> Sent: Sunday, May 02, 2021 at 7:53 AM > From: "Flesner" <fles...@frontier.com> > To: krnet@list.krnet.org > Subject: KR>Re: Jabiru 3300 engine? > > On 5/1/2021 10:27 PM, Jeff Scott wrote: > > This is a common issue with the Jabiru. ex pretty easily. > > -Jeff Scott > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > Jeff, > > Do you recall the amount of MMO they were running in the 3300 that > checked well? 4 oz to 10 gallon of fuel is recommended but I run 4 oz > to 5 gallon in the 0-200 and a bit in the crankcase at oil change time. > > Larry Flesner
I really don't recall. I could send him a text later today and ask, but 4 oz sounds about right. MMO seems to soften the lead deposits causing them to slough more easily and lessening lead build up in the engine. Lead build up in an engine is a constant process where the lead is always building and sloughing away. I once checked a fresh engine 2 hours after I had overhauled it and was quite surprised by the amount of lead that had already built on top of the pistons. Leaning helps to avoid excess deposits, but leaded fuel will always deposit lead on any exposed surface as it burns. TetraEthylLead is used to not only boost octane, but as a sacrificial metal intended to deposit between the valve face and valve seat to prevent valve face/seat erosion due to the valve and seat faces exchanging metals while hot. Newer, hardened seats and valves no longer require lead to protect them. In the Jabiru engines, it seems to cause static valve seating issues. But, if you checked the engine with a boroscope, you wouldn't see any signs of uneven heating or burning of the exhaust valves, so they are not leaking dynamically as that would cause the valves to burn and fail, which would be obvious with a boroscope. It's just something that shows up on a static differential compression test. So, to assure the mechanic that all is actually OK, the mechanic stakes the valves and finds the compression readings recover to normal. It's really not an actual problem with the engine itself. I suspect part of this may come from the Jabirus having small valves and light valve springs, which is actually a good thing. -Jeff Scott Arkansas Ozarks ________________________________ -Please see LIST RULES and KRnet info at http://www.krnet.org/info.html -Change list delivery options at https://list.krnet.org/list/krnet.list.krnet.org/ Affinity List Info Board -Search recent KRnet Archives at https://list.krnet.org/empathy/list/krnet.list.krnet.org/ -Search John Boyea's decades of archive at https://www.mail-archive.com/krnet@list.krnet.org/
