Martyn K Posted April 20, 2015 Share Posted April 20, 2015 This is a follow on from a previous thread. The background is that I bought this engine off eBay for a moderate price - the buyer had good feedback and the asking price (BIN) seemed fair. Engine received OK - looked in good condition - clean etc - and I fitted it (inverted) into the model - replacing an SC70FS that the original owner had in the model (but he kept). So far so good. The engine started easily, idled well and off we went to the strip. The engine was rather smoky (white smoke) especially at tickover - I had put some after run oil into the crankcase via the breather and I thought that may be the cause. Well - the model flew but the performance should have been much better - quite a small aeroplane for the engine size. Take offs were very long and the model had to be dragged into the air rather than allowing the laws of physics to take their natural course (the strip was simply not long enough at about 75m). The engine ran OK and idled OK but the performance was poor. I tried both recommended prop sized (12x8, 13x6) with no significant difference in performance. Vertical performance was especially poor - (the model is a modern-ish 50 sized F3A style model) so this is essential - the model is much better with an SC61 2 stroke on a 12x8) Got the engine back into the workshop and discovered that the tappet setting was incorrect - it looks like the previous engineer had used imperial rather than metric feeler gauges - the gaps were 25x too big. So - I smiled to myself in a smug knowing manner - set the tappets correctly and tried again. Absolutely no difference whatsoever The engine is still very smoky at tickover, (I mean VERY smoky) and the performance is only slightly better - I can now get it off the ground before I run out of strip but that may be as much to do with reducing the length of the tailwheel leg. Checked the revs - the engine rotates at 8800rpm peak with a 12x8 prop - the needle valve position is not critical - but if its too rich or too lean the engine simply dies. So what do I do now? The engine is slowly coming to bits but I am at the point where the valve timing and camshaft need to come out and I don't have the info available to re-time the engine. All the bearings appear to be OK - my plan is to have a look at the bore and piston ring and possibly check that the valves are seated OK. However, I would welcome any guidance from the FS gurus out there. I am not sure if the compression is god or not, I can turn the engine over (just) by rotating the crankshaft (no prop attached) - it seems OK if I was comparing it with a 2 stroke (ABC) engine but I would have though compression should have been a little higher. Thoughts please maestros... Martyn Quote Link to comment Share on other sites More sharing options...
will -0 Posted April 20, 2015 Share Posted April 20, 2015 Hi, you don't need to take the camshaft out to have look at the bore, just pop the head and the backplate off and you should be able to remove the liner and hence the piston/conrod assembly. Have you had a look up the exhaust? If it's coked up it'll be down on power. Compression on ringed 4 strokes can be less than impressive when cold. If you do have to remove the camshaft (which you'd have to do to replace bearings for example), the timing is fairly straightforward: https://www.youtube.com/watch?v=2_OjWeKPHsE Quote Link to comment Share on other sites More sharing options...
Jon H Posted April 20, 2015 Share Posted April 20, 2015 It is possible that the cam shaft is out by a tooth. I did that my accident on my OS91 and it had very similar symptoms. I would also go back to basics, new plug, clean fuel etc. As a benchmark prop use a 13x6 apc and look for 10k+ revs. Will-0's shout on the exhaust being blocked is a good one and can be tested easily by running without the muffler to quickly check the revs. Be aware that the tuning will be all wonkey without the muffler pressure. A guy at my club has this engine prop combo in a 63 inch warbird and it goes like a scalded cat Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Some good tips there - thanks I do want to check the valve timing. Getting the engine to TDC is easy so I'll have a look at the video as well Many thanks both Martyn Quote Link to comment Share on other sites More sharing options...
Sam Wragg Posted April 20, 2015 Share Posted April 20, 2015 Martyn, Asuming your using OS Fs plug 10% nitro18% synthetic oil (minimum). I used to run 20% nitro ( Irvine 20% champion fuel) then check the above + any air leaks around the gaskets/ rubber seals. Can't remember what prop I used on my sons across wot but it was something like 13x10 apc but will get back to you on that. The performance was outstanding Sam Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Cheers Sam I am using Optifuel Optimix 12% Nitro Four Stroke Fuel - so that should be OK. The plug is a dedicated FS plug but I have forgotten what brand I used - may be worthwhile checking a different plug though but I wouldn't have thought it would make that much difference M Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted April 20, 2015 Share Posted April 20, 2015 This vid is much clearer **LINK** Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Thanks for that - what a lovely bit of CAD work - very well presented Audio is a bit low though Martyn Quote Link to comment Share on other sites More sharing options...
