eightyknots Posted August 30, 2014 Share Posted August 30, 2014 Gandalph part of the fun of owning a B brand is the religious desire to defend it and the satisfaction of "winning". You could be right FT, but I don't know enough about Drifters to comment Are they still selling Cs? I thought it was all Ds now Could someone enlighten me: is a Drifter a D Brand? 2 Link to comment Share on other sites More sharing options...
geoffreywh Posted August 30, 2014 Share Posted August 30, 2014 last time I looked the pistons were cast. being holden parts. forged pistons would go a long way to reducing piston problems! neither have I ever seen forged piston pins! machined from drawn round at best... Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 Geoff, they're no longer the old Holden pistons: https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-xfp1/t1.0-9/p480x480/10577206_515657385246600_1268174809877949968_n.jpg Unfortunately for Jabiru, the first batch of these ( I think it was) had the circlip grooves machined off-centre, which was the main cause of the rash of circlip problems. However, it's not so much the pistons themselves but barrel cooling issues that are the main culprits - and research is underway to determine how best to address that problem. 1 Link to comment Share on other sites More sharing options...
Dafydd Llewellyn Posted August 30, 2014 Share Posted August 30, 2014 last time I looked the pistons were cast. being holden parts. forged pistons would go a long way to reducing piston problems! neither have I ever seen forged piston pins! machined from drawn round at best... Yes, well that Bex's guess a load of nonsense. Cast Vs forged pistons is a strength issue, which is principally a concern for high RPM, to my understanding. The Holden pistons with wire circlips gave very little trouble, I thought; was there any other piston problem apart from the circlip trouble? It all seemed to start when Jabiru stopped using the Holden piston - but I was not following the history closely, back then. The Jab. engines do use a fairly "tight" piston to bore clearance, and because of that they are little affected by the gudgeon-pin offset. The CAMit engine has greater piston/cylinder clearance, the gudgeon offset the opposite way (as becomes necessary with increased piston clearance), and piston cooling. Plus they use the wire-type circlips. All little points, but the cumulative effect should be considerable. 1 1 Link to comment Share on other sites More sharing options...
turboplanner Posted August 30, 2014 Share Posted August 30, 2014 The Jab. engines do use a fairly "tight" piston to bore clearance Well, well, well, another little clue perhaps? Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 Yes, Ian Bent has gone for a more 'industry-standard' piston clearance for an air-cooled engine, but again I think it should be noted that the 'scatter factor' of Jab engine problems points in the direction of installation (cooling) effectiveness and probably quite subtle differences in the way they are treated as definitely contributing factors to either problems or alternatively, a relatively problem-free life. However, (as has been discussed before), I think it is entirely fair to consider that Rod Stiff's 'run them hard' remark - taken not as he intended, but as interpreted (and not, I stress, unreasonably - it took Jabiru far too long to clarify what that was intended to mean!) has probably been one of the sillier things that could have been said. Nobody could reasonably blame 'operation' when the operators were not given clear and unambiguous information to follow and yet the effects of failing to best guess that comment shows up as physical evidence in a strip-down. I believe it was a serious own goal in the Jabiru history. 1 Link to comment Share on other sites More sharing options...
Dafydd Llewellyn Posted August 30, 2014 Share Posted August 30, 2014 Well, well, well, another little clue perhaps? Clue to what, Turbs? 1 Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 If by 'another little clue' it is meant that the systemic nature of problems has another factor added to the sum of knowledge, then I think it's a fair comment. It obviously isn't a 'smoking gun' - there is NO 'smoking gun', despite the sometimes idiotic assertions that things like the crankcase material and manufacturing process lie at the heart of everything. What Ian Bent has done is to build up a detailed picture of how the entire engine componentry interacts based on his knowledge of the manufacturing processes, the materials, the actual conditions the engine is experiencing, and then looking for the 'chains' of interconnected factors to determine how changes will be reflected 'down the line', as it were. That has two effects: it isolates primary causal factors and it allows analysis of what a change will affect - so changes are not addressing just one factor but are integrated into a 'system' upgrade approach. It follows the time-honoured 'weak link' principle: you don't just fix the obvious weak link, but you then look at the rest of the system to determine if you've actually improved the capability of the whole system rather than just moved the problem elsewhere - or indeed, created a new problem. Link to comment Share on other sites More sharing options...
bexrbetter Posted August 30, 2014 Share Posted August 30, 2014 Keep digging, Bex, the hole is getting deeper.... About the only things you've stated correctly so far are the pistons and the fact that "Jab bottom ends seem to be as good as it gets by any World standards".Crank, cam and rods are from 4140, not sure about the rockers but they are machined from rod and probably 4140, as are the flanges. Thanks for the insider info Spinner, have always wondered exactly what they did and didn't make where! Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 You're welcome, Bex, always glad to help where I can. Mind you, all of that info is available from the Jab website, and anybody who has ever stripped one would know it also - maybe not the metal spec, but certainly the method of manufacture, it's totally obvious.. Link to comment Share on other sites More sharing options...
