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Proper Maintenance of Your Briggs Stock Class Engine

By Sheldon Gecker of Gecker Motorsports Products

Whether you build your own engines or purchase engines from a reputable engine builder, you will have made a big investment in time and money. Following these few simple procedures between rebuilds will allow you to obtain the most durability and horsepower from your investment. Some of those areas of most importance are the first practice on the engine, the drain plug, fuel, carb diaphragm, carb and tank supports, jetting, temperatures and plugs.

We at Gecker Motorsports have spent years developing cams and headers and building race engines for customers. This has given us lots of exposure to explode engines ruined to poor maintenance practices. Learn from our experiences to help keep your stocker program alive and kicking! Improper maintenance will cost you more then money, it will cost you races. Imagine leading the race with 3 laps to go and out of nowhere the engine acts like it is running out of fuel!

I have tried to isolate the key areas in a proper maintenance program. I find the following areas to be most important or you are the fastest kart than break in qualifying putting you in the back of the pack.

First Practice Session On Your Fresh Stock Engine

Much discussion is shared among builders about the best way to break in a new engine. At our shop we used an electric engine fixture to seat the piston rings. We then dyno the engine allowing the valves and valve seats to go through heat cycles. Dynoing the engines does not complete our break in process though. Even though we break in the engine and confirm the engines ability to produce horsepower, we still recommend that our customers use a blend of regular motor oil for the first practice sessions on their fresh engine. We have found that even though the engine may appear “broken in4, some seal can be lost when the engine is run on synthetic oils directly after dyno testing. Since there is no real way to absolutely confirm that the engine is broke-in, we utilize the following procedures to help make sure:

For the first practice session with your fresh engine, run 10 (OZ) ounces of straight 10W 30 Kendall or Castrol automotive oil and 2 to 3 (OZ) ounces of Marvel Mystery Oil (MMO). MMO is available at most auto parts and K Mart stores. MMO is a great lubricant when mixed with other oils. During break in, the MMO reduces the potential for methanol to cause damage to the engine via lubricity. After each practice session, drain and refill with fresh 30 W and MMO. Before the first heat, drain the 30W oil and replace with 12 ounces of the synthetic racing oil recommended by your engine builder.

This procedure is cheap on the wallet, does not cost you that much in performance and will ensure that the engine is broken in. It is just practice!

Drain Plug

We always use a magnetic drain plug in our engines. A magnetic drain plug will allow you to catch metal particles that eventually circulate in the engine while it is running. The metal particles that circulate in the engine can also grab materials that the magnet would not normally get as the oil will hold brass and aluminum to the metal particles. The magnet then grabs the metal particle with the non-metallic particles attached. If the metal particles combined with other metals do not reach the magnet as the final destination, it will end up in the drain valley that the drain plug screws into. When you drain the oil the next time, the fine particles will make their way out of the engine. The draw of the magnet will bring a quite a bit of the metal down to the drain valley and away from being re-circulated throughout the engine.

Using a magnetic drain plug is especially helpful during the break in period, as inevitably metal will circulate through the engine as the piston rings become mated with the cylinder walls. Keeping metal from circulating during break in of the engine helps to minimize scratches in the cylinder wall and on the piston.

The Briggs and Stratton magnetic drain plug (part number 691663), is a good choice for the price. I recommend replacing this drain plug at least once a year since the magnet can eventually break loose from the drain plug as a result of the engines vibration.

Fuel

Always use clean and fresh methanol. Methanol attracts water making it very important to keep it fresh. Always use fresh methanol that has not been sitting in your trailer for weeks. Expansion and contraction of the bottle that holds the methanol can attract moisture to the bottle. If the methanol does attract moisture, the engine will be temperamental and will not respond normally to jetting changes as a result of changes in weather.

I recommend using a filter to screen the fuel entering the gas tank on the engine as you are filling it in an attempt to keep debris out of the tank. Pay attention to the condition of your fuel jugs to ensure that there is no debris floating on the bottom. Garbage in the pick up screens in your carb can cause a major dilemma at the racetrack, and can also cause the engine to run lean. If the engine gets enough fuel to operate and does run lean, the risk of piston galling is great.

At the end of each race day or any other time where the engine is run on methanol, it is very important to drain the methanol fuel and run straight gas through the engine. You can also use straight gas with a mixture of MMO. Mix the MMO in an 8 to 1 ratio and make sure that you get the MMO out of the tank after you are done running the engine. Methanol is very corrosive and can cause severe damage to aluminum components when left in the engine. The methanol left in the tank can easily attract moisture as the tank is vented.

