Jabiru Letter #149 - through bolts

[old man emu]

Engine leakdown checks have to be done with the engine at operating temps (warmed up). Doing them cold is a waste of time. ...

Gee! I don't recall saying that the leakdown test was done on a cold engine. I just mentioned that because of a failure in that test, we had the aircraft stood down for a while, and decided to kill two birds with one stone. However, the decision was reversed for reasons I don't know (I was on days off when the decision was made), so the through bolts were not replaced, and I didn't follow up on the story.

 

I have to agree with Maj Millard that the manufacturer's requirement to use a lubricant on the threads of the through bolts did raise some eyebrows in our shop.

 

Anyway, the true value of nut torques as determined by the use of any torque wrench can vary widely, even if the torque wrench is calibrated every time it is used. Given that statement, hte best one can say about using torque wrenches is that they prevent overtightening of nuts.

 

OME

 

 

[Modest Pilot]

My engineer brother put me on to the new electronic strain gauge activated torque meters. I bought a 3/4" drive certified one (0% to +1/2% error) on the net that does 20ft/lb to 60 ft/lb for $50 bucks. Gives LED warning lights green, orange , red as well as the LCD read out. Stores the last 50 readings. I agree there are better ways to tighten bolts (check a Falcon auto manual on how to tighten the head bolts and you will get the picture) but you may as well start with a decent tool.

 

 

[Brett]

I wouldn't be too worried about how falcons do their head bolt tension as they use a special head bolt designed to stretch (Torque to yield if I recall correctly) and keep the tension correct in a hot and cold situation ,actually in auto engines I find it all the time,, mostly in head bolts but a lot of late model toyota's and things I have seen on conrod and main bearing bolts ,,,,, I doubt the through bolts used in Jabs would employ this type of method to keep them tight,,,although I have no idea ,, so I guess a correct torque procedure would be critical ,even to following the instructions down to the letter like if it says use oiled threads or something like that ,, I've never seen one of those torque wrenches before that you mentioned ,,, they sound cool :)

 

 

[Modest Pilot]

All bolts stretch it's just a question of how much, it depends on a lot of things including the tempering. A lot of time and money is spent finding out how much! If you think about it, an aircoooled aircraft engine has a whole bunch of different metals madly expanding and contracting a different rates. The pretensioning and a calibrated turn would be ideal. I guess cost will rule it out for low volume production.

 

 

[Jaba-who]

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.

 

 

[Guest Maj Millard]

Mmmmm interesting........................doesn't sound like much fun for the average guy. The fact that you can't even use a standard spark-plug socket on a jab spark-plug doesn't install too much faith in me. It all goes right back to the initial engine designer.................has he kept the basic field maintainer in mind when it comes to basic maintenance.................Mmmm........NO !!..........................sorry not good enough IMOP...........................Maj....

 

 

[Thruster87]

Mmmmm interesting........................doesn't sound like much fun for the average guy. The fact that you can't even use a standard spark-plug socket on a jab spark-plug doesn't install too much faith in me. It all goes right back to the initial engine designer.................has he kept the basic field maintainer in mind when it comes to basic maintenance.................Mmmm........NO !!..........................sorry not good enough IMOP...........................Maj....

My standard plug socket fits just right, no problems at all.Most items that come under the category basic field maintainer I find all easy to reach and service. [Couldn't let this one go] Cheers

 

 

[Guest Maj Millard]

OK not a problem, the one I have used on just about everything else for years certainly didn't fit a 2.2 Jab recently............................................................................Maj....

 

 

[jetjr]

Um ...... yes Id agree, in terms of everyday maintenence including 100hrly the Jab is hard to beat. Nothing special needed.

 

After long discussions with Jabiru there is still a feeling this nut upgrade isnt critical (Im talking about 6 cyl though). I outlined the cost of the nuts isnt the issue but the installation of them. One look sees this as being very problematic Especially without replacing with longer through bolts - which requires full removal of one bank of heads and barrels. They do specify a Snap On crows foot which maybe is smaller than Kinchrome version.

 

This really is an "at overhaul" upgrade, brought forward by pressure from customers and forums like this. Now as an SD we all have to comply in next 200hrs. Any idea what this work will cost if done by L2?

