Mike T Posted June 29, 2021 Share Posted June 29, 2021 A few years back, an old pal was 'divesting' himself of i.c. gear and I bough a .40 Surpass from him. He'd had it second hand and another Club member (a competent technician) had replaced the bearings for him. I put it in my old Junior 60 and it gave nothing but trouble from the off, being very critical on tuning and going 'off the boil' frequently. I cleaned the carb, polished the needle (no grooving, but 'just in case') and changed the tank plumbing and filter several times. Sometimes I'd get a good flight by running it rich and managing the throttle carefully. More often than not, it quit just after take-off or in the first circuit. Knowing the bearings had been replaced, I suspected the timing wasn't right. I took the cover off and not being able to see the dot at TDC, rotated it to BDC, where it seemed to line up with the pushrod - maybe a hairsbreadth away from absolutely in line. Baffled, I put it to one side in disgust and moved on. A few weeks ago, having convinced myself that the passage of time would have cured all ills (plus some fresh fuel) I took it out to play again - with the same results. Now thoroughly fed up with it, I thought I'd nothing to lose by completely stripping and rebuilding it. I checked the timing again, this time having pulled the head, pushrods and cam followers. Now I could see the mark and at TDC it was (just) in line. I then rocked the crankshaft and 'felt' TDC on the piston with my fingers. The mark was now way off line and looking at the 'T' mark on the prop-driver, this was about 10 degrees off. Now the prop driver is located on the crankshaft by just a flat (no key) and over it's life, it had rotated and jammed on the crank out of position, which (I can scarcely believe) I hadn't noticed. I reset the cam gear with reference to the piston (one tooth anti-clock from its previous position) and re-assembled. It runs like a Swiss watch - easy starts, not fussy on the needle, throttles superbly and idles down to 'count-the-bangs-as-it-goes-around'. The wonder is that it ever started or ran in its previous state. Pics show reference line (blue) and timing mark (red). 2 1 Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted June 30, 2021 Share Posted June 30, 2021 I once purchased an OS FS-80 quite cheaply as it was a poor runner. It had not had much use (judging by the exhaust pipe colour), so after a clean and a gentle valve lap with jewellers rouge the culprit was discovered. Timing off by just one tooth. Fixed that, set the valve lash and it started with a few lazy flicks and ran sweetly. Previous owner must have 'fiddled' with it. * Chris * Quote Link to comment Share on other sites More sharing options...
J D 8 Posted June 30, 2021 Share Posted June 30, 2021 Have known Land Rover engines one tooth out on the timing belt, run like a bag of bolts and no power but run and even be driven ! Quote Link to comment Share on other sites More sharing options...
Nigel R Posted June 30, 2021 Share Posted June 30, 2021 The one tooth out mistake is easily made. Fortunately, also easily fixed. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted June 30, 2021 Share Posted June 30, 2021 (edited) You cant trust timing marks . Even the dot or punch mark on the camshaft can sometimes be wrong or non existent and worn components will give false readings. By all mean use the timing marks but check before completing the reassembly of the engine that the timing id correct. If you set engine at TDC then insert camshaft so that the lobes are "on the rock" thats one valve just closing and the other valve just opening then the timing will be spot on . The more tuned an engine is the more critical it gets as the overlap of inlet and exhaust valves can cuase the valves to hit the piston if incorrectly timed and bend them or damge the head etc . Dont forget as you insert the camshaft it rotates slightly so allow for this. Edited June 30, 2021 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Mike T Posted June 30, 2021 Author Share Posted June 30, 2021 6 minutes ago, Engine Doctor said: ... Dont forget as you insert the camshaft it rotates slightly so allow for this. I think this what the previous 'fiddler' overlooked. I was surprised how far I had to turn it back to get it to 'screw' into place correctly. Only one problem left to solve now - why does it always quit with 20% left in the tank? Quote Link to comment Share on other sites More sharing options...
