Episode 13 – Feeding a bear

Building a pulling tractor with a big engine is like getting yourself a large pet … lets say: a bear 🀣

It’s amazing to have one, but at a certain point you need to feed it and fulfill all it’s basic needs πŸ˜‰

In one of the previous episodes, we showed how we will feed the engine with air … the turbos will keep care of this. Having lots of air, you need lots of fuel and this fuel needs to get pumped somehow. Electrical fuel pumps have two disadvantages in our application: they don’t deliver enough fuel and they consume lots of electrical energy, creating the need to somehow get this electrical energy. The solution lies in a mechanically driven fuel pump, suited for methanol, as they are commonly used in racing.

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Nice little pump, has metric bearings in it but someone decided tho have an imperial hex shaft to drive it 🀐

A more basic need is the oil supply of your engine. As explained before, we wanted to use the stock oil pump in the engine, but were made aware (several times) not to do so. Investigating all this showed, that the original one stage, big displacement oil pump spins faster than the crankshaft, pumping to much oil at high engine speeds, combined with the risk of cavitation and the forming of oil foam. The main and connection rod bearings wouldn’t appreciate that foam and their life expectation would decrease drastically. So … how do other people tackle this issue? The solution lies in the use of an external oil pump and commonly people use specific modified, three stage, dry sump oil pumps, as they are common on high performance racing engines. For us the terms “motorsport”, “racing” and “high performance” are always related with high costs for solutions which don’t seem to be that much of rocket science as one would expect for the price. Not willing to spend that much money on “just an oil pump”, it was time to use the might of the internet to find out about the specifications of these expensive pumps. Well, long stories short, we opted for a three stage hydraulic pump, as they would be used on excavators and other industrial machines, with the same flow rates as the dry sump racing pumps, commonly used. We have no weight issue, and we will enlarge the pump ports, so that the pumps can flow without restrictions.

But why three pump stages? As mentioned before, single large displacement pumps appear to be problematic, so that the engine oil supply is split between two smaller pump stages. The third pump stage will be used to feed oil to the turbochargers in a completely separate oil system. This will avoid contamination and allow us to run different oils, best suited for methanol engines and lubricating turbochargers, without making compromises. I think, oil will be worth a complete episode on it’s own πŸ˜‰

Both pumps, methanol and oil, are mechanically driven … how do we drive them from the engine? The solution comes with a system, based on a timing belt …

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Everything will be driven from the front of the crankshaft, no problem. Well … we have to consider transmission ratios an everything has to fit between the chassis rails, due to the very low mounting position of the engine … total width of only 44cm πŸ€”

For the transmission ratios, this meant the pulley on the crankshaft has to be as small ass possible, compared to a large pulley on the oil pump. The methanol pump should be fine with a 1:1 ratio, since the flow rate fits the target engine speed and maximum capacity of the used injectors quite well.

We absolutely wanted to go with one of these aircraft, direct crank drive starters, so this has to fit somehow with our pulley system. Time to find out, what we can machine, on purely conventional machines out of chrome-molybdenum steel.

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Some other, minor stuff 😜, had to go on the front of the crankshaft as well. The EFI system needs a trigger signal at crankshaft speed, which we will get from a toothed wheel. In our application, this trigger wheel needs to clear a pretty large external crankshaft counterweight. The tractor will get some electrical consumers, mainly the EFI system, and we don’t want to solely rely on battery power … a belt pulley has to go on the crankshaft and we will try to find a nice spot (or just space which is not yet overfilled) to mount an alternator.

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Timing belts have a lot of advantages, but are limited in the maximal torque which they can transmit per single tooth on a pulley. Therefore you need a minimum number of teeth from a pulley which engage into the belt at any moment to transmit the needed energy from belt to the pulley or vise-versa. Using small pulleys, we were able to overcome this issue by routing the belt in a serpentine pattern in combination with the needed tension pulley.

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With the pulley and belt system in place, time to find out if everything still fits in front of the engine.

After all the machining, time to think about connecting everything with hoses, content for another episode πŸ˜‰

 

 

 

 

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