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-   -   OS FS-70 Surpass Assembly / Rebuild (http://www.rcuniverse.com/forum/glow-engines-114/3507032-os-fs-70-surpass-assembly-rebuild.html)

John@FLYRC 10-31-2005 09:27 AM

OS FS-70 Surpass Assembly / Rebuild

Moderator w8ye (Jim) suggested I start a new thread for this project. I will ask for advice and direction as needed. I will post results as I go ahead with the project. Perhaps others with similar problems will get something out of it too.

SOOooo folks. this is how it is. I was given an OS FS-70 -- in pieces -- parts missing -- frozen up (MUCH GUM !) etc. I like the Surpass engines. I currently fly a 52 and a 70 plus a couple of Saitos. This exercise is for fun, to see if I can do it and to have another 4 stroke if I succeed. Whatever the outcome I will learn stuff and I like that ! FYI -- I am resaonably handy and have a fairly decent shop.

The first question on this subject was asked (and answered by Bill Robison) in the "Noisy Saito 100---- thread. I asked how to know which way to install the cam. He said that there was a punch mark on the cam gear face and that is should face you as you insert the cam. He also said that the punch mark should be directly in line with the tappet bores (either up or down) when the cylinder is at TDC (top dead center). I installed the cam as directed and it worked out fine -- Thanks Bill

The crank shaft was frozen in place. I removed the prop nuts and washer, taped the shaft and put it in my battery powered drill. I sprayed the innards with carb cleaner and spun it with the drill at low speed. As it freed up you wouldn't believe the "gunge" that ran out. (At this point all the parts got thrown in the carb cleaner.) As the crank got freer I sprayed it with WD-40 and increased the speed of the drill. Crud continued to come out and I added WD-40 freely until it ran clean. I then lubed with a sewing machine oil and spun it as fast as the drill would go. I dried it off and finger tested the bearings. They seem smooth and I won't replace then at this time. All the other parts got polished clean & dry and lubed.

I have gone thru and determined what parts are missing. I got an exploded view off the net (osengines.com) that helped a lot in figuring out what I needed and their part #'s.

Re assembly is as complete as the missing parts would allow. Now I order and wait !


RC-Bearings 11-02-2005 02:13 PM

RE: OS FS-70 Surpass Assembly / Rebuild

I would replace the bearings since you ran them with "crud" coming out. At the very least you should remove and inspect them. If they are rusted you may not feel anything wrong but they will depart shortly after starting the engine.

jaka 11-02-2005 05:12 PM

RE: OS FS-70 Surpass Assembly / Rebuild
You sure have to replace those ball bearings!!
Bearings that has been subjected old, oxidized oil is surely going to be bad.
Just because the crank shaft turns doesn't mean the balls inside the ball bearings run free.
many times it's just the crank that slides on the inner surface of the bearing.

Jan K

John@FLYRC 11-10-2005 09:54 PM

RE: OS FS-70 Surpass Assembly / Rebuild
The saga continues. Thanks guys. The parts arrived and the rebuild is almost complete. I did not put in new bearings yet but I did order them. The re asseembly was smooth and I think I got the timing right (as per Bill Robison).. I set the valves at .05 mm. I haven't run it yet. That is this weekend. If it runs ok then I will complete welding in an exhaust port extension. The compression doesn't seem as good as my other OS-70. Anybody know if it needs to be reseated or anything? I'll keep you all up to speed


w8ye 11-10-2005 11:44 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Valve setting tolerance is .002" to .004".

The comperssion should pick up again after you run it some.

On the Surpass I version, both seals should be removed from the rear bearing.

With the Surpass II crankshaft, it doesn't matter about the seals. Leave them on if you like.

John@FLYRC 11-11-2005 09:58 AM

RE: OS FS-70 Surpass Assembly / Rebuild
Thanks w8 -- I set to .05 mm and that turns out to be .002 inches. Are we saying the same thing? I should be able to run it this weekend and we'll see. -- John

wcmorrison 11-11-2005 10:52 AM

RE: OS FS-70 Surpass Assembly / Rebuild
Check the piston ring. If the rest of the engine was full gunk/grunge, the ring is probably frozen, ergo low compression. If the ring is free, that is it can be moved with out a lot of hula ba loo, then it is probably okay.

Be sure to flow a little oil in from the rocker arm area down the push rods into the camshaft area before the first run. That ensures the camsahft followers are lubed up pretty good before rerun in of your engine.

The OS Surpass 70s is a great engine, jsut take care of it and it will run for years.



John@FLYRC 11-11-2005 08:08 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Chip --
Thanks. When assembling I always use a few drops of Singer Brand light lube oil. I will add a little extra before I run it. The after run oil I use is 1/3 each of Marvel Mystry oil, pneumatic nail gun oil and synthetic engine oil. It seems to be good for that but I prefer Singer oil for assembly. I didn't think to check the piston ring. I plan to disassemble it after the first run and will check for that then
Thanks again -- John

wcmorrison 11-12-2005 11:04 AM

RE: OS FS-70 Surpass Assembly / Rebuild

If it runs, it may loosen up as w8ye says. The four strokes pick up compression with a few runs after a long period of down time.

