Crankshaft end play

Dave P. Wed Sep 05, 2018 8:38 pm

I recently got a new Tee Dee .049 that had not been properly stored and a Medallion that had spent the last thirty years in a coffee can. Disassembled both and found that the Medallion was actually in much better condition than I thought. After reassembly, both have more crankshaft end play than I would have expected. I'm pretty sure that I fully seated the drive plates, but I didn't really reef on them.

The photos show both with the crank fully seated and fully extended. Do I need to give.them both another whack or two, or are they about right? I've got some thrust washers on the way from Cox Int'l, will that be the right way to go? TIA.

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I'm kind of tech-challenged, I hope these pictures loaded right. I could have disassembled and reassembled both in the time it took me to load the pictures. Could have had a couple beers and ate dinner too.

Ken Cook Wed Sep 05, 2018 9:00 pm

Dave, when you say whack are you referring on how you replaced the drive plate? I really wouldn't recommend that method as it doesn't seat the drive plate on the shaft square. A better suggestion is to obtain a 5-40 socket head and nut. Screw the nut onto the screw and then screw the assembly into the crank until it bottoms. Back the nut onto the drive plate holding the allen screw with a allen wrench. You would be surprised how easy and well this works. I'm certain it would go down a few more thousandth's. A washer under the backdown nut would ease turning it.

The shaft needs end play and a little isn't going to do harm. The problem that could occur is if the drive plate isn't 100% seated. Then if you put the new thrust washer on to take up the tolerance this could cause a issue. When the engine is running, it will grab the carb body lock down nut and unloosen it jamming it into the back of the prop. I go as far to sand the nose of the lock down nut slightly to insure the crankcase is out slightly further to avoid this. It's critical to keep the carb body lock nut tight. I'm not suggesting not to use the washer, just make certain everything else is properly installed. The crank more than likely upon re installing has cut it's way into the splines of the drive plate requiring a little more ummph. Ken

Dave P. Wed Sep 05, 2018 9:01 pm

OK, I did have a couple beers. Life is short.

Dave P. Wed Sep 05, 2018 9:12 pm

Whacking it is exactly what I did, with a dowel inside the crank, as the instructions included with the Tee Dee said. Your method is much more what I would have thought right. That's why I didn't really reef on it, didn't seem like the right thing to do. I think I ought to disassemble them and do it as you suggest. Thanks!

Dave P. Wed Sep 05, 2018 9:25 pm

Ken, when you sand the front of the lock down nut, the idea is to have the end play against the crankcase right? How tight should the nut be? I'm an old army helicopter pilot and Iive by torque values and they just don't seem to apply. Quarter turn past contact about right? Thanks again

1/2A Nut Wed Sep 05, 2018 9:26 pm

Oil all the threads to help seal improves compression and helps when your take things apart again.
I also oil the carb body on the inside before I slip it on the crank case to improve the seal.
Do not sand down the carb body alluminum collar will just make the gap worse. You need to
get a good bind with the collar on the carb body, applied pounds of torque will feel like 9lbs in the
hand with the supplied Cox wrench.

Do this instead.
Buy a thrust washer for your Medallion before you mess with that drive plate again.

The Tee Dee looks good there is always some gap always the Tee Dee is not excessive.
I can clearly see it has a thrust washer leave it be.

I have added thrust washers to many of my engines that where missing or did not come
with them.

Bernie or Mark can sell you new thrust washers.
Here you go:
http://www.exmodelengines.com/product.php?productid=17654&cat=266&page=2

Ken Cook Wed Sep 05, 2018 9:33 pm

Your quarter turn should be sufficient. I have had the nut come loose many times and it sounds like you ruined the engine when running. It's essentially harmless but you get concerned real quick when you pick up the plane and the prop won't turn. I have found this to happen when the phenolic style washers were used. If they're not in good condition as they tend to get a groove cut into them, in turn the washer is now sitting slightly further back than when new. The stainless washers are a non issue. You could look at 5 different engines and see that the drive plate on one might be a bit tighter than another. I sand mine if I feel it's a bit too close. I've replaced many of my plastic TD bodies with all aluminum replacements. In doing so, I have come across this problem where I needed to dress the lock nut a bit to avoid issue. I have had this happen on stock Cox replacements and I never measured anything, but I would assume that there was slight differences from on case to another. The bottom line is that just make certain you have a little wiggle.

Levent Suberk Thu Sep 06, 2018 4:24 am

1/2A Nut wrote:Oil all the threads to help seal improves compression and helps when your take things apart again.
I also oil the carb body on the inside before I slip it on the crank case to improve the seal.

Can I use teflon tape between collar and crankcase? Did you try this?

balogh Thu Sep 06, 2018 9:34 am

Yes I did that but instead of wrapping the full thread on the case nose in teflon tape I only added a ring twirled of the tape between the mating surfaces of the collet and the carb body. When spanning the collet the teflon ring is pressed into the thread area too, and seals well.

1/2A Nut Thu Sep 06, 2018 10:46 am

I have not tried plumbers tape in those regards for the carb body, it's a try it and see deal.

I have upgraded many of my TD's with aluminum carb bodies, bought from various
vendors. One vendor on ebay would sell very nice ones with black rubber O rings insetted
on the collar side of the carb body and on the other end was a very nice flat thin silicon washer.
I would oil those up before assembly very nice seal once completed.

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Ken Cook Thu Sep 06, 2018 3:59 pm

Brad, I assume the bodies you mentioned are from Mike Parkin. I spoke to Mike a little over a month ago. He's had no time for playing in the hobby unfortunately. He says that he wants to get back into that a little more. He also said that he had several ideas kicking around to try.

1/2A Nut Thu Sep 06, 2018 11:06 pm

Hey Ken,
It may have been Mike, he has not made any listings for about 3yrs. now.

I have bought all his offerings:
3 TD .020 aluminum backplates
4 sizes of socket type tools for removing / installing .010 thru .09s TD venturi's
Many carb bodies for all the TD size engine to .15's

I have many CNC ideas myself. During the winter months when hobby time goes indoors
I hope to see more offerings from Greg. Has Mike made mention of what he is interested in
adding to his line up?

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Ken Cook Fri Sep 07, 2018 4:35 pm

My conversation was brief, but his last offerings were for the TD .020. I believe it was a backplate. He enjoyed doing that project and wanted to expand on similar ideas. He said I want to do what no one else does. He didn't say when he would return to doing these projects as they were just a way for him to spend some relaxation time away from the big stuff. Ken

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