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Speed,Combat,Scale,Racing => Scale Models => Topic started by: John Rist on January 10, 2010, 05:10:53 PM
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I bought a used OS Max 65 LA on eBay (cheep). I plan to use it in a Fun Scale for the NATS this summer. I put a perry carb on it (I hate remote NVA). I gave it a test run today and it is a strong runner. Good idle, Good throttle responce and strong top end. The only problem I see is that it appears to have a leaky back plate. Lots of wet stuff in that area. It doesn't seem to be leaking out the front bushing and flowing back so it has to be the crappy plastic back plate. As best as I can tell form the Tower web site this engine does not have a gasket.
Doses any one make a metal replacement for this engine? If not would it work to seal it with silicon?
HB~> ??? ??? ??? H^^
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I would do this:
Clean the case and backplate thoroughly. Fill the case with clean cloth or tissue. Smear on a little fine automotive valve grinding paste on the sealing surface and lap the backplate onto the case by spinning it back and forth. In just a few twists, you should be able to see where the backplate isn't touching -- the compound will make the high spots grey. If it doesn't look like much, just lap it to get a good surface. Be very careful to clean all the compound out of the case -- it will eat up the piston and bearings.
Another option would be to clean (degrease) everything and then use some paste wax on the case surfaces where the backplate sits. Then put a thin layer of JB Weld on the backing plate sealing surfaces and bolt on the backplate. Allow to cure for 24 hours min. The paste wax is intended to act as a parting agent to keep from gluing the back plate to the case.
Keep this in mind. There are lots of model engine experts on this forum. I'm not one of them. However, I've been messing with machinery for a long time.
Regards,
John W
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I think a safer way to go would be red silcone high temp gasket sealer. I've used it similar situations with no bad side effects.
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I think a safer way to go would be red silcone high temp gasket sealer. I've used it similar situations with no bad side effects.
Paul,
I suppect I find this at auto parts store?
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Correct.
It's Permatex product in a 3 ounce tube. It will take a lot of abuse from heat, chemicals, and pressure.
I have experience with OS plastic backplates in the 15, 25, and 40. I'm a bit surprised that they applied this material to 65. On the smaller engines, they seemed to think that a plastic-to-metal seal didn't need a gasket.
The more I think about it, considering the dissimilar materials, a resilient liquid-applied gasket is probably the best you can do for plastic to aluminum.
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I found the Permatex red in the parts store. I will let you know how it works (after it warms UP!!!). The good old sunny south is cold right now. n~ I have to drill the crankcase for a pressure tap before I do the next test run. I need crank case pressuer for the smoke system. The OS max 65 is big and ugly but you can pick one up cheep on ebay from time to time. The O.S. 55AX ABL Airplane Engine at $160 weighs less and has the same HP (1.7). I paied $35 for the 65 LA I have. Besides every scale U-control that I have tried (converted rc) was tail heavy. So a heavy engine is a good thing. This is for a fun scale so part of the fun is to keep it cheep.
#^ #^
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Another thought on living with plastic backplates,
My thought on the issue is that the capscrews tend to dig into and bugger up the backplate when you tighten them up enough to do the job.
A level One fix would be to use some "fender washers" that is: oversize washers made by drilling a bolt hole in a piece of cheat metal and cutting it to size with a tin snips. This would effectively spread the bolt force over a wider area.
A level Two fix would be to make a cheat metal overlay with bolt hole the shape of the whole backplate. This overlay would spread the bolt force over the entire area of the plastic backplate.
I've done the Level One, but haven't tried to run a 65 yet, so I never tried Level Two.
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Another thought on living with plastic backplates,
My thought on the issue is that the capscrews tend to dig into and bugger up the backplate when you tighten them up enough to do the job.
A level One fix would be to use some "fender washers" that is: oversize washers made by drilling a bolt hole in a piece of cheat metal and cutting it to size with a tip snips. This would effective spread the bolt force over a wider area.
A Leveyl Two fix would be to make a cheat metal overlay with bolt hole the shape of the whole backplate. This overlay would spread the bolt force over the entire area of the plastic backplate.
I've done the Level One, but haven't tried to run a 65 yet, so I never tried Level Two.
Great minds think alike! y1 I was considering your LEVEL 2 fix. I am sure overtightened and warping the plastic back plates is the problem.
I had not consered washers - not a bad idea.
y1 y1 y1 y1
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Tower Hobbies still sells the METAL BACKPLATE for a .60 FP. Fits perfectly.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCG07&P=7
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Tower Hobbies still sells the METAL BACKPLATE for a .60 FP. Fits perfectly.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCG07&P=7
WOW!! now that's the correct answer!! At under $10 that is the way to go. Of course I will need the 60 FP gasket set also.
Thanks!!! #^ #^ #^ #^ y1 y1 H^^ H^^ H^^