O-540 Firewall Forward

[Wes Ragle]

Guys,

I just got the LORD mounts for my O-540. I intend to start the cowl soon. While considering all of the stuff that is going to go on FWF I realize how much I *don't* know.

I will use this thread/topic to ask questions and chronicle the experience. Please be as kind as you can 'cause I have a bunch of questions.

To start with, per Bob B., I have an O-540-A4 Exp. This is a low compression O-540. I intend to burn mogas. The ears and mount are "Type I". The (correct) LORD mounts are J-3804-20.

Well, I need to hang the engine. The first questions I have are:

1) What is the correct bolt length? I can place the mounts on the engine ears, measure the thickness, add the thickness of the dynafocal where it accepts the bolts, and call that the grip. However that wouldn't account for any compression of the LORD mounts. Well, accept for a washer or two.

2) I have heard some folks say that the two halves of the mounts are different. They sure look the same to me. Are the halves different?

3) Do you torque the bolts according to their size or is there a a different torque appropriate for the LORD mounts?

If there is something I can get my hands on to read that will answer these questions that would be great.

I just need to get'er hung so I can start thinking about the cowl and baffles.

Any and all help and advice appreciated.

Thanks,

Wes

[swpilot3]

I'm going to be where you are soon, so I'm anxious to hear what people have to say. Thanks for asking these questions.

[Bdflies]

The halves of each mount assembly are the same. Some folks use stiffer mounts on the bottom locations. That might be what you're referring to. This is sometimes done to alleviate vibration issues and (I think) some airframe manufacturers call out different top/bottom numbers. Can't say for sure the bolt grip length and yes, there is a bit of compression. There's not so much compression that you can't get a washer and the nut on the bolt, when relaxed during assembly. So, mock up the assembly and measure the total length. That'll give you a pretty good idea of length. I like a large area washer under the bolt head and the nut, but that's just me. Wouldn't be a sin, to put an extra washer, if need be and if there's room for it. Sometimes the end of the bolt gets really close to the case, when torqued up. This might be limited to the 4 cylinder engines, though. Finally, the last two times I had anything to do, with changing mounts, we torqued them to 40ft lbs. You might do some more research, to confirm that, but I can tell you that the engines are still on the aircraft.

Bill

[S Lathrop]

I have just finished the task you are starting. I have the engine mounts finished and the cowl in place with skin clips.

Russ Erb posted a drawing of the Lord Engine mounts, the type 2 mounts. That drawing gave the installed dimensions for the mounts. I made aluminum blocks to those drawings and used the aluminum blocks in place of the actual mounts to build the engine mounting. This way I did not have to worry about heat damage to the mounts as I built engine frame. I would try to get a similar drawing for the type 1 mounts.

I will say that in the case of the type 2 mounts, having the drawing was absolutely critical because the mounts are different top to bottom and the forward and rearward side of the ear.

I positioned the fuselage on my building table and built a stand for the engine. This placed the work area in a better position to do the fitting and welding. I also felt that it was easier to do the measurements necessary for the required accuracy, at least I felt so.

[DRLPatrol]

...

2) I have heard some folks say that the two halves of the mounts are different. They sure look the same to me. Are the halves different?

...

Not sure about that part # but some mounts are the same except one has a ridge around the edge of the rubber part about half way up the thickness. The one with the ridge goes on the compression side, ie. next to engine for lower and away from engine upper. Has to do with helping them not to sag over time.

Doug

[Bdflies]

Below, are pics of an isolator set that's intended to be oriented a specific way. The half that faces the engine, displays the ridge that Doug described. In case anyone is wondering why one half is taller, this set is for a bed mount Continental. In this case, the engine sits on all 4 mounts, thus no top and bottom locations on the engine. While this is an extreme case of not looking alike, when the halves are different, you're going to see a difference. Could be just different part #'s on the halves. I 'think' (but am probably mistaken), when the halves are intended to be oriented specifically, the package will include pretty explicit instructions for the installation.

[Wes Ragle]

Hi Guys,

Thanks for the feedback. Attached is a pic of two of my isolators. Front and back look identical. The holes look to be approximately 7/16". Does that sound right? I'll stack everything up and try to get a length tomorrow.

Wes

[Wes Ragle]

Hi Guys,

I like a large area washer under the bolt head and the nut, but that's just me. Wouldn't be a sin, to put an extra washer, if need be and if there's room for it. Sometimes the end of the bolt gets really close to the case, when torqued up. This might be limited to the 4 cylinder engines, though. Finally, the last two times I had anything to do, with changing mounts, we torqued them to 40ft lbs. You might do some more research, to confirm that, but I can tell you that the engines are still on the aircraft.
Bill

I added up the following to calculate the bolt length needed to mount the engine.

0.135 for the face of the engine mount.
2.3 for the uncompressed vibration isolators (on or off the engine ears)
0.063 for a single AN960-716
--------
2.498

I (gently) placed the isolators in the vice with the center piece in place and found that they compressed ~ 0.2 inches before I had metal to metal. I talked to an A&P and he told me that the isolators were designed to be compressed until they were metal to metal and use the torque spec called out for the diameter of the bolts used.

So the total grip without any washers on the engine side of the bolt needs to be ~2.3 inches.

The best fit listed by ACS is an AN7-30 which has a grip of 2.4375.

Each large area washer (AN970 type) is 0.109 thick.

So it looks like AN7-30 bolts with, like Bill said, one or two AN970s on the engine side.

I'll give that a try and let y'all know how it comes out.

Time passes ....

Got the nuts, bolts, and washers today. They worked out just fine.

