Vev

Quote

Now, the problem often arises where brakes don't perform to specs and overwhelmingly the most common cause of this is brake fluid that is not doing it's job and this is governed by age, type, quality and use. Brake fluid absorbs moisture and for every application of your brakes, degrades in performance. Hard frequent use will effectively 'wear' out your brake fluid.

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Hi Relfy,

Can you explain what happens to brake fluid during "hard frequent" braking that "wears out" brake fluid?

Cheers

Jack

Andy,

These guys make bakes for Jabs including a differential braking set up if you want a Rolls-Royce solution.

Matco Mfg | Welcome

Cheers

Jack

good one Peter

Cheers

Jack

A mate of mine (Ken Ingersoll) is a Corvair expert and has been importing these engines from the US since the mid 60’s were he made adaption kit for VW conversions.

Over the past 2 years he has been developing an aero version (he calls it a Corvaero) for his Long-Ezi.

He has done a great job on the engine and has sorted out all of the problems one usually hears about with Corvair aero engines.

He has used the 145 cubic inch engine being the smaller of the two available (the other being 164 inch) and has mounted the alternator and starter to the rear; this has pushed the c of g back and has reduced the frontal area of the engine.

He has also developed a very robust PSRU (prop speed reduction unit), as the direct drive engines rev too hard for an efficient prop speed and end up with a narrow power band to operate when you pull the power back. He says that his PSRU allows the engine to operate at optimum power setting and has a broader power range and a more progressive power curve for different rev settings. He says the engine can develop a torque value simular to a 0320 of up to 150hp and only weighs 250 lbs ish.

He has also designed a heated manifold and is running an Ellison TBI and hasn’t experience any carby icing issues in his testing date.

He has one of his engines on a test stand with a Bolly 3 blade prop and is running test on it now before he mounts it into his aircraft.

I spoke to Ken this morning and he is happy to chat to anyone that wants to know more about Corvair engines.... He's down at Baxter in Victoria.

If you want to PM me I can send you his contact details.

Cheers

Jack

Bushpilot quote - "The J120, regardless of category, is 430 kg - same as the old ST models."

Chris,

Am I not getting a point you are making? Are you sure about the 120 MTOW ... I thought it was 500kgs?

Cheers

Jack

Bush Pilot, I always hand pull through to make sure all feels normal and then crank with mags off and look for the oil press needle to lift off the stop a little before running the engine. I'm sure it helps reduce wear at start up.

Spacewalker, what viscosity oil where you running in that engine when you ran your pressure tests?

Cheers

Jack

Tomo,

Re Ether and problems with using it in aero engines.

These commercial available sprays are usually made up of 60% Mogas, 30% Diethyl Ether and 10% Ethanol … give or take a few %.

Basically these are designed to increase the cetane number in diesel application, which is gabout helping start a cold engine where the fuel quality is low and in very cold climates.. In Oz we have high quality diesel and it doesn’t really get that cold, therefore it’s a little more difficult to make an argument to use these products.

When you use this stuff in an aero engine it has the same effect of reducing the octane and it speeds up the flame burn and can cause detonation .. Not a good thing for any engine any time.

The chemistry can also impact on seals and other components and can cause plasticisation (make thngs go soft) of seals, o rings etc.

Hope this helps.

Cheers

Jack

I can’t say I love the Bing … the whole carby feels like a compromise of lesser evils and one tends to run the Bing mostly too rich to keep temps down across the working load range ... this is the only way to maintain acceptable levels on the hottest cylinder.

The idea of keeping things simple (no electronics) yet provide the pilot with the opportunity to adjust the mixture in flight is very appealing to me. It would be nice to be able to keep things rich and cool in climb and then adjust from your EGT readings to get set up for optimal cruise mixtures… currently with the Bing you end up with it too rich everywhere less you run the risk of burning a valve and cooking your top end.

