Episode 10 – engine assembly

Since most of the parts for the engine were lying ready on the shelf and blocking storage space, why not just put everything back in and on the block.

We pulled the bare block which was “stored” in the chassis and got it back on our engine stand … time for a final cleanup of the interior and the complete oil circuit. The camshaft with the plungers come in first (sorry that we have no pictures of this, even when we got the camshaft in and out 3 times, due to various reasons), followed by the oil spray nozzles under the pistons. Time for new main bearings …

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After the bearings were in, let’s put the crankshaft in. The crank is a heavy bastard, even without the counterweights … or our engine stand is just to high to carefully lift the crankshaft with two people into the block. Easy task for the crane, but wait … find the error … 🙄

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Main caps on, bolts in an then it’s time for some serious tightening. The needed torque on the main caps and on most of the other parts which will follow feels like the bolts (mostly fine threaded M20s) will shear off any second 😐

The counterweights are bolted to the crank … but before mounting these, let’s put them on the scale and do some math about the forces the bolts have to hold. The heaviest counterweights have around 7kg, let’s assume 3000rpm and the weight traveling at a radius of 12cm around the crank … thus the weight travels 0.75m per revolution and 37.7m per second … physics tell us that the centrifugal force calculates as: F=m*v²/r … resulting in 82.9kN … or ~8.5tons pulling on the crank .. there are 6 weights and we will attach 8 pistons with steel rods to that same crankshaft 🙄

Let’s not further think, what will happen when one of these parts comes of … oh, and the centrifugal forces are proportional to the square of engine speed.

After installing the pistons, all the parts were “in” the block. 3 pistons missing in the picture 😉

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To close the block, we will just put the oil pan on. Actually not. Since we wanted a low center of gravity on the tractor, we are putting in the engine nearly as low in the chassis as we can. Without wanting to build a complete new oil pan, we just shortened an original pan. No problem, until you want to install the oil pump with the original suction tube …

Just a quick check and adjustments for clearance and we were fine.

In fact we came a little forward to make the engine race-ready and were meanwhile advised several times not to go with the original oil pump and setup, and will now go with an external oil pump. The newly build suction tube might become a nice candle holder 😛

Putting the cylinder heads on should be no big deal. Well, it is not, but there are a lot of parts going in the heads after installation and again lots of bolts to torque to the specifications.

Just get the timing gear on in the right position and the engine is back together. No worries, with the turned down pistons, the engine is a free runner (the valves won’t touch the top of the pistons in any position) and we don’t need to install the timing gear before the installation of the valve train.

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All nice and shiny …

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… hard to believe, regarding the state the engines were in before, and that we had to disassemble this particular block with a sledge hammer.

Time to move on with the auxiliary drive and work on the chassis, which will be covered in future episodes.

 

 

 

Episode 9 – Preparing engine parts

Parallel to the build of the chassis we are approaching the assembly of the engine. As stated in the episode about the engine tear-down, we had one engine in a pretty bad shape, but nonetheless we decided to rebuild that engine and keep the good block in stock. The rebuild will start anyway with a bare block, so that this shouldn’t be a problem. After the complete disassembly and a good clean it was time for a fresh coat of paint.

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After tearing down two engines, we had enough cylinder sleeves which are in the specs and only needed a good pass with a honing brush. One could say now: just use new sleeves and new components where you can when you are doing a complete rebuild. You are completely right, but spare parts cost you a lot of money and working on a limited budget … we will just reuse whatever we can.

The original camshaft out of this engine had just to much wear and damage, so that we were forced to use our spare. Camshaft bearings were fine, so that they just got a bit of a polish and were reused.

With the camshaft and cam followers back in place it was time to focus on some other parts, starting with the disassembly of the complete cylinder heads. Some of these were flooded with water and in really bad shape, the others were “just” full of oil coal and other residues from a probably more than 500000 km service life. So we needed to find a way for a good clean inside and outside, which (after first trials) none of us wanted to do by hand. We found the solution in electrolysis. Some hot water, soda and an old battery charger are good for a near miracle on such parts.

