Welcome to David and Janet Ribbans blog

We live in Adelaide, South Australia and enjoy travel in the Australian outback in our Oka 4WD motorhome, hence the blog title.

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Wednesday, 20 May 2009

Reviving Oka Door Catches

Are your Oka doors difficult to open? Do you have to slam the doors several times to close them properly? Do they fly open unexpectedly on rough tracks? We've experienced all of the above so I investigated further.

Dust and grit are the first suspects for making the door catches recalcitrant, followed by wear and tear. Fortunately the door catches are industrial strength and are quite easily fixed.

Dust and Grit

The door is held shut by a 2 position ratchet and pawl system. (See Pic 1 centre). Grit and dust can dry out the grease between moving surfaces increasing frictional forces. This makes closing and opening difficult since the plates won't slide smoothly and the pawl won't always drop into the ratchet, despite the strong spring. A full overhaul requires the removal of the door mechanism from inside the door, see the Power Door Lock blog post for details on how to remove the catches (about half way down).
Pic 1. The Ratchet and Pawl System.
Degreasing and cleaning out all the gritty sludge from the mechanism is the best solution followed by a full re-oiling of rotating components and re-greasing of the sliding plates. Also ensure that the ratchet to pawl spring is not stretched and is correctly fitted. It should be quite difficult to remove as it's quite strong.

Dust can enter via the rectangular cut out in the side of the door through which the catch protrudes, particularly the depressed rivet area, (see pic below), which allows free access for dust into the door cavity. The answer is a layer of thin closed cell foam strip stuck around the opening before the catch is refitted. The foam will compress during assembly and form a good dust barrier.
Pic 2. Dust can enter here
Wear and Tear

The next problem is wear and tear on the barrel which transfers the tension from the external latch to the internal ratchet and pawl system. Normally the ratchet plate is in line with the pawl, but when the barrel shaft or sliding surfaces are worn, under extreme shock (eg from a bump on a rough track or the door being slammed shut), the plate can move out of line. The pawl can then jump out of the ratchet and the door flies open, or won't close securely. (See Pic 3).
Pic 3. A worn barrel allows the ratchet to jump free from the pawl.
Wear on the barrel creates a gap between the door catch and the barrel spacer (see Pic 4). This is more difficult to fix since the plates at either end are sweated on and peened over to prevent movement.
Pic 4. The gap caused by wear on the barrel.
A simple solution is to wind one or 2 turns of fine galvanised fencing wire around the outside of the barrel to take up the wear gap. (See Pic 5) This reduces the inward movement of the internal ratchet plate and prevents the pawl from jumping out of the ratchet.
A large circlip would be a better solution but would be difficult to insert. By contrast, fencing wire is quick and easy to fit.
Pic 5. Wires can fill the gap.
You don't even have to remove the catch to make this fix. It can be done from outside. It might not last for ever but it's cheap, quick and effective, and easy to replace. It can also be done on the rear tailgate catches on the bus model.

The last(?) wear and tear problem is the latch plate which hits the striker. This is often worn and won't hold the striker rod tightly and securely.
Pic 6. This latch plate (from a tailgate) has been heavily repaired and is badly worn.
The only easy solution to this problem is to lay some weld on the worn "C" shape (it should be a nice "U" shape) and file it down so it fits and turns on the striker rod smoothly. It's not a quick job but will make a lot of difference to door closing and retention.

If the striker rod itself is worn, as mine were, you could wrap a layer of steel shim around it to pack out the wear. This worked surprisingly well for several years. Alternatively, weld could be laid on the worn part of the rod and filed/ground round.

Finally, ensure that the striker plates on the door frames are adjusted properly (so that the door closes tightly without slamming and doesn't rattle) and the Allen headed screws done up tight so the plate can't move. BTW, never remove all the Allen screws at the same time. The threaded lock plate inside the door frame can drop down, never to be seen again.

And why not grease the door hinges while you're at it? I'll bet that doesn't get done very often because I've found it's necessary to remove the door stay strut on some doors to allow the door to open far enough to access the grease nipples.

Replacing the Oka Springs

Replacing the springs on an Oka is a straightforward but heavy and time consuming job. Springs are heavy (60-70 kgs each) and unwieldy things to move about and locate with any precision and safety. 
A Simple Spring Trolley

I built a small but sturdy trolley to make it easier to manoeuvre them around the workshop and locate the springs under the Oka. It was constructed out of scrap timber and fitted with some old skateboard wheels recovered from long abandoned children's play equipment (the skateboards, not the children) . The sets of wheels were modified to rotate through 90ยบ so the trolley can be moved sideways when under the vehicle, to locate the spring eye in the mounting bracket. It needs to be a "U" shape to go round the end of the axle and wide enough to avoid the brake callipers (and steering rods on the front). Blocks can be added as necessary to rise or lower the height of the spring as it is being located under the vehicle.

