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 …

 

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