The cylinder heads got the needed machining to fit a spark plug and then it was time for a valve job. Valve and valve seat wear was at a point, that it was nearly impossible to just regrind the valves in their seats with grinding paste. The valve seat material is much softer than the valves themselves, so that grinding with paste would just wear the seats with nearly no impact on the valves. Since we don’t have a valve grinding machine, we became creative with a fixture to regrind the valves on the belt grinder. To drive the valves in the fixture and for the following grinding in the cylinder heads it worked just great to hot glue two valves with their faces together and use a power drill.

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Before reassembling the valves with their springs, it was time to test spring pressure. The specs for the valve springs give you a minimum spring pressure at a given length of the compressed spring. This is usually done in a special machine. The keen reader of this blog will know us well enough by this time … we build our own test fixture 😉

A scale with a maximal load of 5kg, a well calculated lever and the Z-axis of the mill in combination with some special calibrated counter weights …

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Some tests for repeatability and we were able to select the needed 32 valve springs within the manufacturers specs.

The cylinder heads, together with the valve covers, got some new paint and after a good clean of all the bits and pieces, the valves were reinstalled.

During the machining of the pistons we already found out about different pistons designs. Getting the parts ready to reassemble the pistons with the rods for the installation, we found out that even the piston rings had slight differences from one piston version to another. Resulting from the stuck pistons, lots of the piston rings were damaged to a point that they couldn’t be reused. Somehow we managed to find 8 complete and fitting sets.

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In our application, the engine will take a lot more abuse than it was initially designed for. This results in a lot of stress of some key parts, which can result in a major engine damage. One of the worst case scenarios is your engine getting stuck due to gripping piston rings. The rings are designed with a ring gap when installed, so that it will allow the rings to expand when they heat up. On the other hand you want that gap to be as small ass possible to get no compression leakage. To be on the safe side, we added some ring gap. Again time for a fixture …

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The ring gap is measured, by just installing the rings in the cylinder bore, with a feeler gauge.

When it comes to major changes in the basic engine design, we also decided to go for a slightly bigger main bearing clearance on the crankshaft. The argument is the same as with the piston ring gap … avoiding your engine getting stuck. Grinding and polishing a crankshaft, you might have guessed it … we need a custom setup and machinery.

Handheld belt grinder, with an old dryer motor to use it on the lathe.

The results came out better than we imagined. We were able to reduce the main bearing diameters by an exact value and the measurements for all five main bearings ended within 0.5/100 of a millimeter.

Before …

… after …

After the polishing you can see the finest grinding marks 😦 , but this should be up to the job.

Cleaning some more pieces, including 64 cylinder head bolts and we can proceed to the engine assembly in one of the next episodes. Stay tuned …

 

Episode 8 – ROP

… Roll Over Protection

As one of several mandatory safety devices, the ROP is one of the most important parts, but on the other side it is also a big part of the tractor’s appearance. Thus there needs a lot of thinking to go into the ROP, but it is also a challenge in terms of manufacturing.

The first problem starts when you want to organize the needed material. ETPC rules ask for a seamless steel tube and gives specifications  on the dimensions in relation with the material you use. The use of chrome-molybdenum steel (25CrMo4) is recommended, but you can use normal seamless tubes, used by boiler makers, when you go with a thicker wall thickness of the tubes. Knowing that we wouldn’t have a weight issue on the tractor, we could have accepted the 20% extra weight of the ROP and just go with the boiler tubes … well, sometimes you have to set yourself a challenge 😉

How tough can it be? In the literal sense, talking about chrome-molybdenum, we learned our lessons.

Knowing what we want, it was time to call about every steel supplier available in our area. None of them was able (or wanted) to sell us the material we needed. Even a call at a specialized steel supplier in Germany wasn’t successful. With the help of the internet we located a web-shop in the Netherlands, which would even sent the material to us.  Apparently, the well known shipping companies are not to excited to ship seven meter long material, so we had it directly cut into the needed pieces, with some spare material … that might be useful, regarding our non-existing knowledge about tube bending.

