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PostPosted: Sat Sep 20, 2008 11:19 pm 
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SooperDooperMiniCooper ExpertEngineering
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Location: Under the bonnet son!
A job that always seems to be considered voodoo is the refurbishing of rear trailing arm bushes. I have rebuilt them before, but never reamed them myself. I figured I would give it a go this time and see if I could remove some of the mystery using easily available commercial tools.
Having the job done by a machine shop is very expensive, so the cost of the expanding reamer will simply be offset against the potential bill. And you will have another string to your bow. Anyone in the Melbourne area wanting to do this same job may ask to borrow the tool, or use my tool bench and vice to ream them out...just ask.

I'm not a Fitter/Turner machine shop guru, so I will appreciate any techniques or tricks that may make the job a little easier.

The rear arm rebuild kits are easily (and relatively cheaply) available. You get everything needed to rebuild the arm of course, needle roller bearing, bronze bush, grease guide tube, radius arm pin, two (differently sized) thrust washers, two nuts, spring washers and a grease nipple to boot.
Image
The bush in question lies on the outer end of the radius arm. On the inner is a needle roller bearing. Funnily enough it is most often the needle roller which fails and not the bronze bush. The needle roller only moves through 20-30 degrees of movement through it's entire life despite it's complexity, and once water gets into the needle roller it will rust solid and lock the bearing to the radius arm pin. Often the result is that the mild steel pin will snap.

Removing the Bushes
Removing the bearings is a little hard to describe. It features the use of a large hammer and drifts (tricky, brutal and rough) or the use of a dremel to cut a groove in the bearings. Once the groove has been cut the bearings will push out quite easily as a triple unit. Push from the bronze bush end (using a drift) and the bronze bush will push the grease guide tube, which will push the needle roller out. If you push in the opposite direction, the needle roller will fall into the hollow internal cavity of the radius arm and get stuck. This is because the bronze bush's journal diameter is smaller than the needle roller. So lookout....

As my dremel was currently out helping a neighbour with a reluctantly fitting V8 gearbox, I was forced to thread a hacksaw through the radius arm to cut the groove. Patience is the name of the game when removing these bushes.

This is what you will greet you once the bush, tube and bearing is removed. You will see two bare bearing journals and an awful lot of grease in the middle.
Image

You will find that the inside of the arm is in fact hollow to an extent. And it WILL be filled to overflowing with 40 year old grease despite the guide tube. Removing this grease might be a poor decision. Once the radius arm is reassembled, the grease gun will try to squeeze grease back through the tube to the inner roller bearing. Once again the same conditions will exist to make the grease push out past the grease guide tube and into the radius arm. This will involve pumping a lot of grease to refill the cavity and grease will simply not get to the inner needle roller for many, many service intervals. Your needle roller may be ruined long before the grease ever gets to it.
The grease stays there for life as well, there are no conditions to make the old grease want to migrate back into the tube, so the bearings are completely insulated from the 40 year old clay based muck.

At this point: If you are squeamish on completing the job or simply don't have a reamer, take the radius arm and the rebuild kit to a mini specialist. They will complete the job for you reaming the bush out to the correct size, but you have saved perhaps a couple of hours of labour and that will return money to your pocket. The difference might pay for something very blingy for another part of the car

DO NOT INSTALL THE NEEDLE ROLLER AT THIS POINT
Do not touch it.

If pushing the bearings out was difficult, then replacing them is pretty easy. The bronze bush will go in without the use of a dolly, and since it has to be reamed and a considerable amount of material removed, it's not too critical a job to get it in.

DO NOT INSTALL THE NEEDLE ROLLER AT THIS POINT
Put the needle roller down and move away from the needle roller. Bad mini mechanic...

