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Engine sag

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MarkCFI

Well Known Member
Patron
It’s winter in upstate so I’m trying to get through a bunch on maintenance items on my 6.

I’m just through the first 100 hours on a vans rv-6.

I was not the builder.

It looks like the engine has sagged down a little. I’ve reviewed several writeups on inserting an additional washer on the lower mount but what I’m not clear on is whether I have to remove the upper mounting bolts to raise the engine enough to pull the lower bolts and insert the washer.

It seems like I would attach the engine hoist, remove the lower bolts, raise engine slightly, insert washer and install the lower bolts.

Is that basically it? Is there a specific writeup I should refer to that’s best?

Thanks
 
You are correct. You can either use some thin fender washers or thicker ones if the sag is really bad. I bet someone on here has the lift (in inches) per thickness of washer you elect to install. This a common issue after engines have ran in, subjected the isolators to heat and vibration. I had to insert a couple of thin washers under mine to get it back to original. You want to make sure you get bolts retorqued to the correct setting which I believe is 40 ft/lbs +/- to get the carter key to line up. You may have to get some thin washer under the head of the castle nut so that your carter key hole stays in the same spot.
 
You should have some alignment bullets for reinstalling the lower bolts. Same size as bolts. One long and one short. Grind/machine a taper on one end and cut the short ones so they will go thru the assembly from rear to front. Line things up with the long bullet, remove and then insert the short bullet and drive it completely thru with the original bolt. Start the nut and washer and then do the other side.
 
You could slot the washers and put them in just by loosening the lower and upper bolts and not removing them. But if the bolts would be too short then replacing the bolts will be required which would not make sense to slot the washers anymore.
 
The arm length / distance ratio for the distance from the spinner to the upper engine mounts ( the effective pivot point the engine will rotate/pivot on), and the distance between the upper and lower mount point is about 2.5 (you can measure the exact distance if you want to be more precise).

Decide how much you want to raise the spinner and divide by 2.5. That is how thick the spacer should be.
You don't have to remove the bottom bolts, You can make a "U" shaped spacer of the appropriate thickness from aluminum sheet and slip it into place between the existing washer and the front face of the isolator.
 
My experince. A standard 1/16” washer on both bottom engine mounts (between the mount and the engine) will raise the spinner by ~1/4”.

Carl
 
Thanks all for the advice.

I think the next step is to pull the cowl and see how long the bolts are.

If I have enough thread length then I think slotting the washers is what I will do. Else I will order the longer bolts and replace them.

One of the writeups I was looking at had to do exactly that so I’ve got the part numbers.

Much appreciated.
 

Lord Mount Replacement

What are the required steps, tools, and approximate time to replace the "Lord" isolators? It appears we'll need some type of lift (chain hoist, engine picker) disconnect the cables (throttle, mixture, carb heat) disconnect governor cable? baffles? If we have the stuff & tools is this doable by...
vansairforce.net

Obviously some steps unnecessary if you are just adding washers.
 
I added spacers last year and replaced all bolts. I had intentions to replace all the mounts but new mounts were on what seemed to be indefinite back order from the couple of places I had ordered them from. Washers were a fairly quick and straight forward job. I have part numbers for what I ordered if needed.
 
kswanson said:
I added spacers last year and replaced all bolts. I had intentions to replace all the mounts but new mounts were on what seemed to be indefinite back order from the couple of places I had ordered them from. Washers were a fairly quick and straight forward job. I have part numbers for what I ordered if needed.
Click to expand...
I have a RV6A 0-360 CS prop 600 hours. I added fender washers last year and did not loosen the top mounts. Put a couple on the 4 bottom points of the mount. Engine hoist to hold engine up and have at it. Looks good now. I did have to use longer bolts, But, had some in the hangar.
My luck varies FIXIT
 
Bavafa said:
You could slot the washers and put them in just by loosening the lower and upper bolts and not removing them. But if the bolts would be too short then replacing the bolts will be required which would not make sense to slot the washers anymore.
Click to expand...
I would advise against slotted washers grinding against your engine case mounts. On the 4 cylinders, they are incorporated into the case. These things move and vibrate around at the micro level. Slots in your washers will grind against your case and then they will have to be machined out or welded up and re-machined. A large washer that puts the edges outside the area is your best coarse of action. The hardest part of this is getting that dang carter key out of the castle nut and then removing the nut. After that, it's not that tough to get the cherry picker to slightly pick up the engine and pull the bolt back to get the new washer in there. I've done this recently and start to finish, by myself, it took about 2 hours for the two bottom mounts. That is including set up and tear down.
 
