King pin top grease cap
Screw caps can be made of Steel or Delrin. Bushes are made from Delrin homopolymer acetat video at bottom
The king pin top grease cap has been a problem for us since time immemorial. Caps fall out and get lost, they don't get fitted correctly, they leak grease and get pushed out, refitting incorrectly can lead to damage to the top bush housing where the plug fits and sometimes I have even seen them welded into position, you try to make the cap shape more concave with a big ball bearing and an appropriate sized socket so it can go into its hole and be seated, and it nearly always leaks or gets pushed out, so it has been a big problem. Even the most skillful of mechanics and fitters may get it in correctly, but an owner doing his greasing routine will dislodge it with too much pressure............ It would have been a far better design if Citroen had made a screw thread at the top, like at the bottom, instead of a pressure fit cap.
I have been able to create a 25mm x 1mm x 4mm deep screw thread in this area and have also made the screw plugs, aided by an O ring, to finally eradicate this grease leakage and plug security problem. See below for photos and a description of the tools and parts needed.
If the top of the cap area or the inside diameter has been damaged, then, it must be cleaned up to the correct size inside again to enable the tap to start to create a thread correctly. I use a type of hole saw with 6 cutting flutes with tungsten carbide inserts, made by the Starrett company.
It is 24mm diameter [the same as the existing hole] and needs to be kept central to the hole. The are various guides to achieve this. One guide fits into the 21mm hole in the hub if the top bush has been removed. The next 17mm guide fits into the bush itself, if it is left in the hub. The final guide fits into the hole in the kingpin. King pins differ with this size of hole [ 8.3mm, 8.7mm and the non Citroen ones are a different size too ] and it is pointless making them until I know the exact size of the hole if the threading is to be done on the vehicle and so be accurate with the drilling. The guides prevent the holesaw from vibrating and going off centre.
It's better to remove the hub from the vehicle and work on the bench. Remove the top and bottom bushes, remove the 2 oil seals, remove the ring nut and wheel bearing and give the hub a thorough cleaning. I, or you, can now proceed to the repair procedure.
Metal hole saw 24mm diameter.
with 21mm guide [top bush removed] with 17mm guide with new screw plug [top bush in place]
2 taps are needed to create a thread to the bottom of the recess. 25mm x 1mm.
The recess is 4mm deep and it is enough for 3 full threads. Luckily, the hole is 24mm diameter and this
is the tapping size for a 25mm x 1mm thread. I prefer a deeper hole and more threads, but, we will come to this idea a little more into this article.
The tap on the right is used first to start the thread, it has a taper on the end of it but cannot reach the bottom of the recess.
Approximately 2 threads will be created with the first tap.
The tap on the left has been ground down to eliminate the taper and so reach the bottom of the recess, being flat.
The new threaded plug can now seat on the bottom of the recess and seal the grease in.
An O ring is supplied to complement the sealing effect 24 od x 22 id x1 mm thick
Hub with new 4mm deep internal thread in the top cap area.
The finished thread Modified G clamp with pilot guide and pointer
Checking that the pointer lines up with the pilot guide
The hub is mounted on the G clamp with the pilot guide inserted into it. . The tap is positioned and the pointer aligned to it, this keeps the tap square with the hole. As the tap goes in, you must keep the pointer in the tap centering hole, under slight pressure, to keep it square and straight and perfectly aligned with the two bush holes, whilst cutting the threads.
Threading a plug on the lathe. Making the thread testing tool
Thread testing tool and its insert The insert is set to a depth of 4mm
Testing that the thread is correct to size The tool is screwed up to the 4mm limit
The plug is sawn off, oversize, on the bandsaw. The plug is machined to 4mm wide, whilst held in the thread testing tool.
The plug has 2 flat bottomed holes drilled in it, to 3mm deep.
The finished steel plug 4mm depth Steel 8mm deep plug with 4mm recess
Screwed plug showing 3 threads x 4mm depth Steel plug 8mm thick, 7 threads.
Fit the sealing O ring onto the base of the hole landing, with a little grease.
The plug is installed.
Loctite is an option to prevent the plug loosening, however, the compression of the O ring will also prevent this happening.
The plug can be tightened but NOT excessively, you must not damage the O ring.
A pin wrench is needed to tighten and remove the plug 17mm between the pin centres
Fitting the plug to the hub. It must be flush with the top of the hub when finally tight. There is very little clearance between the top of the hub and the drive shaft constant velocity joint. The screwed cap is made to the correct size to be able to go fully in and not touch the drive shaft joint circumference. Care must be taken to avoid any cross threading.
ANOTHER WAY TO SEAL THE GREASE IN
Delrin homopolymer acetal [thermoplastic] kingpin bushes and top screwcap.
