facthunter Posted November 3, 2021 Share Posted November 3, 2021 Up draft cooling would work post shutdown but the actual pressure difference is hardly measurable. Openings in the top of the cowl would increase fire effects and oil mist on windscreen etc. Nev 1 Link to comment Share on other sites More sharing options...
RFguy Posted November 3, 2021 Author Share Posted November 3, 2021 (edited) Hi OK I honestly think, that 165C continuous, all day should be just fine. It might pay to jet some air in there, but honestly getting air in that part of the engine is not simple. ALmost needs an auxilary blower. 170 should be fine for therequired yield strength but given I dont know the history of the engine, and I dont exactly know the ally temper, so I made it 165C. But it doesnt get anywher enear up there. maybe 157 (OAT=22) on a long taxi. keep idle RPM low helps ALOT. stationary certainly it will slowly climb. I'm thinking that the aluminium has been degraded from sustained plastic-region running . The curves all show it going in that direction- IE yield strength at temp X will fall with long term exposure. So its never going to be any good now. Either a new head, or a machine flat and copper or tungsten etc gasket. or a single water cooled head. Edited November 3, 2021 by RFguy Link to comment Share on other sites More sharing options...
facthunter Posted November 3, 2021 Share Posted November 3, 2021 If you know it's been cooked get a new head or at least hardness check it against another good one. I would suggest the condition is in the billet it's machined from. Nev Link to comment Share on other sites More sharing options...
RFguy Posted November 3, 2021 Author Share Posted November 3, 2021 I'll get a new head or water cooled one. ha ha OK, as Nev says, it could be related to the billet is came from, and maybe my assumptions of the billet performance and temper are not sufficiently conservative. Link to comment Share on other sites More sharing options...
Ian Posted November 3, 2021 Share Posted November 3, 2021 Does anyone know what alloy Jaribu use for their heads? That would at least provide some basis for picking temperature limits. Also have the alloys changed over time? Link to comment Share on other sites More sharing options...
RFguy Posted November 3, 2021 Author Share Posted November 3, 2021 Hi Ian I did find out and cannot remember where I wrote it down. The problem is for those billets, there isnt super precise control of temper, and we are up in the temperature versus yield strength region where small changes make a huge difference, and hence Nev says maybe the billet was is a bit low on the curve. So, I am looking for a new head. Link to comment Share on other sites More sharing options...
RFguy Posted November 3, 2021 Author Share Posted November 3, 2021 OR I have two jammed hard stuck lifters, but two sick ones adjacent to each other ? no way ! Recall I DID have in the rebuild, I found ONE lifter that was assembled incorrectly from factory ! either way, needs to come apart. wanted Gen3 single 3300 head, or LCH head. Link to comment Share on other sites More sharing options...
Old Koreelah Posted November 3, 2021 Share Posted November 3, 2021 7 minutes ago, RFguy said: …wanted Gen3 single 3300 head, or LCH head. So, you’re installing one LCH where the air doesn’t reach? Link to comment Share on other sites More sharing options...
RFguy Posted November 3, 2021 Author Share Posted November 3, 2021 ahhh Based on my previous measurements, I think there IS enough cooling even though not much air back there because I think the previous numbers for temperature difference were about worse case. SO I am pretty confident now I have a bad head material, or super stuck lifters. Needs a new head, really. might not easily get one, so LCH head would do the job (with the liquid) . could machine and add copper heat spreader gasket....the copper would very slightly improve the heat distribution. so, yeah, new head or LCH head. Link to comment Share on other sites More sharing options...
Ian Posted November 3, 2021 Share Posted November 3, 2021 If you're sick of piston engines you might want one of these. Ex RAAF PC9, It will be interesting to see what they sell for. Though the running costs might be a bit high. Link to comment Share on other sites More sharing options...
facthunter Posted November 3, 2021 Share Posted November 3, 2021 When you are machining from a billett you have to choose one that machines fairly well as supplied and also does the job. The stipulated operating max temp is usually based on the NEED to not exceed the temperature at which the head will be permanently softened and is quite high on components that are cast and then heat treated. Hardened from quite hot and then quenching and then tempered back by heating to a lower temper temp. IF the operating temp exceeds the original temper temp then the head is softened permanently as I'm not aware of re heat treating the finished product being a success in aluminium alloys because of warpage. Nev Link to comment Share on other sites More sharing options...
