jetpack

My Feedback: (1)

What size hole is used to bleed off crankcase pressure on an 049/051? Im having trouble understanding this, a small hole will keep starting easier i imagine, and a larger one will pump up faster......am i on the right path? Im not really interested in using a "one-way" valve, and dont really think its necessary is it? Also, how does this affect things if i plan on using a tarno carb or exhaust sleeve?

combatpigg

My Feedback: (3)

Your question made me curious, so I checked. The hole is tiny, I don't have a drill bit or piece of wire small enough to slide into the hole. I estimate the hole is just a couple of thousanths of an inch. So small that the tiniest fragment of dust would clog it, mine was clogged, I had to use a syringe to clear it. The check valve keeps the accumulated pressure build up where it belongs, in the tank, and eliminates the possibility of flooding the crankcase with a back flow of fuel. FOREMOST sells them for just a few bucks. The pressure build up makes the carburetors' job difficult, you would need a carb with 2 or 3 seperately metered circuits to regulate the force fed mixture well. You can limit your engine speed range with a standard carb that is being pressure fed, but your idle will be more like 1/2 throttle, which is usually enough to land a 1/2A model or do touch and goes anyway. If you want crankcase pressure to mimic muffler pressure, then it might be interesting to introduce an adjustable air bleed in the tank, to try to balance the pressure.

Some kind of enclosure [muffler] that is clamped around the exhaust ports is still useful to retain heat to keep the glow plug lit, and with a pressure tap, this would be the most trouble free setup, just like NORVEL does it

skaliwag

My Feedback: (1)

Here is a scan of the '95 instruction sheet on the TD.049/.051....Says to use a #60 drill bit.

Jim Thomerson

I've run TD 049's and 09's off backplate pressure in FF and CL applications. A oneway valve is really needed. The 049's need the KK fine thread NVA, but the 09 is OK on the stock NVA.don't know about throttle.

Jim

combatpigg

My Feedback: (3)

SKALIWAG, that instruction is for tapping the plastic carb body isn't it? I don't know anybody who could keep a line attached to that plastic nipple. COX wouldn't have provided it if it didn't work, but I never could get that tap to work.

Larry Driskill

That tap on the plastic is said to be a "timed tap".

I assume that means it is only open when the piston is on the down stroke and thus the pressure from it would be higher than from the backplate.

Jim Thomerson

I never understood the Cox crankshaft tap. In the first place it is in the way of the engine mount. Secondly, is it in the right place? The Super Tigre tap place is on the bottom side of the crankshaft. Design man has posted a method for modifying the plastic nipple so that fuel tubing would stay on, but I don't recall the details. I bought a used TD 09 which ran erratic. I had cut the nipple off, of course. I swapped it out and was fooling with it. Lo and behold, a bubble came out of where the nipple had been--the previous owner had drilled it out. So I sealed the plastic with soldering iron and fixed that problem.

Jim

jetpack

My Feedback: (1)

I bought a used one that was drilled at the nipple. Good thinking as to how to block that with the soldering iron. I was aware that the front take-off worked lousy with other reports, and its true about how any kind of fuel tubing wont stay on it. The nipple itself is tapered to pop out of the mold, inherently wrong from the start to hold anything tight on it.
The hole size that combatpigg mentioned that was in his backplate, is pretty small...smaller than the #60 drill for sure. I'm wondering if using a one-way valve eliminates this need for such a small hole, and thinking this speck of a hole is designed for "valveless" installs. An orifice this size leads me to believe it is to restrict the airflow BACK into the crankcase, so the piston can keep up with sending pressure until it is equalized.
If this is the case, any size hole (6-32 nipple) would work fine then if it had a one-way valve right after it. No need to attempt trying to drill/peen a hole this small as described, which is fine in my book cause the only way I could think of making the hole would be to drill as small as possible and smash it closed till it reached the size, or find a hair-sized stainless steel wire that i could solder inside the nipple, and then pull it out after it was cooled.

Jim Thomerson

Actually, I have been running a backplate with a 6-32 pressure tap on my TD 09's. But I use a Kustom Kraftsmanship one way valve in the pressure line. KK at one time made tapped backplates with a built in one way valve. I have one in the 049 size. I understand Rojett has nice oneway valves, but I have not seen one. Missed getting a KK valve on ebay. Didn't want it bad enough. Back in the early days, a #80 drill was called for to make the hole. I actually hand held a 4-40 bolt and drilled a #80 hole down it to make a pressure tap. Probably couldn't do it with a CNC machine today.

Jim

jetpack

My Feedback: (1)

Well, you sparked an idea Jim, and thats great. I have tons of aluminum 4-40's around from my rc buggy box, and a hex head capscrew is just the ticket, because using a 6-32 nipple down inside the backplate would be hard to tighten, unless you use a socket wrench maybe....another tool in the flight box to worry about. A small allen wrench is already in there. And an aluminum screw is pretty easy to drill i would imagine, especially with such a small drill. I'll probably just clearance drill down close and then finish with the #80. And if i fail, theres always a bunch more to try. I should be good at it by the time i reach the tenth one i figure.[sm=rolleyes.gif]

Larry I thought about what you mentioned also, with the crankcase take-off being a "timed" tap. Studying the rotating timing of the crank, that port is only open like you said, on the downstroke....then it closes off (except for the slight undercut of the crank in that area). This method (in theory) eliminates the one-way valve, as it becomes its own valve. As far as getting the fuel tubing to stay on it is another matter. You mentioned using a soldering iron to close it off, and my experience with hot forming plastic...if I use "half" of your method, and just hold the iron close up to it...a small ball will form and mushroom an end to help hold the tubing. And if that doesn't work...well it will be a mess...lol...na, I think I would just finish closing it off because the nipple would be trashed then (sort-of-speak) and just go with the backplate method. Before all the backplate ideas, I did find some small tubing at Hobby Lobby in the "Beads and Necklace" section, but I haven't tried it yet for fuel-proof, but it does fit nice on that nipple.

Combatpigg, I want to thank for the help on the hole size...If my drilling efforts fail (i only have ONE #80 drill..lol), I do have a stainless steel cleaning brush that I could pluck a wire from, to help hold a hole open when I solder.

Skaliwag thanks for posting that copy of the instructions. I never owned a new TD, and having that as a reference is great.

I included a picture of the motor we been talking about just for joy. Im gonna try and couple the exhaust sleeve to the Tarno, hoping for a nice idle...although sounds like running pressure might kill the thoughts on throttling....anyways, Im hoping first to get good power, and a throttle would be secondary if it works.

DesignMan

Hi guys! The nipple pressure works well, and is sufficiently low to allow use of the standard needle.

There are several ways to keep fuel hose on:

1. Take a 2x56 blind nut, turn the flange down to make a nipple end, and then screw it onto the side nipple on the engine. JB weld would be good insurance for a perfect seal.

2. Use a sharp knife and run a faint score around the nipple at two locations. This gives the nipple some bite.

3. Clean everything really well and CA the tube to the nipple.

My personal preference is #1.

EASYTIGER

My Feedback: (119)

Retract tubing will stay on the nipple.
It also work on 02 and 01 carbs.