Jab engines

[Old Koreelah]

4 hours ago, RFguy said:

OK, understood. I'll fly up there  and say hello when I get the 230 back together.. cheers

Glen you’d be made very welcome, as would any visitors. Just let me know when you’re coming and we’ll kill the fatted calf...chicken?

[RFguy]

very good!. I'll stay in touch, cheers.

[turboplanner]

On 25/02/2021 at 8:18 AM, facthunter said:

It will show bore scratches and rust and that's about all.  Nev

If you can see that, you have an indication of whether there's a problem.

If the rust is just powdery the rings will scrape it off.

If the scratches are shallow you might not be losing any seal because they fill with oil.

If you see mild bore scratches and rust and the engine is turning over ok, then do a compression test. That will show up any leakage due to the cracks or rust ridges.

For racing engines I normally hand rasp the sides of the piston which allows the piston to hold a lot more oil, helping to cool the sides and augmenting the ring seal. (I didn't just think this up one morning, it comes from Phil Irving, one of the best engine designers in the world). However, remember that racing engine pistons are pulled out after a very short life, so I wouldn't recommend doing this on a standard engine, I just metion it to show that a scratch in the bore may not necessarily be causing a loss in compression.

[RFguy]

Hi Turbs, you make a good point on the engine runtimes.  As a kid with Datsun engines for track I used to run a pipe cleaner through oil galleries and actually removed quite alot of rubbish , in attempt to improve oil flow. Those internals were generally cast (rough) finish that I think tended to catch and buildup.

 

What is state of art these days for block lube paths ? I used to (30 yrs ago) have dreams of aux high pressure oil sprays up the bottom of the piston and walls from a separate oil pump ..... oil foaming and bubbling  was stuff I didnt really understand how to avoid/correct then. glen

[turboplanner]

On 01/03/2021 at 7:01 AM, RFguy said:

Hi Turbs, you make a good point on the engine runtimes.  As a kid with Datsun engines for track I used to run a pipe cleaner through oil galleries and actually removed quite alot of rubbish , in attempt to improve oil flow. Those internals were generally cast (rough) finish that I think tended to catch and buildup.

 

What is state of art these days for block lube paths ? I used to (30 yrs ago) have dreams of aux high pressure oil sprays up the bottom of the piston and walls from a separate oil pump ..... oil foaming and bubbling  was stuff I didnt really understand how to avoid/correct then. glen

There are still engines with flow problems in galleries and manufacturers select oils which will handle the problem, or specify more frequent oil changes to do the equivalent of your pipe cleaner. I once connected one bank of a Ford 272 cu in V8 from a gallery with good flow to overhead gear on the opposite side with a piece of steel brake line. Worked like a charm.

[facthunter]

 A couple of places you may have trouble with 

(1) where a bearing is used to meter a low flow it will have a part cut out so the flow is interrupted IF the bearing gets worn (as in some OHV Fords Y block) you get very little oil to the rockers.

  (2) Another spot is the OHC Pinto motor( 2 Litre Fords" where there are small oil holes to spray the Cam lobes located in a larger pipe'. Mostly oil galleries except Hudsons and T models were machined in the block and have plugs each end which should be removed and all checked for grunge at overhaul time. De Haviland have large caps on each side of the crank throw where it's bored through the place where each crank pin is, Mainly to lighten the crank and will sludge up due centrifugal action  just as a milk separator will.. Nev

 

[Mhalc]

I have completed testing on the test stand of a supercharged Jabiru 3300.  The tests were conducted with a Bing 94/40 carburetor and Rotec mkII 40mm TBI.  With a modified fuel system the Bing operated well with manifold pressures to 36 inHg generating ~137HP.  With the TBI the engine operated well with manifold pressures to 38 inHg.  

 

I have started installation on my aircraft (Gen4 3300, with new pistons as part of a Jabiru recall).  Ground testing should start in a week or so, and when all checked out, flight testing.  Short term goals are to identify practical operating manifold pressures (target is 40” MAP takeoff power and 34-38” cruise), validate boost control computer software (SL thru 16,000’ DA), and aircraft performance. 

