Conical mounts and bolts

[Gordon Misch]

Since the part numbers are the same except for the suffix, I wonder if they're just different hardnesses.

 

[superbad]

I have a set of the standard Lycoming Bushings PN #71032 on the shelf but they just don't look right/similar. I know they expand under tension but appear to be a much smaller diameter.

 

[Steve Pierce]

I have never seen anythoing other than the Lycoming 71032 engine mount bushings on a conical mount O-320. I have installed several sets lately and can now obtain the factory Lycoming bushings from Aircraft Spruce. Never had much luck with aftermarket bushings. I made a gauge that is 1.84" wide that fits over the baffle to measure the compression on the bushings. I merged a couple of threads on the same subject so all the information is in one place.

 

[mike mcs repair]

so?, is 8-44 length for ALL installations?

the parts book i looked in was for a small engine...

I will be putting an O-360 with conical on a 8"? lowered backcountry engine mount.....

 

[Steve Pierce]

Yes, all the Lycomings from PA16 up to PA22

 

[MTcubbldr]

so?, is 8-44 length for ALL installations?

the parts book i looked in was for a small engine...

I will be putting an O-360 with conical on a 8"? lowered backcountry engine mount.....[/
On the 150 Lycoming
-44 bolts with NO washers
Just the think large mount washer only
Approximately 1 thread thru nut will give you the 1.84 dimension

 

[farm_boy252]

I have never seen anythoing other than the Lycoming 71032 engine mount bushings on a conical mount O-320. I have installed several sets lately and can now obtain the factory Lycoming bushings from Aircraft Spruce. Never had much luck with aftermarket bushings. I made a gauge that is 1.84" wide that fits over the baffle to measure the compression on the bushings. I merged a couple of threads on the same subject so all the information is in one place.

curious how many hr job is it for someone experienced?

 

[Steve's Aircraft (Brian)]

Old thread but thought I would share my new Conical engine mount bushing torque tool…

I did a quick drawing using Alibre Design.. Exported it as a .STL file and my son printed it up on his 3D printer… It’s a 3 hour print at 10% infill… Tested it today and it worked pretty slick..

Brian..

 

[Kodiakmack]

So we replaced these 100 hours ago, torquing to measurement with our fun new tool to measure the squish. We noticed at this annual that they are no longer within those dimensions. Question is if we should re-torque, and if so to do with the weight of the engine on them, or with the engine lifted to relieve weight pressure?

 

[Steve Pierce]

What brand bushings did you use? I have not had Lycoming bushings move other than sag over the years.

 

[Kodiakmack]

What brand bushings did you use? I have not had Lycoming bushings move other than sag over the years.

I’ll look for certain but I believe they were either lycoming or superior. And they don’t really appear to have sagged, just spread if you will, which admittedly doesn’t make much sense. But we torqued them to the correct dimension when we put them on, coffer keyed, and torque sealed the bolts and there’s no indication of movement from that torque seal.

 

[Kodiakmack]

I’ll look for certain but I believe they were either lycoming or superior. And they don’t really appear to have sagged, just spread if you will, which admittedly doesn’t make much sense. But we torqued them to the correct dimension when we put them on, coffer keyed, and torque sealed the bolts and there’s no indication of movement from that torque seal.

confirmed. They are lycoming bushings.

 

[DENNY]