Jon H Posted June 30, 2021 Share Posted June 30, 2021 ED is quite right. I have encountered two Thunder tiger, one ASP and one Enya with timing marks punched in the wrong place or incorrectly assembled at the factory. This caused great confusion for their owners! On engines with crank driven cams i always set them with the bare case only holding the crank. I can then put a finger in through the backplate or cylinder hole to hold the crank pin where it needs to be. once assembled i then check it as suggested by seeing what is happening at tdc of the non compression stroke. Both valves should be open equally, or on occasion (laser and enya for sure) slightly more open on the inlet 2 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 30, 2021 Share Posted June 30, 2021 (edited) Same level, everytime at the motor cut is a statement. Pin hole pressure leak etc At my field, they say indignantly " but it's a new tank, and new pipes " Yes but It's still leaking pressure, is the reply Edited June 30, 2021 by Denis Watkins 1 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 30, 2021 Share Posted June 30, 2021 9 minutes ago, Mike T said: I think this what the previous 'fiddler' overlooked. I was surprised how far I had to turn it back to get it to 'screw' into place correctly. Only one problem left to solve now - why does it always quit with 20% left in the tank? Clunk internal tube not long enough perhaps... Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 30, 2021 Share Posted June 30, 2021 By that I mean the fuel flexible tubing to the clunk ? Does the engine manufacturer give valve timing info, eg. Exhaust closes ( closed ) at XX degrees etc., at a know valve working clearance etc.... 1 Quote Link to comment Share on other sites More sharing options...
Mike T Posted June 30, 2021 Author Share Posted June 30, 2021 (edited) Thanks guys. The tank is a SLEC 'blue'. I've renewed the plumbing and looking at the long, narrow clunk, it seemed to have a much larger bore than necessary, so I thought at low fuel levels it might be prone to drawing, causing a lean cut. So I sleeved the clunk and turned the end down so that the (smaller) hole is right down in the corners. Still no joy! However, I did get the feeling when screwing the feed pipe back in that a fraction more of a turn would cause it to strip, so there may be an airleak there, so a swap-out is the next step, or maybe a tank with a conventional bung. @Rich Griff - the internal tubing is sized to get the clunk in as far as it will go and just clear the base of the tank when wiggled vertically. Not too concerned about valve timings now as the engine itself is now running just fine ? Edited June 30, 2021 by Mike T addition Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 30, 2021 Share Posted June 30, 2021 (edited) Do you miunt the tank vertically ? I fit mine so they are horizontal with the clunk being able to sit on the tank floor, which is the tanks side really... The clunk has a "bevelled" or slightly tapered end... I make sure the clunk cannot be " sucked" onto the tanks internal walls causing fuel starvation etc... From memory the blue tanks are relatively small, I use the from memory yellow tank in my 40 powered wot4 type model, which is waiting for a service/check over and new tank... You will never run the tank absolutely dry of fuel, there will always be some fuel left in the tank unless you drain it by the 2 tank stubs, the filler and exhaust pressure pipe stubs, needing the model positioned to do so...nose down and upsidedown usually... Of course your set up may be completely different to mine... Edited June 30, 2021 by Rich Griff Quote Link to comment Share on other sites More sharing options...
Mike T Posted June 30, 2021 Author Share Posted June 30, 2021 (edited) No I meant when you hold the tank up, you waggle it to make sure the clunk is hanging down so it just misses the bottom. Lots of people adjust it so it just misses the corners, but it can then scrape the base as it swings about. In the plane, the tank is mounted conventionally: NB - the tank centreline is fractionally below that of the NVA Edited June 30, 2021 by Mike T addition Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 30, 2021 Share Posted June 30, 2021 (edited) How does muttly see where he is going ? Ah, periscope of course. Muttly is one heck of a pilot ! ? Edited June 30, 2021 by Rich Griff Quote Link to comment Share on other sites More sharing options...
