Webb

Webb

Well Known Member
Sponsor
I've noticed that my engine has dropped about a 1/4 inch. After reading posts about how to raise the engine, it appears there are 2 basic ways to accomplish this. Put the washers between the bottom mount and the engine or between the firewall and the engine mount.

Is one method better than the other?
Is one easier than the other?
 
When you really study this issue, it seems the engine does not drop at the front so much as it drops straight down parallel to the thrust line.

When you add washers, you are changing the thrust line.

A friend of mine fixed his by switching from the Van's to the Lord mounts.


As far as your original question. it would be much easier to put washers behind the mount to the firewall than to mess with the engine bolts. This puts some stress in the mount though.
 
I would advise against putting washers between your engine mount and firewall. The accepted method is to swap the washer around on the engine mounts themselves, or replace your mounts with stiffer ones.

Given the variability in putting these things together, I doubt seriously you'd have to worry about the thrust line changing, but I'm not an engineer.
 
Q on bottom engine mounting bolts

Engine sag? Even if not, a Q check on the bottom engine mount bolts (to firewall) is not a bad idea.
 
Are you sure?

Webb, are you sure you have the correct rubber mount s in the correct location?

The reason I ask is two fold, mine has about 280 hrs. and it has not sagged at all. I do loops and rolls in it also. The other reason is because I heard from a buddy that a couple guys at his airport put theirs in the wrong location because the local "expert" told them wrong and their engines have sagged.

I don't have the instructions in front of me but I am thinking that the ones with the washer molded in goes on the bottom. Check the instructions to make sure.

I'm using the mounts that Vans sent me.
 
Last edited:
I added a couple of extra washers on the engine mount. I cut slots slightly larger than the bolt into the washer. This let me install the washers by sliding them on over the bolt without removing the nut. I just loosened the nut and used a engine hoist to raise the engine. Still painful to get at the nuts, but at least I did not have to pull the bolts and get them restarted through the dynafocal mount.

Definitely raised the engine up.

I had about 500 hours on the engine before I noticed that sag. It gradually got worse until I put in a couple of washers per side at 800 hours. I now have 850 hours. I do regular aerobatics, including 3g loops.

Randy
 
bhester said:
Webb, are you sure you have the correct rubber mount s in the correct location?

The reason I ask is two fold, mine has about 280 hrs. and it has not sagged at all. I do loops and rolls in it also. The other reason is because I heard from a buddy that a couple guys at his airport put theirs in the wrong location because the local "expert" told them wrong and their engines have sagged.

I don't have the instructions in front of me but I am thinking that the ones with the washer molded in goes on the bottom. Check the instructions to make sure.
Click to expand...

Positive - I checked them about 15 times before I hung the engine. All 4 are the same. Top and bottom are oriented differently.

Ironically this post showed up this morning. The wife is out of town, it's raining, and I was looking for something to do. Washers showed up in the mail yesterday. Hmmmmm....somebody trying to tell me something here?

It's not a bad drop but it bothers ME. I talked to Ken at Vans and his comment was it wouldn't change the thrust line enough to effect flight characteristics. It is more "cosmetic" in nature and effects the builder's temperment.

One thing for sure, if my airspeed goes up, is was needed. If my airspeed remains the same, it was cosmetic. If my airspeed goes down, I'll jerk 'em out and live with the drop. My guess, it's cosmetic. I'm flying to Atlanta tomorrow and will report back any changes.
 
Engine Sag

I have the same problem on my -6A.

It has been suggested to me by a DAR to shorten the stop tubes inside the top set of mounts since this is what you are torqueing the bolts against.

I haven't done it yet but it seems logical.

Dave Gehle
Heber Springs, Arkansas KHBZ
RV-4, RV-6A, J3-C65 (in pieces)
 
Lord, Barry or VIP mounts used????

Bobby, Randy and others,
Please edit your posts to include what brand (and model if you know it) of mounts you are using. This will aid those who have not decided what brand of mount to buy.
Charlie Kuss
 
Brantel said:
When you really study this issue, it seems the engine does not drop at the front so much as it drops straight down parallel to the thrust line.

When you add washers, you are changing the thrust line.
Click to expand...

