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 amessageto...@gmail.com) On Wed, Dec 2, 2020 at 8:23 AM Ian Williams <i...@agcon.co.nz> 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 <amessageto...@gmail.com> 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 <i...@agcon.co.nz> 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 >> >> >> >
