Barrie Galley Posted June 18, 2018 Share Posted June 18, 2018 I have a SC52FS which I've been running for a couple of years (probably about 20 flights) with no problem. I've now come out of my shell, as the weather's got warmer, and I now find I have a sick engine. It starts perfectly and idles smoothly at around 1,200. However, when I open the throttle the speed only increases to around 3,900 no matter the main throttle setting. I've cleaned out the tank and filter, renewed the piping, cleaned the main jet and the silencer nipple. I've been assuming that as the low speed is OK that I haven't got a leak around the carb, but I haven't investigated further. I've never taken an engine apart before so I don't want to go that far until I've investigated all other options, so, any suggestions please? Edited By Barrie Galley on 18/06/2018 16:59:10 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 18, 2018 Share Posted June 18, 2018 OS F plug Barrie, if you have one Also I doubt your motor would tick over at 1200rpm, and it will be more like 2200rpm in reality. Perhaps the Tacho is misreading and your 3900 rpm could be 5900? So, check the tacho as you may be better off than you thought Does it fly the model? Quote Link to comment Share on other sites More sharing options...
Don Fry Posted June 18, 2018 Share Posted June 18, 2018 Try your tacho on a fluorescent light fitting, it should give you 3000. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted June 18, 2018 Share Posted June 18, 2018 Also check the valve clearances now that the engine has had time to bed in. 20 flights is probably about 3 hours or so of running so it's well due for a valve check. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted June 18, 2018 Share Posted June 18, 2018 Posted by Don Fry on 18/06/2018 17:22:10: Try your tacho on a fluorescent light fitting, it should give you 3000. ...unless it has a modern HF electronic ballast! Quote Link to comment Share on other sites More sharing options...
Barrie Galley Posted June 18, 2018 Author Share Posted June 18, 2018 Thanks for all your replies. I'll test the tacho tomorrow against other models/tachos at the field tomorrow (we don't have fluorescent lights in our house) but, nevertheless, the engine is definitely sick and has no power. It performs nowhere near the identical engine I've replaced it with. The model only just lumbers across our grass strip into the air whereas previously it was a greyhound! Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 18, 2018 Share Posted June 18, 2018 I would agree that valves sound a likely source of the problem depending on the prop you should be up around the 9000 mark Quote Link to comment Share on other sites More sharing options...
Simon Feather Posted June 19, 2018 Share Posted June 19, 2018 Some modern LED lights will also give the 3000 rpm reading on the tacho, it's not just fluorescents! But I suspect that's not the issue here, though it is a useful confidence check. If, as has happened to me before, the blade count switch has been knocked from 2 blade to 3 blade in the flight bag... it'll read 3000 rpm on a two blade setting, but only 2000 rpm on the 3 blade setting, which if you then use to measure a 2 blade prop is going to give you a low reading against the engine! Quote Link to comment Share on other sites More sharing options...
Barrie Galley Posted June 19, 2018 Author Share Posted June 19, 2018 Thanks for all your help. Today has seen the problem solved. Firstly, I had a problem with my Tacho. I discovered late last night that it worked on energy saver bulbs which let me to find that its default setting was for 2 blades and mine had changed to 3 blade as suggested by Simon. After that I re-ran my engine and found that it idle'd at 2,200 but was still low at the high end at 6,500. So, after 2 hours of shopping I found a set of feeler gauges that measured below 0.1mm.. I then had a look at the valves and immediately found the problem: one of the lifting bolts had shattered and the threaded portion and the locking nut were resting between the two rocker arms. That's undoubtedly what has been causing the loss of power. I therefore need to replace at least the lifting bolt but I suspect that I should also have a look at the pushrod to make sure that is still OK. I've never had a look inside a model engine before but I've found a utube which shows this engine being dismantled, so I feel confident that I can manage it. Surprisingly, apart from being only one cylinder, it looks remarkably similar to the head of the Vauxhall Viva I had about 45 years ago and I managed to carry out all the repairs on that myself! Thanks again all of you who offered advice, you were all correct and it has given me a result! Must get in touch with Just Engines. Quote Link to comment Share on other sites More sharing options...
Barrie Galley Posted June 21, 2018 Author Share Posted June 21, 2018 The parts have just arrived from JE (21 hours from ordering to delivery!). They're now fitted and the engine is running fine. A result for from all those who gave me advice. Thanks again to you all. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 21, 2018 Share Posted June 21, 2018 Great stuff Quote Link to comment Share on other sites More sharing options...
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