Topic: 1973 cb500 four camshaft and bearing surface bad

[Rudeavenger]

Hello all, I’ve had this bike since highschool. Built it back last year, and in the process pulled the engine apart and did a top end rebuild. Ran well for a while then quit on me. Did a compression test and found no compression on one cyclinder. Thinking it was rings, i decided to pull the motor apart again and found this. Is my only recourse to replace the head and camshaft? Looks like no oil was getting to the end of the cam. What might cause this. Did a great build on the bike otherwise so I am very disappointed. Any idea how to source these parts?
Thank you in advance

[denward17]

Welcome to the forum, sorry for your damage.

Put in a Wanted ad here in the Wanted section, and search Ebay for used parts.

Probably need another head, cam,  and a valve cover.  Tear down will tell the story, give us some pics of the head/cam.  Probably lots of aluminum/metal particles everywhere, so bottom end may need to come apart to inspect things.  Check with the oil pan off the oil pump filter screen, proceed from there.

Does a '77/'78 550 pinned valve cover fit?

As to oil flow, assuming you have good pressure on the other side, might be a plugged oil jet on the bad side.  Did you use any silicone sealant anywhere?

Also, post the same questions in here for better views and quicker answers:
http://forums.sohc4.net/index.php/board,2.0.html

[Rudeavenger]

No silicone. Didn’t put many miles on it, maybe 50 or so. Looking on Facebook locally and have found a couple of engines, just no way to tell if they are good. Couple of things on eBay as well. Everything else looks good, but I stopped when I got the valve cover off. Any way to check if oiling is good without running the bike? Hate to put it back together and have the same issue.

[bryanj]

Need replacement head, cam, cam cover complete with rockers plus cylinders need to come off the clean the restrictor jets in the dowels at base gasket.
When you rebuild it DO NOT fit the cam cover and spin it over on the starter with no plugs fitted,  oil in and oil filter fitted, oil should pour out of the end bearings when light goes out.

AFTER fitting cover, read the manual carefully!, leave off the steel end brackets that the end covers bolt to and spin over again, oil should flood out of the bolt holes where the bolts that hold those steel brackets go which is why there should be a soft alloy washer between the bracket and cam cover.

NOTE:-

You are relatively lucky in that ALL 500/550 SOHC head and cam are the same the 77/78 cam cover is supposed to be better

[Rudeavenger]

Thank you this is great info. So to be clear any 500/550 head, cam and cam cover will work with the rest of what I have?

[bryanj]

Yup, if you look them up 71 throʻugh 76 head, cam, cam cover have same part numbers only 77/78 cam covers are different as the pivot pins for rockers are locked instead of floating and they will fit if complete assembly used

[Little_Phil]

Wow that's bad. I feel your pain.

[HondaMan]

Like Phil mentioned: it takes very little to block those oil metering jets in the bottom of the cylinders. Make sure the bottom end of the engine is clean: at least drop the pan down and clean anything out you might find down there, now.

[Rudeavenger]

Ok, I’ve got the parts and the top end and cylinders are off. Gotta get the new head clean and will drop the pan and clean everything really well.

Here’s a second question.
Before I took the valve cover off I checked compression. I did this because when it stopped running it gave me the symptoms of lost compression. I had replaced the pistons and rings when I did the initial rebuild. I got 90 lbs on three cyclinders and 0 on the far right hand cyclinder. I thought the rings might have been broken on that cylinder as I had a difficult time getting the block back on and had broken several rings in the process. So I took the block back off na d the rings look fine. Not broken, and no scoring on the cylinder wall.  Valves in the head look ok too. Could the lack of oil caused a valve to stick? Can’t see any other reason I would have no compression on that cylinder. Head was tight and head gasket looks good too. Want to make sure I get everything right before I get it back together. Compression was good when I tested before firing it up after the rebuild.

Thanks again for any help here!

[PeWe]

Engine paint can also block the oil channels to the head.
It has been written  on this forum. Bottom end with cylinder studs were painted.
The 2 studs where oil flow up to the head got painted too that blocked the oil orifices when paint fell off when running.

This was a CB 750 but might happen any bike if parts are painted were oil flows to the head.

[HondaMan]

A cracked or broken ring, or other ring troubles, would usually show as a low compression number, not as 0 very often. But, a valve, even slightly open, will result in 0 PSI compression at cranking (or kicking over) speeds. This could be as simple as one of the cylinder #4 valves just being set too tight (in the valve clearance), or a bit of carbon (or other gunk) trapped in the valve face somewhere. This can happen just from taking the engine apart and reassembling it in a dim garage (I did it myself with my SuperHawk once, too).

[Rudeavenger]

Ok new question, as I am cleaning the replacement head, I filled the intake ports with wd40 and it leaks out the valve on two of the cylinders. The valves do not appear to be burned, but now I think I should remove them and lap them. This will be my first time doing this, and while I understand the concept, I need some guidance on best practices. Does anyone know of a video that would be a good guide for me?
Also, I am thinking that I should replace valve guides and seals but what about the valves? Would it be best to reuse the stock valves?
Should I just have a professional do it?
Would love to hear feedback.

Thanks all!

[newday777]

Ok new question, as I am cleaning the replacement head, I filled the intake ports with wd40 and it leaks out the valve on two of the cylinders. The valves do not appear to be burned, but now I think I should remove them and lap them. This will be my first time doing this, and while I understand the concept, I need some guidance on best practices. Does anyone know of a video that would be a good guide for me?
Also, I am thinking that I should replace valve guides and seals but what about the valves? Would it be best to reuse the stock valves?
Should I just have a professional do it?
Would love to hear feedback.

Thanks all!

Guides are not for you to do without proper tools and training.  Leave it to professionals.
Hondaman does it.

[bryanj]

You need  a proper valve spring compressor for motorcycles of the Honda type.
You DO NOT change guides, if excessive wear you have it done proffessionally as seats need recutting.
Remove and lap in all the valves and replace  stem seals

[Rudeavenger]

Found a great video on lapping the valves

Definitely something I can do. I won’t touch the guides unless I find an issue when I take the valves out.

Thanks again!

[HondaMan]

Looks like you're off to a good start! Lapping isn't hard to do, and it is REAL hard to do something wrong when you do it.
In your gasket kit there should be new valve seals.
When you remove the valve springs: there are 2 very thin washers under the valve springs, one for the outer and one for the inner spring. These serve as the hardened valve seats: they often stick to the springs, so don't lose them! Oil them when you put it all back together, too. Put the small one on BEFORE the valve stem seal when reassembling them: then you won't have to take the seal back off to install the smaller washer-seat.

[pekingduck]

I'm curious if you bead/vapor/sand blasted any of the engine parts.  My experience is that it's almost impossible to get all the residue out of the aluminum pores and crevices.

[newday777]

I'm curious if you bead/vapor/sand blasted any of the engine parts.  My experience is that it's almost impossible to get all the residue out of the aluminum pores and crevices.

A very good point and need to hear the answer from Rudeavenger as to what they did in the build a year ago as any residue left in the motor could have blocked the oil ports and restrictors.