drop in plug in a wen mac

chevyiron420 Sun Apr 26, 2015 5:33 pm

I know there are videos showing the use of the drop in plugs in wen mac engines, but my experience's havent been so good. The shallow threads in the cylinder just wont allow room for shims. With one cox shim under the plug you get about one thread engaged on the clamp. I tested one of my engines with this set up and it screamed about 18600 rpm and got hot and started slowing down in probably less that a minute. What do you guy's think about installing a .010--.015 shim under the cylinder? I know it will change the exaust and intake transfer timing but....? I have to figure out something cause i'm running out of glow heads. I do have a conversion head but I really want the added performance of the glow head.
Phil

chevyiron420 Wed Apr 29, 2015 6:37 pm

I modified an old mecoa conversion head into a clamp. It had been milled down to far for any other use. I know you can modify a old glow head but I wanted the extra cooling fins. The poor thing looks like crap from the corrosion it got in storage years ago. The engine is a Testors McCoy, 5 1/2x3 tornado prop, Merlin drop in plug with two shims. I dropped the nitro down to 10%. Over all I am happy with it. I made several 1/2 oz. runs and it made 17500 pretty consistently. The needle is pretty touchy with the 10% but usable. Just out of curiosity I tried the 20% and it went 18600 and got hot fast, so I shut it down. I dont know if I am going to try shimming the cylinder up or not. It runs good on the 10%, I may just stick with it.
Phil
drop in plug in a wen mac Img_0222

Oldenginerod Wed Apr 29, 2015 6:54 pm

It's my understanding that extra nitro should actually have a cooling effect. Not sure why it would be getting hot. Maybe fit a couple of extra gaskets for an experiment. Also, the 10% nitro is probably what's causing the touchy needle setting. More nitro makes needle setting much more stable generally.

Rod.

chevyiron420 Wed Apr 29, 2015 7:27 pm

Oldenginerod wrote:It's my understanding that extra nitro should actually have a cooling effect. Not sure why it would be getting hot. Maybe fit a couple of extra gaskets for an experiment. Also, the 10% nitro is probably what's causing the touchy needle setting. More nitro makes needle setting much more stable generally.

Rod.

Rod, you are right, but like I said in the first post, the shallow threads in the cylinder wont give much room for shims. With the two I have in there I'm only getting about one thread on the clamp.
Phil

Oldenginerod Wed Apr 29, 2015 8:15 pm

Is it possible to chuck up the insert and take a skim off the top to thin the flange?

chevyiron420 Wed Apr 29, 2015 9:57 pm

Rod, you know it might be. I have thought some about that. The chuck on my lathe is so bad it wont tighten up any where near true or the same place twice so I would have to rig up something to hold the glow plug.
Phil

Oldenginerod Wed Apr 29, 2015 10:37 pm

I'd thought about trying to do the same to a Gilbert .074 head, but it has exactly the same trouble of not having enough threads for the clamp ring to hold securely. Also, I don't have a lathe or the skills to do it, but I would think that you could safely take the flange of the insert down fairly thin before it would cause any problems. I don't have any inserts to measure so I may just be talking through my hat lol!

Marleysky Wed Apr 29, 2015 11:53 pm

Phil - just in case you missed it, Rod posted this link to a bunch of wen mac 's that includes 6 or 7. "Working" glow heads, and plenty of cylinders to play around with.
http://www.ebay.com/itm/Wen-Mac-AMF-049-Model-Airplane-Engine-Parts-Lot-Used-/221754954868?pt=LH_DefaultDomain_0&hash=item33a1a01474. As a side note, I did purchase some "homemade" aluminum heads that fit testors, if I recall they were made buy a couple of guys from down under under the name Bri-sun. I bought them a few years back when the testors glo heads were going for 7 - 8 bucks each.

Rod- there is some irony here. You as "OldengineRod ".... You send us a link to a guy on ebay.....named "oleengineguy" located in Ada, Michigan, which is only 15 to 20 miles from my location. Reminds me of that ride at disneyworld.....it's a small, small world!! lol!

Oldenginerod Thu Apr 30, 2015 4:18 am

The "oldenginerod" tag came in a hurry when I was signing up for the first time on ebay. Didn't think about it much, just came to me in a vision lol!

Seriously, I'm not only into old model engines but have a bunch of vintage stationary "pop pop" engines also, along with old tractors. I figured the tag covered all bases.

Rod.

p.s. The "old" refers to the engines, not the owner. Affraid or WOW!

Oldenginerod Sat May 02, 2015 6:28 am

Just spotted this. Might be handy for our new crop of Testors/Wen Mac fans. Heads are supposed to be functional.
http://www.ebay.com/itm/Vintage-Testors-Model-Airplane-Engine-Glow-Plugs-Wrench-and-Battery-Holder-/331540152300?pt=LH_DefaultDomain_0&hash=item4d31553fec

Rod.
(I'm not in the market- over $26AUD postage to Aus. Just $3 for you guys in the USA.)

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