Aden Rich said:
I would advise against slotted washers grinding against your engine case mounts. On the 4 cylinders, they are incorporated into the case. These things move and vibrate around at the micro level. Slots in your washers will grind against your case and then they will have to be machined out or welded up and re-machined. A large washer that puts the edges outside the area is your best coarse of action. The hardest part of this is getting that dang carter key out of the castle nut and then removing the nut. After that, it's not that tough to get the cherry picker to slightly pick up the engine and pull the bolt back to get the new washer in there. I've done this recently and start to finish, by myself, it took about 2 hours for the two bottom mounts. That is including set up and tear down.
Click to expand...
There is or should already be a washer between the case and the mount. This sloted washer can go between the existing washer and the mount and never touch the case.
 
Bavafa said:
There is or should already be a washer between the case and the mount. This sloted washer can go between the existing washer and the mount and never touch the case.
Click to expand...
I agree and what I posted earlier.
I have done this on a number of RV’s and it causes no problems.
 
I need clarification. I thought washers went between firewall and engine mount, but here I'm seeing references to the Lord style vibration mount location. Which is it, and does it matter?
 
Aden Rich said:
I would advise against slotted washers grinding against your engine case mounts. On the 4 cylinders, they are incorporated into the case. These things move and vibrate around at the micro level. Slots in your washers will grind against your case and then they will have to be machined out or welded up and re-machined. A large washer that puts the edges outside the area is your best coarse of action. The hardest part of this is getting that dang carter key out of the castle nut and then removing the nut. After that, it's not that tough to get the cherry picker to slightly pick up the engine and pull the bolt back to get the new washer in there. I've done this recently and start to finish, by myself, it took about 2 hours for the two bottom mounts. That is including set up and tear down.
Click to expand...
I’m heading up to the hangar this weekend and will take a look and a picture. For some reason my recollection is that there is a metal locknut on the mount bolt and not a castle nut.

Currently searching for a used engine hoist on marketplace. Came up dry trying to borrow one so far. Will need it again when I hang the engine on the RV-8 I’m building.

But I’m not 100% sure.
 
revenson said:
I need clarification. I thought washers went between firewall and engine mount, but here I'm seeing references to the Lord style vibration mount location. Which is it, and does it matter?
Click to expand...
No, the common practice is just to move the engine from the engine mount and not the entire engine mount. This means to leave the engine mount alone and just deal with the two bottom bolt that go thru isolators and hold the engine in place.
 
MarkCFI said:
I’m heading up to the hangar this weekend and will take a look and a picture. For some reason my recollection is that there is a metal locknut on the mount bolt and not a castle nut.

Currently searching for a used engine hoist on marketplace. Came up dry trying to borrow one so far. Will need it again when I hang the engine on the RV-8 I’m building.

But I’m not 100% sure.
Click to expand...
where are you located, many have them that you can just barrow it and if you are near me, you would be welcome to barrow mine. I am at KPVF
 
revenson said:
I need clarification. I thought washers went between firewall and engine mount, but here I'm seeing references to the Lord style vibration mount location. Which is it, and does it matter?
Click to expand...
It is the rubber isolators ('Lord' is the manufacture mostly) that hold the engine to the engine mount that become compressed over time which causes "sag" of the engine.

In my installation I replaced all 4 bolts so I could use metal lock nuts instead of castle nuts
 
Bavafa said:
where are you located, many have them that you can just barrow it and if you are near me, you would be welcome to barrow mine. I am at KPVF
Click to expand...
I’m at KITH. Ithaca NY.

