From:Steve Marks e-mail:steve@microdesign.ltd.uk
Subject:RE: oil pan cases Date:Sat Dec 12 09:07:34 2009
Response to:2697
Hi Guys
For anyone who is interested, here is the way I cut the threads on my K model. The upper half of the case was fine, the lower case was completely shot so I got hold of another one. Needless to say, the threads in the two halves didn't line up - that would be too much to hope for! The threads in the new lower half were welded over which left a good thread in the top half - nothing in the lower half so a tap was not really an option. The pictures show the set up I used. A couple of people asked to borrow it after I'd finished with it and it successfuly cut several cases. Unfortunately it didn't come back from one of them.....
The actual thread cutter was a 14tpi HSS chaser from a Coventry Die Box so had the correct form. This was ground down to leave just the threaded end which was then brazed to a short length of 3/8" dia rod. This rod was clamped in a cross drilling on the 1" shaft. Depth of cut was altered by loosening the clamp and tapping the cutter in or out to alter the cutting radius. The pictures should show the general idea. The following notes are the instructions I gave out with the cutter.
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Oil Pan cutter – operating instructions

The main jig body needs to be bolted in the upper half of the crankcase using the four studs meant for the countershaft gear unit. This needs to be done accurately! Recommended procedure is as follows:
1. Clamp the two bronze spline shaft bearings into the threads in the upper half of the crankcase using U bolts, G clamps or whatever. Just laying the bearings in the case will not do!
2. Slide a 1” diameter silver steel rod through the bearings and check that it rotates freely.
3. Now include the jig body by sliding the steel rod through the right bearing, through the jig body and into the left bearing. If you are lucky the shaft will still rotate with the jig body resting over the four studs. If the shaft won’t go through, then it’s likely that the height from the stud face to the spline shaft is less than the height of the jig body. It will be necessary to machine a little off the jig body to reduce its height.
4. Almost certainly, clamping the jig body to the four studs will cause the shaft to lock up. It’s necessary to place shims under the jig body and play with the alignment until the jig is firmly bolted to the four studs, the bearings are clamped tightly in the crankcase half and the shaft rotates freely. This is quicker to describe than it is to achieve but it is vital to get the alignment correct!
5. Remove the two bearings and replace the silver steel rod with the cutter shaft fitted with a rounded cutting tool.
6. Bolt up the welded lower half of the crankcase making due allowance for gasket thickness used in the final assembly.
7. Adjust the cutter depth and use a wheel brace on the hexagon end of the cutter shaft in order to rotate it thereby removing excess weld from the lower crankcase half. Increase the cutter depth as necessary and repeat this process until the core diameter of the thread form has been achieved - just clear of the peaks of the good thread in the upper crankcase half. Take a little at a time and use a cutting compound. This will improve the finish and is recommended. If there is not too much to remove, this operation can be done without the need for the threaded collar on the jig. If however the welder has been too enthusiastic it may be easier to use the threaded collar to feed the cutter through the bearing as it rotates. It may then be necessary to rotate the threaded collar a little and repeat the process in order to achieve a smoother finish. This is not too critical as the cutter to be used has the full thread form on it.
8. Now replace the rounded cutter with the thread cutter and fit the threaded collar if it’s not already in place. Adjust the depth of the thread cutter and rotate the threaded collar until the cutter fits snugly in the good thread in the upper crankcase half then lock the threaded collar in place.
9. Reduce the depth of cut on the cutter – it’s a little too ambitious to expect to be able to remove all the thread in one pass! Then wind the cutter through – the threaded collar has the same 14tpi thread and so will feed the cutter through at the correct rate. Adjust the cutter depth and repeat, taking a little at a time until the full depth is reached. When close to the full thread, remove the cutter shaft and try to screw in the bearing. If it’s tight, replace the cutter and take out a little more. A little patience will achieve a nice snug fit.
10. Once one side is completed, remove the cutter shaft, take off the threaded collar, place on the other end of the jig body and repeat the process for the other bearing.

There are some important points to watch:
1. Take time getting the jig body mounted correctly so that the shaft rotates freely. This is so important, it cannot be over-emphasised. When the jig was made, the plate was bolted to the four studs and the circular sleeve was free to slide on the 1” diameter rod. The two parts were then welded together using the connecting plates. After this initial welding the shaft no longer rotated which was not entirely unexpected! The jig was removed and the welding completed. When refitted, shims were needed as outlined above in order to achieve a satisfactory alignment.
2. Once the two crankcase halves are bolted together, keep them that way until the whole operation is done. Note that the threaded collar can be adjusted, removed and refitted to the other end by reaching through the crankcase bearing holes.
3. If you get carried away with the thread cutting and the bush ends up being a loose fit in the case, make an oversized bush. It is very important that the bushes are clamped tight when finally assembled - just think of the strains and stresses being carried by these bushes!
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----- ORIGINAL MESSAGE FOLLOWS -----
Russell, could you show a picture [or you Mark] of how to thread or re thread the transmission cross shaft bearing threads and the jig necessary for this? Most are not aware you can't just put unmatched cases together without fixing this area.