Cb360 Reassembly Help

cb360j

Member
Background Story:

I’m newer to the world of Vintage Motorcycles, having had newer Ducati’s but never anything old enough that the dealership didn’t work on... shame on me as I’m an engineer and should be doing more. The bike is a 1976 cb360 I got from my neighbor for free, and I decided to just do a full rebuild.

I did all the frame work I wanted, put on a cool snazzy new seat and repainted the frame. Had the cylinders bored in order to put .50 over wiseco pistons in due to the rings being stuck to the old pistons. I am now in the process of reassembling the engine before I put it back into the frame, put the pistons in, cylinders on, head on, all bolted down according to spec.
Now it is time to put the valve covers on, I filled the oil baths with oil and put the gasket sealer from common motor collective, then proceeded to place the valve cover on and bolt it to spec. Before I put the valve cover on, the engine turned freely and I heard air coming from the cylinders. Obviously with the valve covers off, the rocker arms were not pushing down on the valves. The problem is that the engine will spin about half a rotation till it comes to a dead stop, not trying to bend a valve, I don’t push down on it any harder and I take the valve cover back off.


Here is my thought process so please help me with this and correct me where I am wrong: the valve cover off means the engine can spin freely with no worries of the valves coming in contact with the engine. When the valve cover on, the rocker arms push the valves down and cause them to come in contact with the piston causing the engine to not complete it’s stroke. Assuming the timing is off, or the valves need adjustment, Is this a problem I need to address with the valve cover off? If so, how do I go about this. Thank you in advance.



Here is some pictures of the bike in its current state in case y’all wanted to throw some opinions at that too Haha
 

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crazypj

Split personality, I fake being smart
Sounds like cam timing is off or you didn't tighten cam sprocket bolts fully?
Trek will be along shortly 8)
 

cb360j

Member
crazypj said:
Sounds like cam timing is off or you didn't tighten cam sprocket bolts fully?
Trek will be along shortly 8)


You’re one of the people I was really hoping would help with this.
The bolts are tightened all the way. One thing I wasn’t sure of as I couldn’t find it in the service manual, is if there is a correct orientation that the cam sprocket should bolt to the cam, one side or the other?

How do I go about setting cam timing?

Thank you!
 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
You need to align the two hash marks on the cam sprocket with the top edge of the head when the motor is at TDC. Please confirm this is the case.
 

crazypj

Split personality, I fake being smart
put left cylinder at TDC then it's just a matter of lining up cam sprocket lines with gasket face. Don't rotate crank, you 'walk' chain around sprocket and when it's in correct position (with front run tight) it will slip onto cam. then rotate cam to line up bolt holes
Just downloadedm picture so I could enlarge it. Looks like cam timing is way off?
 

cb360j

Member
crazypj said:
put left cylinder at TDC then it's just a matter of lining up cam sprocket lines with gasket face. Don't rotate crank, you 'walk' chain around sprocket and when it's in correct position (with front run tight) it will slip onto cam. then rotate cam to line up bolt holes
Just downloadedm picture so I could enlarge it. Looks like cam timing is way off?


I set the left cylinder to top dead center, then did as you said to walk the chain around the cam till the hash marks aren’t aligned with the face of the head surface. I put the cover back on and when’s rotating it still slightly catches. I’m not entirely sure if this is correct or not still. Any insight?
 

irk miller

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DTT BOTM WINNER
cb360j said:
I set the left cylinder to top dead center, then did as you said to walk the chain around the cam till the hash marks aren’t aligned with the face of the head surface.
walk the chain around the cam till the hash marks are aligned with the face of the head surface. Is that a typo?
 

cb360j

Member
Haha! Yes that is a typo.

So I restarted undid the bolts to the sprocket and took then cam chain tensioner out.

Here is my steps

Put tensioners in place.
Align Left top dead center
Align sprocket hawk marks
Tighten down sprocket bolts
Install cam chain tensioner holder
Put cover on just to see if anything was better but it still is catching.
Thoughts?
 

irk miller

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DTT BOTM WINNER
Can you see where it is catching? It could be a lot of things, and without any idea where the catch originates from it will be hard to figure out. What does your cam chain tensioner look like, out of curiosity? There will be loops at the bottom and the top. Which way do they go?
 

cb360j

Member
I can’t see where it’s catching as the valve covers are on when this is happening.
The cam chain tensioner is brand new.

Here is the way the tensioners are put in before I put the tensioner cover on.