Carb Diaphragm

We recommend that racers replace the carb diaphragm every race day or every other race day. Many racers will continue to use a carb diaphragm for several race days not realizing that this is a mistake. After the second race day, the carb diaphragm will not pump the same amount of fuel that it pumped when it was new. Not pumping the same amount of fuel will cause changes in how the engine will perform on the racetrack. If your engine builder has set up your carburetor a little lean on the fuel curve, a poorly performing diaphragm can cause real troubles in performance and tuning. “Chasing4 your carb setup based on a faulty diaphragm can frustrate you as temperatures will be erratic and jet changes complicate and confuse the situation. The main problem of the faulty diaphragm is the carbs ability to pump fuel properly throughout the RPM range of the engine. From the picture, you can see the bulging of the diaphragm where the spring and cup sit. When this bulge is present, the diaphragm will not pump the same amount of fuel as the spring recedes into the orifice in the carb.

We have determined that a poorly operating carb diaphragm can cause as much as a 10% drop in fuel velocity at the short pick up tube. We have also noticed that the fuel bowls do not stay as full of fuel as they do when a newer diaphragm is installed in the carb.

Carb and Tank Supports

It has been our experience that a carb and tank support is an effective measure to prevent breakage. Currently there are many different types of carb and tank supports available to you.

For the fuel tank, you can weld in a brace from the bottom of the tank to the brace that mounts to the block or you can purchase the aluminum tank support that hose clamps to the tank and fastens to the tank brace with a long Allen bolt. We prefer welding the tank brace as our engine stickers also go on the back of the tank! Actually, we prefer the welded tank-brace, as it appears to provide more durability than the aluminum brace does. With either brace you will be minimizing the potential for the tank to leak and crack during a race. There is no question that a tank can crack over time and cost you a race. The amount of vibration that occurs with the engine, tires and track surface can make Briggs and Strattons fuel tank look like junk when in fact they are not that old. Proper tank supporting will extend tank life tremendously.

For the carb support, you have many choices. The carb support that bolts to the top of the blower housing and attaches to the back and on the side of the carb has provided us with a good level of durability and is easy to use. This type of carb support does not impede the drivers ability to adjust the carb during the race and allows you access to all areas of the carb in the pit area.

To eliminate carb breakage at the throat near where the carb attaches to the block, use the aluminum collar style clamp that attaches with Allen bolts.

Always remember that good running carbs and race victories are “hard to come by”. A small amount of preventative maintenance on sensitive areas as the carb and the tank can pay dividends later.

Ensure that the carb and tank stay clean and free of debris between and during race days. Keeping the carb and tank clean will allow you to identify cracks that may occur in the tank or the carb body before either breaks on the racetrack.

Jetting, CHT, EGT and Spark Plugs

There is much debate that goes on regarding the best way to measure an engines air fuel ratio to temperature level while the kart is on the racetrack. Many people feel that cylinder head temperature (CHT) is more critical than exhaust gas temperature (EGT) in identifying the engines performance level. It is my contention that EGT is by far a better measure of engine performance and proper air fuel ratio but both measurements are critical in establishing an adequate fuel curve and combustion process for the engine on a particular day. Although, a properly prepared and dyno tested engine should not require much adjustment at the racetrack. If your having to make significant changes to your engines air fuel ratio at the race track then there was a breakdown in the what your engine builder set the air fuel ratio at (on the dyno) or what you set it at.

Monitoring and establishing the proper temperatures based on air fuel ratio in your engine is critical to the life expectancy of your engine. If you continuously run your engine too lean or to rich, your engines performance level will suffer quicker as internal components will distort and loose seal.

A memory gauge is a necessary tool in tuning your combination of air and fuel. A Mychron or Digatron memory gauge can provide you real time temperature data for each lap that the kart is on the racetrack. It is very important to always insure that a higher CHT or EGT number cannot be associated to a 3bound up," tight or poor handling chassis. Often, elevated CHT and EGT numbers can indicate chassis problems. Before chasing CHT and EGT numbers through jetting and tape, make sure the chassis is “free” and not “locked down” in the corner.

Through my findings, EGT is the measure of the carbs ability to deliver the proper air fuel ratio and burn it and CHT is the result of the engines ability through ignition timing and combustion chamber effectiveness to ignite that mixture. You will use CHT to determine if you combustion process is off and if your improper air fuel ratio has the potential to cause damage to the engines ability to seal. When the engine obtains an extremely high combustion temperature, the cylinder can go “out-of-round”, the top ring face can go “out-of-round4 and the top ring can become weak. Valve and valve seat seal are also negatively affected. You will use EGT to determine the proper air fuel ratio for the engine. If the combustion process is flawed, you will modify the engines air fuel ratio (lower or raise EGT) to accommodate the ineffectiveness of the combustion process. Certain combinations of parts may never yield ideal results. In this case, constant observation of temperatures will always be necessary.

