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 <amessageto...@gmail.com> 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 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 >>>> >>>>