Tube bending is the next keyword. To bend tube, you need what? Exactly: a tube bender.  Not being to confident about buying a tube bender from the PRC, plans were made to build one ourselves. On Youtube and in the deeps of the internet you can find very useful information and creative solutions … or you just know someone in town having and old-school tube bender made in western Europe.

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After some measuring and calculations we felt confident and started with the first pieces. Just to have a good feeling, we filled up the pipes with fine grid sand, compressed on both sides of the tube with a wooden plug. The two rear loops with a single 90 degree bend came out perfect, and we were able to take some more measurements to get a good setup for the front loop with it’s multiple bends.

We figured out, that it was all about the perfect alignment of the tube in the machine, doing multiple bends. This said, we marked a 3 meter piece of tube and the disaster started. Here we learned our lessons with chrome-molybdenum … once it’s bend and twisted in the bend, you are f****d. It’s nearly impossible to fix or clamp the tube well enough to correct your bend in any direction.

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One piece for the scrap container, of to the next one. We had a steep learning curve and with some corrections the next part came out just perfect.

Time to do all the other little pieces, to finish the complete roll cage. Having all the parts bent, it was time to start assembling. Assembling just works with lots of adjusting, measuring and of course tube notching. Not having a special made tube notcher, we just made a jig for the lathe. This setup is certainly not the safest, but even with doing small steps, you can reach your target.

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By the way … even the best hole saw learns it’s lesson the hard way in chrome-molybdenum steel 😉

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We were finally able to complete the ROP and we think that it came out pretty well.

Everything is tag-welded in place and will be welded with the rest of the rear axle.

 

 

 

Episode 7 – Steel puzzle

With the laser cut parts it should be easy to assemble the tractor in a few hours 😉

Time to check if all the parts for the rear axle fit like planned.

So far so good, but do you remember the plan to build our rear axle out of two separate truck axles? Time to get these parts prepared. The Rockwell differential carrier fits like a charm after we were able to take the needed measurements of the flange and reproduce it in CAD.

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For the MAN planetaries it’s a little bit trickier. The interested follower might have observed that the planetaries come from a front axle an thus you have to deal with the stearing knuckles of these. Easy … after several cutting disks and a run on the lathe, eveything we don’t need ist gone :-/

The nice thing with steel is, that after you cut everything completely apart you can fit it back together … but will it weld? Time for some welding test pieces with a TIG root pass and the filling with TIG or a stick welder and different filler materials. Good preheating will not harm and the hydraulic shop press will show any weakness.

Welds good and seems not to crack, so its time for some weld porn.

Get a piece of ground, round stock, turn some fittings and everything can be aligned for tack welding the complete rear axle.

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The front axle was no big deal, just like Lego with a welder 😛

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Alignment of the complete drive train in CAD was easy, but will it fit in real life? How to align the engine block with the rear axle and make sure everything is straight, square, parallel an whatever geometrical property one can imagine? We are in the 21st century, so every problem can be solved with a laser. Some modifications on a cheap, self  leveling cross line laser from the super market and it becomes a high-tech drive line adjusting tool.

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Looks not too bad. Time to start thinking how to realize the roll-over protection (ROP) according to the ETPC rulebook. Do we know somebody with pipe bending experience? Not really, so this will become a fun challenge :-/

Episode 6 – CAD

Since we have already collected a lot of parts and you have to start building somewhere, it is time for a plan. Luckily we are living in the 21st century with the availability of free CAD software, so it was time to create a digital model of the future build.

Measuring, measuring, measuring and modeling of the available parts …

The nice thing about CAD is, that you can just virtually align the complete drive train from the crankshaft to the rear wheels, set the correct draw bar position according to the ETPC rules, …

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… and you can design the rest (in fancy colors) around it 😉

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All finished, a few more mouse clicks and you have ordered your tractor as a steel puzzle …

Looks pretty easy 😛

The puzzle will be solved in the next episodes …

 

Episode 5 – CH3OH

A question everybody asks: Why methanol? Well …

There must be reasons why tractor pullers, drag racers and a lot of other people in motor sports use methanol as a fuel. Time to compare some numbers between diesel, gasoline and methanol. We will use freely available data from the deeps of the internet for this purpose.

