This project is a bit out of the ordinary for what I usually work on, but now that I have moved back to Seattle, my “services” are called upon sometimes to help with some upkeep around my folks’ place. Last winter a large limb came down in the back yard and I offered to help them out by cutting it up with the small 1976 Skilsaw chainsaw I have had (and used) for many years. I figured it would be an easy Saturday project, that is until I tried to start the saw!

You see, as it turns out, I was the last one to use it and that was over seven years ago, right before I left for graduate school at MIT. Worse, I had last filled the saw with gasoline containing 10% ethanol (aka “gasohol”). Oops. As I have since learned, one should NEVER use gasohol (as is found at the vast majority of gas stations in the US) in small or vintage engines for the following reasons:

1. Ethanol will, over time, attack rubber gaskets, hoses, and diaphragms. Gasoline, primarily made of hexane, is a purely non-polar solvent. Water, by contrast is a purely polar solvent. The old saying is “like dissolves like,” so ethanol, which is missable in (mixes with) both non-polar and polar solvents can dissolve materials that purely polar or purely non-polar solvents cannot. Nitrile rubber (aka NBR or Buna-N) was commonly used for fuel lines, gaskets, and carburetor diaphragms before gasohol was common. It is nominally insoluble in ethanol, but if allowed to soak for long periods of time (months / years) or if the rubber is poorly vulcanized or already partially degraded it will cause the rubber to swell and eventually turn to a sticky black mess as it is degraded and/or depolymerized.
2. Ethanol is hydroscopic which means it absorbs water. Not only is ethanol is missable with water but worse it actually absorbs water out of the air like a desiccant. This is a serious problem because water in the fuel will not only cause an engine to run poorly but will also start to corrode metal parts if allowed to sit for a long period of time.
3. The third problem with gasohol is the worst. Just as wine turns to vinegar if exposed to the air for a long time, ethanol oxidizes to acetic acid by the following equation:
   
   This means that if gasohol is exposed to the air the ethanol in it will degrade into a concentrated solution of acetic acid (vinegar). This is really bad because a mixture of gasoline (a strong non-polar solvent), water (a strong polar solvent), ethanol, and acid will attack most common materials. I have seen old gasohol completely corrode a brass carburetor float to the point that it would fall apart when disturbed. Worse, an attempt to properly store an engine by “running it dry” before putting it away for the off season has the effect of assuring that the residual gas in the system is now thoroughly mixed with plenty of air and so it can oxidize quickly and completely. Oops!
4. Finally, and this is only somewhat related to ethanol content, a lot of small 2-cycle engines are actually high compression. Ten to one is not uncommon in chainsaw engines for example. Thus, they should be run with a high octane fuel to avoid knocking.

It is thus strongly advisable to only run small engines on pure gasoline, ideally high octane, and combined with a fuel stabilizing additive. There are some gas stations left that still sell “ethanol free premium” (Spirit is the one that happens to be close to me) but barring that ethanol free gasoline can be found at most marine gas stations or places that sell aviation gas. You can also get high quality ethanol free gasoline (including pre-mixed 2-cycle fuel) in cans at any hardware store under brands like “TruFuel.” Yes, this is several times more expensive than fuel from a gas station, but if you are like me and go through at most one gallon of fuel in small engines per season, the cost is much lower than having to dismantle and rebuild the fuel system of your equipment every spring! Plus, I enjoy the convenience of not having to mix 2-cycle fuel.

OK. With the cause of the problem identified, it was back to surveying the extent of the damage. The first thing I saw was that the fuel hose was cracked near the carburetor. I tried to pull it out of the tank and quickly realized that the whole fuel system needed to be rebuilt:

1. The fuel line was soft and gooey – it was completely degraded.
2. The carburetor needed a total rebuild – the diaphragms were stiff as cardboard and the whole thing stank of vinegar.
3. The fuel and oil tank gasket needed to be replaced – it broke when I took the tank apart and was obviously swelled and melted.
4. The fuel filter was shot – it is made of polyurethane foam and crumbled when disturbed.

Figure 1: Photo of the bad fuel system parts

This would all be pretty easy if parts were still available, but alas, very few still are for this saw. Knowing me, though, I couldn’t just walk away from the project. What follows is my (slightly heroic) efforts to revive it and some very useful information for the next poor tinkerer that needs (or wants) to work on one of these fine saws.

Before beginning I needed a manual. I found two sources for one – there are paper reprints available for sale on eBay and I eventually found a scanned version of the manual as well. Note that this manual corresponds to the original version of the Skil 1614 and 1616 without the chain brake. There was a later version as well, but mine is the original.

Before I could rebuild the saw I had to find replacements for the bad parts. I started first with the easy one – the fuel line. A quick bit of work with a caliper and it turned out to be 1/8″ID x 1/4″OD x 7.5″ long. Note that both the inside and outside diameters are critical since it must fit tightly over the nipple on the carburetor and the outside of the hose must seal to the rubber grommet in the fuel tank. The original material is nitrile, but Viton fuel line with these dimensions was easier to find and should hold up better. I ended up buying a length of fuel line off of eBay which worked perfectly.

