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Author Topic: Fox engine i.d.  (Read 1813 times)

Offline George Truett

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Fox engine i.d.
« on: March 14, 2018, 05:38:01 PM »
I was wondering if anyone can tell me more about this engine.  I bought it out of a group of Fox engines on another forum.  I flushed it out and ran it for a minute, it will turn a Zinger 8.5x7 about 15.5 K on 10% nitro fuel.  It looks like the venturi may have been cut off but it is cleanly done so maybe there was just an insert and that's how it came.  Also a possibility it was an R/C engine with carb, holes have been drilled out and it has C/L spraybar and needle but that may be a mod someone did.  Thanks for any info, George.
« Last Edit: March 14, 2018, 06:13:00 PM by George Truett »
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Offline phil c

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Re: Fox engine i.d.
« Reply #1 on: March 14, 2018, 06:55:40 PM »
Looks like the propdriver  is reddish.  That would make it a modified Mk IV.  The same case, which had a longer shat than the Mk III, was built as a 29 and a 40 with double ball bearings and further as the Mk V with a cheaper plain bearing version, which could still run pretty well.
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phil Cartier

Offline bill bischoff

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Re: Fox engine i.d.
« Reply #2 on: March 14, 2018, 10:29:26 PM »
Didn't the mk IV say "Fox Combat Special" on the case? To me it looks more like mk VI era. Knowing the crank diameter, and the piston/ sleeve metallurgy would help with the ID. It could be a .36 version of the 1/2" crank series of "sport" engines, especially since it is marked "36" instead of "C".
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Online Paul Smith

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Re: Fox engine i.d.
« Reply #3 on: March 15, 2018, 12:17:33 PM »
The "Combat Special" molded onto the case was used on Mark III.

The vertical bar with the blank space was on the IV and VI.  It could be stamped C, 36, 40, or maybe something else.  I would call this a IV, converted to throttle use.
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Offline bill bischoff

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Re: Fox engine i.d.
« Reply #4 on: March 15, 2018, 02:52:00 PM »
...you might need to fact check on the case markings...

It also looks as if this left the factory as an RC engine, judging by how the intake is cut off.
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Offline George Truett

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Re: Fox engine i.d.
« Reply #5 on: March 15, 2018, 04:38:06 PM »
I was really curious so I went ahead and pulled it apart.  Crankshaft is 1/2" diameter the entire bearing surface so while the rear bearing is much larger, both bearings are same 1/2" i.d..  Not sure what that means but I think it means it's not any version of a Combat Special.  The piston and liner are ABC, bad news is the piston is scored in the front its entire height, inline with the wrist pin.  There is a corresponding groove in the liner but it is small right at the edge of the transfer port.  It has been smoothed out but the damage is done as far as that goes.  I gambled $30 buying from a bad picture hoping I might get lucky, doesn't look like it this time.  Thanks for the help,  George
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Offline C.T. Schaefer

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Re: Fox engine i.d.
« Reply #6 on: March 15, 2018, 04:43:19 PM »
It should accept the Mk 4 piston and cylinder. Does it have muffler mounting holes?  TS
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Offline George Truett

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Re: Fox engine i.d.
« Reply #7 on: March 15, 2018, 04:50:17 PM »
yes, it has threaded muffler mounting holes.
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Offline phil c

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Re: Fox engine i.d.
« Reply #8 on: March 21, 2018, 05:30:07 PM »
Quote from: George Truett on March 15, 2018, 04:38:06 PM
I was really curious so I went ahead and pulled it apart.  Crankshaft is 1/2" diameter the entire bearing surface so while the rear bearing is much larger, both bearings are same 1/2" i.d..  Not sure what that means but I think it means it's not any version of a Combat Special.  The piston and liner are ABC, bad news is the piston is scored in the front its entire height, inline with the wrist pin.  There is a corresponding groove in the liner but it is small right at the edge of the transfer port.  It has been smoothed out but the damage is done as far as that goes.  I gambled $30 buying from a bad picture hoping I might get lucky, doesn't look like it this time.  Thanks for the help,  George

Sounds like it lost a circlip on the wrist pin at some point.  Try it and see how it runs before giving up.  It may run OK, but probably not as well as an undamaged engine.
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phil Cartier

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