Engine Overhaul: Case Measurements / Camshaft Lubrication Mod / Making the engine Experimental

A note on the Service Table of Limits

To use the service table of limits, you first work out the letter for your engine. In our case is it an "S". However, if there is an "S5" (or an "S6") listed, then we need to follow that tolerance / measurement, as this is a special mesurement for our engine.

 

You then look up the item you want to find the measurement / tolerance for, and select the one with the "S" in our case (or "S5"/"S6"). The "E" agaisnt the tolernece, means "Permissible wear on crankshaft (rod and main bearing journals) to be minus 0.0015 diameter"

  

So in our case, the main bearing journals need to be between 2.3745" and 2.3760 inches. We had previously meausred the crankshaft, and verified that it had been ground down to M03 - aka, 3 thousands under the normal dimension. So the amended tolerances for our crankshaft, using M03 bearings would be 2.3715 - 2.3730". So the crankshaft is looking good and has been ground down properly. In service it can be reduced to 2.3700" (the -0.0015" "E" tolerance"). 

Note that the front journal "1" position average diameter is 0.0004 smaller than the rest - remember this for later!

Case Measurements

Before paint, we needed to check the measurements of the bearings under torque, as well as crankshaft end float. This is to check there will be sufficient clearance between the crankshaft and the bearings for an oil film.

We coated all the bearings, and case internal mating faces in blue marker dye, and bolted the case together. The bearings were then measured to make sure they had enough room for oil - i.e. they need to be larger than the crankshaft by a certain amount. The tolerance on this is tiny - 0.0011" to 0.0045" (this is 1.1 thou to 4.5 thou!). To do the measurement, the gauge was set to the average crankshaft diameter of 2.3730", then each bearing was measured in 3 locations radially. The larger front bearing was measured at the front and back, hence why there are 4 measuremetns (1/ and 2/). The numbers were written down and averaged, and the "oil gap" was calculated.

The cases came back looking great - much nicer than when we sent them!

The bearings came in these special boxes - like the crown jewels!

Each one was coated evenly with blue marker dye

The channels in the bearings are insteresting - the holes allow oil in from the galleries in the case, and the channels spread the oil around the crankshaft journals. The triangle sections allow oil out the front of the bearing to the oil slinger, and out the aft of the bearing to the thrust face.

Bearings were verified as M03. 

We then pulled the cases together and torqued them up.

The gauge was set to the crankshaft average diameter (2.3730). We then measured each bearing and noted the delta (difference) on the chart below. These were the measurements of the inner diameters of the bearings under torque in the case, and show how much larger they are than the crankshaft average. The measurements at the 1/ position will show 0.0004 bigger, as the crankshaft average is 0.0004" smaller at this location (see above crankshaft measurements). So the front 1/ position actually averages at 0.0040" minus the 0.0004" = 0.0036". The remainder of the bearing meausrements are 2/ 0.0029 3/ 0.0024 4/ 0.0026 - all within tolerances! So we are all good. 

The black marker is the outline of the accessory case to aid in masking later.

We then pulled the case apart and checked that the blue die had transferred between the bearing outer faces and the case, so we knew the bearings were seated properly in the case. We also checked the mating faces of the left and right case halves - this is not a check called out in the overhaul manual, but something the shop likes to do to make sure the case was machined suitably flat. It's not a perfect check - as we didn't have the cylinders installed, so didn't have full torque across the case.

This is the aft case join and shows the case is nicely mated.

This is the other side of the same mating pair.

The centre location didn't mate very well. We can lightly remove some matrial from these bearing to close up this gap later. We have enough tolerance in the bearing measuremetns to do so. We are talking a couple of swipes on some emery paper.

We also removed the bearings and checked that they had seated in the bore properly - they were all fine, but i didn't get any photos. 

This shows how the front bearing was seated very nicely in the bore, but there were a couple of small areas where the case didn't quite mate (the missing blue on one side, and darker blue on the other).

The next check was the crankshaft end float - this is a measurement between the crankshaft and the thrust face, and the forward part of the case and the oil slinger. This was done by pushing the crankshaft backwards and taking a measrement with some feeler gauges, then pulling it forward and measuring again. 

The green part is the thrust face - i think this is amazing. It's such a small area - if you imagine the propeller is connected and pulling the crankshaft forward, and the case with the aeroplane is pulling backward, with the whole weight taken on this little area. Amazing! 

This shows no gap at the trust face with the crankshaft pulled forward.

The measurement is done in two steps - and at two places. Point A is between the forward face of the crankshaft and the aft facing thrust face, and Point B is beweeen foward side of the case, and the aft side of the oil slinger on the crankshaft.

The results were:

With the crankshaft as far forward as possible, there should be no gap at the thrust face (Point A), the forward gap at Point B should be between 0.002 - 0.007. We were at 0.006", so all good! 

With the crankshaft as far back as possble, at Point A (the gap between the crank and the thrust face) should be 0.0009 - 0.0016". We were 0.0011" so within tolerance and all good. 

Cam Shaft Lubrication Mod 

We had perviously chosen to do a modification to the camshaft and the case, to allow oil to lubricate the lobes of the camshaft where the lifters will run. This entails capping off the internal passage in the camshaft, then drilling a hole in the front of the camshaft where it runs in the case. The same area of the case gets a channel to allow oil to flow into and fill up the camshaft internally. There are then weep holes drilled in the camshaft lobes to allow the oil to escape and lubricate the mating faces between the lobes and the lifters. Hopefully this does it job well (and we don't see lower oil pressure etc as a result). 

This is the supply hole in the forward bearing area of the case. 

That little hole gets oil from this channel - machined into the case during the case overhaul. 

These are the supply holes to the lobes.

One last little (but important) mod to the engine!

One last little modofication to the engine - since we have now officially made this engine an experimetnal engine, by making modificaitons which cannot be undone, we need to make sure the case is identified. Lycoming Service instruction 1304K states:

• For all commercial engines in which the basic model has been altered or converted to another model designation, the letter “C” added as a suffix on the engine serial number indicates a change from its original manufacture

This is important, as the serial number shows the enging is an IO360-C1E6. We are changing the sump to forward facing, changing the ignition and fuel systems, all in addition to oil modification to the camshaft and case. If anyone ever found this engine in the field, we don't want them installing it back into a Seneca! So we figured we better add a "C" to the Serial number on the case:

I let the professionals have at the expensive case!

Before (below) and After (above)

Finally, i put the cylinders and case into the back of the car to bring home for painting. I am pretty sure i have just more than doubled the value of the old Mazda 6.