Low power from hyd tappet engines

[xair1159]

Ref . 2200 hyd tappet engines, particularly when used in colder parts of the world.

 

Any comments on the points below?

 

• General lack of power, shown up by props that work fine on solid tappet engines being too much load for the hyd. engines, which gives low rpm’s and then wrong EGT’s. The factory is advising finer pitch props are required for the hyd. engines, which is basically admitting to a power reduction.
   
   
  
• Further loss of power, typically 150-200 rpm in cold weather, which may not occur in your sunny climate. Preheating the oil shows this appears due to the hyd. tappets giving reduced valve lift until oil temp is at least 90degC.
   
   
  
• Signs of piston/barrel overheating due to lack of cooling oil flow.
   
   
  
• Are the above just a limited batch problem?
   
   
  

 

 

 

There are also known barrel distortion problems caused by the base nuts giving blow-by and high oil consumption, plus stiff engines when hot due to tight piston/barrel clearance. Early – mid hyd engines went through several variations in cam duration and high/low leakage tappets.

 

Are current production engines actually better? They are supposed to have cured some of the above with the 260 cam, a further version of the tappets, reworked base nut installation and increased piston/ barrel clearance. Have they also fitted the 3300 pump or any other mods to improve oil flow?

 

If the current engines are improved and back up to solid tappet power output, any chance the factory will offer an update for the older ones, or is going back to solid tappets the way to go?

 

Intersted to hear any opinions,

 

Nick

 

 

[Tomo]

What oil are you operating in it?

 

 

[xair1159]

Tomo,

 

This problem is showing up on a number of a/c of at least two different types. The usual oil round here would be Aeroshell 15W-50 or W80 as per the book.

 

Nick

 

 

[facthunter]

Hydraulic Tappet Performance.

 

I personally am not a fan of hydraulic tappet aero engines. Period. I will make a few points.

 

The valve tappet, in serviceable condition, would not leak down quick enough for reduced lift to cause a power loss. If there was reduced lift due to the development of excess "lash" the lift action would be very violent, as the initial lift would be miles off the ramp on the cam, and put high inertia loads on the valve train, and cause a failure in a short time.

 

It is more likely that the valves are "riding" due to pump-up. Jabiru have made the point that adjusting the oil pressure relief valve too high can cause this. Over-revving can cause this in race motors but could be discounted as a cause in this application.

 

There is a possibility that the hydraulic set-up also puts a bit of extra strain on the crankcases. The decision to go hydraulic from the point of Jabiru can be understood. Lots of people don't want to be working on their engine and one of the reasons that the 912 Rotax is so popular is that you dont have to fiddle with the basic engine.

 

If you are using the recommended oils (Well there is really ONE now), I dont think you will find the cause there. Hydraulic lifters are not tolerant of foreign matter in the oil but usually only one will be affected at any one time and it is pretty rare . Nev

 

 

[xair1159]

Nev,

 

You're right, I should have said incorrect rather than reduced lift, pumping up and effectively valve float seems more likely with thick oil. One engine here is being used as a guinea pig and has been updated with parts supplied by the factory to see if it fixes the problem. These included the 260 cam and either high leakage or another new variation of lifter. It should be flying again this week.

 

As I understand it, the various cam profiles are much the same except for a quicker initial ramp as the hyd tappets have to "hit" fairly sharply for the valve to seal.

 

Nick

 

 

[Vev]

Nick,

 

Have a read of the July Jab Chat ... they talk about the mid range torque reduction on the hyd version, which has a 150rpm reduction in egine speed in static performance.

 

They also refer to a need to increase in leak down on the lifters too.

 

Try this link and go to Jab Chat news .... July news letter

 

Jabiru Aircraft&Engines Australia

 

Cheers

 

Jack