. Can you give a better idea as to what part of the engine you think is making the noise like up top or more one side then the other. The first thing that I thought was loose cam chain sprocket or bolt rubbing but there is probably a 1% chance of that but you never know 
   Idles nice. Is that actual mileage on the speedo ?

[754]

Did you isolate it, listen with a rod or screwdriver ?
 It may be not oiling on one side of cam , check thru outer rocker caps on oily side. Look for less oil  on some calve collars than other. If drier get in with strong light in darkened room look for shavings or see if you can see the cam lobe.
 Ever had it seem to stick then turn ovrr again a short while later ?

[rotortiller]

Maybe pull the oil pan and have a look at the primary tensioner and look for metal or plastic. Might not hurt to have a look under the ignition plate and clutch cover too just in case it is something stupid.

[Dunk]

I was thinking it was primary chain tensioner related. Now I'm not so sure. The chains measure in spec at 65.89mm and the rubber on the tensioner is soft, not notched from the chain rollers or otherwise torn up. An oddity I noticed is that the tensioner seems somewhat loose, I can wiggle it side to side a bit. I have never been into the bottom end of a CB750 before so I don't know if some sidewards movement is normal or not. I also don't know how much tension it should be putting on the chain, but it doesn't feel like a whole lot. I can lift the tensioner off the chain relatively easily with my fingers. When using the kicker, the bottom of the chain becomes tight and pushes the tensioner, then when releasing the kicker the tensioner immediately tightens the chain. The thought occurred to me that maybe the tensioner bolt could have loosened, given the side movement.

When turning the engine over and listening from below, the noise seems to be coming from the above, move so out of the exhaust ports than out of the crankcase. More so from the front of the engine than the gearbox or clutch area. I was thinking primary chains but I'm not sure now. Now I'm thinking maybe a worn wrist pin. The bores would have to be real sloppy for this to be from a loose piston, but maybe it could be a broken ring or ring land. Previous owner said he had the top end off, though I don't know if he went into the bottom end, but it's plausible a ring or piston could have been damaged on assembly. It runs great though, for whatever that's worth. I'm thinking it's gotta come out, so I'll carry on getting it ready and probably wait until I can get a hand with it rather than strip more off the bike to lay it over and do it myself.

I'll add speedometer is not original but I got the original with the bike. It was just shy of 15k miles when I got it almost 5 years ago, should be around 18k miles now.

[PeWe]

Primary chain slack almost like new chains!
I think new has 65mm.
I measured my heavy duty chains when new, a little bit under 65mm, maybe 64.5mm.

Service limit is 70mm so there is much life left.
The speedo tells the truth, this is a really low miler, right?

Valve lash OK on all?

Cam chain adjusted when engine is not running? My owners manual I got with my bike said to idle 1200 rpm and open the screw   It only got worse!

I usually opened the lock screw, put a pin inside the tensioner holder's hole back side that got contact with pin inside.
You will feel how it moves in-out when using the kick. Lock screw when your pin is in the inner position.
An allen tool or screwdriver work fine for this.

Or rotate crank to 15°ATDC:
Spark advancer pass the T for 1-4, continue to the left side of the spring post. That's 15° past TDC. Set the tensioner and button up.

[754]

Like I said before, use a rod or screwdriver to pinpoint where the noise is.
 One more thing, valve springs can break , but I don't know what it sounds like.
One of two things will happen.... you pull the motor.... or you get a frame kit and pull some of the top end apart.

[PeWe]

A sudden job like this make a frame kit needed!
That's how I had to make the "horrible" decision to use a tiger saw into my beloved bike.

Franks frame kit perfekt to install on a complete bike, just lift tank

That is  the best mods I have done to it. I have modified that bike a lot during all years. It is a correction of Honda's design and really needed.

I have lifted head, cylinders several times after that. I had a 3 cam test during 4 days 2 years ago.
Easy to pull/mount engine alone when head and cylinder are removed before. Reversed way in.

All talk about cams in other threads wake up ideas to try another one if getting one for an OK price.

Here a very informative thread about the weldless frame kit. Several guys installed and attached photos. I did mine too.
I'm very satisfied how I cut it. Max opening used a lot.

Measured front with ign switch on +1/2 lenght of clamp, cut there. Rear, 1/2 lenght  of clamp in front of the weld.
Drill the 4 holes for the triangle 2 brackets first and  mount it. Now cut the tubes 4 times.

http://forums.sohc4.net/index.php/topic,62832.msg1505097.html#msg1505097

[ekpent]

Might want to make sure the rod in the cam chain adjuster is not seized in the housing and all that is set to spec as mentioned earlier.

