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Feb 07, 2005, 10:54 AM
S.A.D. member
ivanc's Avatar
9x6 will be OK but you should consider 9x5 (a better choice IMO). If the engine runs reliably on 10% nitro or less, use the lower nitro content fuel. I'm using 5% nitro - the pink fuel (with castor) especially for the bushing type engines.
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Feb 07, 2005, 09:52 PM
Registered User
downunder's Avatar
I've come into this a bit late and you've got the engine back together again, but did you put the conrod back on the right way round? Here's a thread that explains what I mean.

As for fuel, I'm fairly sure the 25FP has a cast iron piston which means a fuel with castor, and lots of it. You might get away with 20% but 25% would be much better. Don't even think about using all synthetic!! If you use an electric starter make sure that shim steel washer has been put back on between the crankcase and the prop driver.
Feb 07, 2005, 10:07 PM
Castle Tech
Joe Ford's Avatar
downunder...well, you made me second guess myself so I went downstairs to check it the process I broke off a piece where the muffler connects to the now its worthless. Wish I hadnt listened.
Feb 07, 2005, 10:14 PM
Castle Tech
Joe Ford's Avatar
worst part is I had it right to begin with
Feb 07, 2005, 10:29 PM
Castle Tech
Joe Ford's Avatar
any way to fix this or is it just a paperweight now?...this is really of the last connections I had to my father
Feb 07, 2005, 10:37 PM
uhh registered user
I feel your pain, well I hope you get it running again, well good luck and your dad may be laughing at your sollemness, so it may not be too bad.
Feb 07, 2005, 11:46 PM
Castle Tech
Joe Ford's Avatar
Well I put the pieces back in...used JB Weld to try and fuse the pieces together. We'll see if it worked in a couple days...gonna give it plenty of time to harden since its so close to the piston. Dont know if it will handle the heat of the combustion process though. Pieces fit back together fairly well, one little piece wont line up with the original muffler attachment line (in 2nd pic on the right side)...might have to grind it down. Will post pics in the am...made sure I turned the motor with the muffler outlet facing down so any excess (if any as I used a minute amount) will go away from the piston assembly. Keepin fingers crossed.
Feb 19, 2005, 08:19 PM
Castle Tech
Joe Ford's Avatar
Well good news everyone. I just went downstairs and cranked her up...using a MA 9x6...she turned over EASY....sounded much better than before oddly enough. Way more rpms and with a bigger prop...dont know how that is but trust me...was blowin papers all over the place. Had to dremel a bit of the excess JB Weld to get the muffler to mount flat again. Stuck paper towel in the exhaust exit so as not to get any particulate matter in there. There is a little seepage but I suspect thats because I also have no gasket there...also because perhaps I didnt get it EXACTLY flat. Close enough for me though. And thanks ivanc for the tip on the MA props...they were MUCH easier to see with the white stripes...especially in fluorescent lighting. Kept the engine running for a good 5 minutes in 70 F setting. Long enough to test if the JB Weld would hold. Guess I got my answer...I am a happy camper once again. Sorry I snapped at you downunder. I did follow some of your advice and bought non-synthetic 15% (as that is still useable with my 46FX)...could the problem with rpms before have been due to the fact that I was using fully synthetic? Why? I think I'm going to stick this engine in a 3D profile plane as it is the ONLY type of plane I dont have yet...anybody have any recommendations??? Thanks again to all.
Feb 19, 2005, 11:08 PM
Registered User
downunder's Avatar
Originally Posted by DrkSdeOTM
Sorry I snapped at you downunder.
Hey, no problem...I understand your frustration but from now on you shouldn't have too much trouble stripping down and rebuilding an engine. They're very simple but there's a few tricks to there only being one correct way for the rod to go on.

A lot of the problem with your original revs could have been the rod stuck to the wrist pin. The wristpin then can only rotate in the piston boss which is NOT good because that wears out the piston boss. For some reason (and I don't know exactly why) it's known that this will reduce the peak revs even before the piston is worn out. The moral of the story is that even if you free up a gummed engine you must always ensure that the rod is free at both ends which usually means stripping it completely.

Your original all synthetic fuel could have played a part too because a bushed engine needs castor for the crankshaft even if it's an ABC type. The crankcase around the shaft should stay almost cold if it's working properly. Synthetics just won't support the loads so it heats up...and heat comes from friction which reduces power. There's one thing about oil though...too much oil has never killed an engine
Mar 01, 2005, 09:51 PM
Castle Tech
Joe Ford's Avatar
Dont know why this didnt pop up in my subscribed threads Wish I had seen it sooner, I would have responded. The conrod must be free now cuz man is that thing a screamer. I've been adding after run oil after every run, keeps getting stronger and stronger it seems like. Now I'm trying to find a plane to put it on but I've only found two...the Lanier Extra 3.25 and the Fat Free Taco. Both are kits and I've never tried one, but hey, gotta start somewhere. Stripping these things apart keeps getting easier every time downunder ...stripped down my 46FX in about 5 minutes...wanted to inspect the bearings as I've been noticing a "backfire" sound when I go from full throttle to partial throttle. Would this be a good indication that new bearings are needed? What else could be causing this sound? I'll include a pic of the rear bearing...dont know what its supposed to look like so I'm hoping one of you can tell me if its shot. Any idea what they go for it that is the problem??? If so is it absolutely necessary? ie-will it ruin the engine if I dont get a new one? I'm kinda strapped for cash right tuiton, rent, bills, work is slow...and on and on and on. Let me know if you could would be most appreciated. And BTW downunder...thanks for that thread you posted about proper conrod direction...I forgot to mark mine when I disassembled the 46FX and that made it SOOOOO much easier.
Feb 10, 2012, 12:10 AM
Registered User
DL8698's Avatar
Sorry for reviving a very old thread, but since it has most of the info I am seeking to restore a very, very....very old OS Max 35, I felt there's is no need to start another thread. It is my first RC engine, which I had stored after running in (long ago) and then soaked in castor oil. I thought that was the right thing to do.

