Replace Engine Mounts

[Chimpanzee]

A question to the more knowledgeable:

The vibrations in my M20 C are not bad, but noticeable. So, I thought about changing the engine mounts, as I have no idea how old they are. What I do not know is if it would be possible to change one after the other (while keeping the engine where it is) or if the engine has to come off completely (and all the nice cabels and attachments have to be removed).

Any ideas?

Cheers
Norbert

 

[1964-M20E]

Have you had your prop balanced?

 

If not try this first it can make a big difference.

[N201MKTurbo]

If you hang the engine from a hoist, you can change the mounts without disconnecting everything. It is still a PITA!

 

I wouldn't expect a big change in vibration.

 

I would wait until you need to pull the engine for some other reason and then change the mounts.

[rbridges]

They replaced mine with a hoist. Took my IA lots more time than he expected. One was torn. I honestly cant feel a difference. I did it more to address prop sag.

[N33GG]

Norbert:

What prop do you have on your C?

[Shadrach]

Check to ensure all of the metal baffle and cowling pieces are tight.  I had a weird buzz that started a few weeks after annual. It turned out to be a broken fastener in the front baffle. The area in question had failed before and a doubler was installed with a right angle bend. The doubler fractured right along the bend. I replaced it with the next size up in sheet metal thickness. and reinforced a few other week spots. Presto, the "buzz" disappeared.  

 

Also, a dynamic balance can make all the difference in the world.  

[orionflt]

Norbert,

Look at your engine mounts, if you see that they are dried out and cracking then replace them, other then that you will notice the bottom mounts being compressed. If your prop is saging, measure from the ground to the tip of your prop with the prop in the vertical position. You should measure around 9 inches clearance and equadistanced from the cowling. Easiest way to tell is to look from the front, does it look centered in the cowl opening or is it lower in the opening. Note: worn landing gear shock mounts will also lower your clearance to the ground, the 9 inch clearance pertains more to worn landing gear mounts then engine mounts. Most vibration caused by engine mounts is due to a broken mount vs a worn mount, if you have your prop balanced the shop should be able to tell you how much vibration is being created from the mounts and if the need to be changed. If you do change the engine mounts, rebalance the prop.

Brian

[Bob_Belville]

My prop has been pretty far out of line with the cowl since I bought the plane. I had decided to change the Barry mounts which date to the new engine install - 12 years and 700 hours ago - but before I ordered the mounts I had my prop strike (@ 6B6 2 weeks ago today as reported elsewhere) so we'll take advantage of the engine removal for prop strike inspection to change the mounts. We were going to change w/o removing engine.

 

BTW, I have Barry on this '66E. While I'm at it I wonder if anyone has any comments on Lord vs. Barry? I have not checked on Lord availability for this installation.     

[Chimpanzee]

Thanks guys,

as usual mooneyspace provides lots of good advice and feedback. I must admit that the idea of replacing the mounts comes only from the small vibration. It is not bad, and I might make it sound more that it is, I have a three blade Hartzell prop, and as far as I can tell there is no noticeable sag. And the mounts do look ok. (as much as I can tell). I did have the prop dynamically balanced, it made some difference, but the mechanic who did it said the imbalance was little anyhow. Maybe I make too much out of it. Since I would like to avoid an unneccessary PITA, I will take the measurents as suggested by Brian, and if that does not reveal anything more, leave the mounts unchanged for the time being.

Cheers and thanks again
Norbert

[N33GG]

I had a 3 blade prop on my C when I bought it, and it had quite a bit of vibration.  There is more than a little debate and opinions on this issue, so I am just saying what I have heard and done...  I have heard that it is very difficult to balance the 3 blade with the O-360, more so than other engines.  Beats me if it is correct, but that is what I have heard from some people that have had a lot more experience with airplanes than I have.  I put a 2 blade scimitar on my plane, and it is incredibly smooth.  Vibration is history. 

FWIIW and YMMV

Good luck.

[rbridges]

My prop has been pretty far out of line with the cowl since I bought the plane. I had decided to change the Barry mounts which date to the new engine install - 12 years and 700 hours ago - but before I ordered the mounts I had my prop strike (@ 6B6 2 weeks ago today as reported elsewhere) so we'll take advantage of the engine removal for prop strike inspection to change the mounts. We were going to change w/o removing engine.

 

BTW, I have Barry on this '66E. While I'm at it I wonder if anyone has any comments on Lord vs. Barry? I have not checked on Lord availability for this installation.

Lord mounts are available at spruce. I went with them based on recommendations.

[rbridges]

I had a 3 blade prop on my C when I bought it, and it had quite a bit of vibration.  There is more than a little debate and opinions on this issue, so I am just saying what I have heard and done...  I have heard that it is very difficult to balance the 3 blade with the O-360, more so than other engines.  Beats me if it is correct, but that is what I have heard from some people that have had a lot more experience with airplanes than I have.  I put a 2 blade scimitar on my plane, and it is incredibly smooth.  Vibration is history. 

FWIIW and YMMV

Good luck.

No personal experience but I've heard the same thing about 3 blade props

[Hank]

Some engines vibrate with 3-blades, some don't. Mine doesn't, at least not that I've noticed.

[N33GG]

I didn't really think mine vibrated that much until I put the scimitar on it.  The difference was amazing.