Now this is the mysterious expanding reamer tool, and it's own matching guide bar. The guide bar has a free spinning, sliding knuckle fitted to it which serves to centre the guide bar universally in tubes when taking cuts.
The reamer features six parallel cutting bars which are fitted into six grooves on the reamer itself. they are retained by the nuts above and below the cutting bars. The grooves become progressively shallower as they go up the shank. As you screw the nuts along the shank, the cutting bars will be pushed further out, or further in depending on direction of movement. Each turn will extend the cutting bars out by a very small increment. The correct reamer for this job has a complete diameter change of 1.6 mm from 25/32 - 27/32 (19.8 - 21.4mm). It is a H9 reamer easily available from tool suppliers or eBay.
http://cgi.ebay.com.au/HSS-Blade-Expand ... dZViewItem

The guide bar simply screws onto the end of the reamer to align the reamer in use. It is optional when you buy a reamer (and not included), but you will need one. They will be available from the same source as the reamer.

Image

Setting the size of the reamer involves using a set of vernier callipers. You simply set the verniers to the size you are after and adjust the reamer until you have this size. you measure across the cutting bars noting that the leading edge of the cutting bar is a different height to the trailing edge. this means rotating the reamer as you test its size to ensure you have measured the diameter correctly. Also ensure the vernier is at right angles to the reamer to ensure accuracy. Measure both ends of the reamer to find the greatest diameter; this is the ultimate size the hole will be reamed to and therefore the most important reading.

I'm not using the best measuring technique in the picture below as I am holding a vernier, reamer and guide bar while trying to take a picture!

Image

The reason I did not install the needle roller at this point is because there is a considerable amount of material to be removed from the bronze bush before the job is finished. This swarf will try to find it's way into the needle roller if installed and will be very difficult to remove completely. Also if you install the needle roller this means the plastic grease guide tube must be installed as well (Don't forget this tube come time to fit the needle roller or there will be much sadness.. ). The plastic guide tube warps a little as it is pressed in between the needle roller and the bush (It's a little longer than the gap between the bushes to make some sort of ineffective grease proof seal). Reaming will possibly damage the plastic tube somewhere along it's length and also give another place for swarf to lodge. Swarf lodging in the remaining grease in the hollow arm is not a problem as the grease will stay there in perpetuity and hold the brass in suspension. It will have no reason to migrate back into the arm.

Now to the Reaming..
You don't need to set the reamer to any precision size at this point, simply it needs to be set to the inner diameter of the bush plus a small amount for the first cut (ream) to be made. While you are there, set the vernier calliper to the exact diameter of the new 13/16th radius arm pin and lock this measurement with the vernier lockscrew.

This will be your oversize alarm.

Each time you reset the reamer to make the next cut, test the reamer's size against the vernier calliper (Both ends of the reamer, rotating as you do so). If it is smaller than the calliper measurement, then you are safe to make the next cut.

An important factor in reaming the bronze bush is that the bush inner walls must be reamed parallel to both the pin and the needle roller. The problem with the commercial reamers is that the guide bar is too short to do this easily. Many mini specialists have had guide bars specially made to ensure they are long enough to do the job comfortably, and there are reamers available with this especially in mind. Old Holdens required the same reamer I am told, so they are available. The reamer I have used here falls in the 'barely adequate' category as it is a little short, and it takes some careful use to ensure the job is performed correctly.

Setting the reamer for the first cut, I simply ignored the use of the guide bar and reamed the first cut through letting the bush guide the reamer. You twist the reamer as it is passes through the bronze bush. The cutting bars will take a cut of brass and also tend to draw the reamer through as it turns. It will simply pull itself through by a small amount for each turn. Gentle pressure to push the reamer through, or to start it on it's way may be required if you have taken an aggresive cut. Do not tap the reamer in under any circumstances, you will damage the bearing and drive the reamer off centre. It gouges deep channels into the bronze bush which may not be removed when finished.

For every second cut thereafter however, I used the guide bar and the tapered free sliding knuckle fitted on it to align the reamer through the journal on the needle roller end of the radius arm. Doing this made every second cut a little difficult to make due to the short length of the reamer, but ensured accuracy. As I got down to the last cuts I used this method each time as the last cuts are the final finish and are therefore very, very important.

