Kit 17 - Differential Gears

ModelWorks 4 inch Scale Burrell Agricultural Traction Engine
Kit 17 was delivered Friday 1st July

Friday: I don't think this kit is going to take long to assemble but it contains a lot of expensive machining.  As usual the machining of the gears is impressive particularly the bevel gear BU41702 since it is integral with a spur gear.  To machine this as one piece I assume a shaper rather than a milling machine was used.

As expected this kit contained a replacement reverser quadrant (see) but we will have to wait until next month for the crankshaft spur gears.

Rather than rely on the jacks I have put the Burrell back on blocks.  So far I have fitted the inner bevel gear at the pinion gear and the other end of the shaft.  A fair amount of fetling was required but noting I could not sort with a file. 

The differential is wondrously complex and as it is hidden I intended to include shots to show the internal works.  The shot below shows the four prong locking ring that may be slid out to lock the differential.

 
Saturday: My first task was to assemble the compensating centre that houses the bevel gears.  I noticed that the top and bottom pinion bushes as bagged did not agree with the isometric drawing. I concluded that they were in the wrong bags and that the fat bush goes closest to the hub (as per ISO 17C). 

The apertures in the compensating centre need to be enlarged to accommodate the bushed pinions.  I have deferred this until I have completed dry assembly so that I can see which face it is best to attack. For now I have omitted the top bush.   

(3/6/05) When it came to it I reduced the thickness of the of the bottom bush (the fat one) such that the assembled height of the bushed pinion was 1.000".  This was far easier than trying to file the cast iron centre. I noticed that the pinion was turning in the bush rather than the pinion shaft so I Loctited the bushes to the pinions.
 

As the bronze centre bush is a tight press fit I needed to improvise a bearing puller. There are four flats on the bush and they must exactly align with the recesses in the centre.  I scribed lines on the bush to mark the position of the flats so that I could start it off in the correct position.  Despite my precautions the flats were slightly misaligned (about 1/2mm around the circumference).  I was miffed to discover that this was enough to prevent the prongs of the locking ringing ring engaging. Fortunately I was able to rectify this by re-milling the flats using my milling machine.  Had I known the criticality of alignment I would have taken more trouble to ensure perfect alignment of the flats.

On fitting the centre to the engine I found that I could engage the locking ring but it was a lot stiffer than I would like - something I will have to work on.

Again the outside bevel bush was a tight press fit into outside bevel gear requiring the use of an improvised bearing puller.  I found that I had to ease both the inside on outside circumference of the thrust washer in order to get it to fit.

To investigate the cause I removed the compensating centre and found that this freed things up.  Initially I suspected that the centre was binding between the inner and outer bevel gears, ie that the thrust washer was not thick enough.  This turned out to be a blind ally and I had to look else where for the source of the problem 
A rubbing sound alerted me to a clash between the brake drum and one of the bolts securing the hornplates.  My first thought was to remove the washer but this did not provide sufficient clearance to prevent the rub.  I have now temporarily removed the bolt and am able to tighten up the differential without it jamming.

A word of warning - the small dowel that locks the RH main gear spur washer can easily disappear into the second shaft as the hole is deeper that the length of the pin.  Either Loctite it in place of partially plug the hole.

The last part of the instructions alerts us to a clash between gear guard and the outer bevel gear (red arrows).  I also observed that there is insufficient clearance between 1st gear and the guard (green arrow).  I will probably trim about 1/4" from the edge between the two top supports. 

I shall now remove the differential so that I can paint it.  As usual I am in a quandary as to what to paint and what to leave bare.

Tuesday 19th July: Now that I have returned from the rally I have turned my attention back to the Burrell.  Despite my loathing of angle grinders I decided to follow Steve recommendation.  Using a pair of dividers I scribed a line 1/4" down and clamped the guard to my workmate.  By taking light cuts with the angle grinder I was able to produce a fairly straight neat edge.  I finished off with a file and to my surprise found I had hardly scratched the paint.   I am hopeful that I can get away with a partial respray to attend to the freshly exposed edge.

Saturday 23 July: Today I turned my attention to sorting out the right hand side of the engine.  Despite receiving the steering at the beginning of October I have not fitted it to the engine.  I am a bit unsure how the fit the steering chains as only abridged instruction were included with kit 15 pending further instructions at a later stage.  I could not get the tension just right using the full length of the chain and for now I have one of the chains bolted onto the third link back.  I would not be surprised if this is covered in our next instructions.

Once fitted I immediately disabled the steering by removing the front shackles and tying the chains to the perch bracket.  The reason for this that it is much easier to maneuver the Burrell around the garage by pushing on the tops of the front wheels.  Not only does this provide agile steering it provides additional leverage. (Move the Burrell back 1" and the top will go back 2" giving a velocity ratio of 2)

The only other "new" component to fit was the gear guard.

Monday: Spurred on by Mikes report (see Gallery) on having all parts fitted I have continued to fit some of the residue I have dotted about the house.  Today I tackled the cylinder cleading.

The cleading was a joy to fit since the pre-bent shape was an excellent fit and all of the holes lined up.  I am glad I did not have to make it from scratch!  I have just given it its first coat of paint.

I have also been working on the ashpan and grate.  I don't how durable it will be but I have painted it with high heat matt black paint which I originally obtained from Halfords.