Has someone studies this and gotten data to prove this is true?
I can believe it does happen to a small degree, but I find it doubtful that all of the movement typically seen is due to the entire engine dropping lower.
Since the top vibration isolators are generally loaded in tension and teh bottom ones in compression, there is a pivoting moment that exists approx. centered vertically between them. Considering the arm length fwd. to the spinner/propeller. it takes very little shape change in the isolators to translate into an 1/8" vertical movement at the front.
 
chaskuss said:
Bobby, Randy and others,
Please edit your posts to include what brand (and model if you know it) of mounts you are using. This will aid those who have not decided what brand of mount to buy.
Charlie Kuss
Click to expand...

I have the same issue with my -6. I replaced the mounts with new isolators from Van's. It made no difference, as I still have a about .375" sag at the spinner.
Some time ago, there was another thread on this issue, with one message that gave the calculations for washer thickness required to raise the spinner 1/2".
I have carefully inspected my engine mount for cracks, distortion, etc., but found no apparent damage. It appears that adding washers to the best solution is to solve this problem.
If anyone happens to have a fresh set of Van's or Lord isolators, it might be beneficial to see if there is a diference in the mount dimensions or the spacer tube.
 
Anecdotal Evidence

Originally Posted by Brantel:
When you really study this issue, it seems the engine does not drop at the front so much as it drops straight down parallel to the thrust line.
Click to expand...

Originally Posted by rvbuilder2002;
Has someone studies this and gotten data to prove this is true?
Click to expand...

Originally Posted by Webb;
.....I talked to Ken at Vans and his comment was it wouldn't change the thrust line enough to effect flight characteristics. It is more "cosmetic" in nature.....
Click to expand...

Scott,

I have no reason to dispute Brian Chesteen's observation. After 200 hours, the engine on my -6A fitted with Van's rubber mounts, began sagging (at least to the point I first took notice)...and as Brian correctly predicted, straight down. In the final quote, Ken Scott is said to have opined....."has not changed the thrust line enough to effect flight characteristics." True enough, but cosmetically? Yes, it does bug me. This is precisely why I fitted the cowl on the -8 project in such a way that (anticipated) engine sag will only serve to enhance the position of the spinner relative to the cowl.

73dr0z.jpg
 
Last edited:
rvbuilder2002 said:
Has someone studies this and gotten data to prove this is true?
Click to expand...

All the data I need is at any RV flyin. If you study the planes with sagging engines, 90% of the time the spinner backplate is still parallel with the front of the cowl. If the engine was drooping in the front only, the backplate would be closer to the cowl at the bottom than the top. Saw it first hand on a friends new RV6 and Van's mounts within just a few hours of first flight. New Lords brought it right back up where it belonged and it has not sagged yet.
 
Brantel said:
All the data I need is at any RV flyin. If you study the planes with sagging engines, 90% of the time the spinner backplate is still parallel with the front of the cowl. If the engine was drooping in the front only, the backplate would be closer to the cowl at the bottom than the top. Saw it first hand on a friends new RV6 and Van's mounts within just a few hours of first flight. New Lords brought it right back up where it belonged and it has not sagged yet.
Click to expand...

I guess I'll have to just change my user ID to "skeptic" then.;) I am not convinced.
The spinner is only 13" in diam. The distance from the spinner to the isolaters is about twice that or a little more. Doing some rough math in my head says that with an 1/8" drop in the spinner the most change you would likely see in spinner gap is 1/32" (probably a bit less than that). Since very few spinners are perfectly parallel to the cowl right from the start, I think the 1/32" change could easily be missed when looking at flying airplanes.
I am not disagreeing with teh idea that some of the movement is the result of the entire engine sagging down, but I don't believe that all of the movement is the entire engine.
Just my opinion based on experience from building a dozen or so RV's.
 
Scott is correct...

rvbuilder2002 said:
Has someone studies this and gotten data to prove this is true?
I can believe it does happen to a small degree, but I find it doubtful that all of the movement typically seen is due to the entire engine dropping lower.
Since the top vibration isolators are generally loaded in tension and teh bottom ones in compression, there is a pivoting moment that exists approx. centered vertically between them. Considering the arm length fwd. to the spinner/propeller. it takes very little shape change in the isolators to translate into an 1/8" vertical movement at the front.
Click to expand...

...it is about a 3 to 1 ratio.

A 1/16 washer on both lower mounts will move the prop up about 3/16 inch.