Let me cover my bases here:
- the left cylinder is set to top dead center when the “LT” mark is aligned.
- and the hash marks should be completely horizontal to the head surface (top side).
 

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cb360j

Member
Correct, spins freely without top cover on. But when it is on, I will rotate the crank the correct direction and about a half rotation later it will stop and not want to move further. I should have looked at what position this was happening to give a better reference.

Tachometer drive gear is perfectly fine. Spins freely, does not seem to have anything wrong.
 

crazypj

Split personality, I fake being smart
Do you have thrust washer on cam end? (right side)
It's unlikely but rocker pressure could push cam sideways enough to make things 'catch' ?
You did back off all the tappet adjusters so there was no possibility of them catching on top of valve stems?
It is possible to bend tops of valves enough for them to stick in guides (unlikely but possible)
You did have the front run of chain tight? (all the slack at rear where tensioner lives)
Can you see any 'witness marks' of something catching? (sprocket is 'flat' against mounting flange)
 

cb360j

Member
crazypj said:
Do you have thrust washer on cam end? (right side)
It's unlikely but rocker pressure could push cam sideways enough to make things 'catch' ?
You did back off all the tappet adjusters so there was no possibility of them catching on top of valve stems?
It is possible to bend tops of valves enough for them to stick in guides (unlikely but possible)
You did have the front run of chain tight? (all the slack at rear where tensioner lives)
Can you see any 'witness marks' of something catching? (sprocket is 'flat' against mounting flange)


I do not have a thrust washer, and in all honesty, have not heard of this but I will be reading of this immediately. Is this something that is required?

No, I did not back off the tappet adjusters, but I will be doing so as soon as possible.

Correct, front run of chain is tight.

No witness marks of anything. I do not understand what you mean by the sprocket being flat against mounting flange though.


Again, thank you to everyone who has helped thus far.
 

irk miller

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DTT BOTM WINNER
In the first pic, it appears that your cam chain is all the way at the edge of the tensioner. This is likely due to the missing thrust washer. The thrust washer takes up the slack from a small gap at the end of the cam. You should've had to remove it along with your cam. But, as PJ would know better, this may have been a service bulletin and not originally installed at the factory. I can't remember. Pretty sure he's suggesting that it's possible that the bolts or some part of the cam mount for the cam sprocket is hitting the head.
 

crazypj

Split personality, I fake being smart
I've seen one or two with burrs and nicks on cam flange causing sprocket to run out of true, a couple have 'bent' flanges (pretty much just about to break) making chain 'run out' never seen one bad enough to 'lock' motor though.
Can you post pic of inside of rocker cover?
Just in case it's something simple. ;D
If motor turns over with tappets backed out level to rocker arm, cam timing is still 'off'
You can adjust them one at a time to see which is causing problem then pull head and check that valve is OK.
 

cb360j

Member
crazypj said:
I've seen one or two with burrs and nicks on cam flange causing sprocket to run out of true, a couple have 'bent' flanges (pretty much just about to break) making chain 'run out' never seen one bad enough to 'lock' motor though.
Can you post pic of inside of rocker cover?
Just in case it's something simple. ;D
If motor turns over with tappets backed out level to rocker arm, cam timing is still 'off'
You can adjust them one at a time to see which is causing problem then pull head and check that valve is OK.

In my "infinite" wisdom (complete sarcasm) of my 22 year old self, I somehow skipped over the thrust washer part in the manual.. shame on me.
It is quite possible I took it off when initially removing the cam and then forgot to put it in, but I do not remember the cam having one.

As soon as I get home I will post picture of inside of the rocker cover, it would be a blessing if it was something simple haha.

backing out the tappets is just adjusting valve lash all the way out correct?
 

crazypj

Split personality, I fake being smart
Backing adjusters out gives about 3~4mm 'lash' and should allow motor to turn over even if cam timing is still out
Adjust one valve to spec (0.003" ex, 0.002" int) and turn it over.
If you post a pic of cam position before fitting cover I should be able to tell if cam timing is right. I have pictures of 'degree'sd in' cam in m y 360 build/blog so you can see how it should look.
http://www.dotheton.com/forum/index.php?topic=11736.150
Reply 159
You do have the top tensioner holder in place?
 

Sonreir

Oregon
It might also be worth noting that you should have the followers in the "down" position when you put the rocker cover on. Otherwise the tappets might lodge beside the valves instead of sitting over them. This would cause the whole assembly to lock up and possibly bend a valve stem.
 
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