Roadside Mechanics Series #3

That is right, what Jen said. "Hell Yeah Mexico!" 

So how did that happen. Two days ago we were fighting a broken starter, and xs500 still did not want to start right with the kick starter. Yes it was running well, when it was running, and did a great job on our test ride to Boca Chica, but it was not perfect. 

So, yesterday morning our baffling motorcycle problem of extremely hard cold starts, and a screeching noise that occured on while the engine was starting was finally exposed. 

I was recommended to perform a cold engine compression check by Vanya, an "old motorcycle" mechanic whiz on advrider.com. The procedure for the test is the same as in our earlier blog post for the Roadside Mechanics Series #1, except the test is performed while the engine is cold. The idea behind performing this check was that our hard cold starts were caused by a small air leak that can only be present when the engine is cold. Therefore, the air leak did not effect the operation of the motorcycle at normal operating temperatures because as metal heats up it expands thus closing off the air leak. 

So first thing I did at 7 am on the day we are supposed to leave for Monterrey, Mexico, was pull the gas tank, remove the plugs and setup the compression tester. Our initial results for both sides were very poor at 90psi and proved Vanya's point. We had a cold engine compression leak.

Vanya suggested that if this test resulted in poor compression, I should check that the eight head bolts were tightened to 25 ft-lbs. This is where I discovered our  problem! The head bolts were just loose enough that they did not created a good seal with the cylinders until the engine was warm. That is why the warm compression check didn't expose the problem with our compression.

Through this process I have learned that discovering the origins of a problem in a troubled engine requires following a series of steps to make sure that the three main systems of compression, spark, and fuel are opereating properly when you perform a tuneup, and that to check them in that order. First, make sure the engine has good compression. The main check should be when the engine is warm, but if your engine will not start then a cold engine compression test could expose the underlying problem of why the engine won't start. Then, and only then, should you proceed onto checking the electrical system to make sure that a healthy spark is being delivered through the spark plug, and that it is being delivered at the right time. From there you should go onto check the fuel flow. All of these ingredients combine to make up a running engine, but the first systems have to be functioning flawless make sure that you are diagnosing the true problem.

After I tightened the head bolts I got a healthy reading from both of our cylinders.

The motorcycle started right up when I put it back together, and is a breeze to start with the kick starter when warm, all of our gear is strapped on, and Jen is sitting on the back of the bike. Hurray!!!!!

Benjamin

p.s. Now I am going to go through the other systems and make sure they are functioning flawlessly with the correct compression. Just another step in maintaining a 1976 Yamaha xs500 in Jen and the Art of Motorcycle Maintenance. 

Roadside Mechanics Series #2 Check, Double Check:

The fuel line was clogged in the petcocks. I had forgotten there was a filter in there. Jen and I had even cleaned them in Dallas, and before we left New Orleans, but I forgot about checking them in Galveston. There was just enough crud getting through the old filters in the petcocks to make it look like our in line filters were doing their job and giving me the false impression that our fuel system was clean. Check, double check, and get it done right the first time.


Our gas tank was in need of an overhaul due to rust. There are many methods to clean out a rusty gas tank. Some people would say the best method is to go on ebay.com and buy a new one, but for our situation we were going to have to get dirty. The prevailing methods for cleaning out a gas tank use a three part system with the last step being the addition of a plastic liner.

I went with the first two steps. This involved shaking the tank excessively with a handful of nuts and bolts inside for over an hour. I even tried to sell this bit of work as a workout and get others to pay me to do my work. Unfortunately that didn't pay off, but my labor did. After the nuts and bolts were drained, the tank was ready for its acid bath. For this part I used a ten percent solution of muriatic acid and filled the tank all the way to the top. I let this sit for 2 hours while I cleaned out those pesky fuel petcocks. Once the acid bath was complete I washed the tank out with cold water, and dried it with an acetone to remove the last bits of water. Now it looks like a brand new tank on the inside.

Our engine starting is still hard. When cold, I can't kick the bike to life, but the starter button gets it going in about twenty seconds. The screeching is still there and the one mechanic that looked at the bike said the noise was related to an air leak. When warm, I can usually get the bike to start on the first kick. The starter button tends to hesitate when the bike is warm, but quickly gets the juice from the battery that it needs to complete the job, and it fires up in three seconds.