I did this on my Tiger to move the engine sideways to line up with the cowl - not too big a deal, but a few swear words are needed to complete the job...:)

The Tiger Parts Manual has washers "As Required" in a spacer position between the engine case "ear" and the front of the donut mount. On top of the exisiting lower washer if you have a O-360.
 
Washers installed

I forgot what a pain in the glutius maximus it was to get the bolts in the vibration isolation mounts (aka: engine mounts). Compound this by having to work around things like the exhaust that wasn't there on the initial engine hang.

After multiple hours of work, many scratches, multiple explicitives, and a few wishes that the hanger fridge had cold beer in it, the washers were installed.

Also, many thanks to the couple of hanger neighbors when I needed an extra set of hands.

The large washers used are 1/8 inch in thickness just like the ones that come with the mounts. It raised the spinner top approximately 1/4". The top of the spinner is now equal to the top of the cowl. Cosmetically, I am thrilled.

Since I'm flying out tomorrow I will be able to compare my travel TAS speed with previous trips. I don't know if I will see any gain but I am hoping to see an increase. My theory on it. #1 - I reduced some frontal area that was showing on the cowl by moving the spinner up and #2, if the thrust line was moved down a degree, it would potentially change the angle of incidence on the wings and possible reduce induced drag. Probably hypothetical horse manure but that's my story and I'm sticking to it.

Real results will be forthcoming.
 
Last edited:
Results - Maybe, just maybe a knot.

What I did notice is that I seem to have more vibration now. Go figure. Maybe the mounts have to "settle" in again after being re-installed.

Now for a question - how much better are the Lord's mounts than Van's?
 
Any one "over thirty" knows to plan for a little sag. That's what I did on my 6, lined the top of the cowl up with the top of the spinner. Just waiting for that old girl to start sagging with the coming years, just like someone else I know.
 
Webb,
Where did you get the washers? I've got about 1/8" sag on my RV7 using Lords mounts and didn't find them on Van's website.

Thanks

Rocky
 
Rocky - Washers came from Vans....I called them and they looked it up and mailed them. Rise was about 1/4 inch from them.

My opinion - for only 1/8 inch, leave it alone. I've induced a vibration and going to verify that the mounts are truly tight. I can live with the small drop, not the vibration. This will be Saturday morning's project. If the mounts are tight, I'm taking the washers out to see if that was the cause.

I'm also going to get a dynamic balance on the prop.
 
Auch!

Quote:
"Just waiting for that old girl to start sagging with the coming years, just like someone else I know"

Chuck, if your wife reads this, I sure hope you have a comfortable doghouse (or a couch in the hangar)......:D
 
Rockyjs said:
Thanks Webb!
Please give us an update on your vibration

Rocky
Click to expand...

I took the top of the cowl off yesterday and low and behold, the right baffle's front corner was touching the cowl and had rubbed a small area there. Out came the trusty tin snips and the high area was removed and filed. Let this be a lesson to all of us that when we get a warning sign that when something just isn't right, check it out. Otherwise, I would have had to have a glassin' session and repaint. As most of you know, I hate to do glass work.

Since I didn't feel the vibration in the stick or buttocks but did see it on the panel and could feel it when I touched the panel, I suspect I found the guilty culprit.

Will fly it this morning to test it out but I feel confident that problem is fixed. I'll let you know the end results.

Speaking of sagging, It reminds me of the Rodney Carrington Song, Dear P...., I don't like you anymore.
 
Thrust LIne

Does anyone know for sure if the thrust line is parallel with the fuselage waterline or is it positive or negative? Just staring at my -6, it looks like the thrust line is pointed up (positive) in relation to a line thru the fuselage centerline. Hmmm.
Jim
 
49clipper said:
Does anyone know for sure if the thrust line is parallel with the fuselage waterline or is it positive or negative? Just staring at my -6, it looks like the thrust line is pointed up (positive) in relation to a line thru the fuselage centerline. Hmmm.
Jim
Click to expand...

The old -6 plans have full welding diagrams for the engine mount.

It shows 1.25 degrees right offset and zero vertically.

All referenced to the firewall.

What might look a bit visually confusing is the the center of the dynafocal ring is offset 0.5 inch to the left of the planes centerline, presumably to put the spinner on the centerline.
 
thrust line

Thanks Gil.

I am chasing a trim problem and sort of grasping at straws trying to find anything that is out of the ordinary.
 
You must log in or register to reply here.