GrahamWh Posted April 20, 2015 Share Posted April 20, 2015 If timing is okay try a bigger prop - I run a 14x6 on my ASP 70FS. This may run at the same top revs if the revs are being limited by weak valve springs for example. (My ASP runs a 13X6 at about the same speed as a 14x6). The bigger props act as flywheels helping a 4 stroke through the non-powered part of the cycle. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Cheers Graham, something else to try Martyn Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 I have just been out to have a look at the camshaft timing gear position: Engine at TDC - Sorry about the blurriness Camshaft cover off Zoom in on the Dot The red arrow line points to the dot shows the timing mark which according to the two Video links above, should be in a straight line angled so it is in parallel with the pushrod tubes and passing through the centre of the camshaft. I think that it is one tooth out.. Would you concur maestros? (By the way - that is oil and associated residue not rust on the metalwork) Martyn Quote Link to comment Share on other sites More sharing options...
YakMad Posted April 20, 2015 Share Posted April 20, 2015 Check for a sticky valve, if the engine was run on castor oil its possible to have coated the exhaust valve stem, just take off the rocker cover and gently push the valve down by hand it should feel smooth. I had this happen to me on a few engines and the engines were down on power, its an easy fix just remove the valve and lightly polsih the valve stem with fine wet and dry. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Thanks - will do. Now I have got this far its going to get a full overhaul and service Martyn Quote Link to comment Share on other sites More sharing options...
.. Posted April 20, 2015 Share Posted April 20, 2015 Posted by Martyn K on 20/04/2015 14:34:01: I have just been out to have a look at the camshaft timing gear position: Engine at TDC - Sorry about the blurriness Camshaft cover off Zoom in on the Dot The red arrow line points to the dot shows the timing mark which according to the two Video links above, should be in a straight line angled so it is in parallel with the pushrod tubes and passing through the centre of the camshaft. I think that it is one tooth out.. Would you concur maestros? (By the way - that is oil and associated residue not rust on the metalwork) Martyn Yes I would agree Martyn. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Thank you Quote Link to comment Share on other sites More sharing options...
Hangar 9 nut Posted April 20, 2015 Share Posted April 20, 2015 I agree it looks one tooth out,also check valve clearance as well ! I have just got one of these off the BMFA not run it yet so hope all is well ! Martin be carefull not to lose the small ball bearings in the end of the camshaft ! Quote Link to comment Share on other sites More sharing options...
Jon H Posted April 20, 2015 Share Posted April 20, 2015 I would agree. Its a tooth out Quote Link to comment Share on other sites More sharing options...
Concorde Speedbird Posted April 20, 2015 Share Posted April 20, 2015 My one will take my 45" biplane vertically into the clouds. Once you have corrected the timing hopefully your one will be fixed. CS Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Thanks CS I have just reset the Camshaft - initially went two teeth and then brought it back one and it looks about right now. I have lifted the head and checked for sticking valves - they seem absolutely fine. Judging by the amount of carbon on the head (none - although both valves are slightly blackened), the engine does not appear to have had a lot of use so I have reassembled it - just need to set the tappets again and I'll check for carbon in the exhaust. I'll try and bench run it tomorrow sometime if I get a spare 30 minutes or so. Thanks all for you assistance, I'll let you know how I get on. Martyn Quote Link to comment Share on other sites More sharing options...
GONZO Posted April 20, 2015 Share Posted April 20, 2015 From the JE test on the ASP 70FS **LINK** you are 1000rpm down on the APC 12x8 prop at 8800rpm instead of the 9800rpm achieved with the ASP. I would expect the OS to match or better the ASP. Agree on the one tooth out. 13x7 is a good prop for the 70FS. Edited By GONZO on 20/04/2015 16:49:08 Quote Link to comment Share on other sites More sharing options...
Tony Richardson Posted April 20, 2015 Share Posted April 20, 2015 Also Martyn check your intake manifold for leaks/cracks if the smoke is still present. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Cheers Gonzo That engine is a direct copy isn't it? I forgot to mention - I didn't remove the liner as I couldn't see any alignment marks and it is essential that the ring and piston and bore line up exactly as it runs or I would have problems. However, the bore looks like it has been freshly honed. - no sign of any wear at all Martyn Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 20, 2015 Author Share Posted April 20, 2015 Hi Tony - that's easily done. Will do Martyn Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 20, 2015 Share Posted April 20, 2015 Posted by Martyn K on 20/04/2015 16:54:04: Cheers Gonzo That engine is a direct copy isn't it? I forgot to mention - I didn't remove the liner as I couldn't see any alignment marks and it is essential that the ring and piston and bore line up exactly as it runs or I would have problems. However, the bore looks like it has been freshly honed. - no sign of any wear at all Martyn When you remove the liner there is usually a telltale circular mark where the gudgeon pin access hole is on the rear of the cylinder, which will enable you to realign the liner. You could always use a scriber through the hole to be certain... Quote Link to comment Share on other sites More sharing options...
Sam Wragg Posted April 20, 2015 Share Posted April 20, 2015 When I run YS an old trick of mine was to rub the joint face of the rocker cover against a flat oil stone to ensure it was flat, as any leak around this area can upset the performance of the engine. Still can't remember what prop I used tho Sam Quote Link to comment Share on other sites More sharing options...
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