Topic: 1972 CB750 Engine Ticking Sound

[TheWiredNinja]

I took the bike out of hibernation and all was well during my ride until I noticed a ticking / tapping sound that was louder than usual.  Consistent with engine RPM.  Clutch, gears, and speed have no effect on sound.

It seems like its coming primarily on the left to middle side of engine case (cylinders 1-2).  I have checked all valve clearances, timing chain reset (including full dismantling, cleaning, checking spring tension, and lubricating the plunger,), and also a carb sync out of precaution.  Issue remains.  Bike has good power and vibrations are nothing out of the ordinary.  Ticking does get slightly louder at higher RPM and when blipping throttle.

Again, the bike previous to hibernation was working just find without these issues, so my ability to check timing and valves is not the issue.  I would really like to have an idea of what it could be even if I have to pull the motor - this one is a strange issue as performance is top notch and the vibrations aren't something that's very noticeable...

Here are two YouTube video's of the bike:

[Stev-o]

I would have concern if it was my bike making that noise after the checks that you have done.

Time to pull the motor and head cover and check the cam for excessive wear. Good luck.

[seanbarney41]

try pulling valve inspection cover on exhaust side with engine running, you should have oil splashing out, check both ends of engine.  If there is little oil at either end of the engine, oil is not getting to the cam and the cam is probably shot.

[TheWiredNinja]

Top end has oil and both sides are good!  I forgot to mention I pulled the oil pan off to see if there were any interesting bits and pieces in there - it was clean!  Oil looked fairly decent as well (ie. no flakes, or chunks of metal) which means nothing broke internally, or at least it hasn't yet. 

If I were to guess it may be a valve rocker that has become loose or perhaps a rod bearing gone bad.  The weather was slightly cooler out... I am just hoping there is perhaps something else I'm missing before it has to be pulled for a complete rebuild

[desertrefugee]

That's definitely concerning.  More so as it appears to be bottom end related - based on its frequency.  If the noise had been focused more on the right side, it could almost sound clutch'ish.  But not in this case.   

I also wish you the best of luck.  Always sucks to run into things like this just as riding season is about to start!  That's why one MUST have more than a single viable fun machine!

🛵🚑🛴🏍️

[newday777]

That is disconcerting for sure. Well done on your checks.
When was the oil changed last? Just before hibernation or???
What are the temps outside and in your shop when it's happening?
Are all cylinders firing at equal temps on exhaust pipes when started?

[seanbarney41]

Top end has oil and both sides are good!  I forgot to mention I pulled the oil pan off to see if there were any interesting bits and pieces in there - it was clean!  Oil looked fairly decent as well (ie. no flakes, or chunks of metal) which means nothing broke internally, or at least it hasn't yet. 

If I were to guess it may be a valve rocker that has become loose or perhaps a rod bearing gone bad.  The weather was slightly cooler out... I am just hoping there is perhaps something else I'm missing before it has to be pulled for a complete rebuild

so...how does clean oil in the pan tell you that it has been anywhere near the camshaft?  I have heard that engine sound twice.  Both times resulted in complete destruction of the camshaft and most if not all of it's associated parts in less than 40 miles.  You can hope I am wrong or checking for oil in the top end takes all of 2 minutes.

[Stev-o]

This is what happened to my K4 engine the last time I heard a bad noise, it happened so quickly....

[desertrefugee]

This is what happened to my K4 engine the last time I heard a bad noise, it happened so quickly....

The original Big Bang Honda!

[JLeather]

This is what I found in my K1 engine that was making a similar noise.  At least it got me 200 miles back home

[seanbarney41]

JL, look carefully  for all 4 little o-rings that are supposed to go under the cam tower, 2 on the inside around the oil jets, 2 on the outside to seal the ends of the oil passages.  That is about what I have seen if any of these o rings are missing or damaged...the cam will last longer than with a plugged oil jet, but not much.

[TheWiredNinja]

This is what I found in my K1 engine that was making a similar noise.  At least it got me 200 miles back home

Did you find a cause for that?

[Tracksnblades1]

This is what I found in my K1 engine that was making a similar noise.  At least it got me 200 miles back home

Did you find a cause for that?

It’ll find its way out, if left unattended…👀

[bryanj]

That would have been caused by a partialy blocked jet so enough oil to stop a sieze but not enough to carry heat away or keep a proper oil film

[HondaMan]

I have also heard that noise after a long-ish winter sojourn when the intake valves got a bit of rust on 2 of them (on several bikes) because they sat open in humid climes. This made them rust slightly, and the rust increased the rocker tappet clearances on the 2 valves. The first time, I adjusted the clearance back to the tighter spec (they were more than 0.004" in that case) only to find, 100 miles later, that they were tight and had to be loosened back up. On subsequent bikes that did this, I left the valves alone and after some miles the valves wore the rust away and returned to their normal clearances. Since then I just leave them alone, in similar situations.

