Have you ever broken a barrel base stud?

[facthunter]

Lean mixture

 

When you run a motor very lean there is unconsumed oxygen which is still there in a high-temperature environment to do damage by oxidising metals.

 

NO aero engine puts out the sort of horsepower per litre that high performance cars/ bikes do. (nor should they).

 

This lean out argument has been back & forth for a long time, and I've yet to see an engine that was damaged by running a bit rich. I've lost count of the number that I have been aware of died of excess leaning. If there is any doubt , err on the rich side.

 

All engines in aero applications run rich on take-off power, when everything is most critical.

 

My statements are not just theory. Nev...

 

 

[Guest J430]

Plenty of reasons why I am still happy with my Jab engine. Its going like a rocket, will be keeping it for a while longer too, and not because I can't afford something else, because I can!

 

Plenty of Rotax engines fail too......one yesterday possibly, and a nasty prang too. Plenty of Lycomings and TCM's have failed and killed people.

 

J

 

 

[Admin]

Hi Guys

 

I have edited some posts in this thread - my apologies but I hope it helps to keep it on track :) - thanks!

 

 

[Guest disperse]

sorry for the OFF topic... can you run the 2 jab engines on unleaded or are they strickly avgas thanks

 

Troy

 

 

[Guest J430]

AVGAS V UNLEADED

 

Jabs can be run on unleaded, and if you could get a true 98 all the time, without methanol, and it was fresh, I would. Trouble is its not a reliable fuel. It has a shelf life of a couple of weeks, it may or may not contain ethanol and its not that available.

 

For those that just do weekend sorties around the ridges and back home, keep only enough fuel and add fresh stuff all the time from a known reliable source, and you are fine. We fly ours all over the country, yes i mean all states, so its not so easy.

 

So we accept that the dirty deposits will build up, and thats the price we pay for a secure fuel.

 

J

 

 

[Captain]

Ian

 

No worries about your edits to my posts as "You da boss" of this Forum and one of the reasons it is as successful as it is comes from your control of the posts.

 

Mike (pelorus32) and I have exchanged PM's and all is sorted.

 

Regards Geoff

 

 

[Admin]

:big_grin:

 

 

[Captain]

Does anyone know whether titanium valves need special material in the seat?

 

 

[facthunter]

Seat material.

 

Titanium valves.

 

I think that it does require special seat material, and from memory, the material is very toxic. It is a special kind of bronze & one of the alloying elements is nasty.

 

Titanium is a very difficult metal to work with. It is expensive and hard to surface finish & may have unsatisfactory fatigue characteristics. Its main attribute in valve applications is its lightness, in very high revving engines to reduce the inertia loads in the valve mechanism and allow light valve springs to be used. I'm not sure whether it is the answer to your problem N...

 

 

[hfrensch]

Mogas shelf life.

 

I agree with the statement that its not a reliable fuel due to the reasons you described , but the shelf life of mogas is no different than avgas.

 

When buying from a oil company site the chance of getting the wrong octane rating is very small but it could happen where with avgas it will be the correct octane.

 

The main difference with mogas is that it gets blended every month to compensate for the predicted ambient temperature. The Fuel Volitility Index is increased as the temperature drops.THere are different fuel blends in all states due to the temperature variations.

 

In a extreme case if you used mid winter fuel on a hot summers day you would experience vapour lock.

 

Avgas is roughly the eqivalent of summer fuel therefore in winter it can be more difficult to start your engine.

 

In my previous life before retirement I worked in the engine development and testing for a car manufacturer and we would conduct extreme temprature testing both hot and cold. We would use test fuel which was fuel we decanted from our main tanks certain times of the year depending on our volitility requirements then had it annalysed for confirmation. This fuel was then stored untill required, the time frame before we disposed of the fuel if we did not use it was 18month.This allowed a sefety margin and I think fuel that is 2 years old could still be used.

 

Cheers Helmut

 

 

[facthunter]

Valve seat material.

 

The bad metal in the seat alloy is berylium. (from memory) nev..

 

 

[vk3auu]

Not only is mogas different from one state to another, but some oils are also different. For instance, a diff oil bought in Queensland may be formulated to operate in a higher temperature environment than a similar oil sold in the same package in Victoria.

 

 

[Modest Pilot]

Broken barrel base studs usually caused by slightly loose bolts (more than 1 thou) that result in fatigue failure. It's not perfect but the best you can do is check the bolts torque from time to time. Be sure not to have anything other than machined flat steel brackets (not alloy) under any bolt.

 

Source EAA Jan 1958 Sport Pilot