Second was the carburetor rebuild kit. There were two carburetors used in this saw, the Walbro WA8 (aka W8A), and the Tillotson HU-4A. My saw uses the Walbro which needs a Walbro K10-WAT rebuild kit. This kit is nominally obsolete, but both OEM and aftermarket kits are still readily available. I got one marked as OEM (but which I think is actually a good quality aftermarket kit) from Amazon.

Third was the fuel tank gasket. To reproduce this part I carefully glued the original gasket back together, placed it in a plastic bag, and scanned it with a flatbed scanner. Then, working from the scan in Rhinoceros 3D, I attempted to create a drawing of what the original gasket would have looked like before it was distorted from being compressed in the saw. Once I had what I thought was an acceptable drawing I cut a sample out of paper to make sure it fit. A couple of go-rounds of this and I had a workable gasket design. I could have cut them out myself, but instead opted to have it done by Gaskets to Go, a small company that specializes in making custom gaskets. The results were acceptable but not great. I was expecting them to use a CNC cutter to make the gaskets, but they were instead made by hand and looked very hand-made. Next time I think I would go with a different service or just cut them out by hand myself. In any case, even if they didn’t look great, the new gaskets worked fine. The scans and drawings are available at the end of this article.

Figure 2: Original and replacement tank gaskets

Finally, and the hardest, was the fuel filter. This is where things got interesting. It is important that a chainsaw be able to run no matter if a cut is being made horizontally or vertically. This means that fuel must be able to be drawn from the tank in both orientations. Most saws accomplish this by having a weighted fuel filter that is free to fall to the bottom of the tank. However, this saw uses a more ingenious method. The fuel filter is made of a very fine filter foam which, like a fuel cell in a race car, soaks up and holds gasoline like a sponge allowing the engine to be fed a continuous supply of fuel in either orientation. The original foam was totally disintegrated and needed to be replaced. With a bit of research, I determined that it was most likely made of reticulated polyurethane foam. Reticulated foam has the walls of the individual foam cells were removed to leave only the thicker strands of material between the cells, thus making the foam “open cell” and allowing fluid to pass through it. The critical parameter of reticulated foams is the density of cells, measured in pores per inch or ppi. To measure the ppi of the original filter I set an electronic caliper to 0.1″, placed it on the foam filter, and counted the pores under a microscope. I got approximately 100ppi.

Figure 3: Measuring the pores per inch of the fuel filter foam

Next I contacted a couple of companies about having custom foam filters made. New England Foam was very helpful and offered me a very reasonable price on new custom-made filters. It took a couple of go-rounds and a new tool, but in the end I got very high quality replacement filters at a reasonable price. These filters are currently available for sale on this site and on eBay; just search for “Skil 1616 Fuel Filter”. (Note that the same filter will also work in the Skil 1614.)

Figure 4: Original and replacement fuel filters

After tracking down replacements for the bad parts, the next step was to actually rebuild the saw. Initially, I wasn’t sure if I should pull the crank-case apart or not, in the end I decided to go for it, just to make sure that everything was clean an in order. To do that, I had to pull the flywheel. Luckily, I was able to use my Harbor Freight bolt puller set to pull it off without too much trouble. The trick was to reuse the crank case bolts that go with the saw since none of the bolts in the puller kit were small enough.

Figure 5: Pulling the flywheel

Once I got the crankcase open, I was very glad that I went to the trouble to do so. Sometime in the past (presumably before I owned the saw) someone had used it without an air filter. I have never seen so much debris in a crankcase before!

Figure 6: Sawdust in the crankcase. Don’t use a chainsaw without an air filter!

With that much dirt in the saw, I decided it was best to totally tear it down completely and clean all the parts. The disassembly was pretty easy except for removing the clutch assembly from the crank shaft. The problem is that the only way to turn the clutch body is via two small rectangular slots in that are made to fit a special spanner wrench. I didn’t have the correct wench, so I cheated by using a pair of cheap needle nose pliers (don’t use good ones) with one jaw inserted into each hole. I clamped the pliers in a vice (with the vice as near as possible to the jaws for best leverage) and put a wrench on the crank shaft to turn it. Note that it is a reverse thread. The photo below shows the clutch.

Figure 8: Clutch assembly showing where I inserted needle nose pliers to loosen it.

I washed every piece in detergent and water and allowed them all to dry thoroughly. Here is what a chainsaw looks like in pieces.

Figure 9: Skil 1616 chainsaw completely disassembled.

The trickiest parts to get cleaned were the piston, crankshaft, and rod since they are assembled with tiny needle bearings and must be put back in the same orientation as they were taken out since that is how they wore together. However, by being careful to take pictures of everything and wash one piece at a time the process went relatively smoothly. Here is what the crank assembly looks like totally disassembled.