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To start with, one can see that it is not evident to find a chemical formula for diesel or gasoline fuels. Diesel and Gasoline are blends of hydrocarbons, with a variety of carbon atoms per molecule, and additives. Thus, it is possible to change the characteristics and behaviour of diesel and gasoline fuels for specific applications and there are marginal changes in the numbers for the heating value or specific weight of theses fuels, depending on your source. For methanol it is easier. Here we have a so-called mono-fuel which only consists of a single type of molecules. The first advantage of running pure methanol is that you can clearly define its chemical behaviour. Methanol can be created, using different methods, including renewable resources like natural gas or bio mass. Using methanol as an alternative fuel, made from renewable resources, results only in carbon dioxide, water and the release of the energy under the form of heat.

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The specific weight of the fuels is not a big concern in our application. It should only be mentioned, that methanol is hydrophilic, which means that methanol mixes with water, compared to gasoline and diesel, which don’t. Therefore, it is easy to stop a methanol fire (tough the alcohol flames are hard to see) because you just mix the burning methanol with water to the point where the solution isn’t flammable anymore. On one side an advantage, on the other side a disadvantage, since the hydrophilic characteristic of methanol lets it mix with air moisture, thus contaminating your fuel with water. Measuring the methanol density, weight per volume, gives you the possibility to check for contaminated fuel. Water is “heavier” then methanol, so the specific weight will rise with contamination.

Most of us know that the “O” in the chemical formula stands for oxygen. Therefore, methanol is an oxygen carrier. This does not mean, that you are able to burn methanol without air, but it brings the disadvantage that methanol is corrosive, since a lot of materials will react with the oxygen in methanol and the products which form during methanol combustion and find the way into your engine. Therefore, care has to be taken when choosing the right materials in a methanol fuel system.

Methanol is not ethanol. Compared to ethanol, methanol and its vapours are highly poisonous and you cannot just mix it with a Coke to have a fun time 😉

Motorsports are about power, so let’s have a look at the energy contained in methanol. Comparing the heating value of methanol one can clearly see, that it is just about half of that from gasoline or diesel … not so good. This only applies, when you burn the same quantity of the fuels! But how many fuel do you have to burn?

Engines not only need fuel but also air. To start let’s think about a piston engine just as being a big air compressor. Without fuel, there is only air pumped through the engine. We are mainly interested in the air quantity aspirated by our compressor during the intake cycle. This quantity is preliminary defined trough the mechanical construction of our engine and will not change when we are changing our fuel. To achieve an ideal combustion, we want to consume all the air (oxygen in the air) during combustion. The quantity of fuel needed to use all the air is expressed as the stoichiometric air fuel ratio of a fuel. This ratio is the mass of air you need to burn one mass unit (kilogram) of fuel. Doing the math, you will find out, that for the same amount of air, you “can” or have to use 2.3 times the quantity of methanol compared to gasoline which results in an increase of nearly 14% in energy fed to your engine. This isn’t economical, but in theory methanol can make more power.

Feeding that much methanol to your engine helps also cool your engine. When you are  heating up a liquid, it consumes heat energy and will eventually change into a vapor state. How much energy it takes to heat up a liquid with a mass from 1kg by one °C (Kelvin to be correct 😉 ) is expressed through the specific heat capacity. The specific heat capacity of methanol is 26% higher compared to gasoline. Considering that you are burning 2.3 times more methanol then gasoline in your engine, methanol takes 2.9 times the energy to be heated up. The energy to heat up the fuel in the engine comes from hot intake air, the engines compression cycle and radiation or surface heat of engine components. Thus methanol “cools” all these elements.

