Small Victories

While doing all of these other activities I have still been trying to tear down the engine on the 1981 GS650L so that I can replace the broken cam chain guide. The next step was to remove the clutch cover and move further in to removing the engine internals. There are 10 Phillips head bolts holding on the clutch cover and they didn’t not want to move. Since I have time and would rather not break anything else, I have been slowly beating on it with an impact screw driver and penetrating fluid when the time was available. Finally, this weekend all of the bolts came loose. I thought the last one was going to strip before it came out, but they all came out successfully. I will be investigating options for replacement bolts before putting everything back together.

The bolts in the following picture were removed from the clutch cover in a counter-clockwise pattern from the bolt on the far right which came from the upper right of the clutch cover. The bolt four from the right was the one that ended up giving the most difficulty to remove, but none came out right away.

Once the clutch cover was off, it as time to get in to the clutch. First was the removal of the clutch pressure plate using the Tusk clutch holding tool. The pins on one side first hold the pressure plate and later the arms hold the clutch basket in place.

Springs and plate removed.

The next step is to remove the clutch mounting nut which unfortunately I did not have a socket large enough. I confirmed that it was 32 mm using an old bicycle head set wrench.

So I am off to find a 32 mm socket. I will leave the clutch plates in place until I am ready to remove the entire clutch basket.

Cylinder and Piston Removal

Continuing to tear down the engine of the 1981 Suzuki GS650L to replace the broken cam chain tensioner. Next to come off was the cylinders and pistons. All of the bolts were previously removed with the cylinder head removal, so it was just a matter of lifting the cylinders off of the studs.

Top view of the cylinders removed:

Bottom view of the cylinders removed:

And the crankcase with the pistons and connecting rods exposed and getting closer to removal of the broken rear timing chain guide:

It is amazing how much crud gets in and around the studs that tie everything together in the top end of the engine.

Next is removal of the pistons from the connecting rods. First is removing the cir-clip at the outside end of the wrist pin. I was expecting a clip with holes at the ends to grab with snap ring pliers, but it was just a heavy gauge wire. All came out easily except the No. 2 piston where the cir-clip was not exposed at the slot to grab it. Rags were placed under each piston so that the cir-clip would not be dropped lower into the engine even though the whole engine case is going to be split apart to replace the rear timing chain guide.

Pistons 3 and 4, the wrist pins slid out with just finger pressure.

And the three components of the piston, wrist pin, and cir-clip:

Pistons 1 and 2 were a little bit more difficult to push the wrist pins through with finger pressure alone, so I used a pin puller. Still didn’t need to use a wrench to pull them out, but it was much easier with something to grasp and pull them out.

With these components removed, I will now spend some time making sure that the cylinders, pistons, and rings are still within service limits, or if any further modifications need to be made.

Valve Removal and Specification Check

Continuing the investigation of the loss of compression in Cylinder No. 3 I am removing the valves and checking them against the wear limits and tolerances identified in the service manual for the 1981 GS650L.

As with most tasks, any parts removed from the engine that you plan to reinstall should go back to the same location that they came from. Therefore, it is important to keep things organized.

First was the removal of the valve shim buckets and shims. An old egg carton is handy for keeping these pieces organized for re-installation later.

Next you can use a valve spring compression tool to depress the valve retainer against the spring and remove the valve keepers. It is very easy to compress the springs with this kit that I have from Pit Posse. I have seen people use large C clamps and old sockets with the side of the socket hacked off, but that seems like more work than using this kit.

Here are the components of each valve when removed. Intake valve shown, but both are setup the same.

There was a bit of carbon built up on the backs of the intake valves, most likely from some oil dripping on to the backsides of the valves, and more build up on the exhaust valves. I soaked each pair of valves in parts cleaner for 48 hours +/- to try and remove some of the build up. The before picture is on the left and the after on the right.

Now the fun part to determine if the valves are still within specification for Valve Face Wear, Valve Stem Runout, Valve Head Radial Runout, and Valve Stem Wear. These measurements are measured in hundredths of a millimeter or thousandths of an inch. The gauges that I already have available will measure to thousandths of an inch.

The wear limit for the thickness of the valve face is 0.5mm or 0.02″. Not the easiest thing to measure, so I just set the calipers to this minimum measurement to make sure that all were greater then the minimum. No problems were found.