That doesn't absolve the above-mentioned problems if the rockers have suddenly developed a LOT of clearance (like 0.005"+) for no apparent reason, when they were previously correctly set at 0.002": that can indicate lack of oil that is wearing out the cam and rocker.

[scottly]

Top end has oil and both sides are good!

If I were to guess it may be a valve rocker that has become loose or perhaps a rod bearing gone bad. 

A bad rod bearing makes more of a knock than a tick. Recheck the valve clearances, doing one cylinder at a time. Also, an exhaust leak at the cylinder head can make a ticking noise; does it sound louder at the front of the engine?

[Scootch]

Try the old school method of using a wood dowel up to your ear and probing spots on the motor to locate where the sound is emanating from.

[TheWiredNinja]

So it has been awhile since I've posted here and worked on the bike, but as you all know, life happens!  Anyway, I'm determined to get my back on the road and I have in hand some real nice goodies for this rebuild.  In the meantime I've posted pictures of the engine being dismantled and I'm curious if you guys think... I'm trying to yet pinpoint the cause of the ticking sound, despite the problematic area's that I have noticed.

Background:  This bike (1972) has been sitting for around 30 years (based on the last plate renewal) and although I got the bike (surprisingly) started and working perfectly for a good season (good compression and ran great!), unsurprisingly the bike developed issues and the oil burning issues began, specifically in cylinder 4.  This then developed to harder starts, more oil burning, rising engine rpm on its own at idle when the engine warmed up, and finally the distinct "ticking" sound. 

I initially thought that something must have clogged the head oil jets causing a lack of lubrication which started to slowly destroy the cam/rockers/valves.  However, after opening her up, everything looked quite good with no obvious signs of problems - in fact, I'd be comfortable reusing everything.  I took off the head and things started to paint a picture what was going on...

Cylinder 4 was covered in oil and as a result, of burning the oil, it was cleaner on the face than the others



Closeup of Cylinders 4 and 3



Closeup of Cylinders 2 and 1




This is the condition of the underside of the head, clear showing alot of carbon buildup, especially #4 (left)




Here are the bores 4 and 3




Bores 2 and 1




Although the bores showed signs of corrosion, they were quite smooth!  I could not feel much roughness or anything too noticeable aside from the slight bore scoring near the bottoms.  This can also be seen on the pistons themselves here:

Pistons 4 and 3




Pistons 2 and 1



This is when I noticed the oil rings on piston 4 were stuck.  All the others pistons and rings were free to move and looked good.  This was clearly the major cause of the oil leak on that piston




So with all that said, I'm curious if that ticking sound could be due to that #4 piston?  I should also mention that I had initial trouble with a stuck valve on #3 that I managed to free up and then seemed to ran fine.  Obviously several things could account for the lean condition at idle including the poor sealing valves etc.  But the ticking on the other hand... I would really like to avoid opening up the cases if I can.  Is there a way to confirm all is well with the crank and bearings without having to do this?  Or is the ticking identifiable here?

[bryanj]

That needs a rebore and oversize piston kits PLUS i would check valve stem to guide clearance, the F2 was notorious for exh valve guide wear but other models can do that

[TheWiredNinja]

That needs a rebore and oversize piston kits PLUS i would check valve stem to guide clearance, the F2 was notorious for exh valve guide wear but other models can do that

Oh definitely, the bike is a K2 btw.  I thought ahead and got some nice parts from M.R. - little preview of what is to come is attached.  Any idea on where the ticking issue could be?  Could it just be the worn valvetrain? The stuck oil ring on #4? Again, no indication of major wear on the camshaft, rockers or towers (and related parts) as far as I can tell - granted, I'm not positive if it's the valves themselves as being the source despite them being very crusty looking...

I'm hoping this new head and an 836 JE piston kit with new bored cylinders from CycleX will do the trick.  My major fear is that it's the rods making the noise or something of that sort.

[TheWiredNinja]

It's come to my attention the pictures above may look too large for some (you can scroll right using the arrow keys to view the full picture) so I've posted them again on here as attachments.