 

A short video of the last ground test with the boost control computer configured for boost pressures of 3psi/36”MAP

 

https://newtube.app/N530MH/qZqXzbc

[RFguy]

Nice

but...

Do you know if the preload on your thru bolts is sufficient  when operating at > MSL atmo ??? 

[Mhalc]

The test stand engine is an early Gen2 and I monitored through bolt and head bolt torque for the duration of the ground testing.  Neither exhibited any change during the test cycle.

 

BMEP increased by ~18% at the tested boost levels, I am more concerned with piston/wrist pin wear.  I expect the overall life expectancy will be reduced (as with any performance modification) and plan top end inspections as I transition from flight test to general use.  I’ll need to accumulate some real world hours before I really know the impact.

 

To answer your specific question, I did not calculate force caused by an increased BMEP/IMEP as it translates from the crank->cases->through bolts.  But was and will be monitored during the remaining test phases.

[RFguy]

Hi

very good

Most calipers can measure across the top thru bolts as to measure bolt stretch. 

Hard to do the lower ones..

 

If you only have 18% bang increase, that would be inside the preload if the preload is right....  (I've used the ARP Ultra torque lube and used stretch for tension).

cheers

 

[Mhalc]

The goal here is not gobs of HP, but altitude performance.  Keeping a modest HP increase (14%-20% at SL) through a wide altitude range.  In my case I routinely fly between 9,000’-13,000’ DA.  The modest HP increase and critical altitude of ~16,000’ DA I hope to see a 25-30kts increase in cruse speed (flight tests this month will tell!).

[facthunter]

Supercharging doesn't always increase internal loads. It's a more sustained push due more combustible mass of  stuff. HEAT is you main consideration. The inlet charge is heated adiabatically by having it's pressure increased and the POWER put out also increases heat correspondingly.. . Nev

[Mhalc]

That would be true where if the supercharged engine was operated as a “normalizer” where boost pressure was regulated to 30 inHg (which is an option for this system).  Otherwise boosting an engine increases its effective CR which develops higher BMEP/IMEP, hence the concern for piston/wrist pin wear.

 

Yes, heat is a concern.  As for my gen4 3300, the first 150 hrs have demonstrated its ability to run cool and shed heat nicely.  Burning more fuel generating more power will surely increase the heat as will the compressors inlet air temp.  With the TBI and Jabiru’s fixed timing the only protection I have against “knock” is the boost controllers monitoring of the inlet air temp’s and reducing/eliminating boost if I get any where near the knock limit.  In addition I only use 100LL fuel which will also help control “knock”.

 

For simplicity and based on ground testing only, I have not install an intercooler but have provisions for installing one if needed.  I know I am leaving some HP (and increasing heat) on the table by not installing one now, so I’ll see how flight testing goes.

[facthunter]

Run cooler plugs also.  The intercooler is difficult and bulky. Have you considered water meth injection for boosted take offs? It may eliminate carbon build up also. Nev

[kgwilson]

I haven't visited this thread for a while so a couple of comments. Jab 3300A Gen 3 with standard Jab airbox connected to the carb via a custom made sideways mounted bulbous Cobra Head with adjustable vane for directing air L/R into the carb inlet.

1. My borescope has a tiny round mirror attachment which is angled to look back at 170 degrees or so. I can rotate the probe 180 degrees to see the whole head and valves. I've always run Mogas so it is pretty clean.
2. I have never noticed any change in rpm with carb heat on runup but did when I was on base one time & a C172 whose radio had failed flew under me on final & I had the carb heat on. I forgot about it & went full throttle. The engine would not develop full power & then I realised carb heat was on. Pushed it off and instant power so it does work. As for mags there is only a noticeable drop when checking at idle, none at 2000 rpm runup.

