Jaba-who

Not sure where the issue of spark plug socket arose. I have a pretty standard one from repco which fits the 3300. It needed to be a thin walled one to fit in the recess with the CHT probe as well. But it was an off then shelf item.

With regard the throughbolt change. Just so everyone is aware, the 200 hours only applies to engines with >500 hours in service or >200 since overhaul. (But it is likely the 12 months rule will beat you on that). All others (like me) have only 100 hours (or 12 months) to comply.

The cost to me was just the postage. I phoned them up and although the invoice has the cost of $134 (2 sets of nuts ) they have done a credit as well with the notation "WARANTINF" which I presumed is a warranty of some sort. So I just paid for the postage. Very fair of them.

I am going to ask Jabiru later this week what it will cost and how long it will take so I will post here what they charge. I will have a period of about a month when I won't be flying later in the year so I think I'll book it in for then and they can do it then - maybe they'll have their induction chamber worked out too by then and they can change it as well!

I have had the same problem.

Noticed it would work fine for about twenty minutes then start to swing from about the right RPM to full deflection and back and then stop ( I am not sure if stayed at full deflection or if it dropped back to zero) and the LCD display went off.

When I started up next time it was the same. OK for a while then play up.

I pulled all the wire/connectors off and cleaned them and it worked well for a while then started again. Rechecked the wires and one of the wires had come adrift - touching but obviously off the post. Checked the push on plug and noted it was fairly loose fit. Crimped it down a bit tighter and all has been well since.

That would be worth a quick look.

Getting back to the original subject of the thread.

I got a bunch of new nuts from Jabiru and went out to the hangar today with another Jab builder to do the change over of nuts.

Well after 4 hours we had changed 4 nuts (the easiest ones) and have abandoned doing it myself. Changing the nuts that we did was difficult enough but I could see after those were done the rest would start getting more and more problematic. I could see the aircraft being in bits for the next month or so. This is the beginning of our flying season so I just don't want the plane to be unusable for that long.

I could also see some potential problems occurring that might make me wish I had never started. So we installed 4 new nuts and called it quits. I have till the end of the year so I will take it to Bundaberg (only a 6 hour trip for me from Cairns) and get them to do it.

The issues:

Access is the major problem - even though it doesn't look too bad it is actually very problematic. The fin cut outs are minimal so you have no room to maneuver and almost no room for standard tools. Forget using sockets, torque wrenches that fit into sockets and most standard shaped tools. The nuts in all but the front four or five through bolts will require removal of engine components to gain access.

Access to even the easy nuts: My crows foot wrench ( Kinchrome brand) doesn't fit on the new nuts properly when abutted against the minimally cut away fins. The thickness of the crows foot stops it turning freely so I ended up not being confident the torque was correct. (Going to go back tomorrow and redo the torques). The crows foot jams against the last fin when you do it up and I had to back the nut off to get the crows foot out then re-torque it (after cleaning all the locktite off and starting again!

I have now heard that other people have had to resort to making their own ring spanner/cut off & welded a square end to fit the torque wrench.

We have worked out that to gain access to the nuts at the back and underneath we have to strip the whole engine of all the add ons (exhaust outlets / Induction tubes, starter motor, oil filler hose/assembly/oil filter (and I have just done an oil change so have to drain and dump new unused oil).

I rang the local Jabiru mechanic who confirmed this and he advised borrowing his engine stand and take the engine out of the aircraft to do it as he finds it easier than trying to work around the airframe. That was something I hadn't planned on!

Studs - the front nuts on the right side and the rear ones on the left are studs not bolts and I started to get worried if they loosened while trying to undo the nuts then I would have a real problem of separating the nuts from the studs then reinstalling studs.

Undoing and tightening the nuts - They are really finicky from a practical point of view. You are constantly turning one nut against the other when doing it up or undoing it. This of course then undoes the other nut while you are trying to do it up.

We had to make a "tool" - a 3/8 bolt cut off with thread about an inch long then squared off at the far end so we could put a spanner on it. This bolt then gets screwed into some exposed threads in the nut/bolt to make a lock stud against which to turn the opposite nut. But they never work smoothly, the nuts don't run on easily half the time and the other half the time the locking action doesn't lock. So every seemingly small move took multiple attempts.

We had to redo both throughbolts twice because by the time it took to get the nuts on using the threaded tool then they would jam up and the wrong nut wound up and then backing them off & redoing etc etc etc - the locktite was cured and torquing just broke the locktite.

All in all, for me, the job is way bigger than the SB implies and I suspect just not a good use of my time to try it. And to persist with what could well turn out to be a poor job just doesn't seem to be a good use of time.

I'd much rather get the factory to do it properly.

I see your problem.

I guess you should talk to the engine shop at Jabiru and see if they can give you some idea just how far out the temps will be if you put them closer than the correct distance.

