Fox 049 standard

Marleysky Sun Mar 27, 2022 9:52 pm

Hey! I recently got a Fox 049. Bought some gaskets and stuff from Matt at EX-Model Engines to make it look operational. Except...it has a large dimple on the top dead center of the piston! Can anyone advise if this is “normal” or is the con-rod about to push thru the top of the piston?? I kinda think its normal because of the Fox add I found showing a raised bump on the piston:

Mone:

**Cribbs74** Sun Mar 27, 2022 10:04 pm

I don’t know if that is normal or not. I have two Fox .049’s and one .07 and none of them have a raised bump. In your picture it does look like it was machined that way. If it is indeed a poor fitting con rod then it will have an audible click when turning over and if disassembled it will be obvious if it’s pushing through.

Ken Cook Mon Mar 28, 2022 4:06 am

The identifier for the .049 piston is the raised bump. The .07 is a flat top. The piston isn't poking through. The piston is cast and it will shatter like a piece of glass if you try and reset it. The identifier for the cylinder is the base thickness at the bottom, the .049 has a thick base and the .07 has a very thin base due to it's longer stroke. The other is the amount of cooling fins, the .049 has 9 fins whereas the .07 has 7. I could also be reversing those numbers as I always forget but one has more fins.

Oldenginerod Mon Mar 28, 2022 4:18 am

I believe the "bump" is actually some sort of rivet. It is a sure way to distiguish the .049 from the .07.

Marleysky Mon Mar 28, 2022 2:55 pm

THANKS GUYS! It seem that the OEM (FOX) used a rivet to assemble the piston and Con-rod Socket together, so the dimple is OK. I do remember reading your post Ken, on how you shattered a piston in a attempt to re-set the ball socket, so I'm definitely NOT gonna do that! lol!

EXModelEngines Tue Mar 29, 2022 3:09 pm

Oldenginerod wrote:I believe the "bump" is actually some sort of rivet. It is a sure way to distiguish the .049 from the .07.

Correct as the piston and socket were made separately. I'll try to dig out some of the socket parts. There were a small handful when we bought all the parts from Doug Martin.

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