[Mhalc]

The first 2 test flights of a supercharged Jabiru 3300 (Gen4) are complete.  Still several issues to work thru but in general the overall performance is working out to be with in 5% of the design targets.  With modest boost levels (32 inHg) @ 5000’ DA my Lightning cruised at 171 mph (up from 145 mph).  The fuel consumption increased ~ 1 gph, which is consistent with its normal 25 mpg running normally aspirated.  In addition the takeoff run and climb performance improved by ~20%.  These are very preliminary numbers and more test flights will zero in on the final performance levels.

 

The next series of tests will be conducted with higher fuel pressures, allowing higher boost levels.  I plan to limit the total boost levels to 36 inHg which should yield 180-187 mph between 5,000’ and 12,000’ DA.

 

https://newtube.app/user/N530MH/91LQNga

 

[Yenn]

I just had my oil pressure drop to near zero. It has always been very good, mid way into the green, but the other day I started up and it came up to below the green then gradually sank back to near nothing. It took a few days for me to get another gauge hooked up to check if it was the gauge or a real drop in pressure. The non electric gauge shows good pressure even at low rpm, so it was a faulty gauge or sender. Replacement bought and should be going OK tomorrow. The original gauge was a Vdo and it seems the failure mode is just dropping of indicated pressure, even though the real pressure stays high.

My past experience with gauges was that they usually failed high or nil, not varying. You live and learn.

[Old Koreelah]

8 hours ago, Yenn said:

I just had my oil pressure drop to near zero...

It took a few days for me to get another gauge hooked up to check if it was the gauge or a real drop in pressure.

Yenn I have a separate oil pressure gauge to test the VDO; so far they agree.

I also fitted a low oil pressure warning sensor (set at 180kPa) in the hole just around the corner from the standard oil pressure sender. Yesterday it  momentarily lit up on late final, with the engine idling. The factory tells me the pressure in that gallery is slightly lower.

[kgwilson]

I had a VDO gauge sender fail when it went to 500kPa on climb out one day, then returned to normal only to go crazy again when I was taxiing in. Initially I didn't suspect the gauge or sender & thought it may have been the pressure relief valve. Senders seem to be a bit problematic. The sender on my Westach carb temperature gauge failed along with both EGT senders. Before I even got to replace the carb temp sender the indicator needle broke off the gauge rendering it useless so I haven't even bothered replacing it.

 

All of the other gauges I have are VDO automotive and have functioned faultlessly. Given the cost of Aviation gauges you'd think that they would be more robust.

[facthunter]

Oil pressure senders are notorious  for failing and probably always have been.. Nev

[Old Koreelah]

3 hours ago, kgwilson said:

Before I even got to replace the carb temp sender the indicator needle broke off the gauge..

My fuel pressure and fuel flow gauges (bought second hand from Maj Millard) have worked faultlessly for over a decade, but the fuel pressure needle flutters about, presumably with the engine pump pulses.
I’m sure it‘ll break off one day.
One thread suggested installing a ‘T’ junction and a short length of hose full of air to dampen or remove those oscillations.

[facthunter]

If you have a diaphragm to the air reservoir and a restrictor to the gauge that will work fine.   Nev

[Yenn]

GA aircraft usually have the oil pressure sender mounted on a manifold away from engine vibration purely because they know the vibration caused sender problems. To do that you have to have a flexible connection between manifold and engine something else to go wrong.

[skippydiesel]

44 minutes ago, Yenn said:

GA aircraft usually have the oil pressure sender mounted on a manifold away from engine vibration purely because they know the vibration caused sender problems. To do that you have to have a flexible connection between manifold and engine something else to go wrong.

Pleasure explain how mounting on a manifold (usually connected solidly to the engine) will reduce vibration ?

[jetboy]

wearing out of oil pressure senders on the jab has been going on for 2 decades - the fix is to shift the sender to the correct location i.e. after the external oil cooler and the oil filter.

yes the pressure reading will be lower but it is the gallery pressure not the pressure spikes straight out of the pump and before the restrictions of the external cooler and hoses that is the more important reading.

I fitted a switch to the original port wired to the idiot light for backup indication, when the original sender packed it in - pic attached.