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                                     
>> 
>>  

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