Goodbye crank bearings

Well the head is off, head gasket looks good, probably reusable. I don’t see any major signs of damage, wear, or any big pieces of metal. I see the cam chain is slightly discolored like it has worn down in the center. It could just be me wanting to see things that aren’t there. I’ll add the pictures and y’all tell me. I don’t see where it could have worn against. 

When you put the engine together last time you say you locked the tensioner before installing it?  I'm guessing you unlocked it after the timing was set and re-locked it after it took up slack.  Please confirm if that's what you did.  This time when you took the tensioner off it was locked, but when you unlocked the screw the tensioner did not move.  Please confirm if this is correct.

I've never seen a tensioner stay locked when the bolt is slacked off.  the plunger is tapered so that the moment the bolt backs off the plunger is forced forward.  Is the spring still OK?

Before you took the top idler off was there any slack in the chain?

When the chain is loose it can skip through the upper idler and screw up the timing.  This can cause bent valves.  How do your valves look?  Any sign of damage?  How do the cam caps look?  Any sign of heat or wear?  

The 650/750 crank runs on journal bearings as you probably know.  For this reason the oil pump operates at much higher pressure than a 1000.  (From memory the pressure is around 36 psi vs 2 or 3 psi on the 1000.). The journals must have oil to allow the crank to "float" on a film.  (The 1000 uses roller bearings so the oil film isn't necessary.)  If there isn't enough oil or if the film is too thin (The M8 bolts need to be torqued correctly.  Too tight means there may not be enough clearance for the crank to run on an oil film.).

The cams operate in a similar manner although there are no journals...just the caps over the cam shafts.  Oil enters under pressure from underneath the cam.

On the top of the upper case there are two flow restricters, one on each side of the case.  They have a tiny hole to allow oil to flow up to the head.  Does your engine have those restricters in place?  If not you might not be getting proper pressure for the oil for the head.

Assuming all of the above is fine then I would guess your problem is a crank journal.

 

Thank you for the reply hardrock,

I will try to upload a video of the current state of the tensioner.
To describe how it is acting is that the shaft of the actual tensioner is somehow not allowing a free motion when the tensioner is assembled. Meaning that once it was placed back in its place, the lock bolt was removed, and it never sprung back to apply any pressure whatsoever.
The springs are okay and spring well. I am not sure what you mean by top idler. 

One thing I had failed to mention was the knock went away at a higher RPM. It was very loud at 1-3k rpm but it disappeared once 4K rpm was reached. I have never had an engine to do this to me so I wasn’t sure if this was important to note. 

all valves are intact and not bent or damaged in any way. No signs of any damage to cam shafts or cam caps, the head had plenty of oil when I shut it off and pulled the valve cover. The restrictors for oil pressure at the head are intact and are not blocked in any way. 
 

"Well the head is off, head gasket looks good, probably reusable."

Hi Elfarm, the head gasket CANNOT BE REUSED no matter how good it looks. I get the temptation given the price but the gasket compresses when the head is torqued down so would not seal if reused. 

If you look closer you can see scratching marks from the HYVO cam chain. You have to change the cam chain rubber guide in the valve cover or better all chain guides. It could be also the cam chain is to much streched and end of life, so the tensioner can´t do his job properly.

 

I see, that is why I uploaded that picture. Do you think that wear is from the lack of tension? 
is there a way to confirm that the cam chain is at the end of its service life? Why do the guides need replaced? 

I will order a head gasket to replace the one that was removed. Thank you Wookie. 

So it's sounding more and more like your issue is in the timing chain mechanism.  Yes, there is a way to check timing chain wear but you will have to take the chain off to do the check.  There is a procedure described in the manual.  I think the check is to compare the length of 20 links to a spec.

OK, so you don't have a top idler like the 650 engine.  If the tensioner doesn't function properly then you should replace components.  Does the shell look good when the spring and plunger are removed?  Any evidence of wear inside?

wrote:

I see, that is why I uploaded that picture. Do you think that wear is from the lack of tension? 
is there a way to confirm that the cam chain is at the end of its service life? Why do the guides need replaced? 

I will order a head gasket to replace the one that was removed. Thank you Wookie. 

As mentioned, there is a maximum stretch specification listed in the service manual. You put tension on the chain and measure the distance between a certain number of pins.
if the rubber guides are badly worn, there will be too much slack in the chain for the tensioner to compensate for. The manual shows how and where to take the measurements. Engines with a hyvo chain like you have do not use rollers, top, bottom or elsewhere, so don’t worry about that.

I’ll pick up a new caliper soon to measure the chain stretch. 

I’m considering going with a manual tensioner by APE but I’m unsure of how easily adjustable it will be with the carburetors in place since the old one is nearly covered up by the carburetors. I’m also unsure of what the adjustment setting would be, a preload? 

No experience with the APE but I had my little brother make me one; adjustment was a bit of a pain, but once it's set you shouldn't need to fiddle with it for a good while. I think the tightening sequence is sort of do it finger-tight while rotating the engine (to make it to the loosest spot) then back 1/4 turn. Surely someone will correct me if I'm wrong. 

After that I adjusted it by ear with the engine running, it's pretty simple. I think I prefer the automatic tensioner in the end though. 

Alright, head gasket, APE manual chain tensioner, all hardware for side covers being replaced with stainless steel Allen screws, And some miscellaneous items that were neglected but while I’m buying may as well fix everything. The only thing I have left to buy is a new oil filter because I’m definitely not leaving the old one in it. I will also be painting the intake sides so they don’t look 40 years old and sun baked anymore. Ordered fork seal kit and fork oil as well as the upgraded steering neck bearings.