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Engine basics => Engine set up tips => Topic started by: DanielGelinas on August 06, 2012, 02:20:16 PM
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I just started using a used fox 35 stunt I purchased a few months ago. I mounted the engine in my super clown.
I have found that the piston binds (or sticks??) in the sleeve. I added some after run oil to free it up before actually trying to start it. Still, the piston sticks.
Because the piston sticks (or binds) in the sleeve, I am unable to start it. I'm of course using 29% all castor fuel.
This indicates to me it either has varnish build-up or the cylinder is warped?? Or could it be something else?
The engine <<MAY>> start if I used an electric starter but I'm afraid it may cause more damage... Usually all my fox's start easily by hand.
Any ideas?
Thanks!
-Dan
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I just started using a used fox 35 stunt I purchased a few months ago. I mounted the engine in my super clown.
I have found that the piston binds (or sticks??) in the sleeve. I added some after run oil to free it up before actually trying to start it. Still, the piston sticks.
Because the piston sticks (or binds) in the sleeve, I am unable to start it. I'm of course using 29% all castor fuel.
This indicates to me it either has varnish build-up or the cylinder is warped?? Or could it be something else?
The engine <<MAY>> start if I used an electric starter but I'm afraid it may cause more damage... Usually all my fox's start easily by hand.
Any ideas?
Thanks!
-Dan
Dan
Is this the used one you got from me with the new piston and sleeve in it? if so it will require break in, They are tight from FOX
Randy
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Dan,
I've seen warnings about uneven head screw torque warping the liner. Might be worth the effort to remove, and re-torque the head screws.
Someone here with experience at this can give you the best method, or point you to an article somewhere. (I've never had to do this myself).
One thing I know for sure, is that you have to be careful that you don't disturb the cylinder liner position in the cylinder! (Don't ask me how I know that this can ruin the break-in fit, and accelerate the engine wear!) HB~>
You should also check to see that the small (upper) end of the rod is not binding on the wrist pin. This can be done by using a small Allen wrench slipped behind the rod to pull it back, then push it forward with your finger. Repeat as necessary to ensure the rod is free to slide on the wrist pin.
Hope this helps.
Bill
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Are you using a strap on muffler that is too tight?
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I got a stunt 35 back from Fox, with new piston and liner, and a note saying it was tight. It was, in fact, tight part of the way up, but not at the top. I took it apart and fooled around with putting another piston and liner in, which was fine. I decided the liner was warped or bent. I lapped it with Dupont white rubbing compound. I could see where the compound was working on one side of the liner. I got it freed up and feeling good. I've run several tanks through it on the bench and it starts and runs fine.
In 1977 there was a sale of Fox stunt 35s for $12.95. I bought four and started flying stunt. I lapped all four before break in with the Dupont compound. Around 1990 I sent them all to Fox for fixing or whatever. Only one received new piston and liner, the one discussed above. I had badly mistreated it trying to fly stunt with crankcase pressure. I've been flying one of the others for several hundred recent flights. It likely has several thousand flights on it. It has excellent compression, usually one flip starts, and reliable run.
I have no problem with lapping an iron piston and liner if I think they need it. I don't advise it unless you have a good idea what you are doing, and willing to sacrifice an engine if you are wrong.
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Dan,
...good idea NOT to force-start that engine! The following may take a while to read, probably longer than it takes to do...
20 or more years ago, several runs of Fox 35S were released with the heads tightened on without regard for a "torquing sequence," and felt tight because of the distortion created.
I've never had a warped sleeve in one, but have had one or more that had a VERY SLIGHTLY distorted crankcase casting. Proved this just as Jim T did, except other sleeves were as tight as the "bad" one I was checking. And there was no bind on the OEM piston in its OEM sleeve when they were out of the casting.
Used a worn-out sleeve and a thin Lava soap grit paste to lap the casting to a uniform, slightly looser fit. Cleaned it scrupulously, afterward, of course.
If you do disassemble your engine, you'll very likely disturb any run-in surfaces that had formed, but with the problem you describe, it is better to disturb it, correct the fit, reassemble it carefully, and give it an abbreviated repeat of what a proper break-in would have been.
Reassembly:
Not a bad idea to see how cleanly the head fits the top of the sleeve. A drop of the lapping paste, above, between the head and top of the sleeve will polish up any high spots where the head can't sit square. Probably won't turn up any, but only accomplish a cleaning of that joint surface... Clean all traces of the lapping paste off the parts. (Lava bar soap is mostly pumice. That's soft enough that it crumbles down to less than running fit clearance before it can cause serious damage, but why take the chance anywhere you don't need to.)
You can likely find 4-40 X 1/2" Allen socket head bolts at a good hardware chain store (red, orange or blue jacket stores) These are much easier to use for good results as replacement head bolts...