[madmtnmotors]

I just recently had a ticking noise in the racebike. If I covered each V-stack one by one I was able to determine the noise was in the #1 assembly. I only heard the noise at idle and it would go away as soon as the rpms started to climb. The V-stacks seem to amplify valve train noises and I was able to narrow it down to excessively worn exhaust valve guide. My troubleshooting consisted of pulling the head, checking valve "wiggle", and replacing the head with a used head that had tighter valve guides.

No more ticking.

[TheWiredNinja]

I just recently had a ticking noise in the racebike. If I covered each V-stack one by one I was able to determine the noise was in the #1 assembly. I only heard the noise at idle and it would go away as soon as the rpms started to climb. The V-stacks seem to amplify valve train noises and I was able to narrow it down to excessively worn exhaust valve guide. My troubleshooting consisted of pulling the head, checking valve "wiggle", and replacing the head with a used head that had tighter valve guides.

No more ticking.

Thanks for that.  I am now also leaning to the valve guides as being the issue.  They were rusty to begin with and with one valve actually being stuck, I knew I was on borrowed time.  Looks like the build will continue without having to crack open the cases

[rotortiller]

If it were me I'd clean the piston with solvent and carefully scotch-brite clean then hone the rusty cylinder, just enough to remove the rust, then measure, also evaluate pitting. Then I would look for any radial play on the rods, I would suggest check-torque of the rod bolts and main bearings. Sometimes things look worse than they are in pictures. I can see lathe marks still on the pistons under the crud I believe. The cylinder ridge where the rings stop sweeping can offer indications of use. Shop manual has suggested piston to cylinder clearance limitations. While it looks bad, is it really pooched beyond limits?

[ofreen]

Can't say for sure if it was the issue of course, but an exhaust leak between head and header can sound all the world like a ticking from the engine.  I've seen it happen enough that it is the first thing I look at.  Usually tightening the nuts/bolts cures it.  If not, new exhaust gaskets are needed.  They will only compress so much.

[TheWiredNinja]

If it were me I'd clean the piston with solvent and carefully scotch-brite clean then hone the rusty cylinder, just enough to remove the rust, then measure, also evaluate pitting. Then I would look for any radial play on the rods, I would suggest check-torque of the rod bolts and main bearings. Sometimes things look worse than they are in pictures. I can see lathe marks still on the pistons under the crud I believe. The cylinder ridge where the rings stop sweeping can offer indications of use. Shop manual has suggested piston to cylinder clearance limitations. While it looks bad, is it really pooched beyond limits?

If I hadn't bought new cylinders to move on towards an 836cc, then I would absolutely try and rehone these cylinders.  I agree that they look way worse in the pictures and could easily clean up nicely - like I said, no gouge marks or pitting whatsoever.  Maybe a .25 or .50 overbore at worse case.  Great idea on any play or issues with the rods with the pistons off - I want to avoid opening the cases as much as possible.

Can't say for sure if it was the issue of course, but an exhaust leak between head and header can sound all the world like a ticking from the engine.  I've seen it happen enough that it is the first thing I look at.  Usually tightening the nuts/bolts cures it.  If not, new exhaust gaskets are needed.  They will only compress so much.

I would tend to shy away from this suggestion as I'm fairly certain there wasn't any exhaust leaks.  In fact, I checked this for this before without issue.  At this point, I'm inclined to believe it was rusty valve guides and excessive play - I can actually see unusual wear marks at the very top of valve #3 on the exhaust side.  I'll see if I can inspect further and take a picture

[scottly]

Please post smaller pics!!! Also, post pics of the cam lobes and rocker surfaces.

[newday777]

If I hadn't bought new cylinders to move on towards an 836cc, then I would absolutely try and rehone these cylinders.  I agree that they look way worse in the pictures and could easily clean up nicely - like I said, no gouge marks or pitting whatsoever.  Maybe a .25 or .50 overbore at worse case.  Great idea on any play or issues with the rods with the pistons off - I want to avoid opening the cases as much as possible.

  At this point, I'm inclined to believe it was rusty valve guides and excessive play - I can actually see unusual wear marks at the very top of valve #3 on the exhaust side.  I'll see if I can inspect further and take a picture

Welcome to the forum TheWiredNinja

In my reading through this thread you have running, your video noises, your replies (and the bits of information you have added through the thread and some missing information from the beginning of your situation) and waiting on some missing information from you on the internal conditions and pics of key parts, #3 valve end wear, your stuck valve, the valve guides and valve end play, wear on cam chain guide and slipper, (and you didn't say how long you rode it before tearing it down between your posts in April and you coming back yesterday to fill in more updating), I've screen shot they key points in my takeaway. The short video clips points to top end not bottom end noises. But you didn't say if you did a stethoscope pinpoint of the noises.
Bottom line, you are on the right track in going to the 836 bore(as Hondaman has said in the past the bores get egg-shaped and if you go by looks alone without internal bore mic checking, your saying you would have just honed and new rings would have been disappointing 😞).
The head you bought I hope has new valves, guides and springs?(you didn't elaborate on the new head).
If you haven't bought them yet, replace the cam chain guide parts with new parts as well as the cam chain so they don't fail on you shortly.
Hope this helps you along on your bike.

