by loucrane » Sun Jun 21, 2009 4:12 pm
Walter,
I've had occasion to fiddle "inserts" for various engines over the years. If you have a few tools - a drill, possibly also a Dremel and some points, some X-Acto knives and saws - You may be able to work with 'reasonably available' materials.
Almost all our engines have round venturii - exceptions: III-series ENYAs, Fox engines based on the Combat Special case have rectangular casting openings. Your Stallion's is round.
Even with local hobby shops being scarce, chain hardware stores almost always carry racks of K&S hobby metal shapes and materials. The throat of your Stallion's insert is probably near parallel in section; the bellmouth should be toward the outer end, or perhaps it doesn't bell-out if a throttle was originally mounted.
If you have a set of drills, you could use them as go-no go guages to find the inside diameter at the spraybar location. Likely a typical 1/16" to 1/4" drill set won't be big enough for the Stallion's throat. If so, clean and dry the engine and go see 'your friendly hardware man' whether his jacket is red, blue or orange. Carefully, so you don't mar their stock, find the aluminum tubing size that fits best. If you're lucky they'll stock it in 12" lengths, so there's less waste of metal and money.
If you have a Dremel with a cutoff wheel, cutting a short length, when you're ready, is simple. If not, you can "roll-cut" K&S aluminum tubing easily with a good pocket knife blade, or an old X-Acto long whittling blade.
If the largest tube that fits is still a loose fit, two possibilities: you may be able to 'wallow it out' enough for a proper fit, or you could also get the next larger telescoping size - the one that doesn't fit - and saw a lengthwise slit in a short length of it with an X-Acto razor saw. If THAT's still too big to slip into the throat, the aluminum is soft enough that dragging a piece of, say 180 grit, sandpaper through the slit can open it a little at a time.
It's unlikely the ID of this tube will be the diameter you want, so the smaller diameter tube, also slitted if necessary, can be fitted inside it. And, again, if you still need a smalller ID...
"Wallowing out" is simply wobbling a broader, tapered object, like a fairly short-jaw pair of needlenose pliers or an old-fashined center punch, inside the outer end of the tube(s.) That can form a nice bell-mouth and stretch the entry area for a closer fit. This can also help you reach intermediate IDs - the telescoping tubing steps by 1/32".
Fitting a spraybar across the sleeved-down throat isn't too difficult. Slip the insert in and mark where one side the casting's spraybar hole is. (I usually line up any slits with this first hole.) Drill for the spraybar on the side you marked. Check that it fits the spraybar. Slip the insert back in, and use that 'right-size' drill to go through the other side.
GENERAL ADVICE: Before doing any metal cutting near the innards of ANY engine, take precaution that NO metal chips can get into the engine. One way is to remove the shaft before going through a process like the above, another is to pack the shaft end of the intake with tightly wadded paper towel, or similar.
ALSO: At all stages of working on the insert tubing, cut or file off any burrs left by your tools, and clean out ALL the 'chips.' For inside diameters, the aluminum is soft enough that you can 'carve' the burr out with an X-Acto #11 blade.
Sound difficult or complicated? Not really, though it can seem a bit tedious. There's no voodoo about 'choke' ID, really. For example, a Fox 35 'choke' ID is about 1/64" over 1/4" at around 0.260 plus or minus. A 0.281 choke ID is simply 9/32". A 0.297 is simply 19/64". Most decent 1/16" - 1/4" drill sets step by 1/64", so you're all set to talk about those super-hi-tech sounding decimal numbers. For your Stallion, I'd expect either a 0.281 or a 0.297 will work with the K&B NVA.
And if it doesn't, you know how to tackle fixing it.