Thursday, 26 June 2014

Mainwheel Tyre change

After the last taxy run we noticed that one of the mainwheel tyres on the port side had lost part of its tread and was showing signs of de-laminating further.

As the taxy run was the last one of 2013 we decided to leave the tyre until into the following season, the tyre was holding pressure and was fine for standing the aircraft on and it did not interfere with engine runs and other winter/spring maintenance.

Now the season is here and pending taxy runs are on us, we decided to tackle that particular wheel this last weekend. As far as taxy runs go this has been a late start due to events around the site and the Tour De France coming through the area 5th/6th July.

The Victor and identical Vulcan mainwheels are a single wheel with twin tyres and are of a split rim construction. The first job is to ensure the tyres are deflated and the valves removed. The outer locking ring is removed and the outer tyre with its two sliding removable beads is taken off first. Usually this involves a lot of cursing and sweating, with large rubber mallets and pry bars. If the outer tyre is the culprit (as in this case) then the inner wheel can be left alone. However, an inner tyre means a full wheel strip down and it is hard work. Under the sliding beads and between the main rim and bead are large sealing O rings, these can get stuck to the sliding bead and are difficult to sometimes free up. Especially if the wheel has been built up for a considerable time. Fitting new tyres usually means changing the O rings as well (if they are available). If the O ring is flattened then its unlikely to be re-useable. We have found silicone grease is the best product to smear the O rings with in order to help seal and protect them.
Outer tyre removed

Ollie returning the wheel to Lindy 'wheelie good!'
Once the wheel is rebuilt it is then test inflated to check for leaks. Because there are so many seals the tendency for leaks is very real and likely. 100% leak free wheels are a rarity when you don't have access to most parts in a new condition.

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