You often hear people talking, that methanol burns faster or slower then gasoline and there is a lot of arguing about this. Let me give you two examples, based on gasoline:

  • Throw a lighted match into a full can of gasoline on a very cold winter day (at your own risk 😛 ). There will probably not happen a lot. Maybe some fuel vapours ignite at your cans opening.
  • Poor half a shot glass of gasoline into a 200 liter fuel barrel filled only with air on a hot summer day. When you come just close to the barrels opening with a lighted match, the barrel, your pants and probably a lot of other vital stuff of you will be gone … so don’t do it at home or at another ones home !!!

It’s all about boundary conditions like:

  • air/fuel ratio
  • temperature
  • pressure
  • fuel state (liquid, vapor)

A lot of stuff to take a deeper look at in future episodes 😉

Episode 4 – From Diesel to Otto

As mentioned before, we are not interested to keep our engine running on Diesel fuel or any alternative. This brings the need, that we have to modify the basic engine design from a combustion ignited engine to a spark ignited engine. Basically you are just replacing the Diesel injectors by spark plugs, feed the engine fuel (methanol in our case) with the intake air and you are done … well, no 😉

An internal combustion engine needs a certain amount of energy to ignite the air/fuel mixture in the combustion chamber. In a compression ignition engine (Diesel) the air in the cylinder is compressed during the compression cycle, and following the first law of thermodynamics, the reduction of volume results in an increase of pressure and temperature. The temperature is high enough, so that the fuel auto-ignites when injected. The moment of ignition is given trough the injection pump, theoretically just in the moment, when the piston passes the top death center (TDC).

Diesel

A spark ignited engine usually has it´s fuel directly in the intake air and the compressed mixture is ignited by the energy released trough a sparkplug, when the piston passes TDC.

Otto

Compressing an air and fuel mixture by the same amount as in a Diesel engine will result in an uncontrollable ignition of the mixture long before the piston reaches TDC.

The amount by which the cylinder volume is reduced during the compression cycle is called compression ratio of an engine. The compression ratio is obtained, when you divide the cylinder volume before the compression cycle, by the volume after the compression cycle. A high compression ratio results in a high pressure and temperature after the compression cycle of the engine. To transform a compression ignited engine to a spark ignited engine, you need to reduce the compression roughly by a factor 0.5. Easy … well no. Thinking about this, gives you several options, limited trough the basic design of a piston engine:

  1. Get a thicker head gasket or run an additional spacer plate with 2 head gaskets.
  2. Shorten the connecting rods.
  3. Turn down the pistons, if their is enough “meat”.
  4. Remove material in the cylinder head.
  5. Reduce the cylinder stroke, by offset grinding the rod pins.
  6. Reduce the cylinder stroke with a custom crankshaft.

Options 5 and 6 are impractical, because they will both result in a reduced overall displacement, and option 5 weakens the connection rod pin, not talking about the cost.

Option 1 is common when turbo- or supercharging gasoline automotive engines. No real option for us with individual cylinder heads, and the additional need for longer cylinder head bolts.

Option 2 is also impractical, because the pistons will hit the crankshaft before the bottom death center of the stroke.

Option 4 wouldn’t work due to the cylinder head design, and the need to remove the volume of a full cup of coffee … per cylinder 😉

Time to find out how much material we can remove on the pistons, without weakening them to much.

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That should be enough. Now, how can one determine the volume you remove, without 3D scanning and CNC machining? Interpreting and adapting the principle of an old Greek guy named Archimedes solved our problem. Time for a lot of aluminum chips 😀

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Modifying the cylinder heads to mount spark plugs was a piece of cake. Drill out the injector hole, tap and your done. Well, this time it was actually that easy. A little bit of flattening the bore for spark plug sealing, but that was it.

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Some people will now say: “Yeah, right, but this is not it!” … and they are right. Maybe we will talk about mechanical compression vs. overall compression, volumetric efficiency and some further “small” details on alcohol fed turbo- and supercharged engines in a future episode 😉