Next was valve stem runout which has a service limit of 0.05mm or 0.002″. This will determine if the shaft of the valve has been bent. Here is my setup to test the runout of each valve.

Handy to have the nice smooth surface of my table saw and the magnetic locking base of the clamping system. The V blocks are machinists blocks that are about 3 lbs each so that they don’t move around very easily as your are rotating the valve.

None of the valves exhibited any valve stem runout except for the No. 3 intake valve, but it was still just within the service limit.

Next was the valve head radial runout with a similar testing setup as the valve stem runout. The service limits for the valve head radial runout is 0.03mm or 0.012″.

Again, every valve was well within the service limit except for the No. 3 intake valve. Most valves were about 0.004″ of runout. The No. 3 intake valve was 0.020″ of runout. Almost double the service limit.

The last measurement was for valve stem wear. The valve stem limits are 6.960-6.975mm (0.2740-0.2476″) for the intake valves and 6.945-6.960mm (0.2734-0.2740″) for the exhaust valves. All valves were still to the upper end of the service limits. An intake valve is shown below.

All parts are kept together by their respective cylinders and intake or exhaust valves until they are ready to back into the cylinder head.

Looks like I will only need to find a replacement for the No. 3 intake valve as expected.

Combustion Chamber Cleaning

I now know that I need to go deeper into the engine to replace the rear cam guide that is broken, but I wanted to spend some more time investigating the valves that may be causing the low compression in Cylinder No. 3 and figure out what other parts I need to obtain.

Before removing the valves, I wanted to remove the carbon deposits in the combustion chamber of the cylinder head. Leaving the valves in during this process ensures that no damage/change to the valve seats will occur if the valves can be retained.

Here is the the current condition of the combustion chambers:

Not terrible after 27,000 miles, but pretty well coated in a layer of carbon. Here are the cleaning tools:

The Mopar Combustion Chamber Cleaner is intended to spray the whole can into a running engine, but it works well with some manual labor too. The Popsicle sticks do the bulk of the work without damaging the aluminum surface of the cylinder head.

After about 45 minutes of spraying, soaking, and brushing/scraping, this was the result:

The cleaning process also confirmed that the intake valve in the number 3 cylinder is not fully seating, as was expected by the increase in the valve clearance measurement for this valve. This was confirmed by the accumulation of cleaning solution in the intake boot that bypassed the closed valve.

Previously I also replaced the gaskets on the exhaust headers thinking that there was a possible leak. Since I have only run the engine for a short period of time since the gaskets were replaced, it was also confirmed by the condition of the gasket for the number 2 cylinder that there is indeed still a leak occurring on that exhaust header.

None of the of the other exhaust gaskets show this discoloration on the trailing edge of the gasket. The gasket is also loose within the port.

Onward to removing the valves and determining if they are still within spec.

Cylinder Head Removal

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.

Back to Square One and More

Back in September I thought that things were in pretty good shape with the mechanical systems of the 1981 Suzuki GS650L and I was enjoying cruising around the local area. This turned out to be short-lived.

I was rounding a corner when a car pulled out of a driveway in front of me and I needed to quickly come to a stop. When I attempted to resume my travel, the engine was near stalling, I had no power at all to get going, and it just didn’t sound good. I put on my emergency flashers and slowly made my way along the shoulder. Luckily I was only a couple of miles from home when the problem occurred and was able to limp the bike back to the shed for investigation.

My most recent work completed was within the electrical system. The regulator/rectifier was upgraded and I did the coil relay modification to improve the voltage drop at the ignition coils, so I suspected an electrical problem, but I still had strong spark on all four cylinders.

I then checked the compression. Cylinders 1, 2, and 4 were good at 175 psi, but cylinder 3 was extremely low at 105 psi. Early on, before the engine was even in a running condition, I checked compression on the cold engine and this cylinder was at 165 psi. 142 psi is the low service limit for compression on this engine. Adding some oil into the cylinder  did not improve compression, so it is starting to look like a valve issue.

I pulled off the valve cover to verify my valve clearances. Everything was good again except for the intake valve on cylinder No. 3. The clearance was more than double the spec now, 0.24 mm clearance. The valve shim bucket still moves freely, not stuck, so something is preventing the intake valve from closing. Is it bent?

I bought a cheap WiFi endoscope camera that would fit down the spark plug hole to see if I could tell if there was any valve or piston damage before taking off the head. There is no going back once you take the head off.