Ideally, most unrestricted stockers we build perform best (based on our air fuel ratio) with an EGT around 1360 degrees and a CHT of 410 degrees.

Following are a few ways to adjust your air fuel ratio and temperatures at the racetrack:

Jetting

Increasing or decreasing your jet sizing can modify your CHT and EGT temperatures. Depending on how your engine builder prepared the carb that is on your engine, you will have some level of adjustability in getting to proper temperatures. The adjustability will give the engine the best performance level and minimize the potential for damage. Most people know that increasing jet size will cool the temperatures slightly and decreasing jet size will increase temperatures slightly. If your carb is set up to pull a lot of fuel, your adjustments to make the carb provide more fuel in order to cool temperatures is limited but your ability to cool the temperatures is less limited. If your carb is set up to not pull a lot of fuel, you have more adjustability to cool and heat the engines temperatures.

Your ability to adjust temperatures with jet is going to be limited regardless of how your carb is set up. If you make a significant change in jetting, lets say .0104, you will be preventing the engine from getting the proper amount of fuel for the entire RPM range that the engine will go through. Significant changes in jet size can create fuel delivery issues thereby causing the engine to stumble on the lower or the upper sides of the RPM range. While adjusting temperatures with jetting, make small changes in jetting, but make big changes with the heat ranges of your spark plugs.

Spark Plugs

There are many spark plug type that racers use. If the air fuel ratio and combustion process are effective, you can run an Autolite 411 spark plug or a spark plug with a similar heat range. Modifying the heat range of your spark plug is the best way to modify temperatures at the racetrack without disturbing the carbs ability to provide adequate fuel for the combustion process to be effective. If you need to modify engine temperatures, Nippon Denso (ND) spark plugs provide a wider heat range of plugs to accomplish your goal. ND plug part numbers W-24 through 31 provide a good range. The ND 24 plug is the hottest in this range and the ND 31 is the coolest. You will be looking for a heat range of plug that will allow the engine to obtain consistent CHT and EGT temperatures.

We find a plug gap range of .028” to .0324 to be effective. There appears to be no real big changes in performance or temperatures as a result of plug gap.

When changing your spark plug in an attempt to create changes in temperatures, be sure that the spark plug is indexed (open end of the gap) toward the exhaust valve and away from the intake valve. In order to get this right, you will need some copper spark plug washers. These washers are available at every kart shop. We recommend using a Sharpie or permanent marker to mark the outside of the spark plug where the open end of the electrode is facing. Once the spark plug is marked, you can remove and install the spark plug with combinations of spark plug washers until you have the proper location set.

Replace spark plug every two to three race days. Spark plugs can perform poorly due to methanol fatigue, with no visual signs.

Air Filter

Always run an air filter and filter cup on your engine. Running without an air filter can cause significant loss of cylinder seal and can shorten the life expectancy and the performance level of the engine.

If you race on dirt, you should change the filter at least once each race day. It is a good idea to have an extra filter cleaned, oiled and ready to go so that you can change it quickly after your last practice.

If you are racing on asphalt, you should clean the filter after each race day.

A pre-filter such as foam or an Outerwear is very effective at keeping dirt out of the air filter whether you are racing on dirt or on asphalt.

There are many methods of cleaning the air filter. K & N and S & B make cleaners that do the job. You can also use Simple Green or Super Clean. We prefer a product we sell called Sak. Sak is mostly a degreaser and does a fantastic job of removing particles and getting the filter clean.

Make sure when cleaning your filters that you spray the cleaner on the outside and rinse the filter from the inside. Rinsing the filter from the outside will cause loose particles to be driven back into the paper of the filter.

After your filter dries, make sure that you oil the filter with K & N or S & B filter oils. The filter oil will trap the particles and make it easier to get particles out of the filter the next time you clean it.

Headers

Improper header maintenance can cost you races. Always make sure that your header is braced sufficiently and safety wired so that the header cannot come loose on the engine. If the header comes loose on the engine, performance will drop and damage can occur to the valve, valve spring and the valve seat. A loose header can also cause your exhaust bolt threads to become stripped.

Occasionally (during the week), inspect your exhaust bolt threads to confirm that they are not in need of replacement. Performing repairs to threads at the racetrack is time consuming and can cost you valuable time in determining what changes you need to make to your chassis in improving your lap times.

Proper maintenance of your stock class engine will ensure the longest life possible before a rebuild is necessary to restore the engines performance level to new again. A good maintenance program can also minimize your potential of dropping out of races and taking away from valuable setup time while you are at the racetrack. Paying attention to the few areas I have outlined above can make your racing experience a happier one.