RFguy Posted November 9, 2021 Author Share Posted November 9, 2021 (edited) Hi Nev. agreed. Does anyone have some pexperienced suggestions on a gasket material (if I take the head-bore interface back to flat in a mill and put a gasket there) One wants some heat isolation I feel to isolate the hot barrels otherwise the recession just occurs again... so copper may not necessarily be the wiseest choice. Some of those hard metals can be tricky to machine/punch/cut. I guess oculd be a ceramic. Edited November 9, 2021 by RFguy Link to comment Share on other sites More sharing options...
facthunter Posted November 9, 2021 Share Posted November 9, 2021 This problem occurs on a lot of head face surfaces that scrub due to dissimilar expansion rates and running temps and usually the gasket takes the shear causing it to have a limited life and it scrubs at the ends. Long heads are the worst affected, naturally. . Maybe a multilayer (3) thin steel rings option ? Cut with plasma. Nev Link to comment Share on other sites More sharing options...
Blueadventures Posted November 10, 2021 Share Posted November 10, 2021 (edited) 5 hours ago, RFguy said: Hi Nev. agreed. Does anyone have some pexperienced suggestions on a gasket material (if I take the head-bore interface back to flat in a mill and put a gasket there) One wants some heat isolation I feel to isolate the hot barrels otherwise the recession just occurs again... so copper may not necessarily be the wiseest choice. Some of those hard metals can be tricky to machine/punch/cut. I guess oculd be a ceramic. Maybe a silly idea; but could you lap / mate the head to cylinder, then take some metal out of head and or piston crown to maintain the compression ratio??? Would if works save getting a special gasket made. Edited November 10, 2021 by Blueadventures Link to comment Share on other sites More sharing options...
RFguy Posted November 10, 2021 Author Share Posted November 10, 2021 not a bad idea but I want to get the cylinder thermally isolated and also some load spreading action. Nev- the plasma cut steel laminations layup is a workable idea. Mark suggested some 2000 (AL/Cu) alloy - that look salso good. (same alloy used in Lycoming heads) Link to comment Share on other sites More sharing options...
facthunter Posted November 10, 2021 Share Posted November 10, 2021 A gaskets are something else to fail. Most head/cyl joints try to have a good heat transfer. I doubt the cylinder is hotter than the hot parts of the head. Any colouring due heat is closest to the exhaust valve and is due to THAT part being hotter. UNEVEN heat is the cause of distortion. Nev Link to comment Share on other sites More sharing options...
RFguy Posted November 10, 2021 Author Share Posted November 10, 2021 (edited) true that top inch of the cylinder is going to be hot. and from my POV just another heat load for the head interface which with the jabiru is a problem- hence trying to isolate it but I dont precisley know exactly which way the heat flow is there. IE whether the bores would suffer from having no where to put the heat. I wouldnt think they're care abotu being a bit hotter, but how much is a bit. dunno. If the cylinder interface area was doubled, there would be NO PROBLEM whatsoever because the tension of the head bolts would be MILES below the pressure limit (due to double the area). The head yield strength /temperature (as I have droned on abotu is right in the curve where it starts to steepen.) but to get a good seal, really needs a little bit of compliance somewhere... sandwich gasket - soft copper- steel - copper Edited November 10, 2021 by RFguy Link to comment Share on other sites More sharing options...
facthunter Posted November 10, 2021 Share Posted November 10, 2021 More face area, less pressure and harder to keep true. About 3 bolts are the ones that take up , right? It's localised. and always the same place. You will need a paint that changes with a temp being reached to get the answer to your question. as to which is hotter and what actual temp you are getting or have a direct reading temp sensor near it. If you have colouring of the cylinder Inside then a temper colour chart will give you an idea. I have seen BLUE on all cylinders of a 2200 engine and obviously maintaining an oil film at that temp would be difficult. The bores were scratched. PLENTY of engines run OK though. Particularly when fitted to faster planes. If climb temps climb, speed up. Nev 1 Link to comment Share on other sites More sharing options...
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