Torquing sequence: Look at the 6 bolt locations, pick one as 12 o'clock position. I use the front one... Fit the head on loose, and run the six bolts down until you feel them touch. Back them all out a half turn.
Start from your 12 o'clock bolt, and turn it in a quarter turn. Got to the 4 o'clock position bolt and do the same. Then the 8 o'clock bolt. They are all still loose, right? Okay...
Cross over the head to the 2 o'clock bolt - same. Then the 6 o'clock - same. Then the 10 o'clock - same.
Turn the shaft back and forth to make sure nothing is binding. If it is back 'em all out and start over.
If all is well after this first cycle around the bolts, again cross to the 4 o'clock bolt and continue the sequence. Just barely turn these to where you feel resistance. This sequence is 4 - 8 - 12 o'clock.
Again, check that the shaft, piston and sleeve do not bind. Contrinue the sequence with a small increment - say another 30° of wrench movement - until you've gone around all 6 and checked free motion. Each pass around all six draws a sort of Star of David pattern with the overlapped triangles.
Continue until all six bolts are as tight as you can get them using small, even increments with ONLY the short arm of the key.
At any time, if any bind appears, back off at least one step and recheck.
This takes a while to describe, but once you've done it it goes very quickly. The fully-torqued engine shaft rotation and piston motion should feel just as free as before it was tightened at all. (A good piston fit might feel snugger near top dead center, or like an ABC engine, not go through TDC when turning the shaft without mounting a drive washer or prop for leverage.)
For an older engine, of course, as mentioned in prior posts, conrod freedom to move on the piston pin is important. Gummed, in the wrong position, it can increase wear.
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Guys,
Thanks for all the very great information.
I will try to re-torque the head and see what gives. If I remove the head and all the resistance goes away, I'll know that is the problem.
If It still sticks, then I'm to assume it's varnish, warping or just plain not broken in yet.
This is a 1955 fox and as far as I know, is original. There is no strap on muffler.
Randy,
This is not the engine I purchased from you.
THANKS!! H^^ H^^
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.........(good advice).......
Lou,
would you re-torque after a few heat cycles from running though?
(I would. y1)
Thanks.
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Hi Guys,
NO muffler on this 1955 fox.
I just removed the head and I still have what I think is stickiness more than binding.
This leads me to believe it hasn't ran in a while. There doesn't seem to have any varnish though...
So, I would like to crock pot the engine, to remove the stickiness. Is this a good move?
Problem is I can't remove the liner. I have tried a Popsicle stick in the exhaust while gently turning the prop. Nothing is moving.
Anyone have another trick? Heating the casting maybe an retrying the popcycle stick??
Or is there a simpler way to get rid of the stickiness
Thanks,
-Dan H^^
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Hi Guys,
NO muffler on this 1955 fox.
I just removed the head and I still have what I think is stickiness more than binding.
This leads me to believe it hasn't ran in a while. There doesn't seem to have any varnish though...
So, I would like to crock pot the engine, to remove the stickiness. Is this a good move?
Problem is I can't remove the liner. I have tried a Popsicle stick in the exhaust while gently turning the prop. Nothing is moving.
Anyone have another trick? Heating the casting maybe an retrying the popcycle stick??
Or is there a simpler way to get rid of the stickiness
Thanks,
-Dan H^^
Heat it with a monocoat heat gun while trying the popcycle stick should do it
Randy
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A different problem is that the fit between the liner and case may allow leakage from the bottom of the case out the exhaust port. A few runs with all castor fuel will varnish up the outside of the liner and the problem will go away. Varnish on the outside of the liner shows that your engine had this problem. H^^
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What I do on all Fox 35's and some other engines also, is to loosen all the head bolts and retorque. I take the plug out, put a prop on, and see how tight the piston fit is. I then start loosening bolts one at a time about a 1/32 of a turn, and try to get the least amount of drag I can get. If loosening a bolt does not give me less drag, I tighten that one up and go to the next one. There will be one or two that will decrease the drag on the piston quite a bit. I then put it on the test stand and break it in. I do this on all new engines and ones that I have had apart for any reason. Probably not right, but it works for me. I remember reading about loosening and tightening the bolts on Johnsons while the engine was running to get peak RPM. I haven't had the guts to try that.
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Guys,
Problem fixed #^ #^
I removed the liner after heating with monokote heat gun. The bottom of the liner had lots of caked varnish. I used 00 steel wool soaked in alcohol to remove the varnish. I then added after run oil to the liner and reinstalled.
Then, I carefully torqued the head on and VOILA... no more sticking and a good compression.
BTW, I made sure I marked the liner to reinstall in the same position.
Thanks for all the tips guys ~> ~>
-Daniel H^^ H^^
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Good idea marking the liner! BUT, don't forget to mark the con rod too. most only install one way. y1
W.