You simply take the cut, remove the reamer, readjust the size (comparing against the vernier for safety) and take another cut. Clean the reamer at every opportunity of swarf or it will become very hard to turn and adjust.

When you get close to the size of the vernier, move in very small increments on the reamer (perhaps half a turn of the adjusting nut per cut). A little bit slow, but will ensure a well fitted radius arm pin. After each cut trial fit the pin into the bush, if it doesn't fit take another cut until it does. The reward for all this hard and careful work will be reached shortly...

Image

DO NOT TOUCH THE NEEDLE ROLLER YET.
NO.
NO.
LEAVE IT ALONE.


Not until you have inserted the grease guide tube into the radius arm.

Once you have done put the grease guide tube in, then you may pick up the needle roller and push it into the arm.

If you have forgotten to install the grease guide tube (I told you not to touch the needle roller...) then the needle rollers are available individually for a few dollars. They are the same needle roller as used in the front upper suspension arms. Don't think you will get away with splitting the tube down the middle and inserting it through the needle roller. Grease pumps pump at up to 8000 psi and will simply push past the plastic tube and into the inner arm, old dirty grease will eventually be forced back into the other end of the plastic tube as you do so and ruin all your hard work.

If you have been careful in your reaming then at this point you will be rewarded with a radius arm pin that will push through the bronze bush and down through the needle roller without binding. If there is a little binding, take the reamer and re-insert it through the arm using the knuckle on the guide to align in the needle roller and take a fine cut using the same diameter you used on your last cut. This will realign the bush's inner walls to the correct angle. It's not the preferred way to finish up, so careful use of the reamer prior to this will minimise the cut you need to take here.
Clean the swarf out as carefully and thoroughly as you can from this final remedial cut and reassemble with the new pin.

The grease nipple end will go to the bronze bushed end of the radius arm, and note that there are two sizes for the thrust washers. the smaller is on the bronze bush end, and the larger on the needle roller end. The grease passages machined into these washers face into the radius arm.

Image

Take a breather and admire your work, then repeat on the other radius arm.

Edit: There are a few differnt technical ways to approach the reaming, one approach would be to leave the old needle roller in while you ream the bush. This will make the guide center a little more easily, but may make it more difficult to remove later. As long as you aproach the job with an accurate finish high on your list of priorities, then you will be rewarded.

8)

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All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.


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PostPosted: Sun Sep 21, 2008 12:20 am 
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848cc
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Thanks Mick this is excellent info! This is a job I've been meaning to tackle for a while.


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PostPosted: Sun Sep 21, 2008 8:59 am 
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This space for rent
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Sensational, Mick!

This is a job I'll have to complete on the van but have always shied away from, but maybe I'll give it a go now :D

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PostPosted: Sun Sep 21, 2008 9:29 am 
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gahh! why didn't you post this two days ago!!! :twisted:

:P

great write up! next time I'll maybe tackle it myself! get this into the howto's ASAP!


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PostPosted: Sun Sep 21, 2008 2:33 pm 
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Top job Mick!!!!
It may be worth noting that after making a cut with the reamer it is good practice to remove the reamer from the bush by continuing to turn the reamer in the SAME direction (clockwise) as you gently pull it out of the bush (dirty snigger). This helps overcome the possibility of cutting additional grooves etc. in the bush as you remove the reamer.

Mods please place this in the How To section.


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PostPosted: Sun Sep 21, 2008 5:00 pm 
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SooperDooperMiniCooper ExpertEngineering
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Joined: Fri Apr 29, 2005 9:46 am
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Location: Under the bonnet son!
Thanks. It's a fiddly job which will make you appreciate brake bleeding for the enjoyable job it is.

Yeah, I meant to describe the action of passing the ream through. As you turn the ream it will pull itself through to an extent. You simply continue to turn the ream until it passes completely through the bush.

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PostPosted: Sun Sep 21, 2008 8:13 pm 
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excellent - a job I've been lining up for a while now

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