I assume all are using the shells around the outside of cylinders per tech bull 44. They do not reduce the CHT much (usually that is mixture issue) but by keeping air in close to heads around fins air works harder getting through and gives a more even temp around the cylinder.
Limbach Heads, have definately improved over the years including shape in combustion chamber is very interesting. Over years the direct drive oil temp gauge (240 deg movement hand) in time underread. The 12v powered ones (about 80deg of needle movement) tend to be more reliable and accurate be it harder to read at low end. On first flight we have discovered that running engine for about 5 mins then shut down and do something else for 10 min the heat will disperse through whole engine and oil temp will show above 50 deg. I find apart from the first 100hrs if the tappets do not need adjusting each 50 hrs then can get 800hrs with zero head issues. Needing to adjust valves regularly means something is not right. If engine is overheating and compression is down then I have found pulling cylinder off the top ring is overheated and did not push out as hard as it sould when compared with next ring down. While on oil leaks make sure the dip stick has a felt or leather ring under the tiny cap of dip stick and it sits, square on the tube from engine. . At full power if in poor condition the felt/leather will lett a fine mist of oil through engine. My 2c worth Ian McPhee +61 428847642 Box 657 Byron Bay NSW 2481 Australia. On Wed, 2 Dec. 2020, 10:34 Ian Williams, <[email protected]> wrote: > Yep all understood. I think that realistically looking at the VW head > design compared to a Lycoming for example the total cooling surface area is > a lot smaller on the VW. So heat removal is a bit more critical > But no real drama. It just means good maintenance ... watching tappets > clearances and mixture. I wise plug colour as a guide setting the mixture > which has been quite OK > I reckon that if the engine only needs a valve grind after 500 hrs we are > doing real well > > Best regards > Ian W > > > Sent from my iPhone > > On 2/12/2020, at 10:56 AM, Rob Thompson <[email protected]> wrote: > > The exhaust side of the inlet valve seat cops a lot more heat so can be > prone to distortion and heat hardening. > Nigel was investigating ceramic coatings inside the heads and ports to get > the exhaust heat out the pipe not into the metal. > Approvals to use ceramic coatings may be a problem. Possibly not for > coating the inside of the exhaust ports.If the coating fails it will just > get blown out the exhaust pipe. > regards > Rob > > Rob Thompson > 0429 493 828 > (Please note that my new email address is [email protected]) > > > On Wed, Dec 2, 2020 at 8:23 AM Ian Williams <[email protected]> wrote: > >> Hi Rob. Sorry didn’t. Engine is back together again. What I saw was >> that as I was lapping in the valves there was a darker area on the inlet >> valve seat where it passes by the exhaust seat which I couldn’t get rid of >> by lapping. >> >> Ian W >> >> Sent from my iPhone >> >> On 2/12/2020, at 9:56 AM, Rob Thompson <[email protected]> wrote: >> >> Do you have photos of the distortion/damage to the valves and seats? >> regards >> Rob >> >> Rob Thompson >> 0429 493 828 >> >> >> >> On Tue, Dec 1, 2020 at 6:55 PM Ian Williams <[email protected]> wrote: >> >>> Hi All, >>> >>> >>> >>> I thought an interesting situation I have had with these little engines. >>> >>> >>> >>> I “look after” ie the maintenance engineer for 3 limbach powered >>> aircraft … 2 Grob 109’s and our Dimona. One Grob has an L2400 engine >>> originally in a Stemme S10. >>> >>> . >>> >>> The G109 with the L2000 lost compression after about 100 hrs (new heads >>> from Nigel Baker) A leak down rest clearly indicated leaking inlet >>> valves. The fix was to regrind the valves )not just lapped) and all OK. >>> >>> At the time I did think that the reason for the valve seat distortion >>> was overheating as the L2000 in the Grob does run hot (as compared with the >>> Dimona. >>> >>> >>> >>> Hoever I am currently working on the Dimona engine. It has done 500 >>> trouble free hrs (apart from a failed Magneto condenser) It has had a >>> frustrating oil leak so I have replaced the rear oil seal and was planning >>> to lap in the valves. >>> >>> Here is the interesting bit …. There were clear signs that the inlet >>> valve seats were slightly distorted in exactly the same area as the Grob >>> engine. (but at 500 hrs, not 100) >>> >>> >>> >>> However our redesigned baffles etc of the Dimona installation does mean >>> the engine is running very cool (CHT’s around 110 to 140C and oil around >>> 65C) >>> >>> >>> >>> Apart from what I am talking about, I am impressed with the overall >>> condition of the engine. I had the valves reground in an engineering shop >>> as just lapping the valves didn’t totally seal the inlet valves >>> >>> >>> >>> So my conclusion is that there could be an issue that the heat sinking >>> around the exhaust / inlet area is not as good as it could be. This is not >>> serious though but if an L2000 has low compression that could be an area to >>> look at. >>> >>> >>> >>> Best regards >>> >>> >>> >>> Ian Williams >>> >>> ZK-GCB >>> >>> New Zealand >>> >>> >>> >>