So, for a type I mount for an O-540 it took:

Four LORD J-3804-20 Vibration isolators.
Four AN7-30.
Four AN310-7
Eight AN970-7
Eight AN960-716
Four yet to be selected cotter pins.

Wes

[AKKen07]

Thanks for posting this Wes! yeah, I know it was 5 years ago but still...

[Wes Ragle]

RIGGING THE NOSE BOWL:

While waiting on engine bolts I was reading and thinking about rigging the nose bowl.
No matter what, if I get that wrong, things will not turn out good.
This is what I came up with:

1. I cleco’d the nose bowl halves together and made sure the prop side laid flat on the bench.
2. I made an outline of the spinner rear bulkhead centered on the nose bowl opening.
3. I pulled out the prop and measured from the back of the spinner spacer to the back of the prop, the face of the flywheel.
4. I measured the height of the rear spinner bulkhead.

The measurements I came up with are:
2.185 from the spinner spacer on the prop to the flywheel .
1.342 from the forward face of the rear spinner bulkhead to the rear of the flange of the bulkhead.

I will shoot for a 3/8” gap.

So: 2.185 – 1.342 – 0.375 = 0.468 should be the spacer from the front of the flywheel to the front of the prop flange on the nose bowl.

I rummaged around and found a piece of scrap plywood that measured 0.45 thick
Adjusting for the .018 discrepancy leaves me with a gap of ~ 0.393.

Now here is the lucky part. While looking for the plywood I stumbled across a rear prop bulkhead that I had long since forgotten I had. It has the exact bolt pattern and crank diameter as the O-540. It is a little smaller than the spinner I got from “Avipro” (long time ago) but it is obviously round and so must be useful :-)

Continuing the steps:

1. I traced the spinner bulkhead onto the 0.45 plywood.
2. I placed the lucky bulkhead dead center of the traced pattern and transferred the hole pattern.
3. I cut the traced pattern out and carefully located it on the face of the nose bowl as if the imaginary prop were level.
4. I drilled and cleco’d the pattern in place.
5. I clearance the plywood for the seams in the nose bowl and transferred the pattern to the rear of the nose bowl (subtract a bit of clearance for fiber glass thickness) .
6. I transferred the center line down so I could mount a level reference out of the way of the prop bolts.

At that point I had to stop. I have been working on fixing up a house out in the boonies and a bunch of my tools are there. The chuck on my air drill is too small to accept the 2 ¼ “ hole saw I need to cut the hole for the crank.

I think that when finished I will have a nose bowl that will bolt right onto the engine and hopefully be very close to perfectly centered.

If someone sees something I’m doing that is going to get me in a mess, please speak up.

Thanks,

Wes

[Wes Ragle]

MORE NOSE BOWL

Hi Guys,

I received the nuts, bolts, and washers and was able to hang the engine. Once the engine was hung, I put the jigged nose bowl on and located what I believed to be the four corners of the cowl top

I really, really wanted to keep going but I couldn't stand the thought of finishing the cowl only to find that I misjudged something.

So, I cleco'd a piece of scrap from the bottom of the nose bowl to the firewall for future reference. Then, off with the nose bowl, on with the prop, back on with the nose bowl, cowl and piece of scrap. I think it's came out OK.

I'll get the prop off and the jig back on tomorrow and carry on.


Now, picture this. I'm on the top step of the step ladder with a very expensive piece of my airplane cradled in my arms. I'm trying very hard to hold this thing in place, all the while admonishing my bride of 39 years to please get the bolts started and hurry every she gets. Just about the time I start quivering the bolts get started. Now it's just a matter of working our way around the prop , jiggle and tighten, jiggle and tighten ...

Just as the crank started to seat in the the prop hub things started to bind. Well, it's my fault, is says right there on the plug "Remove Before ...." So we took it back off, rested a while, and did it again :-)

Wes

P.S. Sorry for the hi-res pics. My camera died and must have defaulted. It's fixed now.

[JimParker256]

I can SO identify with the "it says right there on the plug..." comment! Sometimes we are so excited about taking the next step that we overlook the simplest things... Glad it worked out for you. Looks good!

[Bdflies]

That sure is a gorgeous engine! I might have to consider a lexan cowling, if I were you. Regarding the prop install/removal, two thoughts; make a sling, from nylon ratchet straps and hang the prop (horizontal) from your engine hoist. This makes for an easy one person install or removal. Or, my personal choice, have the wife hoist the prop whilst you attend to all the bolts!
Looking really good, Wes.

Bill

[Wes Ragle]

Hi Bill,

Thanks a lot for the tip. I'll do just that (option #1). Taking the prop off is more horrifying than putting it on. You don't know when it is going to let go.
Funny, last night I kept thinking "I wish my straps would reach the rafters". That with the hoist sitting right there.

As for option number two, Millie is now invested to the tune of one broken nail. As I understand it, the repair will take weeks. I have to spread things out a bit :-)

Wes

[Bdflies]

Regarding Millie's nail, I understand more than you could ever know. I understand!
But we Love 'em, don't we? 😎

Bill

[Wes Ragle]

Cowl (Some Progress)

Hi Guys,

The cowl is pretty much fitted. I was going to proceed by applying the fasteners but had second thoughts. I should probably fuss with the air box while things are easy to remove and reinstall.

Questions: Bob supplied a Marvel MA4-5 carb with the engine. Does anyone know what air box I need and where to purchase it? Is there a better/easier solution than the standard air box?


Thanks,

Wes

[whee]

Looks great! I'm so excited to start on my cowlings. Really makes things feel like they are coming together even though I will have strip my airframe back down for paint.

[Wes Ragle]

Thanks Whee,

I am still fretting over the induction system. I don't like the standard solution but if I get too far off track it can cost a lot of time. Cogitating ...

Wes