Ask for Don Richter he has the most experience with the engine. But I admit Don can be a bit blase about the figures at times. He told me moving the CHT sensor to the hole in the ridge between the plugs gave exactly the same figures as the ring under plug probe. But when I tried it they were fine for temps below 85 but then they diverged once the temp was above that. At operating temps they read 20 degrees low. All he could say was I had cured my high temp problem! Discussing this with a number of people who have followed the Jabiru advice they found the same thing. So maybe need to be circumspect about what he says.

But anyway maybe they do have some figures for EGTs taken at other distances and they just don't publish them.

Unfortunately this discussion is a bit moot.

1. Experience across a large number of Jabiru owners & internet discussion groups and Jabiru themselves (and my own experience matches) is that you need all 6 EGT probes.

The spread of temps (and thus fuel:air mix ) is so variable that if you don't have all six you have no idea what is going on. The cost of getting them all is far less than the cost of an overhaul every 400 hours!

2. You MUST put the probe at 100 mm - 120 mm from the flange (The manuals now seem to imply that anything in this range is acceptable) .

You are not just trying to get "some numbers, any numbers." You are trying see what YOUR cylinder is doing compared to a standardized cylinder on the test bed in the Jabiru factory. To compare your engine you must set it up the same as the test engine. Only then are you able to decide if each of your cylinders is running leaner, richer or same as that ideal engine. If Jabiru have their probes at 100 - 120 mm and then produce a set of figures for you to use - you must take your temps from the same place.

If you place them either closer or further then the temps you get will be meaningless, unless you have the capability of then converting those temps to what they would be if the probe was at the same position as the Jabiru test figures. Which is probably too difficult to do, especially when you can just put the probes in the right place to start with.

With probes at variable distances you are just deriving a bunch of useless numbers. Putting them in a mixed /common part of the exhaust line would be totally useless. You have no idea which cylinder is contributing what amount of heat to the mix.

The reason you need both is threefold:

1. EGT tells you about heat production. Heat is generated by the richness/leaness of the burn. The only way to tell how rich or not the cylinder is by measuring the EGT. (Not CHT)

2. CHT tells you about the final balance between heat production and cylinder cooling.

3. AND If you know about heat production (from EGT) then from CHT you can also derive how effective your cooling is.

(Why do you need 6 and not just 1?

Jabirus are notorious for highly variable distribution of fuel/air after the carburettor which is caused a known problem of swirling/spiralling air through the carb throat. Jabiru now recommend a baffle in the precarb induction tube ("Cobrahead") to make the flow more smooth. A group of us have done extensive testing with crossed baffles, grid baffles and single planar baffles with results that are definite but slightly variable for different engines - you have to try each in an individual engine to see what works best)

The second component is individual cooling of the cylinder (by whatever means - air flow, cooling fins etc) This is then reflected by the CHT. You can have a hot burning cylinder that has great cooling and the final CHT will be good. But conversely you can have a cool burning engine (good EGTs) but with poor external cooling and the final CHT will be high.

So in summary What I hope I have said is:

You need all 6 EGT and 6 CHT

You have to place them where Jabiru tell you to place them.

Vev,

Thanks for that. I didn't think to look in the 2200 manual - assumed it would be "same" as the 3300 manual. But that image is OK for what I needed. I just wanted something to visualize what the divider was like.

Thanks.

John

Splitting plenum

Does anyone have a diagram of the plenum chamber and the aforementioned divider? Or a pointer to a diagram if it exists in one of the jabiru manuals. I have downloaded all the manuals etc but can't find a diagram of the internal workings.(only a couple of very limited external views)

John

Mmm. You're right. Starting to look unattractive...

That weight would affect C of G and would be a real problem in a Jabiru. You would have to add more weight in the tail to get the balance back. Not quite 30 kgs because the arm is a lot longer but still probably another 5 or 6 kg. So add that in & you decrease the usable load by 30 - 36 kg. That's a significant amount.

I don't know that you would need a complete overhaul each time there was a top end problem might be limited to a single cylinder job but still is going to be a fair cost.

Oops. That's odd! When I first looked at the page my previous post was not there. Then reposted the question and it suddenly appeared. Sorry guys. Must have been a cached page. Disregard my last post!

With regard the valve guides and wearing down. I noticed a little oil had seeped out from under a spark plug the other day. Spoke to Jabiru and they suggested the valve guide might be worn allowing oil to by pass and get into the cylinder. They didn't actually say the Jab engine was prone to it but the way he talked I got that impression. I am in the process of getting a LAME with Jab experience to have a look at it. But I suspect maybe a need to pull the cylinder off and send back to Jabiru.

John

Tried posting this before but it didn't seem to make it there.

What problems with the top end have you seen or heard?

Mine is getting into that hour range and would like to have an idea on what to watch for.

John

What problems have they had?

Mine is coming up to 240 hours so is right in the time frame you mentioned.

Better know what it is I have to look out for.

John

Hi Gary,

Have a look at this website. Lots of info.

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