gandalph Posted August 30, 2014 Share Posted August 30, 2014 FT, I mentioned that some raw forgings are Chinese derived, but machined to the fine tolerances in Oz - the rub here is those Chinese forgings are most likely Australian sourced steel or minerals anyway. Gents, I think you have all taken the bait that Bex has cast. As an engine developer I'm sure he would be fully aware of what goes onto his potential competitors engines and how they are produced. I think he was just having a little joke with us and playing the "China card" right back at FT by linking China and forging in the same sentence. 1 3 1 Link to comment Share on other sites More sharing options...
Dafydd Llewellyn Posted August 30, 2014 Share Posted August 30, 2014 If Bex was trying to be clever, he's going about it in a strange way. The information he's gained, he could just as well have obtained by looking at the Jabiru website, and listening to Ian Bent at Temora. Almost all of it is in the public domain, or will shortly be. Fishing on a forum like this is a bit silly when you can get that sort of info direct from the horse, simply by asking politely. It would be completely futile for a manufacturer to seek to hide this sort of information, when anybody can easily get it by examining one of these engines. What you will NOT get is the drawings, process specifications or work instructions. Link to comment Share on other sites More sharing options...
bexrbetter Posted August 30, 2014 Share Posted August 30, 2014 Answers to questions can be gained in more than one way. FWIW, I am genuinely happy to hear what is still being done in Oz. Now excuse me, have to get back down to the tip and gather more coke cans for my castings .... 2 1 Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 Bex, with your deep knowledge of the Chinese manufacturing industry, I assume you have caught up with the fact that the Chinese piston manufacturer that supplies Jabiru with pistons delivered something like 5,000 pistons to Jabiru with the circlip grooves machined off-centre. What you may NOT know is that that caused Jabiru to have to strip and re-assemble several hundred engines twice - once to have the pistons re-machined, and then a second time to replace the 'replacement' circlips supplied (by a Chinese manufacturer) that were not to spec. for holding tension once installed. The samples delivered for inspection, passed inspection. The bulk of the order, did not. Let's not go there with different interpretations of the term 'forged'. Link to comment Share on other sites More sharing options...
eightyknots Posted August 30, 2014 Share Posted August 30, 2014 Bex, with your deep knowledge of the Chinese manufacturing industry, I assume you have caught up with the fact that the Chinese piston manufacturer that supplies Jabiru with pistons delivered something like 5,000 pistons to Jabiru with the circlip grooves machined off-centre. What you may NOT know is that that caused Jabiru to have to strip and re-assemble several hundred engines twice - once to have the pistons re-machined, and then a second time to replace the 'replacement' circlips supplied (by a Chinese manufacturer) that were not to spec. for holding tension once installed.The samples delivered for inspection, passed inspection. The bulk of the order, did not. Let's not go there with different interpretations of the term 'forged'. That would have been a very expensive episode in the history of the Jabiru company. Link to comment Share on other sites More sharing options...
Oscar Posted August 30, 2014 Share Posted August 30, 2014 That would have been a very expensive episode in the history of the Jabiru company. Absolutely - but they copped it on the chin. I have no idea of the commercial arrangements, but presumably they were unable to demand re-supply of correctly machined pistons (which suggests to me that dealing with Chinese suppliers is a different world from dealing with suppliers from other countries). The old adage that 'you gets what you paid for' seems to be apposite. A small company in Bundaberg can't compete with Chinese prices, but if you've visited CAMit, you'll see why their products deserve the QA cost. 2 Link to comment Share on other sites More sharing options...
jetboy Posted August 30, 2014 Share Posted August 30, 2014 and all the while I thought it was the owners / maintainers fault when a valve drops or a piston breaks Jabiru still holding the line that the circlips are all perfect just someone doesnt install them proper. http://www.jabiru.net.au/images/Piston_Circlips_Iss2.pdf I suppose they expected those re-machined pistons to take the original sized circlips too? I like the move to the valve clearance recess in the pistons but really wonder if thats not going to lead to another issue later on. Will it alter the dynamic balance of the piston, and will it cause hot spots / preignition and is there any issue with weakness to the ring grooves or crown because of this machining? At 475 hours I'm nearing the time for a new set of rings and these discussions reveal many factors which are not published where they would be helpful to maintainers. I dont mind if the airframes are molded in SA and painted in Oz or the pistons come from China so long as this is not misrepresented (like the website probably still says Repco pistons) and the serial number change is stated so if an issue arises it has traceability Link to comment Share on other sites More sharing options...