I appreciate the offer but I’m thinking you may be a little bit of a drive 😁
 
kswanson said:
I added spacers last year and replaced all bolts. I had intentions to replace all the mounts but new mounts were on what seemed to be indefinite back order from the couple of places I had ordered them from. Washers were a fairly quick and straight forward job. I have part numbers for what I ordered if needed.
Click to expand...
I apologize for thinking I knew what I needed. Not the first time. Based on the writeup I was following I was going to just add an AN970 washer to the lower mounts. And when I went to ACS I came across what are called engine mount washers. Those were about $17 dollars each.

Can I use a standard AN970 washer to shim the bottom mounts? And if yes is it permissible to add more than one washer.

If you have the part numbers you ordered that would be great. It’s about an hour drive each way to the hangar for me so trying to get what I need before I head up.
 
MarkCFI said:
I apologize for thinking I knew what I needed. Not the first time. Based on the writeup I was following I was going to just add an AN970 washer to the lower mounts. And when I went to ACS I came across what are called engine mount washers. Those were about $17 dollars each.

Can I use a standard AN970 washer to shim the bottom mounts? And if yes is it permissible to add more than one washer.

If you have the part numbers you ordered that would be great. It’s about an hour drive each way to the hangar for me so trying to get what I need before I head up.
Click to expand...
It’s an experimental aircraft, so you can do what ever you want, but shimming the bottom of the engine mount will be more difficult, and it will be applying a change at a location other than where the sag induced change is focused.

Secondary is that the bolts might be too short with an additional washer so you will then have 4 bolts to replace (easily more cost than the large washer).

By the way, contrary to what others have said, a spacer made from 2024 – T3 aluminum is totally acceptable between the vibration isolator and the spacer washer at the bottom bolts for the engine. The benefit to this is you can easily choose a material thickness that gives you the amount of change you want instead of being stuck using a specific thickness of washer.
 
rvbuilder2002 said:
It’s an experimental aircraft, so you can do what ever you want, but shimming the bottom of the engine mount will be more difficult, and it will be applying a change at a location other than where the sag induced change is focused.

Secondary is that the bolts might be too short with an additional washer so you will then have 4 bolts to replace (easily more cost than the large washer).

By the way, contrary to what others have said, a spacer made from 2024 – T3 aluminum is totally acceptable between the vibration isolator and the spacer washer at the bottom bolts for the engine. The benefit to this is you can easily choose a material thickness that gives you the amount of change you want instead of being stuck using a specific thickness of washer.
Click to expand...
I apologize again. I mistyped or meant to convey a different message. I was still planning on inserting a washer between the isolater and the spacer washer at the bottom engine bolts.

I just wasn’t sure that I could use a standard AN970 washer as was called out in the write up I was following. I actually don’t have any aluminum stock at hand so I was thinking the washer was the quick route.

It sounds like that should work as a spacer “if” it provides the proper lift. I was going to order extra and two of the longer bolts once I get up to the hangar and lay eyes on how much thread I have available on the bolts. I suspect I will need the longer bolts.

Does this make sense now? I see how my message could have looked like I was going to shim at the firewall. Not what I planned but what I typed.

Much appreciated.
 
MarkCFI said:
I apologize again. I mistyped or meant to convey a different message. I was still planning on inserting a washer between the isolater and the spacer washer at the bottom engine bolts.

I just wasn’t sure that I could use a standard AN970 washer as was called out in the write up I was following. I actually don’t have any aluminum stock at hand so I was thinking the washer was the quick route.

It sounds like that should work as a spacer “if” it provides the proper lift. I was going to order extra and two of the longer bolts once I get up to the hangar and lay eyes on how much thread I have available on the bolts. I suspect I will need the longer bolts.

Does this make sense now? I see how my message could have looked like I was going to shim at the firewall. Not what I planned but what I typed.

Much appreciated.
Click to expand...
An AN970-6 washer is probably close to the same overall diameter as the isolator washers so it will probably work fine.
 
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