[rotortiller]

Might want to make sure the rod in the cam chain adjuster is not seized in the housing and all that is set to spec as mentioned earlier.

I'd exhaust every avenue including the cam chain tensioner before pulling the engine. The Eucker is heavy.

[scottly]

Sounds like tappets to me. Is oil getting to the top end when the engine is running?
PS I have frame kits ready for shipment.
http://forums.sohc4.net/index.php/topic,180860.0.html

[Dunk]

The first thing that I thought was loose cam chain sprocket or bolt rubbing but there is probably a 1% chance of that but you never know 

You win! I guess I owe you a beer or something.

So I got lucky and dodged a bullet letting this noise go as long as I did. Apparently it takes about 3000 miles for a loose cam sprocket bolt to fall out. One bolt was out, laying on the head when I pulled the valve cover. The other was loose, almost 1/2 turn from tight. I snugged the one up and turn it over and the noise when turning with the kicker goes away. Nothing else is loose under the valve cover, no other odd noises.

At minimum I need two new cam sprocket bolts, and I think I'll put a new stopper valve in the oil pump, maybe new gears too or at least inspect them. After sitting since last summer all the oil drained from the tank into the crankcase. There was some metal in the pan which has me a little worried, but a fairly small amount compared to other engines I've had that ran fine.

My concern is if I should dig deeper or not. I got this bike from a fellow forum member, and quickly discovered many loose fasteners on the bike that must have been only hand tight or not sufficiently torqued, including a couple that'll get you dead if they fail. I went over everything accessible and was shocked by all the loose fasteners, but safe afterward. Finding the cam sprocket bolts loose has me wondering about the everything else, since from the looks of the primary chains and tensioner they may have been replaced. If he was in the bottom end may he have overlooked proper torque on anything there? I don't know. What do you guys think?

Oh, and pulling an engine solo when you're too lazy to pull the wheels, swingarm, and forks sucks... The bike was heavy!

[scottly]

Whoa!!! You did dodge a bullet!

[ekpent]

 Whoo Hooo - I get a chicken dinner. Tired of the stuff I have been eating lately during 'lockdown' !    Definitely put Loctite on those two new bolts when you put it back together.

[754]

 Like I said earlier, listen with a rod or screwdriver, you would have found it was coming from the middle within minutes. And I mentioned it more than once.,
 You dodged the bullet, check for cracks on the ears of the cam.
 The strange thing is, they only take about 8 ft lbs, I always torque mine, and maybe use blue loctite..
 I don't understand how they don't get tightened up...double checking your work will catch it every time..

[scunny]

+1 on Franks poor mans stethoscope, bloody handy trying to isolate engine noise location.
I prefer the blue loctite in this regard.

[bryanj]

If those were loose how clean did it go together?

[PeWe]

What else is not tightened or missing?
Open the lower case will show.
Only side cover gaskets that will cost. Cyl and head still on if having no issues. No leaks etc.

Sure all o-rings are where added at assembly? Under cam holders etc... Primary chain tensioner M6 screw tightened too?
I use loctite on that one.
I should check all.

[rotortiller]

Dude, you had a horse shoe up your ass for sure, how that bolt did not go down the shute is beyond lucky!

[Dunk]

I checked the cam tower torque, about half were below lower end of spec so I checked accessible head nut torque as well, all were above higher end of spec. No leaks at all on this engine, not a drop. Waiting on sealer for the valve cover gasket as mine was dried up then I'm done with the top end.

I'm thinking I probably should open up the cases to check the primary chain tensioner bolt torque, and reinstall with blue loctite. So many loose fasteners on this bike. Shame it looks like everything was gone through top and bottom but PO just winged it on torque of some things. I'll check if I have side cover gaskets and various o-rings on hand, if so I could get that done this week and be ready for the weekend when I can have an extra pair of hands to install it. If not I'll re-evaluate the primary tensioner with the engine upside down and go from there.

I got an oil pump stopper, springs, and o-rings to do that. Gears are out of stock, bummer as I almost got two sets a while back to have on hand for whenever I had to do anything to either of my bikes. When I restored my K1 I went through several used oil pumps to find gears that weren't chewed up and had tight tolerances since new gears were not available.

[754]

Many many motors have never had the primary tensioner loosened since new,.

[Dunk]

I was able to reach in the case and feel confidently enough that the primary chain tensioner was not loose, so I left it as it was. New oil pump stopper and o-rings while it was accessible. I did not bother checking the oil pump gear clearances since gears are out of stock. Shame, but whenever they're available again I'll order two sets.

I got it back together and went for a short ride for fresh gas and a loop around town. For the first time since I've owned this bike, September 2015, the engine is quiet. Sounds like a sewing machine, just like they should.