I took the carburetors off today to look at the flaps and fit some new gas lines. I found a little bit of Permetex gasket maker on the right side flap. This is in line with the diagnosis that our system is leaking a little bit of air. I also feel that the our RPMs are hanging at 2,000 when I pull up to a traffic light. I have heard that this is a signature sign of an air leak in the intake.

This is what we want our spark plugs look like after our tune-up.

Jen says this picture looks like the spark plug is going to hit on the motorcycle. Oh baby-baby.

My speedometer went out on me in Galveston. I haven't fiddled with it since then. So no diagnosis yet. I will take it apart and see whats up with it when we get a new front tire. When we started the ride I had to fiddle with it to get it to work right. I am not sure exactly how accurate it is, but most of the time it feels pretty consistent with traffic and those speed indicators that police forces use.

80 mph on the freeway is great. The bike handles well, and has lots of guts still to make passes. At first I assumed that we would be cruising at 60mph max, but soon enough 70 mph rolled around just fine, and when we were in a hurry to get to New Orleans 80 mph was no problem.

Benjamin

Roadside Mechanics series #1 engine compresion test

So I finally broke down and bought an engine compression test kit by Actron, that includes the right size 12mm spark plug adapter for my engine.

Unfortunately, the compression testers you can borrow from Autozone, or O'Reilly auto parts, through their loan-a-tool programs, do not have an adapter for the 12mm spark plugs that our motorcycle uses. The loan-a-tool program has been great for me in many other situations, and this tool is still valuable for most people because they do work for standard size plugs on cars and trucks, and some motorcycles. Beware though, if you do borrow from them, make sure the gauge works, and the rubber gaskets are in good shape.

With my fancy new tool I checked the compression and found out it was low. Real low. I pulled the heads to adjust the valves, a common source of pressure leakage, and this is when I found out why we died on the road.

In order to adjust the intake valves and the exhaust valves on the engine it is necessary to rotate the engine until you have one cylinder at top dead center (TDC) on the timing plate. This position is the beginning of the firing and exhaust sequence, when all valves are closed so the spark plug can ignite the fuel/air mixture. For my motor the sequence begins on the left cylinder side.

When I rotated the engine to TDC for the left side, my valves were engaged! Right away I knew something was amiss. I stepped back from the whole thing and took a second to think about why my exhaust valves were open when my timing plate said my engine should be at TDC. After thinking a moment, I figured the valves were probably where they were supposed to be and the timing plate was probably wrong. Bingo! I looked at the timing plate and the nut that holds the whole thing together was stripped and about to fall off. This my friends was the cause of our breakdown outside of Mission, Texas.

Well, I figured we still have hard starts, and that happened before I ever touched my timing, so I will continue on my line of work checking the compression. Plus, I had the valves open, and I have been wanting to adjust them, and now things were lining up right.

My first check of the compression, before adjusting the valves, in both cylinders, was 60 pounds per square inch (PSI). The importance of having good compression cannot be overstated. This is the third element that is imperative to have in a running combustion engine. The first, is fuel, and that includes air and lots of it. Next is spark. Getting a good reliable spark has been my goal with replacing almost all the parts in our ignition system. I also figured we should do it now while we can still get the parts for a good price. Lastly, and just as important is good compression. Compression in the cylinder is what creates a good seal in the cylinder to draw the air/fuel mixture in, and then compress it, so it can be easily and readily ignited by the spark. That sets into motion the crank, to turn the gears, and get the wheels going. When the piston reaches the bottom of this stroke it comes back up completing its forth stroke, and forces the exhaust gasses out of the chamber, ready for the intake, and TDC. That is the principle behind a four stroke engine. Most cars and trucks run a four stroke engine. Some motorcycles, the really really loud ones, can be two stroke engines.

After adjusting the valves I started to get 90 PSI consistently from each cylinder. This is better than before, but our 1976 Yamaha xs500 likes to have between 128 PSI and 146 PSI on each cylinder, without too much difference between them. So I know that my cylinders are acting the same, and are both producing low compression.

I have some more testing to do tomorrow, so we will leave off here.

I am starting this as the first of a series in Roadside Mechanics. I will go back and change some posts to reflect this, so they will be beta posts of the series. Some will be long, some will be short, but I will try my best to include all of them, and with good pictures. There will be internal linking to cross reference to ideas and things that I have already discussed so look for the links to past entries.

Benjamin