Borescope recommendations - Looking at mid time engines

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,719
Location
Mojave, Ca
If you are looking at a prop strike engine then you are looking for a IRAN inspection before you fly? Unless you know for a fact that the strike was really benign, the fact that the crank dials straight is almost zero help. As you well know, a prop strike is like hitting the prop with a sledgehammer - that shock resolves through a lot of machinery. At the very least, mag the crank gear and replace the bolt.
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
8,006
Location
USA.
Pops,
Are you being sarcastic or think it is a good idea?
I am having trouble finding any good ones. Seems all of the models I will consider have had a prop strike. Crank dials legal, but there are so many other potential issues at the back end too...
Bill
No not sarcastic. I think its a good idea. I think you have it right. I know its hard to find a good mid time engine with no prop strike history and an engine that has not be setting for a long time. But, trying to break in a new MOH engine on a new untested airframe is not a good idea. Much better to use the mid time engine until the test hours is off the airframe and then do the MOH.
 
Last edited:

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,694
Location
Saline Michigan
If you are looking at a prop strike engine then you are looking for a IRAN inspection before you fly? Unless you know for a fact that the strike was really benign, the fact that the crank dials straight is almost zero help. As you well know, a prop strike is like hitting the prop with a sledgehammer - that shock resolves through a lot of machinery. At the very least, mag the crank gear and replace the bolt.
Planning on a teardown and thorough inspection whether they tell me it had a prop strike or not. The big question is if I am insane to buy a possibly damaged engine, and take my chances on what it will cost to fix it.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
12,803
Location
Memphis, TN
It can be cyclical on finding engines. Tons of deals when not looking, none when. I would stay open.

Over on the Biplane Forum there are two engine stories off the top of my head.

One guy is actually on his 4th engine in 100 hours; no accidents. The first engine was making metal, but not a lot. He should have kept flying it because he was never going to fly it to breaking. Sells it. Find another puts it on and it’s all over the place, takes it apart and they scrap the case and crank. Too expensive to ship back to make a table out of. Gets another and just sells it because what if got him. Kicking himself he builds piece by piece and finally has a flying engine again. The first engine could have easily been saved but he did not want to open it. He opened three out of four.

Another decided he was not going to keep his plane. Flew off the Phase flights and sells it. It goes overseas. He bought a 100 SMOH engine. Crank broke on the new guy; off field landing totals airplane. It was nice too. There is a couple more.

It takes about 4 hours to put together a Lycoming. There are usually a supply of cranks on eBay that just missed being certified by a small margin. A couple of shops selling off stock. For a homebuilt should be fine. You can also find a local shop to pre-test the parts. Have them check for straightness and magniflux, then send them off to be officially checked if that would make you feel better.

I would take your time on finding the right engine. If you need something to mock up the firewall forward, scrap cases and cranks that are truly scrap can be had cheap, cylinders too. Something that has thrown a rod is a good template.
 

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,719
Location
Mojave, Ca
The other option is a total run-out from an often used airplane. If a flight school is pulling an engine at TBO and it's still running well then there's an excellent chance you will get several hundred more hours out of it. Enough to get the airframe and systems sorted anyway. THEN rebuild it, and fly to your heart's content.
 

cvairwerks

Well-Known Member
Joined
May 12, 2010
Messages
208
Location
North Texas
Got a recommended supplier for scope rental?
You’d have to do some looking and calling. As I work for a defense contractor, we bought all of ours. Search using test equipment rental should get you enough hits to start. As to cost, no clue. I know our XL’s are way into the 5 digit price with the options we specify.
 

rv7charlie

Well-Known Member
Joined
Nov 17, 2014
Messages
611
Location
Jackson
There are prop strikes, and then there are prop strikes. Lyc says that if a prop blade touches a blade of grass while the engine is running, you should, at minimum, remove the accessory case and replace the cam gear bolt (not the indexing pin, but the bolt in the middle of the gear...). I have to wonder what they say you should do after each water flight in a float plane or sea plane....

If the engine had a metal prop strike (a real one, not a 'blade of grass' strike), there's real risk. If it was a wood prop strike, the equation might change a bit. I bought an RV4 back in 2003 that had almost certainly had a couple of wood prop strikes before I bought it. I flew it for about 400 hrs, and I had a wood prop strike. I did the Lyc AD on the cam bolt, and dialed the crank flange (still straight), so I didn't split the case. I flew it for several more years before selling the plane last fall. I also had a wood prop throw part of the blade, with a prop strike during the emergency landing on a Thorp T18 back in the early '90s when I was a freshly minted pilot, that I continued to fly after dialing the crank (no cam bolt compliance; not even sure the AD was in effect then), but a tornado ate the plane about 30 hrs of flight time after the prop strike, so I can't claim long life out of that one.

My personal opinion is that buying *any* aircraft engine is a bit of a dice roll; even a brand new engine. None of the engine makers are exactly stellar performers when it comes to warranty support, and unless the engine is local and you know both the seller and the plane it's being removed from, there really isn't any way to know what you're getting without complete disassembly and shipping the crank off to be inspected, which means new (stupid expensive) rod bolts, etc etc. If you think about it, even 4 new cylinders will cost you less than the one component you can't really inspect yourself. :)

I like Toolbuilder's answer about a flight school engine; significantly lower risk with a high frequency of use engine that had to have regular 100 hr inspections.

Charlie
 

C Michael Hoover

Active Member
Joined
Aug 24, 2019
Messages
32
A Cont engine is easier to inspected the cam because its below the crankshalf. For the Lyc's with the cam on top of the crankshalf, I don't now without sliding a cylinder back a little from the case.

My mechanic/IA/consultant, who unfortunately lives 900 miles away, says that you can see a Lycoming cam (angle valve if that makes a difference) from the dipstick hole. what say you all with experience?

cmh

edit (left out the word cam and corrected a typo)
 
Last edited:

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
12,803
Location
Memphis, TN
What happens with Lycoming cams when they sit a bunch is the contact lifter to lobe point will rust. While you sleep, it’s rusting right now.
The longer it sits, the pits become more pronounced. The more you run it, the less chance for it to etch deep. If you look at the cam you will see one lobe is holding a valve open all the time. If the rust is on the heel of the cam, not a lot of pressure to grind. The tip of the lobe with all the pressure is just a lathe and cutting tool. If it’s sitting a long time with acidic oil on that one lobe, it will turn bad in the end.

You might get a glimpse of the cam from the oil fill but you can only see if it’s rusty like left in saltwater. Thorough inspection, you pull two cylinders and the rocker arms off the opposite side. Now you can push the lifters back from the cam and look at the faces. How often does this happen? Not very. It can be a lot of work and someone selling just wants to sell. They don’t want you finding flaws and scrapping their engine in their hands.
 
Top