I have had a look at the XXXXX, which looks like a copy of the Ellison TBI other than the regulator is remote, where the Ellison has the reg as an integrated part of the body. They both use a fuel bar which has many very small holes drilled along the delivery fuel tube (sometimes called a fuel bar) that becomes progressively exposed as a flat slide opens… the slide process is simular to a motorcycle slide on a 2 stroke carby. The fuel delivery volume is determined by the fuel bar position (which is controlled by rotating it ) and the angle of attack of the air passing through the throttle body…. By remotely (from the cockpit) rotating the fuel bar you change the mixture and set things up just where you want. The slide controls the volume of air entering the throttle body as well as exposing more of the delivery bar as it slides up. They both have a conventional idle circuit but they do need to be primed to get them to come to life as there is no fuel bowl to store fuel. I guess this is one of the real down sides of the TBI is one could over prime and end up with a lot of fuel over flow and increase the risk of fire at start up.

Intuitively (I’m guessing) the XXXXX approach may be slightly better at creating a more homogenous fuel/air distribution in the atomisation phase and therefore a reduction in the variations in CHT/EGT temps across the cylinders owing to a more even air/fuel mix… may be someone out there can verify or dismiss this my assumptions???

Personally I am still sitting on the fence and waiting to hear more reports from users and get some hard facts regarding performance before I dump the Bing…. However there are a lot of these out there, just not sure how many on Jabs and how they are going?

Cheers

Jack

Agree Tomo ... as a general rule it's aways best to bend as close to the time of use and if you have to store any fuels do so in full high quality containers in a cool place for short preiods.

Old saying ... "There's no fuel like new fuel and old fuel is like no fuel".

Cheers

Jack

There are several ways for fuels to go “off” however in this context I think people are concerned about octane depletion when using Mogas compared to Avgas.

In very simple terms, Avgas has lower volatility and the components that give it its octane doesn’t evaporate off very easily … whereas Mogas has lighter more volatile components which evaporates more quickly thereby depleting the key octane boosting hydrocarbons in the process.

High quality well sealed container kept away from heat will slow the speed of octane depletion in Mogas. Unfortunately aircraft fuel tanks aren’t the ideal container … best not to store for too long in your aircraft.... fresh is best.

Cheers

Jack

Thx DJP,

Good stuff

Cheers

Jack

G'day Matt,

Very well said and written ...

In my mind, there was never a monument built to a critic.

Lets all hope your letter strikes a cord of unification for all that want to fly.

Cheers

Jack

Skyscooter,

As mentioned in a previous post ... the push rod oil feed to rocker gear is already in production on current engine. In fact I retro fitted this system to my thick finned 2.2 head 2 weeks ago.

Cheers

Jack

Hi Phil,

The sail cloth was self adhesive … it comes in a roll and has a paper backing over the glue side which you just peel off before you use it.

Cheers

Jack

Hi Phil,

I have replaced mine twice … first time I used duct tape but it had short life. The second time I went to Whitworth Marine and bought some rip stop sail cloth in a 50mm x 5m roll .. very nice stuff and it’s UV stable too.

Cheers

Jack

I had a good conversation with the South African Jab distributor this evening who has been inserting K liners into Jabs for a couple of years with very good success. He said he has seen engines comfortably run out their 1000 hrs without problem.

However, having said that, he believes that lean cruise burn is the root cause in terms of premature valve guide wear; despite the introduction of rich kit from Jab he says more fine tuning is required in most applications. He is of the view jetting can vary between aircraft owing to minor variations in set up and use… he said to target < 700 deg C EGT at 2750 rpm (being the transition phase on the needle) is good place to start to extend he life of valves and guides.

Any thoughts about these comments are welcome?

Cheers

Jack

Here's a handy file from Jabiru that give you all you need to know about oil dip sticks and oil levels.

Cheers

Jack

Dip%20Sticks%208A035A0D-1.pdf

Dip%20Sticks%208A035A0D-1.pdf

Dip%20Sticks%208A035A0D-1.pdf

Hi Tomo,

Not sure of the a/c you hire have a EFIS fitted ... many of these have G meters as part of their fuction... this is not often known.

Cheers

Jack

Hi Nick,

I can’t say I have seen anything that has excited me in terms of engine breather improvements. There have been a couple of attempts at fitting inline oil condensers before the oil/separator, but these in my view could create more problems in terms of back pressure and therefore higher crank case pressures.

I think the only sure fire improvements to reduce crank case pressure in the 4 cylinder is the larger crank case sumps as fitted on the latest model engines.. However this will be an expensive retro fit upgrade.

