Hi Tom, I am wondering if your valve springs are a little hard and they are beating the seats a little. regards Rob
Rob Thompson 0429 493 828 On Wed, Dec 2, 2020 at 1:07 PM Tom Preisser <[email protected]> wrote: > I replaced both heads recently (575 hrs) and found significant intake > valve "pocketing" on all four intake valves and seats. In other words, the > valve face and seat face were no longer flat but rounded, but still mated > well enough to give good compression. The wear had gotten to the point > where valve sticking could have become an issue. I had wondered why my > intake valves always needed a slight loosening every 25 hours or so. I am > guessing that abrasives that are present after passing through the air > filter are responsible. > Any thoughts gentlemen ? > Best regards, > Slacko > > On Tue, Dec 1, 2020, 15:34 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 >>>> >>>> >>>> >>>