Mike T Posted June 30, 2021 Author Share Posted June 30, 2021 Wash your mouth out! ? That be Snoopy! Anyway, forward views are so overrated - ask Lindbergh ? 1 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 1, 2021 Share Posted July 1, 2021 I'd get the thing on the bench and confirm it can run a 6oz tank dry. I would be highly surprised if it could not. Assuming yes, then take another look at the tank and plumbing in the J60. My money is on the installed kit. Have you done the "fuel tube on needle valve" dodge? Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 1, 2021 Share Posted July 1, 2021 (edited) On 30/06/2021 at 14:46, Mike T said: No I meant when you hold the tank up, you waggle it to make sure the clunk is hanging down so it just misses the bottom. Lots of people adjust it so it just misses the corners, but it can then scrape the base as it swings about. In the plane, the tank is mounted conventionally: NB - the tank centreline is fractionally below that of the NVA The tank is too high. Lower it so the top of the tank is in line with the needle and its likely going to solve the problem. As it is currently the first half of the tank is assisted @ 9.81m/s^2 by gravity, and the bottom half resisted by the same amount. This gives an acceleration change of nearly 20m/s^2 to the fuel as the level drops. As the engine is tuned to work with the assist, it runs lean once gravity is against it and eventually stops. If you lower the tank the engine always sees the same gravity resist so tuning remains more constant with fuel burn and will keep on singing. A thinner tank (in height) will also be an advantage for the same reason. Radio active tanks are good for this as they are thinner and wider than slec so fuel head change is minimised. In an idea world a thin tank with the top in line with the carb c/l is the perfect installation. Edited July 1, 2021 by Jon - Laser Engines 2 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 1, 2021 Share Posted July 1, 2021 I would be surprised Jon if the motor could not run reliably with that tank position, it looks like the 2/3 mark is level with NVA a couple of further thoughts; dismantle and clean out the carb - you might have some crud accumulating around the needle valve orifice try running on silencer pressure check the idle air bleed screw position, usually about half open is right when these motors are in good order they run like clockwork from start to finish, one of OS best to my mind Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 1, 2021 Share Posted July 1, 2021 Quite a deep puddle of oil can accumulate in the silencer pointing upwards If it is your chosen option Then just while the short run is sorted, point it down, just for now Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 1, 2021 Share Posted July 1, 2021 22 minutes ago, Nigel R said: I would be surprised Jon if the motor could not run reliably with that tank position, it looks like the 2/3 mark is level with NVA a couple of further thoughts; dismantle and clean out the carb - you might have some crud accumulating around the needle valve orifice try running on silencer pressure check the idle air bleed screw position, usually about half open is right when these motors are in good order they run like clockwork from start to finish, one of OS best to my mind It will be fine. The needle will be tuned to suit the low position and the engine will be quite happy. I have this setup in my seagull challenger with an OS40fs and it works a treat. Most tanks are mounted too high in models and its the primary reason for in flight mixture change problems. Top of tank, middle of carb is the way to go to maintain the fuel head pressure. 1 Quote Link to comment Share on other sites More sharing options...
John Wagg Posted July 1, 2021 Share Posted July 1, 2021 Regarding Jon 'Laser' suggestion - O.S. recommend the top of the tank, for four strokes at least, be about 10mm above the needle valve. Quote Link to comment Share on other sites More sharing options...
Mike T Posted July 2, 2021 Author Share Posted July 2, 2021 Thanks for the input Guys! ? I've thought before that the tank was maybe too high but I've always resisted lowering it as I believed it was set up in accordance with received wisdom - and OS' recommendations. However, I've abandoned my 'removable folding tank floor' (pat. pending) and dropped the tank so the top is level with the NVA, so we'll see how that works out! It'll be easy to raise it if it proves too low. An added bonus is that Snoopy's forward view is now completely blocked only by the cylinder head... Apart from fuel draw, the engine now runs superbly so no worries on carb cleanliness or the airbleed screw. I've got 3 OS 40s and all have a finely tuned slug of fuel tube fix ? And it usually runs on silencer pressure anyway (the pic above shows the tap disconnected to see if no pressure and a couple of clicks richer improved the situation - it didn't...) Weather is looking crappy for the next few days so testing might have to wait ? Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 2, 2021 Share Posted July 2, 2021 further thought does the stop occur 80% of the tank in, or is it after 3oz of fuel has been slurped? or another way to put it if you try a 20oz tank, does the thing stop with 17oz remaining? I'm wondering if it is a run time cause (heat?) rather than a fuel level cause Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 2, 2021 Share Posted July 2, 2021 (edited) 15 hours ago, John Wagg said: Regarding Jon 'Laser' suggestion - O.S. recommend the top of the tank, for four strokes at least, be about 10mm above the needle valve. As if by magic... I lifted this from the OS 40 fs manual. John is quite right about OS recommending 10mm tank above the needle. however, the fuel level shown on the picture is dead inline with the needle and there is free air space taking up the remaining 5-10mm. As a result, i just recommend top of tank to centre of carb as i assume we all brim our tanks when filling ? Edited July 2, 2021 by Jon - Laser Engines 1 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted July 2, 2021 Share Posted July 2, 2021 "air gap" so no chance of fuel getting into exhaust/engine ? Quote Link to comment Share on other sites More sharing options...
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