 

 

[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!

 

 

[bushpilot]

..... I have not seen one jab engine that does not require constant tinkering/ adjustment and I havent seen one make TBO yet! over.,... end rant!!!!

Just because you "haven't seen" them doesn't mean they are not out there. Of the Jab motors serviced by our L2 (all have done / are doing circuit work) :

 

* 3 have gone full TBO

 

* 1 has 840 hours with nothing more than normal services

 

* 1 has 400 hours with nothing more than normal services

 

* 1 has 340 hours with nothing more than normal services

 

 

[Jaba-who]

"Just because you "haven't seen" them doesn't mean they are not out there."

 

I have to agree with bushpilot.

 

Like everything, the problems and the unhappy comments are the things that get published or talked about. The mundane and happy get kept quiet. Seems from what I hav heard there are a lot that do get full time. Mostly hard workers being used commercially. The ones that get treated very gently(which is a lot of the total) tend to play up. But I can assure you that happens in Lycomings and Continentals as well. I paid a fortune to get all the cylinders flexihoned out on a Lycoming because it sat in the hangar too much. A friend just got his R44 helo all new cylinders cos he didn't use it enough.

 

I was on another forum a while back where someone made a similar comment that Rotaxes never gave problems. That was followed by pages of comment from rotax owners that that was not the case. They give lots of trouble to some people, in some situations. Some people had very little trouble but there were enough people with problems to be able to say that they aren't immune either. Though just what the stats really are I can't say. Would be interesting to have an accurate survey.

 

 

[Thirsty]

I don't believe Jab or Rotax know the true stats. I reckon most people that have problems probably just fix it and get on with it without mentioning the issue to the manufacturer or RA-Aus.

 

 

[Jaba-who]

Quote "I don't believe Jab or Rotax know the true stats. I reckon most people that have problems probably just fix it and get on with it without mentioning the issue to the manufacturer or RA-Aus."

 

Yep. Agree entirely. I know for a fact that plenty of minor problems get fixed or worked around and then never mentioned to Jabiru. Can't imagine it would be any different for Rotax.

 

 

[Jaba-who]

We aren't talking about issues that are always major. Or What's major to one person may have been nipped in the bud as a minor change by someone else, who never realized it had the potential to become major. Plenty of people fix things, wonder whether it is worthy of reporting, then forget or don't bother.

 

Often people hear of an issue, fix it and assume the whole world knows about it and doesn't need to hear about their encounter with it.

 

 

[Guest Maj Millard]

Lets not forget that the 912 is used and accepted the world over, and there are many more thousands of them out there compared to the Jab, which has not been accepted the world over, and in some countrys just the opposite !!..

 

There really is no comparison as far as total numbers go, as the 912 has been in service for around 20 years now also. Rotax does keep tabs on what the engine service is like, and rountinly incorporates successfull upgrades, such as the recent new oil pressure sender, ring engine mount, and ignition soft-start module. Very few of the internal major components have required changes or upgrades, as they were up to the job right from the start, due to proper design........................................................................................................................Maj...

 

 

[Thirsty]

Here's a very well written response to someone on another forum doing some jab bashing - http://www.sarangan.org/www/mhonarc/mharc/html//europa-list/2010-01/msg00145.html

 

I agree with what this guy says - it's all in teh maintenance and operation. Not all the time of course but a large proportion of engine problems come down to poor operation/maintenance. I don't really believe Rotax are THAT much better than jab engines. Much of what we say and read on these forums is hearsay and second hand and just because we don't hear of a lot of Rotax issues doesn't mean they aren't happening. I'm never going to be able to convince someone who believes jab engines are crap - and no-one is going to be able to convince me Rotax engines are bullet proof and never break.

 

 

[brilin_air]

Mmmmm interesting........................doesn't sound like much fun for the average guy. The fact that you can't even use a standard spark-plug socket on a jab spark-plug doesn't install too much faith in me. It all goes right back to the initial engine designer.................has he kept the basic field maintainer in mind when it comes to basic maintenance.................Mmmm........NO !!..........................sorry not good enough IMOP...........................Maj....