Others may know more???

Cheers

Jack

For what it’s worth, I have decided to replace the exhaust valves owing to excessive seat wear and as a precaution … I’m concerned about how much fatigue the exhaust valves may have suffered with the amount of guide wear… the valve are as loose in the guides as Tiger Woods wedding band…. no need to measure the defection in this instance.

I also need to measure and compare the new replacement oil fed rockers (they turned up in the mail today) with the old splash/mist oil rockers as they look to have a different geometry…. This may help reduce the side loading on the guides. ..I will let you all know if different once I measure them.

Cheers

Jack

What an interesting video clip … thanks for sending JR.

My understanding … there is insufficient free air volume in the crank case (see Jabs Service Bulletin JSB 013 -1) which causes a positive pressure and is compounded by a low pressure in the rocker chest from the inlet value guides allowing air to be escape through to the inlet induction. Jabs fix was to get us to all to drill 3/23 holes through the heads to atmosphere to vent the rocker chest… the hole is on the pressure side of the ram air cooling side. Later model engines had deeper sumps which increased the free air volume in the crank case and reduce pressure build up… they also increased the drain back holes at the base of the push rod tubes to improve drain volume to the sump.

I agree again with Nev’s comment … you really don’t need that much oil to lubricant the rockers. In my mind, it’s more about getting the lube into the right place and having it drain away quickly thereby taking away the heat without damaging the lubricant. A long dwell period of lubricant caught in the rocker box just exposes the oil to possible burning and oxidation as well as of loss of the lubrication characteristics. I don’t really think I’m telling anyone anything new as Jab have publicly documented this issue and make this point quite clear in their Service Bulletin.

However I am concerned that their vent fix doesn’t keep up with the pressure differential when the guides wear, which in part starts a damaging cycle of wear on the valve train. Hence one of my initial questions if valve stem seals would have been a possible fix to allow the oil to drain and save the rocker gear despite valve guide wear.

Cheers

Jack

We fitted K Liners to our 2200 engine about 30 hrs ago and all seems good at the moment, I will remove a head in another 70 hrs or so to check whether it has been a good thing to do or not, but at the moment we are very happy.Brian

Hi Brian,

Thanks for your feedback mate .... do you know what type of K liners you used? What made you decide to use them.. did anyone recomend them to you?

Look forward to hearing how things go?

Cheers

Jack

No question in my mind Tomo that the oil is come via the giudes ... also seeing way too much carbon build up on the piston crown and ring lands too.

Nev, I have found wear on the rockers shafts and valve stem contact points. Jab has sent me an upgrade with new hollow push rods and oil gal rockers to improve lubrication around these components. I think the geomertry looks NQR and agree with your thinking that this could be one of the reasons for a short guide life.

I'm also concerned about heat as well as this may place too much thermal load for the lubricant. I dont think it is draining back fast enough to the sump from the rocker chest, despite the factory upgrade to drill a vent hole. I think the warn valve guides are causing a pressure drop in the rocker chest via the inlet guides as it sucks the oil through???

Cheers

Jack

Thanks guys.

The originals guides are aluminium / bronze but seem to have a very short life 300 – 400 hrs … not sure if they are too soft, get too hot or bad geometry of the rockers???

Despite still having a good compression test and leak down result the valve defection is beyond serviceable limits. You can see the amount of carbon build up on the back of the inlet valves owing to oil bypass, which to me suggests that valve stem seals would have been a good idea in the design. I’m at a point in time I need to replace my guides and I’m looking at the alternatives to improve durability as well as manage oil bypass (may be with valve stem seals).

I’m not keen to play pioneer or test pilot but I hear there are engines out there with this mod and would really like to hear how things are going?

Cheers

Jack

At one of the engine forums at Temora I heard about an L2 from WA talk about using K Liner inserts in Jab value guides. I presume this is the same process used on taxis when converting engines to LPG to make the guides more durable?

The L2 at Temora said it has fixed the valve guide wear issues and reduced oil burn to very low levels.

By the way ... why doesn't Jab run valve stem seals?

Anyone out there tried K Liner guides replacements or have a view?

Cheers

Jack