I set myself up with a space heater in the shed so that I could get a jump on tearing down the top end of the 1981 Suzuki GS650L and attempt to resolve my timing chain jump and lack of compression in the number 3 cylinder. There are a number of components to remove so that the cylinder head can be removed. The valve cover has been removed for a while as I was investigating the issue before deciding to take off the cylinder head. Next was to pull out the carburetors so that I could get to the cam chain tensioner and see if that was part of the culprit for my timing jump. I ended up removing the starter cover and air chamber as well to get better access to the cam chain tensioner.
It is important to lock the set screw on the plunger on the left side of the cam chain tensioner before you unbolt it from the engine. This way the plunger will not coming flying out as there is no resistance to the spring. Here is the cam chain tensioner removed.
It appears to be in working order, but I will still take it apart to make sure that there are no gouges or other problems with the plunger that would prevent it from properly tensioning the cam chain.
Next the four exhaust manifolds were pulled from the cylinder head. Once you take off the head, it is also necessary to pull the cylinders and replace the gasket. Better to have everything removed before you unbolt the cylinder head so that you don’t need extra hands to free the parts from each other.
Next was removal of the intake and exhaust cams by unbolting the four cam shaft bearing caps (two each). Each cap has four bolts and should be loosened in a diagonal pattern to avoid any warping. Then it is just slipping off the cam chain and sliding out the two camshafts. I stuck a screw driver through the cam chain so that it would not fall back inside the engine.
There are 15 bolts that hold down the cylinder head and cylinders. Loosen each slowly and in the proper order to prevent any warping of the head. Then it is just a matter of lifting the head straight up off of the threaded studs.
Unfortunately, at this point the rear cam chain guide should be visible, but it is not. I found that the guide was broken in half at the point where the cam chain tensioner would apply pressure to the guide.
And the other piece that was loose in the timing chain bay.
Looks like it was hit a few times by the cam chain tensioner while I slowly limped the bike home.
No one seems to be carrying this cam chain guide as a new part anymore and I am not finding anything aftermarket yet for this engine, so I have ordered a used one from a seller on eBay. Hopefully it will be in decent condition for a replacement.
The next problem is that the engine needs to be torn down all the way through the crankcase to remove and replace this part that is pinned in between the two halves of the crankcase.
The initial purpose of taking off the head was to see if there was any visible problem with the valves in the number 3 cylinder that would explain the sudden loss of compression in that cylinder. This cylinder did have a compression reading of 175 psi and it is now at 105 psi after this mechanical issue. Nothing was visibly wrong with the valves, but the change in valve clearance was only 0.14mm, so maybe not enough to see with the naked eye. The valves will need to be removed and more measurements taken.
Number 3 is the right-center.