Lots of good information here, I have got a fresh cup of coffee so I will add my thoughts. On a Pa 18 the stock thrust line is 4 degrees down. I have seen a change to 8 degrees down over 1,000 hours with stock bushings corrected to 4 degrees by replacing the bushings (with a 3 mph increase in cruse with new bushings) the plane flew fine at 8 degrees down just a bit slower. Now you could also get a Thrust Line mod and go to 0 degrees of thrust line. Most report improvement with this. We all know before the thrust line mod the trick for more speed was to just stack washers on the lower bolts. I would say every plane has a thrust line it likes and flys best at depending on the mission, some of us will go to great lengths to find that sweet spot but in general most won't even notice. But one thing we all will notice is when that flywheel or oil cooler starts wearing its way through the nose bowl!!! At first you wonder if something is loose or broken because it was not like that when you rebuilt the engine 300 hours ago. If you measure the engine thrust line you will likely find it has dropped a bit so what to do? Do you try to adjust the cowling brackets so nothing rubs because you measured the engine mount bolts and put a cotter key in so you know they have not moved. You can try the torque method but that most likely has not changed either. So now we have the answer of simply tighten the top bolts until the the nose bowl matches how it fit with new bushings. Measure the thrust line and it is just how you have it with new bushings and nothing rubbing. So do you replace the bushings every 300 hours so engine mount bolt measurement is perfect and no cowling rub/refit the cowling and accept the change in thrust line/tighten the top mount bolt and realign to proper thrust line?? This will be a dilemma for some of the type A personalities. On a side note the torque or length measurement is pretty much useless unless you can fit that cotter key in the castle nut. If you got the right parts when the key fits it is right. I would replace the bushing every 1,000 hours unless they look bad before. No right or wrong just things to ponder. DENNY

 

[MTcubbldr]

The dimension really shouldn't change. Mounts will compress from heat, oil, & etc.
How old were the mounts when you installed them. They could have been on the suppliers shelf for a long time.
You might need to replace them again, especially if it is a 180 HP engine.
We always use a little DC4 silicone grease on installation to help the bolts slide thru.

 

[Kodiakmack]

The dimension really shouldn't change. Mounts will compress from heat, oil, & etc.
How old were the mounts when you installed them. They could have been on the suppliers shelf for a long time.
You might need to replace them again, especially if it is a 180 HP engine.
We always use a little DC4 silicone grease on installation to help the bolts slide thru.

They were new, and again, aren’t sagging. Maybe they were sitting on spruce’s shelf a while but I don’t see that being a factor here. From what I’ve read (haven’t actually been able to find SI 1007 that addresses this), lube is a no no for this application.

 

[Steve Pierce]

Can you post a picture?

 

[MTcubbldr]

Piper publications on engine mount bushings

Can you post a picture?

Here are the only documents I know of.

 

[Mikey]

Changing out O-320 motor bushings on my PA-12 before the sag more.
Parts manual shows Lyc. 71032 bushings sandwiched between STD-619 washers.
When I pulled my today, the aft washer appears to be a STD-619, but the forward washer on each bolt was some weird eccentric washer w/ an additional small hole drilled in each of them.
Any idea what these were about? Am I good w/ just putting a STD-619 washer on each bushing?
Thanks
Mikey

 

[Gordon Misch]

The standard washer is what's on my -12. I'd bet that eccentric washer is some sort of home-made concoction?

 

[Steve Pierce]

That is from another type of engine mount install. there is only one washer on the engine side, the mount has a washer made onto it.

 

[Mikey]

Cool. Thx Steve. That will gain me a whole 1/16” of clearance on my muffler shroud to mount.
Also explains why it had -46 bolts and a stack of washers instead of -44’s.

 

[tempdoug]

Changing out O-320 motor bushings on my PA-12 before the sag more.
Parts manual shows Lyc. 71032 bushings sandwiched between STD-619 washers.
When I pulled my today, the aft washer appears to be a STD-619, but the forward washer on each bolt was some weird eccentric washer w/ an additional small hole drilled in each of them.
Any idea what these were about? Am I good w/ just putting a STD-619 washer on each bushing?
Thanks
Mikey
View attachment 60983

were they just on the bottom or all 4 bolts?

 

[Mikey]

All 4

 

[Cody Long]

My lower mounts are bulging and the engine is very close to rubbing the engine mount. I measured the bushings at 1.75" at both top and bottom. No rubbing on the nose bowl or cowling. How much clearance is normal?

 

[Steve Pierce]

Should be more clearance than that. From the drawings and the original Super Cubs I have worked on there should be no washers under that nut on the engine mount bolts. Cub Crafters use one washer. Looks like you have 3.