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Ideas for Increasing Cowl Clearance

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  • Ideas for Increasing Cowl Clearance

    I'm finding that I still have too little cowl clearance on the front right cylinder. Does anyone have any ideas for how to improve it, short of building a third cowl?
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  • #2
    If I'm understanding what I'm seeing, it appears that the baffle is rubbing on the cowl door. Correct? Not seeing the back side of the baffle, I can only assume there's no way to trim the height a bit. Seems that would help, but I'm sure you already considered that.
    A number of years back, a friend installed a 200 HP IO360 in a RV6. The angle valve heads are a bit bigger than the parallel valve ones. He ran into similar problems. His solution was to make fiberglass bumps that were riveted into the cowl. The bumps were finished nicely and painted to match the cowl. They not only made room for the engine, but they added a bit of a brawny look to the plane. Kind of like a cowl induction hood on a '69 Camaro.

    Bill

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    • #3
      I had a similar problem and unfortunately the only way I could solve the problem was to add 3/4 inch to each side of the nose cowl

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      • #4
        If the contact area was not there when the aircraft was new and only showing up now perhaps the engine mount rubbers are allowing the engine to torque up and make contact with the cowl.
        Patrol (modified)

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        • #5
          It has always been a tight spot, but it does seem to be getting worse. Do we have any quantitative specs to test for on the engine mount rubbers? These have 300 hours over 4.5 years of flying and 3 years of building before that.

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          • Rollie
            Rollie commented
            Editing a comment
            I was wondering if maybe your engine was starting to sag, but it looks like if that were the case it would ride lower in the front, wouldn't it? Maybe your engine is moving more in flight than it used to. Along the same line though, maybe re-torquing the bolts on the rubber engine mounts might help. The next, least invasive idea is blisters on the cowl door where it is rubbing. I think that might be tough to do with the bend in the doors, at least on mine as they spring back to partially straight when opened. I suppose if you fabricate the blisters with the door closed first and then mount them, that would work.

        • #6
          I agree Jared, you might put a blip in the cowling to clear this area. I did a similar thing to clear my plugs. I did stager them a bit but can't really tell . It's a easy fix. Stinger
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          • #7
            You’ve probably already considered these; so, for whatever they are worth:
            1. I’ve read of RV builders sawing/grinding off the front “ear” for clearance. Downside is that it would kill core value for a replacement jug.
            2. Rework aluminum baffle for lower profile.
            3. Reduce layers of baffle material, both aluminum and rubber.
            4. Thinner rubber.
            5. Use attach screw with flatter head.

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            • #8
              Thanks for the tips all around. I've already ground off the front ear from the cylinder. I'll see if I can eliminate any more baffling, and if that doesn't work and the mounts look good, I guess it will eventually become a fiberglass bump.

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              • #9
                Last-gasp ideas follow, but if you really don't want a blister.... and I know you don't want to make a third cowl!
                • Old engine mounts, to let the engine sag a little lower.
                • Loosen the screwed connections to the firewall a little, so the whole cowl lifts under baffle air pressure.
                • If you have room, slot the holes in the cowl at the cowl-firewall interface, lift the cowl as much as you can, then tighten all the firewall screws to hold it there. Use doublers to re-fix the holes in their new location.

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                • #10
                  Stretching broad area slightly??? Realizing that's easier said than done and probably complicated by being 2024t3. Perhaps shot bag with slapper or mallet; or press; or english wheel. Just reaching for ideas.

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                  • #11
                    If it is not the engine mounts, I would go with the blisters. That was my first thought. Is this a common problem?

                    Looks? On cars, they charge extra fore stuff sticking up from beneath the hood! Put an "S" or an "R" on each blister and it will be a topic of conversation.

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                    • #12
                      Originally posted by marcusofcotton View Post
                      Stretching broad area slightly??? Realizing that's easier said than done and probably complicated by being 2024t3. Perhaps shot bag with slapper or mallet; or press; or english wheel. Just reaching for ideas.
                      I tried a mallet, it's not a good look... You could always fill and sand over it I guess, but they you are basically just making a blister.
                      It is possible if you know someone very skilled on an English Wheel. Bearhawk ZK-FHR has a chin blister made on an English Wheel.

                      Originally posted by svyolo View Post
                      Is this a common problem?.
                      I think it depends which nose bowl and prop combination you select.

                      My cowl is very close there, in fact when I made my second cowl it got dented. The metal baffling piece in the exact same location as Jared has issues, it impacted the cowl. The engine wobbles enough during start-up to leave a permanent dent in the cowl. I was too slow to notice it, before I went flying for the first time. In my case, the baffles are taller than required, so I just trimmed back a 1/4 inch and it was fine, noting my tiny "blister" dent.
                      Last edited by Battson; 08-12-2018, 11:21 PM.

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                      • #13
                        Jared, I used Bob’s nose cowl which gives a bit more clearance in this area. I haven’t worked up the engine cowl yet but thought if it was too tight I would not come up with the baffle to the top cowl 90* from the cylinder. I would work something angled at about 60* and then another break 30* to come to the top. I think even if you can use a stiff baffle material and have nothing there other than that in the area of contact, and support the remaining aluminum somehow, the material against the cylinder itself, i think it would seal OK.
                        It looks like Bob’s cowl will do it for me but it will still be close. Think I have a good 1/2-3/4” clearance from the “bump”.
                        Steve
                        P203

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                        • jaredyates
                          jaredyates commented
                          Editing a comment
                          Interesting, I like this idea.

                      • #14
                        Hey Jared, how did you make out with this? I am at the baffle, bump, cowl sequence now. I'm about 1/2:" clearance now without prop and accessories so will move away some more. I haven't cut the bump off yet but came off the top side of the cylinder with the baffle material as soon as you can with a 90* bend for 1/2" and then up at about 60*. I will cut away the metal near the corner and come up with a bent up second piece between the front of the cylinder and cowl; over lapping and using the same screw hole. The seal will cover this and transition flat between the two parts. I wanted to know what you think is the minimum distance for clearance around this spot. Thanks

                        Steve W P203

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                        • #15
                          Originally posted by Steve W View Post
                          Hey Jared, how did you make out with this? I am at the baffle, bump, cowl sequence now. I'm about 1/2:" clearance now without prop and accessories so will move away some more. I haven't cut the bump off yet but came off the top side of the cylinder with the baffle material as soon as you can with a 90* bend for 1/2" and then up at about 60*. I will cut away the metal near the corner and come up with a bent up second piece between the front of the cylinder and cowl; over lapping and using the same screw hole. The seal will cover this and transition flat between the two parts. I wanted to know what you think is the minimum distance for clearance around this spot. Thanks

                          Steve W P203
                          So far it seems I have found a suitable clearance. All of the various factors combined to increase the clearance slightly, and I think adding more camlocs to the cowl door has helped a bunch, along with using a bent baffle mount. I've probably got half an inch to an inch there.

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