Start with the spring inverted.
(It will still need to be manoeuvred over the brake calliper)
Carefully turn the spring (they are unstable things).
We found it was easier (and safer) to locate the spring under the Oka whilst mounted upside down on the trolley so it will clear exhaust pipes, bodywork, spring mounting brackets etc, and then invert it when in approximately the right place. Be very careful not to crush fingers when manoeuvring the spring!
Now it can be turned upright and moved into position.
Obviously the Oka needs to be securely supported before removal of the old springs. In my case I built a set of very strong chassis stands made from steel girders to support the Oka 1 meter off the ground, which is the height you need to remove an unsprung spring. We used High Lift jack (60 inch model) to lift the Oka while manoeuvring the stand under the chassis. In theory you could raise both sides at once to enable removal of both springs simultaneously. However, the vehicle does not feel secure with 2 wheels off the ground and with the axle is no longer constrained, it can move or rotate, so it's much safer to do one side at a time.
Heavy Duty Chassis Stand
Whilst replacing the springs, I also upgraded the suspension bolts to 20mm (up from the standard 16mm size) plus urethane bushes. I got these in a kit from Peter Wright, see http://okaownersgroup.info/tiki-index.php?page_ref_id=416 (you'll need to log-in to the Oka Ownwers Group website).

It does need some serious drilling of existing chassis holes and the holes in the spring shackle plates, plus welding of support plates, but the end result looks very strong and maybe will reduce the number of suspension failures we have had on our 0utback trips (3 spring eyes and 2 bolts broken so far, and it's not fun repairing these on remote tracks).
20mm Bolts. Note the lead-in on the end of the bolts to make alignment easier.
If there is significant lateral wear on the shackles, chassis plates or spring mounts to allow the spring eyes to move sideways, they will clonk when turning. Steel thrust plates can be inserted to take up the gap, usually about 1 to 2 mm thick but not so thick that all movement is prevented. The spring eyes must be able to rotate in their mounts.
A thrust plate located on a hanging shackle
Fitting the hanging shackle plates is not too difficult, but aligning the fixed eye end of the springs requires manoeuvring of the spring. This can be done by putting a piece of timber under it so the centre bolt doesn't drop into any holes on the axle and then levering the spring along the top of the axle. Once the bolts are in, a more difficult job is to get the spring and axle aligned, because with the spring unsprung, its centre bolt will be no way near its axle mounting hole.

In the workshop I placed 2, 25mm round bars under the rails of an axle stand to act as rollers on a concrete floor, and lowered the axle on to it (the axle weight is not sufficient to cause damage to the axle stand). Using levers, I could then move the axle to and fro a small amount until the centre bolt and its mounting hole lined up. 

Compressing the spring with a separate jack may also help with alignment. With the vehicle jacked up on one side, there may be considerable lateral misalignment as well, due to one side of the vehicle being higher than the other. The answer is to lift the other side a bit to level the vehicle, but be careful, 3 wheels on the ground is fairly stable, 2 wheels is not. A lot of levering will still be necessary and a breaker bar is very useful for this.

Even when greased and carefully aligned, the bolts may still be a tight fit in the spring bushes (if you are using urethane bushes) and mounting plates. Hammering is seldom effective because the bolt "bounces" in the bush and it can also damage the threads. A simple pusher can be made by using a large G-clamp and putting a socket over the thread end of the bolt (and removing the grease nipple from the head end or using a socket to protect it) and tightening the clamp until sufficient thread protrudes to allow the nut to be fitted. The nut can then be tightened up to pull the rest of the bolt into position. Peter Wright's 20 mm bolts have a lead-in protrusion with a removable tapered cap to assist with alignment. This works well.

With urethane bushes, it's important not to over-tighten the shackle bolts since the bushes can be crushed and the shackle plates can bind on the spring or chassis. This will put additional strain on the spring eyes and lead to premature failure. Tighten the nuts to seat the bolt heads fully and then back them off until its washer just won't turn. That's tight enough, the nuts are only there to keep the bolts and spring components firmly in place. Being Nyloc nuts they shouldn't work loose, but if you are concerned about that, holes can be drilled in the ends of the bolts and "R" pins fitted to retain the nuts.

With the new larger 20 mm bolts fitted, the top shackle bolt on the rear of the drivers side front spring fouled the exhaust pipe after passing through the chassis, see pic below. In fact I had to remove the front pipe to even fit the bolt. So after it was installed, I lopped off the lead-in end on the bolt with an angle grinder and pressed a 1 cm depression in the pipe around the area of the bolt head to ensure that there would be no contact when the engine rocks under load. Even the previous 16 mm bolts been touching the exhaust pipe and caused a wear mark. I also rotated the muffler (which has off-centre entry and exit flanges) so as to direct the front pipe as as far from the suspension bolt as possible.
The chassis bolt fouls the exhaust pipe.
We got new rear springs made by Industrial Springs in Adelaide and we had an extra 3rd leaf fitted to provide support to the spring eyes. The fronts weren't too bad (Industrial Springs had renovated them a few years ago with new 1st and 2nd leaves) so we just had them beefed up with an additional 3rd leaf fitted and the springs were reset.