I believe this is the older version of the engine as it has the word "MAX" vertical and the transfer ports are visible on the cylinder side.

The castor oil has hardened and glued everything down. Nothing can move, not the piston or the throttle barrel.

I have removed the carb, cylinder head and backplate. Tried rubbing alcohol to try and free the piston and throttle barrel, no good, although the alcohol appears to be quite effective in removing the dried oil in accessible areas.

Tried tapping the piston down towards the crankcase.. no good. At the moment I am soaking the parts with "PlusGas", a penetrating oil. I am not sure if the piston has rusted on to the cylinder sleeve (I don't really see much of rust anywhere that is visible) or if it is caused by hardened castor oil in the prop shaft (the area between the front and rear bearing)

I tried to take the throttle barrel out of the carb, but it's stuck. I removed the throttle arm and I can't see how the barrel stays in the carb and not slide out as there does not seem to be any sort of retaining feature. I am not sure if I can just yank out the barrel without damaging whatever is holding the barrel in place. I still have the original instruction sheet which shows exploded views of the engine and carb, but I still can't make out how the barrel (called "rotor" in the instructions) stays put.
Feb 10, 2012, 08:48 AM
Registered User
flypaper 2's Avatar
The castor congeals almost into a solid with age although it does make a good engine preservative Get one of those plastic boxes with a lid, big enough to take the motor. Fill it with glow fuel or alcohol. the gas is mineral based and won't do anything to loosen the motor. Let it sit for about 3 days with the lid on it as the alcohol evaporates very fast. Put two nuts on the crank and tighten them together, then with a wrench on the nuts, see if you can rock the motor back and forth even a bit. If you can move it at all, keep rocking it and will go further with each swing. If not, let it soak for a few more days. Do the same with the carb. Put the arm on fairly tight and rock it to see if you can make it move. there should be a screw above the arm on the carb body. This is the throttle stop. If you take it out, it should let the barrel out from the throttle arm side.
Hope this helps.
Feb 10, 2012, 09:24 AM
We shall serve the Lord
kingsflyer's Avatar
Even hardened castor will loosen up with a little heat. I've had good luck using penentrating oil and a heat gun. Use some thick gloves to hold the warm engine (don't ask me how I know about that part). Sometimes it takes several applications of oil and heat, but the castor eventually softens and lets go. If you try to move the piston with the crank, go easy so you don't damage the con rod. If the piston won't move, use more oil and more heat.

I had one engine that I bought at a swap meet that was frozen up solid and wouldn't move. I set it on the defrost vents in my car and it loosend up before I got home with just the heat.

Latest blog entry: LEDs on my T-28
Feb 10, 2012, 10:31 PM
Registered User
DL8698's Avatar
Thanks, flypaper and kingsflyer.

Like what kingsflyer said, I was a bit wary about turning the shaft too forcefully if the piston was the thing that was seized and not the shaft itself. I had no way of knowing.

Finally, managed to get the shaft to turn after I heated the cylinder and shaft housing with a heat gun. Not sure how hot I got it, but was not really very hot as I could just about touch it without getting burnt. After I got the prop drive washer off I found a flat which I used with an adjustable to turn the shaft.

As the piston was at mid travel when I stored it, as the piston moved up it push the cylinder liner along with it. I took the liner off.

Then I found the con rod would not move at all along the wrist pin so I could not get it off the crankshaft pin. Tried soaking with plusgas, no good, tried directing heat on to the bottom of the piston, still no good. Finally I yanked the con rod out real hard, which I didn't want to do initially as I was afraid of bending the wrist pin.

Got the con rod off the crankshaft and when I took the piston out I found I had mad a small dent at the bottom of the piston. And when I tried to hammer the wristpin out of the con rod, I damaged one of the teflon end piece on the wrist pin. Didn't know the teflon could be removed from the wrist pin. Anyway, will just reuse the damage teflon, as I think it's there just to stop the steel wrist pin from moving towards the cylinder liner. I also reshaped the piston skirt as round as I could, not sure how the engine will run, or even at all, with the skirt not 100% round. BTW I found this engine does not have ball bearings, just a very long brass bearing around the prop shaft.

At the moment still trying to yank out the throttle barrel from the carb. All the screws are out, including the throttle stop screw. The sucker is really hanging on!

When I get everything disassembled, I will boil the whole lot in soapy water, oil everything and reassemble.

I still have a can of Castrol compression engine oil and some methanol ( i think both about 20+ years old). Still looks good although not sure if the methanol is useable as alcohol absorbs water very well.

I have forgotten what is the ratio I used to make my own fuel. Probably, 25-35 % Castrol? The rest methanol, no nitro.

And I read somewhere that running in engine should be done with castor oil, not synthetic oil. Why?
Feb 10, 2012, 11:46 PM
Transplant in 1996
I use paint thineer on all the engines that I have bought off of Ebay (27 now), only had 1 that gave me problems. Make sure ebay feedback is at least 97% positive. Have 26 good engines onw.

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