Topic: CB500 Overheating-Seizing

[Little_Phil]

OK apart. Bores all look OK but I don't think it's that. But the faces of the two centre bearings of the camshaft are dull in places so I think it's that. Blew out the passageways with WD40, oil, water. air you name it but didn't see anything come out. Quickly put it back together, oil flows with cam in but is it enough?

[bryanj]

What do the pistons look like, ans are the oil ways in the lower end ok plus the restrictor jets and the oilways from outer cam bearings to inner

[Tracksnblades1]

What do the pistons look like, ans are the oil ways in the lower end ok plus the restrictor jets and the oilways from outer cam bearings to inner

Pictures Pictures….^^^^^^^^^^^^^^^^

Without them or a video it’s just here-say…🤔

[Little_Phil]

After trying to clean out the passageways I've put the head on temporarily to see the oil flow to the cam bearings.
This is a pic of the suspected bearing surface.

[Little_Phil]

I note that the outer bearings oil channel goes out to the sides of the head and thus the oil is forced back past the bearing whereas the channel in the inner bearing surfaces allows oil to flow into the oil cam lobes oil baths. So does the the two outer bearings get a better lubrication system than the centre? Or is this a way of diverting more pressure to the centre?
Outer bearing pic:-

[newday777]

I note that the outer bearings oil channel goes out to the sides of the head and thus the oil is forced back past the bearing whereas the channel in the inner bearing surfaces allows oil to flow into the oil cam lobes oil baths. So does the the two outer bearings get a better lubrication system than the centre? Or is this a way of diverting more pressure to the centre?
Outer bearing pic:-

What is the black coming out the oil port? Permanent, silicone??

[bryanj]

To clean the head passages you either have to pressurise with lots of parafin/air from one bearing to the other OR drill out the plug visible at the ends of the head then find a way of re sealing the hole.
The wear/polish marks do not look excessive to me

[Tracksnblades1]

Phil,
What does the journals on the camshaft look like that match up with the polished head bearing saddles..?

I was expecting some aluminum that moved or some blue journals on the cam..I read it seized..
Was it a “trying your best to maintain rpm with the throttle”, seizure…?
Or did it start pulling down so you just let go down on its own with no additional throttle..?

When they seize and you can’t kick them over there is usually a tell tale sign if you’re looking in the right place..

Does the transmission readily go into neutral when the seizures occur..?
Can you roll the bike in neutral when the engine is locked..?

I’m not sure those cam bearing saddles are showing signs of a lock up..
I’ve seen running 750 camshaft holder bearings polished a lot more than yours are..are they rough like fish scales..?

[Little_Phil]

Ok just getting back to this.started to
When it seized I could feel a braking effect whilst going 60mph. Then as I slowed it started to jerk and then cut out. Started did not work and KS seemed solid. OK again after 5-10 mins and then did a steady ride home (10 miles) at max 40.
I still think that it's this cam bearing so have been cleaning out all the passage ways as suggested. Fill with various fluid and eject out with WD40 or carb cleaner straw aerosols.
Close up of bearing surface. Cam finish is fine (forgot to take a pic)

Put it back together and did 10 steady miles. 4000-5000 rpm. OK so far, but I've lost a bit of confidence in it so will do a few continuous circles of this route and open the throttle up a bit..

[Little_Phil]

Still in trouble with this. It's coming apart again.
I am going to reverse some of the more recent work. Intend to pull the top end and replace the rings with the ones that came out. Check the oil jets (again), fit a replacement head that I have and ride like this.
If this is OK then fit the new rings (again) and ride. If this is OK then the problem is probably the head.

[bryanj]

One thing that is technicaly possible BUT i have never seen OR heard of is a bent camshft, it is unusual to see the polish marks on the bearing half way up, would normally be at the bottom

[denward17]

One thing that is technicaly possible BUT i have never seen OR heard of is a bent camshft, it is unusual to see the polish marks on the bearing half way up, would normally be at the bottom

Could there be a partially bent valve on the other side of the polished cam journal creating a push on the camshaft?

[bryanj]

Doubtfull as the rocker arm is in the way, woth checking valves anyway as incorrect cover fitting bends valves and breaks guides but that dont cause a siezure

[HondaMan]

Ok just getting back to this.started to
When it seized I could feel a braking effect whilst going 60mph. Then as I slowed it started to jerk and then cut out. Started did not work and KS seemed solid. OK again after 5-10 mins and then did a steady ride home (10 miles) at max 40.
I still think that it's this cam bearing so have been cleaning out all the passage ways as suggested. Fill with various fluid and eject out with WD40 or carb cleaner straw aerosols.
Close up of bearing surface. Cam finish is fine (forgot to take a pic)

Put it back together and did 10 steady miles. 4000-5000 rpm. OK so far, but I've lost a bit of confidence in it so will do a few continuous circles of this route and open the throttle up a bit..

That doesn't appear as a seizure, but does look like poor lubrication for a time.

Have you checked the oil pressure, and (uh-oh...) what kind of oil are you currently using?

[Little_Phil]

Ok it's all apart and nothing new to see except! The forward cam chain guide is bent. Should have taken a pic but nearly as bad as this.

[Little_Phil]

I saw a bent guide on a 550 I took apart a few years ago. My bend is nothing like as bad as the pic above and I'm putting it down to an assembly c**k up.
On the subject of oil I don't have a means of checking the pressure. When cold the oil light takes 5 seconds to come on. When hot it comes on virtually instantly with ignition off but it doesn't show at all when ticking over.
Using 10-30 oil as recommended for a cooler climate, same as I've done for 50 years. But did change the oil and filter when I fitted the new rings.

[HondaMan]

I saw a bent guide on a 550 I took apart a few years ago. My bend is nothing like as bad as the pic above and I'm putting it down to an assembly c**k up.
On the subject of oil I don't have a means of checking the pressure. When cold the oil light takes 5 seconds to come on. When hot it comes on virtually instantly with ignition off but it doesn't show at all when ticking over.
Using 10-30 oil as recommended for a cooler climate, same as I've done for 50 years. But did change the oil and filter when I fitted the new rings.

I've seen the tensioner bent like that when it was mis-installed (the lower pin wasn't in the grooves under the cylinder) and it was run for quite a while.

10w30 oil isn't normally used in the 550: at the least it's been 10w40. The crankshaft bearings wear quickly with 10w30 oils in this engine, which can then cause marginal oil pressure problems in the rest of the engine, because so much oil flow is leaking out at the crankshaft's 9 bearings. In the CB500 I have seen this situation then cause failure of the cam bearings in the top end, similar to the scored one shown above.

You might wish to experiment with some 20w50 oil at this point? Castrol makes a motorcycle oil with low detergent, available at most auto parts stores.

[Little_Phil]

That was my bad. The oil used is either 10-40 or 15-40.
The bike now has it's original piston rings installed, a different head and new oil (15-40) and filter. Let's see if this works. I also bought some 20W-50 but we'll see first.

[HondaMan]

That was my bad. The oil used is either 10-40 or 15-40.
The bike now has it's original piston rings installed, a different head and new oil (15-40) and filter. Let's see if this works. I also bought some 20W-50 but we'll see first.

That's good!

[Little_Phil]

After running with the old rings and new oil and filter and the replacement head for a couple of weeks and all seems fine. (but a bit rattly)
SO I stripped it down again and put the new rings back in with the intention of running with these with the replacement head for a while. Block back on and turned over on the Ks by running the cam chain over my hand. The oil up the sides was a bit sluggish I thought so I swapped the oil pump for another one, seemed much better. Now done a couple of 30 mile runs and all is still fine.