Good luck,


John@FLYRC 11-12-2005 06:09 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Thanks Chip -- We'll see -- John

John@FLYRC 03-14-2006 11:48 AM

RE: OS FS-70 Surpass Assembly / Rebuild
Well, we are now coming on spring here in Connecticut. I finally learned how to MIG weld (long learning curve). I turned a new exhaust stub and welded it on the cylinder head. The muffler now fits fine and stays on. The carb body had a chip out that I didn't notice at first. I built it up with PC-7, re-tapped it and the fuel leak stopped. I freed up the piston ring as Chip suggested. The compression isn't as good as my other 70 but I was told that was to be expected

The first tests had the following results. It ran very badly on 10% fuel and would not idle. It was last years fuel so I switched to some 25% and it ran a little better. On the test stand, at full throttle I can spin a 12/6 prop @ 6100 rpm. The idle is very rough and cyclic. By that I mean that at a constant throttle setting the speed varies up and down a few hundred rpm and won't really idle down. I am going to get and try some new 10% and see how that goes.

A couple of questions occur to me -- 1. Will the engine run at all if I missed one tooth setting up the timing gear? 2. Can I expect it to improve as I run it in? 3. Where can I find a help on setting up the low end?

Finally -- Thank you all for your guidance and advice. Any additional help will be appreciated

w8ye 03-14-2006 01:22 PM

RE: OS FS-70 Surpass Assembly / Rebuild
What do you mean by "setting up the low end"? I suppose you mean the idle?

w8ye 03-14-2006 01:27 PM

RE: OS FS-70 Surpass Assembly / Rebuild
I run the engine as slow as it seems it's going to run and adjust the idle to where it idles smoother. Then I reduce the throttle setting some more and re-do the idle mixture again.

If you try to accelerate and the engine quits, try opening up the idle just a little.

Make sure your tank is pretty much centered on the needle valve.

That's not very much rpm, your cam may be off one tooth?

John@FLYRC 03-14-2006 01:48 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Yes Thanks I do mean idle. I'll try what you say. So aparently it WILL run with the cam off a tooth?

John@FLYRC 03-14-2006 01:50 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Oh Yeah -- On the cut finger thing -- Be thankful you didn't pass the final. -- One of the guys in the club recently removed the ends of three fingers. I guess that represents a passing grade??? LOL

w8ye 03-14-2006 01:53 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Not very well

John@FLYRC 03-14-2006 01:57 PM

RE: OS FS-70 Surpass Assembly / Rebuild
OK I'll check it. I got some new 10%. Won't run on that either. Runs smoother with the glow heater on so maybe it is a timing thing.

John@FLYRC 03-22-2006 04:30 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Hey w8ye ! Hurrah ! You were exactly right. One tooth off. As soon as I took the cover off I spotted it . I reset it and the engine runs like a champ ! The compression is much better. It runs just fine on 10% 4 stroke fuel. I still have to fool with the carb a little bit -- Some stripped threads I didn't notice before but other than that I have a working 70 Surpass.

Thanks for all the the help -- Maybe catch you again on the next project. Say -- Do you know of any reasonably high temp sealant? One of my welds on the exhaust was imperfect and I don't want to take it apart and weld it again. It looks like a pinhole and a hairline crack so the sealant would have to be pretty fluid.

Thanks again

w8ye 03-22-2006 06:23 PM

RE: OS FS-70 Surpass Assembly / Rebuild
Glad you got it going the way it's supposed to.

The highest temperature sealant is the red silcone stuff that I think you can get at the NAPA auto parts store?

The highest temperature epoxy like substance is JB WELD.



wcmorrison 03-23-2006 08:56 AM

RE: OS FS-70 Surpass Assembly / Rebuild
Sounds like you got an engine now. Good thread, enjoyed being part of it. Keep the rockers lubed and try 15% fuel. I think she's gonna be one of your great engines.



John@FLYRC 03-24-2006 11:03 AM

RE: OS FS-70 Surpass Assembly / Rebuild
TNX Chip Interesting you should mention 15% fuel. I mix my own fuel and have been trying to go the Aussie way and reduce Nitro as much as possible. You are suggestion I go the other way. Down under they fly some with no nitro at all. They say it makes the engine a bit touchier to tune but gives longer flights and is much more economical of fuel. I understand Nitro is way expensive out there. The touchy tuning probably has something to to with flame front spread. The econony is probably because alcohol has more BTU's / ounce than nitro. Why do you suggest 15%. By the way, do you use any castor at all? I use 3 - 4 % in an 18% total oil mix for all my 4-strokes


John@FLYRC 03-24-2006 11:04 AM

RE: OS FS-70 Surpass Assembly / Rebuild
It seems I am a JOhn and you are a wc. Where would the world be without us? LOL

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