Figure 10: The crank assembly taken down to its constituent parts.

The other part of the saw that provided a bit of a challenge was the carburetor. The high speed circuit contains a small check-valve (called the “Nozzle Check Value” in the Walbro WA series service manual) which is pressed into the body of the carburetor. The rest of the carburetor was so contaminated with old dried gasoline that I really wanted to be able to take apart this valve to be able to clean it out. Getting it out of the body, however, took a bit of creativity. The trick was to make a small custom tool using my Sherline lathe. The tool consists of a brass rod with a hollow end that exactly fits over the top of the valve. Using this tool I could rock the valve back and forth with enough force to break it loose and pull it out. To put it back in, I used the same tool to hold the valve body so I could press it in with a small hammer. See the photo below.

Figure 11:  Pressed in carburetor valve and the tool I used to remove it

Once I had the valve out, I discovered that it was made using a small circle of the same material used to make some carburetor fuel pump diaphragms. Unfortunately, this part was warped and damaged and needed to be replaced. Luckily however, one of the spare diaphragms that came in the rebuild kit but which was not needed for my model of carburetor was almost the same material. The only difference was that the original was 0.0055″ thick and the diaphragm in the kit was only 0.003″ thick. I could have ordered the exact material from Route 21 Trading Company, but the thickness difference didn’t seem to matter and the replacement worked fine. I cut the circle of material using a small punch I also made on my lathe. The photo below shows the new and old parts and the punch I used to make the new one.

Figure 12: Punching a new carburetor valve

With all the sub-assemblies cleaned and rebuilt, I could finally reassemble the whole saw. After all of the other work, this went relatively quickly. A few pictures document the process.

Figure 13: Installing the fuel hose, tank gasket, and fuel filter

Figure 14: All back together except the covers

At this point I was able to start the engine and get it running before I put the bar and chain back on. This was really important because I wanted to make sure that the automatic oiler was working and I knew I couldn’t easily see if oil was coming out once the bar was back on. The engine ran reasonably well and the oiler worked fine after I got it primed. With that done it was time to put the bar back on and tune it up.

Figure 15: Putting the bar back on – almost ready for action!

With the bar back on I could run it at full throttle and get the high speed jet on the carburetor adjusted (running it at full throttle with no chain is not a good idea since it can over-speed the engine). Unfortunately at this point the carburetor still wasn’t acting right. The engine would flood easily at idle and would run even with the low speed jet adjustment all the way closed. I took the carburetor apart again and found that the valve body I had worked on was loose – I had been too gingerly pressing it back in. A more forceful pressing and it started working fine.

Figure 16: First run with a bar and chain – getting ready to tune the carburetor

Finally, I had a working chainsaw and could cut up the limb that came down last winter. A bit more of a project than I had in mind when I offered to do a bit of yard-work, but hey, I had fun learning a lot about foam, gaskets, and small engine repair, so it was worth it just for that.

Figure 17: Here I am cutting up the branch

Figure 18: The branch is cut and stacked on the wood pile. A job well done if I dare say so myself!

In the process of rebuilding the saw I found substitutes or cross-references for most of the consumable parts and I scanned  all the gaskets. The table below contains this information and should be invaluable for anyone else working on one of these saws.

Table 1: Skill 1614 and 1614 Chainsaw Parts Cross-Reference

Notes: The Skil part numbers and reference designators correspond to those in the manual for the saw.

In case anyone was wondering, and at the risk of opening up a flame war in the comments section, I will now give my opinion on the hotly debated topic of fuel mix ratios in vintage saws. From what I have read it should be safe to use 32:1 (or 40:1) fuel mix ratios in vintage saws made for 16:1 as long as the following conditions are met. First, a modern high quality synthetic 2-cycle oil must be used. Second, the saw must have needle bearings and not sleeve bearings for the crankshaft and rod. The Skil 1614/1616 do use needle bearings but some vintage saws from the 1950’s/1960’s and earlier didn’t. For what it is worth, I run TruFuel 40:1 in all my 2-cycle engines and have not had any problems. Do be aware that the carburetor will need to be readjusted if you switch mix ratio. The reason it works to reduce the amount of oil in the mix is that modern synthetic oil has a much higher lubricity than the oils used in the past. In other words, modern engines run on a leaner mix primarily because of improvements in oil rather than improvements in engine design or materials.

As a final note, the early Skil 1616 and 1614 saws (like mine) do not have chain brakes or other modern safety features. However, even if they did, all chainsaws (new or old) are dangerous and need to be operated carefully and only while wearing the proper personal protective equipment (PPE) including chaps, a helmet, hearing protection, eye protection, sturdy boots, long sleeves and gloves. Always be aware of the dangers while operating a saw and never do so under the influence of drugs or alcohol. Before operating a chainsaw be sure to read up on chainsaw safety and never attempt to cut with the tip of the bar. I take no responsibility for any injuries or damage that occurs as a result of attempting to repair or operate a chainsaw.

-Matthew D’Asaro