Tooling

Problem number two that I encountered with the engine rebuild was the pilot bearing. For anyone who doesn’t happen to know, it’s the bearing in the rear end of the crankshaft which supports the nose of the transmission input shaft (notice that I didn’t use the English term gearbox as that has alternative connotations for US readers????) Ok, so there are various tricks on the net to remove this thing and the most popular is to pack the rear with grease and then insert a dowel and give it a good whack with a large hammer. Tried that – didn’t work – bearing was stuck solid. Alternative solution when it’s that stuck – use the factory tool.

factory tool

Well, I didn’t have one and couldn’t get one quick over the weekend when I was working on it, apart from that they are not that cheap. So what do we do? We dig through the scrap box to see if we can construct something.

Scrap shelf

 

Scrap box

So I found a piece of steel tube which when turned slightly smaller on the lathe fitted snugly over the lip on the rear of the crankshaft that centres the flywheel.

Crankshaft end

Here the old bearing has already been removed but a rusted example can be like the one below (found on the web) and then no amount of whacking a dowel with a hammer will shift it.

Rusted crankshaft end

So anyway after I’d prepared a 30mm length of the tube I found an 80mm length of 16mm threaded round bar, a 10mm length of 6mm threaded round bar and a couple of nuts to fit them.

Separate components

Here you can see that I’ve actually turned these odd bits into something slightly more useful. The larger tube has been turned into a cup by brazing a piece of plate steel into one end, turned relatively smooth and a 16mm hole drilled in it.

Basic positioning cup

The 16mm threaded round bar has been bored 6mm to accept the other threaded bar. One end has a couple of flats filed onto it and the other has been machined down to 10mm with a 12mm lip on the end. the turned end was then cross sawed through with a fine saw to form four quadrants. The smaller threaded bar had also flats filed on one end and on the other end a 10mm piece of 6mm i/d tube was brazed over it and then turned to form a taper. So then the smaller rod fits in the larger one like this.

Extractor assembly

So to use it we first place this assembly above into the centre of the bearing and by holding the flatted end of the smaller shaft with a spanner or a mole grip, tighten the nut until the lip expands to fit inside the bearing and locks behind it. Then place the larger tube over the shaft and seat it round the lip on the crankshaft.

Complete assembly

You can then hold the flatted end with a spanner to stop it all turning and tighten the large nut which slowly extracts the bearing. Hey Presto!

Well I did actually spend a couple of hours fabricating the tool for what would have been 5 minutes usage and I can’t actually think when it will be used next, so was it worth it. Well yes… it got the job done and it gives an enormous amount of satisfaction to see that the idea worked and the tool (although a little Heath Robinson) is not a bad design. Anybody need to borrow it?

Although I’ve collected a lot of tools over the years of varying quality, it’s sometimes just not financially viable to spend money on certain special tools. My solution is to try and construct my own. When working on the BMW engine rebuild I found I needed to remove the camshaft from the head to get some machine work done. The factory tool, which seems to be quite well known by the BMW forums community, sometimes turns up on eBay for prices around $300-$400. As far as I know it looks like this and I believe it is known as the Iron Maiden.

 

Whatever – it never seemed like a serious piece of engineering to me so I thought I could do better. This is my take on it.

 

I generally store it like this but it can be completely dismantled. I started with some steel bar stock 50mm x 5mm and 20mm x 3mm. Cut this into 220mm lengths and drill the smaller strips with 12mm holes at 95mm centres leaving enough room to fit a 12mm nut snugly against the edge which will end up against the vertical strip. The bigger strips were drilled for the round bar stock rails they ride on with the centres of the lower hole 20mm from the bottom edge and 300mm between centres. The upper rail holes are at 30mm from the lower between centres (about a 20° angle from the lower) and 250mm between centres from each other. Note that these sets of holes need to be drilled as accurately as possible otherwise the assembly will bind. The pairs of strips were then brazed together at 90° and a 12mm nut was brazed over each hole in the smaller strip, as I said earlier the nut should fit snugly and makes for a neater braze. The rails are made from 10mm round bar stock, 650mm long, tapped at each end. I used acorn nuts to hold the assembly together but functionally standard nuts will do just as well of course. The blocks that also ride on the rails were fabricated from 20mm x 15mm bar stock cut to lengths of 60mm. Through the 20mm side they are (centrally) drilled and tapped 12mm for the bolts performing the spring compression. Through the 15mm side they are drilled 10mm to ride on the rails. Again these sets of holes need to be drilled as accurately as possible otherwise the assembly will bind. The bolts in the blocks are 60mm long and I used hex heads purely because they look better. The next thing we need are a set of cups so that the bolts don’t damage the rockers when you are turning them.

 

The cups are fabricated from steel tube 12mm inside diameter cut to lengths of 10mm. They are brazed to 20mm lengths of 20mm x 20mm steel T bar stock. The lower edge of the T is then radiused so that it rides smoothly on the eccentric visible through the split in the rocker arm. You’ll notice that the curve of the radius is elliptical because of the lateral movement of the rocker compared to the motion of the bolt as it compresses the assembly. This should be well lubricated during assembly. You may have seen this photo on the engine rebuild page but this is how it sits on the head.

 

Home built valve compression jig.

You can’t actually see the underside in this photo but the bolts holding the main supports to the head through the nuts that were brazed to the smaller strips were packed out with a couple of thick washers giving enough room under the head to allow the valves to move without hitting the workbench. When all four supports are in place the blocks can be slid into place above the rocker arms and the cups put into place. It’s just a question of tightening up the bolts to compress the springs and rockers so that the cam is then free to be extracted. It will be noted by some that you don’t actually need to compress all the valves to remove the cam as not all lobes are loaded. In other words you can get away with only fabricating a few of the blocks but then you need to place them on the rails where you will need them depending on where the cam is sitting. I thought that while I was at it I’d just do all 12 and then I didn’t need to think about it, I could just compress all of them making extraction and insertion simpler.

If anybody in the BMW community in the Netherlands wants to borrow it please get in touch.