BTW Go to the new members introduction section and introduce yourself and your bike. Pictures are always welcome and of your history with the bike.

[TheWiredNinja]

Sorry for the lack of information and introduction.  So it is a K2 1972 CB750 that was all original with 11,000 miles that sat for 30 years and I bought it as a covid lockdown project.  I have modified the bike to be a sort of "hybrid cafe racer" but kept to the original design for the most part. It was clear that there was quite a bit of moisture that sat in the engine due to the rust internally on the valves and guides on the exhaust side but the engine did turn over easily.   I wanted to complete the bike 'as-is' knowing the engine will need a rebuild but since the engine started right up after I cleaned the carbs and I unstuck the one valve on #3, I rode it until it became problematic.  I would say I put on around 2000-3000 km since and rode it fairly aggressively without many issues. 

Issues that were present:  rising idle when the engine became hot, oil burning when the engine was hot, and I would say the engine was a little "buzzy" at high RPM but I don't have reference to sorted CB750's (and I'm led to believe they should be very smooth). 

I have attached pictures of the bike and top end parts which all show nominal signs of wear and zero rust.  There is a minor chip on one of the camshaft lobes as pictures but it is offset.  I've attached a picture of the associated rocker as well showing its damage... I don't believe that would be the cause of the ticking, but I'm glad I have replacement parts.

The ticking sound developed after I put it away from sitting outside during the winter and it subsequently became more difficult to start and slight loss in response/power the following Spring.  I double checked all clearances and they were fine.  I did try to pinpoint the ticking sound using all the mentioned 'tricks' but failed to locate it other than it being in the vicinity of the middle of the engine and possibly towards the top end (this may explain why it could be the valve guides, especially on #3).  Speaking of which, I cannot take a picture of the slight abrasion marks on #3 that I noticed as it needed to be pressed downwards by the cam to clearly show this.

Upgrades and new parts include:  new cylinders modified and bored by CycleX to 836cc with JE domed Pistons, RC295 camshaft, M.R stage 3 ported head with oversize intake valves, titanium retainers, Kibblewhite valves, bronze guides, serdi valve job.  On top of that, I have purchased refurbished guide pins and rockers by CycleX just to be safe and ready for the RC295 camshaft.

I have also gotten a new cam chain guide but I think I will keep the exiting chain as it looks to be in great condition with zero pitting and rust (I'd have to open the cases up anyhow to replace and I'd want to avoid that)

Lastly, I just wanted to add that the bores could easily be honed and cleaned up for reuse.  There is corrosion but zero pitting and they are all smooth - I suppose the mileage I put on the bike may have certainly helped clean this up without problem.  I decided to get refurbished head and cylinders because it was more cost effective buying it from the guys who were going to perform the work on the parts, rather than shipping it to them, waiting, and shipping it back (I'm located in Canada)

[newday777]

Good to hear you got the head from Mike. It'll go well with the pistons and cam.

Pictures of the cam chain guide assembly pieces?

[TheWiredNinja]

I've attached pictures of the chain guide assembly - I have new ones on hand and although it looks 'ok' there is a small amount of rust and Hondaman's describes that if there is any rust present, to change it out.

I managed take out all engine studs successfully with the double bolt and vice grip method.  Only one needed the addition of some heat.  The only strange problem I've encountered is that I seem to be missing a dowel on the gearbox side.  The starter gear has a circular shim and what should be a dowel holding it and the gear in place - it was not there when I took the cover off, which is disconcerting... and yes, I checked on the inside of the stator including the backside of the magnets, it is not there.  I fear it may have fallen on the underside of the flywheel gear and into the case :'(

Anyone know the size of this dowel and where I can get it?  Is there a history of these coming lose or losing them in the case somehow?  (god I hope not..)

[bryanj]

More of a shaft than a dowel and yes they frequently stick in the case when you take it off

[PeWe]

Have you measured the  primary chain slack?
Around 65mm when new, 70mm is max, replace.
Should be OK at only 11.000 miles, tensioner rubber might be hard by age.

When cylinder is off, not much extra to replace primary chains and a possible old hardened retainer.
Good to investigate crank bearings too.