Posted by: nwracing | February 9, 2014

Andromeda Engine Rebuild – Part 2

One of the important things to do when you have an engine failure is to identify what the main cause was. Even if it is component failure, identification is important so you can build the next engine with the right combination of parts and hopefully avoid a repeat not to mention expense.

Unfortunately, at NWRacing we haven’t found the cause of our engine’s loss of oil pressure or the reason why it would not fire up and this means that we have to check and double check everything we do when assembling the engine and assume that everything could be wrong.

After the nicely polished crankshaft was completely cleaned it was time for the bearings to be clearanced.  This is time consuming and after what happened I wanted to be absolutely sure that I had not made a mistake, so I decided to use two ways of measuring bearing clearance.

The first is the professional way, with dial bore gauge and micrometer and the second plastigauge an older but nevertheless effective method of measuring bearing clearance. I will try and explain the difference between the two methods.

Using a dial bore gauge can be a fiddly process and if you are not that experienced at using the tools mistakes can easily be made. The process is as follows:-

  1. Measure the crankshaft journals with the micrometer.  It is vital to do this part right. From experience this takes a lot of feel.
  2. The next thing to do is to set the dial bore indicator. This involves zeroing the dial bore gauge to the exact width of the micrometer. A micrometer stand really helps here as this is fiddly.
  3. Next job is to fit the bearings to the engine and torque to the recommended setting.
  4. The final task is then to use the dial bore gauge and read the measurement off. After all this you then have the amount of clearance.
Ni.crometer set to journal size

Micrometer set and locked to the journal size.

Dial bore gauge set

Dial bore gauge set to the journal measurement

The second method is the one I have used since building my first engine and that is plastigauge. I like this method as it very easy and almost foolproof.

The process is as follows:-

  1. Fit the bearings.
  2. Apply the grease to the bearing journal to be measured and cut a piece of the plastigauge and place on the grease.
  3. Apply the other supplied grease to the other bearing surface and then fit the main cap and torque down.
  4. Carefully remove the main cap and then use the supplied gauge and read off the clearance.
Plastigauge ready to use

Plastigauge placed on the journal ready for use.

Plastigauge reading of bearing clearance.

Plastigauge compressed and gauge reading off clearance in thou

In theory the plastigauge method should be less accurate than the dial bore gauge method but as the gauge I have reads to half a thou, the same as plastigauge, there shouldn’t be any difference in the measurements. This proved to be the case and the bearings came up to the spec we were looking for without us having to find other bearings to get the clearance we wanted.

We now know one thing for sure, the bearing clearances in the engine are absolutely spot on so this is one area where we should not need to worry.

Next thing to do is take it all apart again and give it another clean! Then it’s on to the oil pump and sump!


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