can some one tell me the differences in the fox 35 backplates??   stock,stuffer.etc...and the advantages of either?? thanks alot

The reason Alan gives is the one I always get from Marvin, who developed them for Fox.  Others say that a side benefit is that they reduce crankcase volume slightly improving fuel draw and helping the burp.

But MArvinsays it is just to keep the rod in place.

Randy - will this help?

Bob Z.

Hi, Randy - here's some more.

10 minutes of soild modeling. 

Bob Z.

The trouble is you guys aren't near cheap enough.  Take a worn backplate with the 'wankel' pattern ground in to it from rod end play, machine or file it flat and JB weld a piece of tinplate to it.  Turn or file to shape.  No need to spend all that money. Tom H. 

THIS IS AN APOLITICAL POST,  PRECENSORED BY THE COMMITTEE ON APATHY.

Tom !  name calling will get ya nowhere...  We greatly resemble  that remark!!!..  and I have you know that Im as cheap as the next guy

Randy

  Mike, I am not Randy,  but I will tell you what I did.  If you are going to make a custom fit for your engine,   Remove the stock backplate.  With a prop installed and tight, push the shaft as far rearward as you can, and measure the distance from the crank pin end to the edge of the case.  I would take measurements at several locations around the perimeter of the case and use the shortest distance for  the clearance.  Allow 0.005 to 0.010 inch clearance for the backplate  face  to the end of the crank pin WITH OUT A GASKET IN PLACE.  then the gasket will assure plenty of clearance when the engine gets up to operating temperature.
  Have I confused you enough?
  Now I will warn you that MANY (including Duke Fox) have tried the metal you  are proposing to use and other metals as well.  most have developed problems.  If you DO go with aluminum (and 7075 is a wonderful alloy)   you should coat the face where the rod rubs with some material other than aluminum as  when aluminum rubs against aluminum severe galling and spalling will occur.  Nylon is difficult to put on and often comes off with disastrous results.  I would  opt for HARD ANODIZE.  not regular or decorative  or corrosion resistant anodize, but HARD anodize.  It won't flake off nor gall when rubbing against aluminum.  7075 will take anodize readily and easily as does 6051.

   Bigiron

  Yes, a brass sheet on the face of the current backplate will work .  If you attach it in some manner that will assure that it won't come loose, and also brass  will cause aluminum to corrode to some extent.  Stainless steel is better. but to work as the stuffer is intended, the thickness of the facing you put on should place the face to within 0.010 to 0.015  inch of the crank pin and also be attached such that it won't come loose nor leak (such as through loose rivits etc).
  There are TONS of older well used fox 29s and 35 out there and the 35 is still being made  (with the old style backplate).  What wears out first on a stock fox 35--- depends on how it is being used.  In racing (foxberg etc) with low oil content--- the crank pin.   In Stunt conditions with plenty of oil and good settings,  the shaft/bushing .  In any configuration  with a lean run using synthetic oil, the piston/cylinder assembly.
  What breaks?  in racing if pushed too hard  the rod.  If using a Heavy hub or other heavy rotating mass on the propellor  end,  the shaft.  If too much nitro and combined with a lean run,  the piston.

  how do I know---  GUESS.


  Bigiron

Marvin, and other interested parties:

One of my buddies just tried to install a Fox stuffer back plate in a new Fox 35 which came from the factory with the new ceramic liner/piston set.  The piston would not go all the way to BDC with the stuffer back plate installed.
We "think" that the new piston skirt may be just a bit lower than the stock piston skirt, have't had time to do all the measuring just yet.

Stay tuned for future news!!

Jim

thanks for all the info yall...Randy,,,what is the ideal end play for the crankshaft??/ i'm gonna make my own outta 7075 T6 alu.  yeah i'm a machinist, done it for 15 years full time..was just wonderin the what the pros and cons of em were...sure glad i found this forum...a whole lot if nice and. and purty smart folks here when it comes to the little tips and tricks ...i thank all of ya a whole hell of alot.....hope all have a wonderful christmas and a happy new year.....MikeMullis

Hi Mike

Sounds like a lot of trouble when you can buy one for 12.00  , but if you just wanna make it yourself and will not anodize it, use steel, you can make a very thin one from steel, which will work well on wear from the rod

Randy

Hi Mike

Sounds like a lot of trouble when you can buy one for 12.00  , but if you just wanna make it yourself and will not anodize it, use steel, you can make a very thin one from steel, which will work well on wear from the rod

Randy

well i reckon ya right about alot of trouble.....i was thinkin more along the lines of tinkerin..lol...  do all fox 35 have 3 bolt backplates? do you sell the backplates randy?? if so..how much to my door??  i have a fox engine that is supposed to be a 35 but it has a 4 bolt backplate...learnin bout the old foxes...have to excuse my stupid questions.....i bought it thinkin it was a 35...later i was told it was a fox 36???  reckon just what i got here??  lol...it looks to have a stuffer backplate i think...and the glow plug is in the head at an angle...any ideas?....can post pics i think...anyways thanks for all the help yall

Fox 35's have a problem seldom discussed.  They are too light and you have add weight to make your airplane balance.  I do this with the not-recommended heavy hub.  So maybe there is a market for brass stuffer backplates?

...  do all fox 35 have 3 bolt backplates? do you sell the backplates randy?? if so..how much to my door??  i have a fox engine that is supposed to be a 35 but it has a 4 bolt backplate...learnin bout the old foxes...have to excuse my stupid questions.....i bought it thinkin it was a 35...later i was told it was a fox 36???  reckon just what i got here??  lol...it looks to have a stuffer backplate i think...and the glow plug is in the head at an angle...any ideas?....can post pics i think...anyways thanks for all the help yall

   Mike, I missed this question the first time around.  sorry.  No ,All Fox 35s do not have three bolt backplates. Only the STUNT 35.  Fox put out many other 35s and 36s  that had (have) four bolt backplates.  The sport series of which there are at least four versiond all have four bolt backplates and some of them do give a pretty fair stunt run.  Then there is the 35 and 36 X series that have a square intake venturi as well as  the four bolt backplate..  I think most of us here was assuming (without fully comprehending your full question) that you were speaking of the Stunt 35.  As far as I know, there are no Stuffer Backplates for any other Fox engine than the three bolt backplate Stunt 35.
  Sorry for the overlook.

  Bigiron