Q: We recently bored a Lycoming 290-D2 engine to accept 320 cylinders (low compression) with 8.5:1 pistons. The engine has all new bearings and valves, and everything has been magnafluxed, balanced, etc. We retained a very good 290 D2 crankshaft.
From experience, would you say it could make a reliable engine?
Gilles St Pierre, AVIATION BSL (Canada)
A: Gilles, I’m probably not going to win any friends with my response, but my main concern here is safety, which should be the top priority of all of us in this business.
Honestly, I have never before heard of anyone making an engine conversion as you described.
Being retired and not having access to all of the technical information that would be required to research a project like this, I’m going to have to decline to answer.
My personal opinion, just off the top of my head, is that it sounds like you are “trying to make a silk purse out of a sow’s ear.”
Please don’t misunderstand me, it may be a doable project, but like I said, I’ve never heard of it being done and just thinking about it leaves me a little bit nervous.
The thing that causes me the most concern is how you take a cylinder with a 4-inch, 7/8-inch bore and bore it out to a 5-inch and 1/8-inch bore…and that’s only the beginning of several complicated questions that come to mind.
Please accept my apologies for backing away from this one, but it’s just way out of my league.