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Permalink Reply by John Austin on March 7, 2025 at 2:44pm

I don't think it would be economically or practically feasible to modify a Gen 3 to a 4.  The cylinders are completely different - the Gen 3's are aluminum with steel liners and (as I understand it) have looser tolerances to accommodate the difference in thermal expansion rates between the steel liners and the aluminum pistons.  The Gen 4 cylinders are all-aluminum with a Nikasil internal coating so have the same expansion rate as the pistons and tighter clearances.  The heads are bolted-on the Gen 3 and the Gen 4 heads are screwed-on to the cylinders (permanently), the same as Lycoming and Continental.  I "think" the Gen 4 now has a 6 lobe oil pump vs the 4 lobe on the Gen 3.  The Gen 4 exhaust and induction runners are completely differently clamped (rather ingenious!) vs the Gen 3.  I could go on-and-on, but all those differences would be difficult to achieve unless you started with a Gen 4 case and built up from there.

Looks to me it would be much simpler to just sell the Gen 3 and buy a Gen 4!  If the Gen 3 is running well, I don't see a compelling reason to get a Gen 4 - the Gen 3 will be a little slower to warm up, use a little oil (my Gen 4 uses almost no oil!), and sometimes be a little harder to cool (but a careful installation will achieve adequate cooling even in a high drag, low speed airframe such as the 750 series).  However, if I was looking at a 1000 hr top end overhaul or major overhaul, then I would consider just selling the Gen 3 and get the Gen 4 simply because you'll have a new engine with a very generous warranty - 3 yrs or 500 hrs.

John

N750A

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Permalink Reply by Harley Myler on March 7, 2025 at 4:46pm

Thanks for the excellent rundown of the issue!

As it turns out, it's not a 3, it's a 2 (just shows you how much I know about these engines).

It has never been run, s/n 2058, being bought as part of a CH650B project.

Any tips on prep and first run appreciated 😉.

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Permalink Reply by John Austin on March 10, 2025 at 9:50pm

If it is still in the crate and has never been unwrapped and still has the factory inhibiting oil in the cylinders, etc., it might be in pretty good shape.  However, if it was unwrapped, turned over to expel the inhibiting oil, etc., it might be rusty internally.  At a minimum, I would do a borescope exam to assess the condition of the cylinders.  I'm sure Nick at Arion Aircraft, the USA dealer/repair center, could advise you of any other recommended inspections and/or first start procedures, and also perhaps recommend any upgrades prior to running the engine.

John

N750A

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Permalink Reply by Harley Myler on March 11, 2025 at 7:48am

Thanks! Great advice.

The engine has been mounted, but the prop was not, so I think it hasn't been turned. I can find out, but frankly, a little borescope tour is not a bad idea regardless.

Thanks for the tip about Arion A/C, I contact Nick and see what they advise. I also need to check any SBs, etc., because none of those, if any, has been applied.

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