The #2 exhaust spring section 49-16

My #2 exhaust spring is just touching the heat shield. Did others have this issue too? I've tried to move the muffler a little to the left and right but no luck also the if I move to far right the #3 spring hits the water line. Actually both the #3 & #4 springs come very close to the return water lines.

-Ron

Number two Spring!

This has been on the form in the last 2 months. Most first time builders have in stalled the cowl tunnel to high and have found out later that the clearance on that spring and the Exhaust header were to tight and had to modify the cowl after the fact because the engine moves around more in flight than on the ground. So if yo dont have at least 1/2 " space between your exhaust header and the heat shield then you will get something like this after your first flight.


How much space on that spring? Not exactly sure but I would say at least 3/8". How does your space between you header and the cowl look? If its to close then get your dremal out and cut a hole in your tunnel and put new fiber glass matte in the cut out slightly bowed away from your spring and header. Then reapply new heat shield that you had left over from the first time. It will look like this.


http://i798.photobucket.com/albums/yy270/Jetguyii/DSCN2085.jpg

Are we having fun yet?
John
RV12 N1212K

John,

Thanks for the information... I fixed the spring rubbing by bending the tab on the header so it did not stick out so far. The header pipe is another story, I was just able to get a 5/16 drill bit between the header and the cowl cooling duck. That seems to be the closest the header gets the duct, from there it quickly goes to 3/8 or better as the header moves to the cylinder or muffler.

http://picasaweb.google.com/ronedmark/Section_49#5495302904460157634

Thanks,
-Ron

Jetguy said:

Most first time builders have in stalled the cowl tunnel to high and have found out later that the clearance on that spring and the Exhaust header were to tight and had to modify the cowl after the fact because the engine moves around more in flight than on the ground. So if yo dont have at least 1/2 " space between your exhaust header and the heat shield then you will get something like this after your first flight.

Are we having fun yet?
John
RV12 N1212K

Click to expand...

Hey John! Thanks for the heads up. I'll be working on that area when we get back from Oshkosh. Could you provide a little advice as to how to locate the cowl tunnel correctly the first time?? It may save some of us a bunch of time and aggravation.

Thanks, Tom

Exhaust header clearence!

Ron I would say that that header is going to hit the cowl in flight. But if you want just leave it and see what happens on the first flight. Even if it doesn't hit on the ground during the run up remember the engine moves around a lot more in flight.
Tom,
Have the engine installed
Have the exhaust installed
have the lower cowl fitted and installed
Now put the tunnel in and at the back make sure you are lined up with the radiator and then lower the front part of the tunnel so that you have a least 1/2" clearence between the tunnel and the header. Maybe tape a small 1/2" peice of wood to the bottom of the header and just move the tunnel up in place till it hits the wood. If the tunnel is resting on or maybe 1/8" high above the edge of the upper part of the oval cut out in the lower cowl then you will be very close.
My mistake was attaching the tunnel to high. I believe in the directions it shows the rear part of the upper tunnel flange attaching just under the piano hinge line on the lower cowl ( I dont have my directions in front of me at the moment) which is why I mounted mine high. There are a lot of variables here like do you have the lower cowl line up and do you have the exhaust center correctly, etc. It is important to make sure that the tunnel lines up correctly with the radiator and the opening in the tunnel to the radiator is trimmed out as much as possible to allow max air through it, but not to much that it effects the gluing on of the seal between the radiator and the tunnel. You must do the same with the Oil cooler opening, trim it so you have it big enough not to cover any fins. One more hint if you have not made the bracket for the oil cooler yet trim the aluminum edge of the bracket that goes in the front of the oil cooler to max so as not to cover any fins there either. A lot of people are having the oil temps run in the yellow in the summer heat so you want as much air as possible going through the oil cooler and radiator. I live in Texas and its 100F here now so we are heat sensitive. Ok Im ready for Scott to shoot arrows at me now.

John
RV12 N1212K

Jetguy

Ok Im ready for Scott to shoot arrows at me now.

John
RV12 N1212K

too funny John! I hope he's at OSH (he didn't make it to Sun/Fun) so we can give him a hard time...lol

Timely...

Huh, I just trial fitted my cooling tube. As predicted, I got just 1/8 inch clearance under the number 2 exhaust pipe, and that's after moving it down from touching.

Seems a pity as everything else lined up perfectly :-( I'm now wondering whether to modify the cooling tube, or force it down half-an-inch...

Cheers...Keith

Exhaust header clearance!

Keith if you haven't glued in the duct make the change now. !/8' clearance wont work, the header will hit the tunnel in flight cause thats what I had in mine before I flew it. I have another suggestion for you guys and this is just builder technique. Ron I saw the Cylinder temp probe wire in your picture and I would put some form of heat insulation around all those sensor wires under and around the engine. Its does not call for this in directions its just a technique. The temp of the exhaust will be around 1000F so you can imagine how hot it will be around the exhaust and the temps in the coolant hoses will be around 200F. The heat shield is for long term protection against where in tear on those small wires. Here is a link to what Im talking about:

http://www.heatshieldproducts.com/colored_sleeve.php

Pete I think it should be a team effort on Scott.
John
RV12 N1212K

When installing the duct it is important to trim the duct as intended by the scribe lines. The portion that mates with the oval inlet between the 9 oclock and 12 oclock positions (when viewed from the front), that has no flange on it, is intended to be trimmed back so that the edge of teh duct butts up to the edge of the short radius flange of the inlet. The duct should not overlap on the outside of the inlet flange radius. This would push the duct higher than it is intended to be.


Scott will likely be constantly flying demo flights or doing some other very important task (things that know one else wants to do), and thus will likely be unreachable for the entire week of OSH.

hard to see scribe lines

When I prepared my cooling duct I first missed the scribe lines at the front where the flange is missing. I just cleaned tat section up and tried it for size. Very poor fit. So I went looking for an answer, and found faint short sections of the scribe lines I needed. So builders need to know there are scribe lines all the way around the part. You just need to find them.
Rod

John, thanks for the link to the heat-shield product, I ordered some this morning. I wish I had this before I wired the engine.

-Ron

Another #2 spring rubbing

I fit my cooling shroud exactly as outlined, trimming the butt joint for the oval inlet only to the scribe line and fitting it with no overlap. My cowling was all fit with the engine and spinner in place and the scribe lines were nearly spot-on. However, I also encountered minimal (1/8") clearance between the spring and the cooling shroud and as expected, it began to rub with engine movement during the first engine run. I had to basically do similar fiberglass work to what John described earlier in the thread, cutting out an elongated area and then building it back up with a trough. I made mine smaller, as my header seems to have adequate clearance. Just hope I won't have to revise it later.

I think that there is just enough variability in all of these close fitting parts that even installed properly, some will have less than adequate clearance. While the alteration was not difficult, would be nice if a slight change was made in the cooling duct fiberglass mold for future builders such that there was a bit more clearance in this area. It does not appear as though a 1/4 inch drop in the area would have any negative impact on airflow to the radiator.

Jeff

Picture ... deja vu

That picture is identical to the burn through my cowl. When cowl removed imagine my surprise. It didn't touch before the flights.
The fix! opened the hole up more for clearance with the exhaust. Painted the edges of the opening with epoxy (about an inch and a half).
Laid two layers of fiberglass cloth in the hole and pushed it out until a perfect depression molded around the exhaust.
Painted the cloth with epoxy and flox.
After two days layered the depression with two layers of heat resistant.
I see no change in engine temp as a result of the repair.
Live in Texas - John is right - heat is always a factor here.

Dick

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