Maintenance


Home Propeller Service Bulletins

If you are interested in having me assist you with the maintenance of your Yak 52, please feel free to contact me.   If you are interested in learning how to properly maintain your Yak 52, please go to the TRAINING page for more information.

As I find time, I will add maintenance tips to this page.   These are items that are perhaps less commonly known but well worth paying attention to. If there are any specific maintenance items you need assistance with, please email me and I will do my best to assist.
 

bullet

Gear Retraction / Extension Test Procedure

This procedure applies to Yak 52's and CJ6's

- Before you perform this test, refill the main and emergency air bottles.
- With the airplane properly placed on the jacks, open the main air valve.
- Raise the gear using the front gear selector ie: move the gear selector to the UP position.
- Confirm the gear is up and locked (confirm 2/3 red lights)
- TURN OFF the main air valve
- WITH THE GEAR SELECTOR STILL IN THE UP POSITION, open the emergency air valve.
- The gear will most likely relax and some or all of the UP (red) lights may go out.
- Now move the gear selector to the neutral position. The gear should go down and lock.
- Confirm down and locked with 2/3 green lights.
- Turn off emergency air valve
- Squeeze the brake handle until all remaining air is depleted in the system. No "wooshing" sound when the brake handle is squeezed and released.
  (On Yak 52 W's and TW's, open the EMERGENCY AIR BLEED VALVE AT THE REAR OF THE RIGHT SIDE CONSOLE)
- Move and confirm the gear selector is in the DOWN position.  Move the slide lock to the right.
- Open the main air valve
- Move the gear selector to the UP position and confirm you have 2/3 red lights.
- Move the gear selector to the DOWN position and confirm you have 2/3 green lights.
- Turn the main air off.

That's it! Unless you want to operate the gear from the rear cockpit which adds 2 steps. Up and Down.  If you plan on operating the gear from the rear cockpit, FIRST put the rear gear handle in the DOWN position.  THEN go to the front cockpit and put the front gear selector in the NEUTRAL position.  Now raise and lower the gear from the rear cockpit.  Lastly, BEFORE you put the rear gear selector in the NEUTRAL position, move the front gear selector to the DOWN position.  This will prevent the air in the system (actuators and lines forward of the main air valve) from bleeding down because both gear selectors were in neutral at the same time and for a short period of time.

 

bullet

Wheel Bearings

        Thanks to Dave De Simone for this information.  The races and bearings for the Yak 52 wheels
        (mains and nose) have direct US replacements, available at any local bearing supply store:
      
                      Mains:  Timken 32208 and 32209, Nose:  Timken 32207.

bullet

Lubricating the main landing gear (YAK52 & YAK 50)

Most aspects of maintenance are obvious - grease ALL the grease nipples, grease the surfaces of the up-locks and wipe the struts with an oil-soaked rag regularly - but there is one item which is not so obvious. The up-locks are clearly visible but the down-locks are not. That is because they are inside the operating cylinder. If you are familiar with the way a compressed air chuck works, (a sliding ring holding a number of ball bearings against a groove in the air tool connector) you will understand how the down-locks work. It is exactly the same. The problem is that being out of sight and often bathed in moisture (from the compressed air) the balls tend to rust. The lock will then fail to engage properly so that either the gear will not lock down properly or it will not unlock to allow retraction.

The solution is to remove the air hose fitting from each end of the landing gear operating cylinder and a squirt a little air tool oil into the cylinder through each port.

Do this at least once a year to keep your landing gear in good shape.

 

bullet

Ignition problems - persistent mag. drop or misfiring

The weakest part of the otherwise robust M14P engine is its ignition harness. The high tension leads pass from the magnetos through a solid metal conduit to a point behind each cylinder and from there, through a flexible metal tube to each of the 18 spark plugs.

There are two very common problems which are quite easy to prevent but not so easy to fix. Firstly, especially in the Autumn, when the weather turns a little cooler, moisture condenses inside the flexible section of the conduit and permits arcing from the lead to ground. The second problem, which has the same result, is mechanical chaffing of the leads against the rather rough interior of the flexible conduit.

To prevent these problems, undo the nut which secures the flexible conduit to the spark plug elbow and insert into the conduit the straw on a can of WD40 (or similar lubricant/water repellant) Give it a good spray to both lubricate and dry the inside of the conduit. Repeat from the other end. (Where the flexible section joins the rigid conduit.) If your mag. drop was caused by moisture, this will fix it.

If abrasion is the problem, you need to replace the HT lead. An essential tool in this process is a high tension lead tester.  Undo each of the sparkplug leads and connect the tester to each lead one at a time until the bad lead is found. Replacing that lead should do the trick.

One last point.  Consider installing the automotive spark plugs and wires conversion kit.  This will eliminate misfiring due to the wiring harness forever.  Read all about the conversion kit by clicking here.

 

bullet

Low Oil Pressure
 

Starting an M14P for the first time when the aircraft arrives in the US, the oil pressure is sometimes very low. This is usually because an airlock has formed in the main supply line from the oil tank to the engine.   To rectify the problem, firstly undo the pipe coupling on the right side of the oil tank (viewed from the prop.) in the center of the tank. There should be a 90 degree elbow connecting the tank to the large dia. pipe that runs down to the oil screen housing. Slowly pour new oil into the disconnected pipe until it overflows. Reconnect the pipe. This "primes the pump". Secondly, fill the oil tank to at least the 14 liter mark on the dip stick. This ensures a sufficient head of oil so that it can gravity feed until a good siphon is set up. When you start the engine, you should have good oil pressure right away.

If the pressure is still very low, check the brown oil screen and temperature probe housing on the bottom of the firewall. There have been a number of occasions when the housing cracked, admitting air into the oil supply.

Finally, in cold weather, be aware that like many dry sump engines, the oil must warm up before the pressure pump will function properly. If you want to know for sure if the oil is warm enough, increase power a little (say 40 %). If the oil pressure drops, the temperature is still too low. If it stays the same or climbs a little, the oil is ready to fly.