Our operation runs 4 Jabs (3x170, Gen4-- 1x230 Gen2) as well as a Roko.
In the last few months the Jabs (Roko under major repair--tin work) have needed to have their heads removed due to low compression, 6 from memory. Initially it was only the Gen4s and on inspection there was a large amount of lead in the chamber/ex valve seat. Far more than we would normally see. The engines are mid life. We have been running Gen4 since they first came out as part of a Beta test, and have never had a problem like this before.
We run flat out, with a 25 hourly every 2 weeks per aircraft, with a new motor every 2 years.
Typically the lead comes off just by touching it with a finger nail and some of the pieces are the size of a corn flake and break off to bare metal underneath. The remaining deposits only need a light scrape and it instantly powders like corn flour. No real need for a wire brush, though it does clean it up like new, almost instantly. Previously, lead needed quite some work to remove. Not these last few months. The gen 4 also showed signs of gummy/hard deposits in the ring grooves.
Oil was filthy after 25 hours, far more than usual. To keep the rings clean we have reverted (under advisement) to Straight 100 for 25 hours and that fixed the dirty oil problem OK and colour/deposits are now back to normal.
What was going on? At least the 230 is OK, so maybe there is something with the Gen4 we said........Until yesterday.
As well as another 170 with dud compression on 1 pot, the 230 now has comps in the high 40s. This aircraft is on its second motor (first replaced due to prop strike) and mid life. It has always been high 70s/80. What you would call a keeper of an engine. It was very hard to start when we warmed it up for its 50 hourly. Cold pull thru was low as well. This is our touring plane and isn't used as much.
Cyl 2,3 and 6 were lucky to get to 48/80. the rest were at 75/80. Heads off and inspection revealed the same problem as the Gen4. Finger nail touch method removed a lot of the lead, in large chunks and the rest was easily removed with a gentle scrape. After clean up we found some old lead deposits on top of the valve, that you just could not get off easily (just like old times!).
As stated these are training aircraft and flown every day. We have NEVER had a problem like this, so many in only a few months.
So, the committee has decided to run a trial period of MOGAS asap, with a view to completely converting the whole fleet over if it proves beneficial.
I run MOGAS in my Jab with no problems as a private owner and can't see a problem with any fleet use.
I know that many of you run MOGAS in your private planes, but I am interested if any schools are running it in their fleet?
Has there been a bad batch of fuel?
Anybody else note the same in the last 3 months?
I will keep you posted.
Ken