Oscar Posted August 31, 2014 Share Posted August 31, 2014 JB - no, they didn't expect those pistons to take the same sized circlips - though I am aware of at least one engine that mistakenly had the original size circlips installed and had a circlip failure (jeez, who would have thought that?). They had to go from 22mm diameter circlips to 24mm diameter (I think it was, but my interests have been with the CAMit engine so I've not followed the latest Jab engine stuff in any depth) and that's why the service bulletin on circlip installation stresses that they must NOT be over-squeezed on installation. When we rebuilt our engine at CAMit last year, for a complex set of reasons we used the old-style pistons with the wire circlips. This particular engine is a bit of a mongrel; it incorporates some parts that were sitting 'on the shelf' from an engine put together some years ago for a project that stalled, plus a number of CAMit development parts that were tried and proven at that time. It will be upgraded to full CAMit-spec in the future, but we need to do a period of test flying of other changes made to our aircraft and that will roughly coincide with the testing of the full suite of CAMit mods that is about to start, so we decided to hold off and get the hours we need on the airframe up before completing the engine upgrade. When we complete the 'upgrade' work, we'll use the pistons and ring set-up that CAMit has selected running in CAMit barrels and using a CAMit-approved installation for cooling. I don't believe CAMit intends to use the new Jab pistons. I share your concerns re the 'new' pistons, especially the hot-spot potential if using 100LL - but that said, our approach is to rely on the research, development and testing work that CAMit has done and not to think that we have better ideas of what to mix-n-match inside our engine. Having had the invaluable opportunity to be somewhat involved in the CAMit development work (well, at the least, very well informed - talking to Ian Bent about how everything has to work together is a real eye-opener as to how complex the 'systems' working in the engine are interconnected), we're not going to be silly enough to think we have any better answers! If you have time before you need to do the work on your engine to await the completion of the testing runs for the CAMit engine(s), you may find you have alternatives to simply rebuilding/refurbishing a 'Jab' engine that might be very attractive. We're probably talking around Christmas this year for that to be completed and the paperwork done. 2 1 1 Link to comment Share on other sites More sharing options...
turboplanner Posted August 31, 2014 Share Posted August 31, 2014 If by 'another little clue' it is meant that the systemic nature of problems has another factor added to the sum of knowledge, then I think it's a fair comment. Post removed - Mod Link to comment Share on other sites More sharing options...
deadstick Posted September 2, 2014 Share Posted September 2, 2014 I noticed a drop in static compression (prop pull through) with the new pistons, although I like the quality of the item the flycuts required smoothing on the radius's before install. Interestingly and something minor,,, on all the Jabiru engines I've top-ended or rebuilt the old CHT ring under the spark plug setup has shown signs of leaking and never have I seen one with the plug washer removed to equal the install height of both plugs. Might be minor but attention to detail is a requirement with this power plant in my opinion. I recommend removal of the CHT plug rings and fit them to the small hole between the plugs if you get the chance. Another common find is out of round cylinders, leaking exhaust flanges, loose rotors in the distributors, loose high tension leads, untreated corrosion ( prop flange is the most prevalent ). I am crossing my fingers that the latest round of upgrades will increase the reliability of jab engines, however I think they need to make the cooling setup bullet proof for each installation and cool the cylinders as well. 1 1 Link to comment Share on other sites More sharing options...
turboplanner Posted September 2, 2014 Share Posted September 2, 2014 If by 'another little clue' it is meant that the systemic nature of problems has another factor added to the sum of knowledge, then I think it's a fair comment. No, it's not what I meant, nothing to do with what you are posting about. Link to comment Share on other sites More sharing options...
deadstick Posted September 2, 2014 Share Posted September 2, 2014 Here's a pic of an attempt to modify the cooling ducts to incorporate the cylinders its a few pictures in, it looks like its fitted with an aero injector and notice the fuel pumps missing. http://cgi.ebay.com.au/ebaymotors/HIGHLANDER-LSA-FIREWALL-FORWARD-JABIRU-3300A-120HP-similar-to-ROTAX-912-914-/251628226875?pt=Motors_Aircraft&hash=item3a9636093b&forcev4exp=true Link to comment Share on other sites More sharing options...
jetjr Posted September 2, 2014 Author Share Posted September 2, 2014 Good pdf from Jabiru USA site, also can buy between cylinder deflectors, locating thme underneath sure helps stabilise things Link to comment Share on other sites More sharing options...
Oscar Posted September 3, 2014 Share Posted September 3, 2014 No, it's not what I meant, nothing to do with what you are posting about. Ah, ok, then I'll leave you to it. There'll be a heap of research and (calibrated) testing information forthcoming in a few months, so I'll personally wait and see what transpires; I believe in hard evidence rather than theories. Cheers. Link to comment Share on other sites More sharing options...
turboplanner Posted September 3, 2014 Share Posted September 3, 2014 Good idea Oscar Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now