This material is a direct replacement for the steel components, like kingpin bushes and also the track rod end ball cups, is very strong and also has a very low coefficient of friction and is self lubricating. Grease can still be applied with no detriment to the material.
It is ideal for the kingpin application and it will outlive the life of the original steel pins and bushes. A king pin must still be used but the bushes and top cap will be replaced. Please GOOGLE Delrin, to discover this amazing materials qualities.
The steel grease caps are 4mm long, with this next exercise, I will show how to make an 8mm deep threaded cap (steel and Delrin) and insert it flush with the top bush housing and also show a Delrin top and bottom bush.
The cap hole has to be drilled a further 4mm, to 8mm deep, with the 24mm metal hole saw and its 21mm guide.
It has a flat landing face to be able to seal the plug. An O ring 1mm thick is used under the plug to facilitate maximum sealing.
The extra drilled depth can be seen here. At this point, it is 8mm deep.
You may think that you have lost 4mm of the bush length by drilling deeper. Read on.........all will become clear on this point.
Place the hub into the modified G clamp again and centre the tapered tap. Start the thread again.
Check that the tap is squarely into the hole. It's crucial to be in line.
Check alignment from the side view too. Remember that the kingpin is at a 5 degree angle.
Complete the tapping process, using the flat tipped tap, until it reaches the landing flat.
The thread is now 8mm deep.
The Delrin bush is inserted. It is still the same length as the original steel one.[20mm]
You can see the new landing at the sides of the bush, 4mm down from the top of it. This is where the O ring will sit.
The bush top is 4mm from the hub top. There is a gap around the bush which is 4mm deep. There is a 4mm deep recess in the screwed plug and the diameter of the recess is 21.15mm, this enables it to fit over the Delrin bush and down to the O ring. To achieve this the tapped thread must be perfectly in line with the kingpin holes.
Top and bottom Delrin bushes inserted with kingpin in place.
The bushes are machined inside and outside and to length. Once inserted, they compress, slightly. The king pin diameter is measured and the correct reamer is used to make a perfect fit for the pin and creating a perfect circle.
This view shows the bottom of the bush. It must be flush with the flat base. The screwed cap can also be seen.
The bush is 21.1mm od, the outside diameter of the threaded hole is 24mm diameter. There is a gap of 1.45mm all around the bush.
An O ring, 24 od x 22 id x 1 thick must be pushed down to the seat to assist with the sealing effect.
The threaded top cap is 8mm deep and has a 21.15mm diameter recess which is 4mm deep. When screwed into its final position, this recess will fit over the bush outside diameter and down to the new drilled depth. The bush will now have its full integrity as it was when it was a steel one. The lost 4mm length has now been reclaimed.
The top cap has 2 drilled holes to accomodate the use of the pin wrench.
Delrin bushes and kingpin with steel top cap.
Insert the bushes, then the kingpin, and rotate it by hand [it should be a perfect fit], the bottom plug, O ring and top plug.
The Delrin screw cap is tightened down into the newly drilled 8mm deep hole, its 4mm recess is held against the screw wall and over the 21.1mm outer diameter of the bush. The full length of the bush is now being used.
Do not cross thread . Be sure that the plug threads are entering the hub squarely before attempting to tighten it. You will know when it is seated as you can feel it touch the flat landing and the O ring. Simply tighten more to compress the O ring without damaging it, or a leak will occur. The Delrin plug thread is made as a slightly tighter fitting thread, so avoiding any unscrewing or loosening. Test the fitting with your grease gun. You should have alleviated all leaks at the top, apart from grease being able to come out of the bush where the thrust washers fit and the bottom of the top bush. You cannot seal anything in these two positions. It is the top plug that we are concerned about.
These tools are not for sale but may be hired. A repair service, to create the thread in the hub, is available with the supply of the steel plug,
or Delrin bushes and plug and a pin spanner for you to fit all the parts.
Do not overtighten the Delrin plug, just lock it. Steel plugs can be tightened more, as long as the O ring is not damaged.
Extreme care must be undertaken when doing this operation.
Your king pins will last a lot, lot, lot longer if the grease is kept in and the screw cap is kept in place.
Please enquire about this repair service.
Hubs must be delivered to my workshop.
The top cap area must be salvageable
If you need anything else repairing on the hub, ie wheel bearing and oil seals, please advise and a quote will be given.
The bottom screw plug hole can also be reclaimed as well as the bearing ring nut threads.
All hubs sent for repair, will be grease pressure tested before dispatch.
Recutting a damaged ring nut thread Hub mounted in the lathe on a tapered mandrel, through the wheel bearing
The wheel bearing balls are locked by 3 teeth on a special insert.
Reclaiming a damaged lower king pin plug thread The tap size is 22mm x 1mm pitch [ plug tap