Sounds like you need to get a full set of proper spanners Maj you can't condemn something if you can't fix it properly

 

Brian

 

 

[frank marriott]

I was talking to the factory this morning and they stated that if you book into the factory [allow a full day] they will fit the new nuts free of charge.

 

Frank

 

 

[Jaba-who]

Yep. I did the same. They said they are setting aside a full day for each engine. But they are not able to start them till mid May. They are taking bookings for dates after that. As already stated cost is free.

 

I also asked if they could put the new plenum chamber on at the same time. The guy I spoke to said they were about $600 - $700 for the parts. They are not yet a recommended replacement but the engines with them on were getting better narrower spread of figures so were probably going to be recommended soon. I have till the end of the year so will probably wait to see how the plenum chambers go and get them done at the same time.

 

 

[ianboag]

Much of what we say and read on these forums is hearsay and second hand

Now there's a challenge. Here is the story of five Jab-powered planes on our field in the last two years.

 

A 3300 (solid lifter) in a J200 had a pot go soft at 200 hours. Honed and ringed while I owned it. I sold it and it is now having a full top overhaul at 400 hours.

 

A 3300 (early hydraulic lfter) in a J230 burned an exhaust valve at 160 hours. Others were all pitted and had to be replaced. A through bolt stripped during reassembly. Owner had built the kit and installed the engine that came with it.

 

A 600-hour 3300 (solid lifter) had through bolts strip during reassembly.

 

My J160 (early hydraulic lifter) that I bought from the Adelaide Soaring Club with about 900 hours on the engine. It almost made it to 1000 hours. The top overhaul we just did includes cylinders and pistons and a conversion to the latest lifter configuration. It was actually the second engine in this plane - the first one had been replaced at 500 hours because of case fretting.

 

I owned/own and fixed two of these aircraft and watched the other ones being fixed.

 

Then there is a J160 (early hydraulic) which has done 220 hours with no visible issues.

 

I can think of four 912-powered aircraft on the field which in the same period have pretty much just had petrol fills and oil changes and just flown ....

 

Cheers IB

 

 

[Jaba-who]

Can you give a breakdown of how many had full suite of EGT and CHT sensors and what their temps were like in the lead up to the problems?

 

If they had a full set of each and the temps were all good then it gives a different indicator of reliability (or lack thereof) compared to if they were just running in an unknown state or if they were known to be high.

 

 

[ianboag]

I suppose having 4/6 gauges for EGT/CHT is a good idea. Someone should tell the factory .....

 

J200 #1 was built by the NZ Jab agent at the time. It has a single CHT and a single EGT gauge. The new owner is fitting 6x6 stuff to see if he can avoid repeating the head crush he found at 400 hours.

 

I just bought it and flew it the same way I had flown the Cessna I owned beforehand. One temp gauge seems to be considered enough on Lycs and Contis. Noone (including my mate the Jab agent) told me I needed 12 temperature measurements to avoid cooking the engine.

 

Pioneer 300 #2 just had one of each. At 600 hours it was cooked too. To be fair, the cowling was not the best.

 

Jab 230 #3 had single gauges - the owner bought the kit from Jabiru and built it as per instructions and flew it.

 

Jab 160 #4 is a factory-built 160C. It came with one CHT gauge and no EGT gauge.

 

Go figure.

 

None of the 912 powered aircraft ( Zenair, Sky Arrow, Sting, Avid, Gazelle) have 4x4 temperature reporting. That's water-cooled heads for you I suppose. One of them is at 1500 hrs TTIS and still has 80/78 leakdowns. The others are younger.

 

I was there - none of this is hearsay. I freely admit this is a small sample.

 

 

[facthunter]

IF you need one of each gauge on every cylinder of an engine, the situation is ridiculous. You are not supposed to be a flying a "test bed". Watching all those gauges might mean you are not watching other things, that you should be watching... Determine which is the hottest and monitor it , or get a flight engineer to come along with you. I'm kidding aren't I, but I hope you see what I mean.. Nev

 

 

[mkennard]

But with the new glass cockpits you can set alarms and it's a glmpse to see the gauges.