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Author Topic: Fox .15x Assembly Question  (Read 202 times)

Offline Chancey Chorney

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Fox .15x Assembly Question
« on: February 11, 2019, 08:04:57 PM »
Hi all. So, I recently inherited an old Fox .15x from a gentleman. The engine is in overall very good shape, with one exception. I received it as it did have one small problem. Somehow, the piston wristpin had disloged itself forward and locked up the piston. So, I was able to carefully re-install the pin into place using a pair of long needle nose pliers with padded jaws. Problem solved, or so I thought. After another look, the liner was not lined up properly in the cylinder. So I disassembled the engine yet again, and using a heat gun, I freed up the liner and was able to rotate it into the correct position. That is, I rotated it so the 'upright' in the liner was correctly in line with the 'upright' in the exhaust port. The engine has good compression and is ready to run when the snow clears and I have my bench back in the garage. Anyways, does anyone here happen to know why the pin would have slid forward into the gap, or has anyone else ever had or seen this problem before? I just do not want it to happen again while running. As a second hand engine, I do not know how it ended up there in the first place, so I do not know if it happened while running or not originally. Thanks in advance for any help or ideas.


Online Dave Hull

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Re: Fox .15x Assembly Question
« Reply #1 on: February 11, 2019, 08:39:47 PM »
CC's

If I understand your questions....

I believe the .15x has a pressfit wrist pin. You did not see any retainers or brass or plastic caps, right? The comments below are based on this assumption.

The pin could not slide out into the liner unless the liner was mislocated, as you discovered. However, even with the liner properly indexed, if the pin is loose, it may "slide forward" and score the liner.

Clearly, this engine was taken apart and not put back together correctly, based on your observations.

At this point, I would suggest--if you have not done so already--having it taken completely apart. Then cleaned to remove all of the castor baked onto it. Use a process that does not abrade any metal from the parts. Then inspect the liner for damage, especially at the ports where the pin may have hooked it. Check the piston for damage. Either fix the damage or replace the parts (or engine). Next, you have to find out why the pin is floating around. If the pin will not seize in the piston without protruding, then the parts are not going to work. I can't recall taking this particular engine apart, but I think what is needed is to install the rod into the piston with the proper face oriented to the piston baffle, and insert the pin in the correct direction. (The press fit side should be forward.) Then lay the assembly on a shaped softwood buck (2x4 would be good) and using a drift punch, tap the wrist pin into the piston firmly. You need it tight, but without distorting the piston. Then reassemble, ensuring that the baffle is on the bypass side. Finally, the liner orientation must be correct. The exhaust port is the one closest to the top of the cylinder. And the head goes on with the baffle relief closest to the bypass side.

Once together, and with the plug out, check for excess friction. If all is free, try running it.

Good luck. I hope it is not damaged, and you can find a useful home for it.

Divot McSlow


Offline Chancey Chorney

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Re: Fox .15x Assembly Question
« Reply #2 on: February 11, 2019, 08:50:22 PM »
Yes, you are correct. There were no caps of any kind. I guess I will take it apart again to check if the pin is tighter one way vs. the other. The piston nor cylinder liner show any wear or damage. I have had it all apart already, but had not put it in the crock pot for a deep cleaning as I did not want to get rid of the build up it has, as well as so I did not have to break it in again. However, if I should, I will do it as it is not that hard to disassemble, and reassemble. Thank you for your time.

Online Dave Hull

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Re: Fox .15x Assembly Question
« Reply #3 on: February 11, 2019, 08:55:43 PM »
As far as cleaning, I like it clean so I can see any damage and the wear patterns. If you feel you can see whether any metal was disturbed around the port without cleaning it, then that's fine. I agree on older, well-used engines that cleaning off castor may take away the last of the compression. But in that case, the engine is actually worn out and you were living on borrowed time....

My fear is that the pin came loose during running. In that case, I don't see how the liner is going to be undamaged. The other possibility is that the engine was pulled down for some reason, and then, to keep from losing any of the parts, just hastily reassembled without regard to alignment or tightly pinning the wrist pin. And then it sat, perhaps while waiting for parts? And then forgotten about. And then gifted. And then....  (I actually have seen this happen numerous times.)

Again, best of luck getting it running again.

Divot


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