It connects via WiFi to your smart phone rather than buying a fully dedicated unit. Not pictured are thread on accessories for a magnet, hook, and right angle viewing mirror. It also has adjustable LED lighting. The picture is OK and it works fine in the cylinder looking straight down, but I had no success with the right angle mirror to see the valves clearly. Couldn’t focus that close to the lens.

Here is a shot of the No. 3 piston. Looks fine…

As I am cranking the engine over by hand to check the valve clearances, I noticed that there were locations that were harder to rotate through than they should be since there were no spark plugs installed and therefore no compression to get past. So I started to look at where the cams were in relation to the hard spots.

If everything is timed properly you should have the following alignment of the crankshaft and camshafts:

On the exhaust cam, the arrow adjacent to the 1 should parallel to the surface of the head gasket (removed).

Then the 2 on the exhaust cam and the 3 on the intake cam should be pointing vertically with 20 pins between the two timing marks.

Looks good so far. Now the crankshaft should be at Top Dead Center (TDC) which is found by aligning the T on the crankshaft in the viewing window under the electronic ignition signal generator and should look like this:

In my case, when the cams are positioned correctly, the engine is not at TDC. The cams are actually ahead of the crankshaft and the cams look like this when the crankshaft is at TDC.

A significant rotation of the cams which probably bent at least the No. 3 intake valve enough to prevent it from closing fully. Most likely the cam chain tensioner is not functioning properly and the emergency stop caused some lash in the chain, the timing skipped, and valves were bent.

No matter the cause, I am now back to square one and more. The carbs and exhaust will need to be removed and the top end of the engine torn down and rebuilt. Then reinstall everything, check valve clearances with the new valves, re-sync the carbs… Should be fun!

Regulator/Rectifier Replacement

As follow-up to my previous entry that analyzed the health of the Electrical Charging System on the 1981 Suzuki GS650L.

The conclusion of the previous work was that the stator was functioning properly, but that the original regulator/rectifier (R/R) should be replaced so that when it eventually fails, it does not take out the stator at the same time. A much more expensive repair.

I received my new R/R unit, a SH775 – Polaris part number 4012941, from Partzilla.com. This a very common unit used as a replacement for the older bikes. I also ordered a wiring harness kit from Eastern Beaver for this unit. What I didn’t notice when placing the order was that Eastern Beaver was located in Japan so it took more than a week for the wiring harness to arrive at my address.

Here is the new SH775 unit on the left with the original R/R on the right.

The new unit is larger in all dimensions than the original, but the mounting hole pattern is the same. My installation slowed down again as the the original mounting bolts were now too short to install the replacement unit requiring a quick trip to the hardware store for 86 cents worth of new bolts.

And here is the wiring harness and R/R before installing under the the battery box and air filter box.

The R/R and harness are a 5 wire unit which matches the original equipment. The three yellow wires to be connected directly to the stator, the red/positive wire connected to the hot side of the wiring harness going through the fuse panel, and the black/negative wire connected directly to the negative terminal of the battery. I also have a wire from the negative battery terminal to one of the bolts for the R/R mounting as a common ground point for my coil relay mod and any future electrical modifications.

Here is the R/R and wiring harnesses remounted into the location below the battery box.

Then it was just snaking the wires up and making the connections. In the original wiring harness, one leg of the stator runs through the headlight switch which is a holdover from when the motorcycles did not have their headlights always on. If the headlight was switched off, it would disconnect one leg of the stator and only require 2/3 of the stator voltage to be regulated while there was less electrical load being used. My headlight is always on, so I eliminated this connection and just used direct wiring of the R/R to the stator. More old wire and connections removed from the electrical system.

I ran through the stator tests again after replacement of the R/R and my new wiring. All results were similar to what was seen previously except for the voltage reading at 5,000 RPM’s. This reading was lower than spec with the original R/R. The new R/R produced a reading of 14.3 volts at 5,000 RPM which is within the range specified and 1.2 volts better than previous. I feel better now that the battery will be effectively charging while out riding.

I put the fuel tank back on and prepared for a quick test ride around the neighborhood to try out the coil relay mod and R/R replacement. The quick ride turned into a 40 mile ride. It was very enjoyable for my first extended ride on this bike. The only part not working well was the tachometer reading which jumped around during acceleration.