Home › Forums › Free Flight › The Engine Shop › Cox Tee Dee .049-.051 Delrin Plactic NVA Mounts
- This topic has 5 replies, 3 voices, and was last updated 7 years, 4 months ago by Mike Schwartz.
11/24/2015 at 4:09 pm #42396
Yep! I went to my Maverick with the Tee Dee .049 and found that the black plastic carb/NVA mount had the rear split in it at the mold seam. Glad I thought to look at it before driving to a contest. The repro for this fits so loose it is about the equivalent to the OEM with the split as far as induction air leakage. You can goop up the repro with automotive RTV sealant if done carefully. What is happening is that tightening the threaded venturi in to the threaded plastic collar spreads the opening laterally and invites it to split at the seam. Most folks will over tighten this assy. with no thought as to what is going on. Try to save what you have in the factory provided part as much as you can. As an aside, I find it hard to believe that a machined alum. replacement part can attain the necessary tight fit required w/o some RTV carefully applied. I haven’t checked this out though. Here is what to do now.
Machine some .375 aluminum bar stock (2011 alloy is the best to work with) to .312 I.D. BUT start with a N drill bit of .302 and then the .312 (5/16″) drill. If you just drill with the 5/16 to start with, your hole will be o/s and worthless. Cut this off .035 thick. Press this ring onto the plastic carb mount threaded stub to try to contain the material from splitting from the loads imposed.
The dimensions fro the Tee Dee .020 ring are: .242 “C” drill I.D., .285 O.D. and .035 thick. You had better give this some thought if you wish to run Cox Tee Dees in the future. Best, Bill11/24/2015 at 7:49 pm #55626SIMON BLAKEParticipant
Hmm; maybe this explains the drop in performance on the Medallion .049 in my nostalgia Top Banana after I broke the plastic carb assembly last year and had to replace it with a new aftermarket part.11/24/2015 at 11:18 pm #55627Mike SchwartzParticipant
Last year I bought on e bay metal replacement needle valve assembly mounts for the T.D. .049/.051 and the T.D..020. These came with o-rings that were installed at the front and back of the metal mounts which completely eliminated the air leaks. I will try to find the paper work that came with the order so I can post who I got them from.
Mike11/26/2015 at 3:05 pm #55628
Golly Mike, those must have been really thin O rings as there is only a few thousands fore and aft clearance before the retaining collar would begin to collide with the drive washer. Can you develop the thought on this situation a bit further? Yep, interesting if you can find some info on the supplier as it would help a lot. The new 1/2A event proposed will bring forth a lot of these Cox engines needing help. Best, Bill11/26/2015 at 3:06 pm #55629
Golly Mike, those must have been really thin O rings as there is only a few thousands fore and aft clearance before the retaining collar would begin to collide with the drive washer. Can you develop the thought on this situation a bit further? Yep, interesting if you can find some info on the supplier as it would help a lot. The new 1/2A event proposed will bring forth a lot of these Cox engines needing help. Best, Bill11/26/2015 at 3:36 pm #55630Mike SchwartzParticipant
I used the word o-ring just as a description only. I should have said a very thin flat teflon washer which acts as the seal at the front and back of the carb. body. It really works, no more air leaks which T.D.’s are known for with the plastic carb bodies. Being metal they never crack like the plastic ones.
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