Pyro Posted November 8, 2015 Share Posted November 8, 2015 Also please not that the 9000+ rpm was achieved on a prop that is not suited to this motor (pitch too small) so I'm not sure if this is running well yet or not. Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 9, 2015 Share Posted November 9, 2015 Justin - I'll be very interested in the answer to this problem, as I've spent much of the last few months trying to get to the bottom of a very similar problem with an OS70FS. I've tried every possible cure with no change. The club experts persuaded me that it was fuel that had "gone off" so I bought fresh. Which made the problem worse. I'll give you the full details if you want to compare notes. Graeme Quote Link to comment Share on other sites More sharing options...
.. Posted November 9, 2015 Author Share Posted November 9, 2015 Yes Graeme fire away , I have a couple of 70's Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted November 9, 2015 Share Posted November 9, 2015 Posted by graeme jones on 09/11/2015 16:03:50: Justin - I'll be very interested in the answer to this problem, as I've spent much of the last few months trying to get to the bottom of a very similar problem with an OS70FS. I've tried every possible cure with no change. The club experts persuaded me that it was fuel that had "gone off" so I bought fresh. Which made the problem worse. I'll give you the full details if you want to compare notes. Graeme Hello Graeme. You will probably find that your OS has a timing problem brought about by worn or corroded bearings. Many of the 70fs engines I have rebuilt have run like new engines as the new bearing make the timing gears mesh as they are supposed to.just a tiny amount of play allows the timing to move and the performance suffers. To check for wear hold the prop vertically the rock the prop feeling for any play in the crank bearings. Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 9, 2015 Share Posted November 9, 2015 Justin - very similar symptoms to your Saito. Starts OK but wont run above 8000 RPM on a 13X6 (was 10500 in the previous aircraft) and won't idle below 4000. It's in good mechanical condition, correct timing and rocker clearance, new plug, new fuel, new filter, new tank etc. etc. Very frustrating. Engine Doctor - didn't think the bearings were the problem so I've just checked. No detectable play up, down, sideways, backwards or forwards. Although it's an "old" engine (OS 70 Surpass OS No 34000) it hasn't had a great deal of use, about 50 flights in a Wot4. I replaced it in that aircraft with an Irvine 40. It's been layed up full of oil ever since and is in excellent condition with no visible wear. Yes, I've had it apart a few times and yes I have put it back together correctly (I'm not new to this, back in the 70's I was taking HP40's apart and swapping parts to "blueprint" them. More recently I've stripped and reassembled 2 OS48 FS's and 4 OS26 FS's and they all run correctly). Timing dot in line with the pushrods at TDC, rocker clearances both 3 thou (of an inch), good compression, valves moving and sealing correctly, no broken valve springs. By the way, I've also tried 4 different fuels, the original MT 5% 4 stroke, a new gallon ditto, the castor straight that I always used in the Wot4 and some fuel that a clubmate was using in his Saito, all with the same results. Now for the strangest bit. I have another OS 70 FS. This one is an FS 70S II, OS No 34700. It's had more use, about 80 flights, and ran fine last time I used it in April. They are not a direct swap because of different carbs and exhausts, but with a bit of faffing about I swapped it for the old one i.e. in the new aircraft. Confident that this would solve the problem I set off for the field and started it up. Guess what? Wouldn't rev above 8000 or idle below 4000!!!!!! Aha say the experts, it.s overheating inside the cowl. Took the cowl off which made no difference whatsoever. So the problem has to be with the tank, right? Wrong! Strapped another tank to the outside of the fus. and have the same problems. Exit club experts muttering into their beards. Next step is to try each motor in the old aircraft. Graeme Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted November 9, 2015 Share Posted November 9, 2015 Check the engine mount is secure and not cracked over the bolt holes, need to check the security of the firewall ditto. May be worth checking that the air getting to the carb is not heated too much, I'd a laser 80 in a midget mustang that needed an airscoop to provide cool fresh air to the carb, just a thought. Edited By Braddock, VC on 09/11/2015 22:56:37 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 10, 2015 Share Posted November 10, 2015 I once found an OS70 with "variable valve timing" when I offered to investigate a non-running engine for a clubmate - this was in a several years old unrun "new" but second owner engine - and Ripmax replaced it without any quibbling, their attitude was any manufacturing fault should be rectified despite the ownership history. Edited By Martin Harris on 10/11/2015 00:32:37 Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 10, 2015 Share Posted November 10, 2015 Braddock - I've already checked the mount and its fine, like this - there's not excessive vibration and, as I've said, taking the cowl off made no difference. Also the installation is very similar to the old aircraft in which the Mk 2 ran fine. Justin - one thing I forgot to say is that the exhaust note sounds "wrong", rather like your Saito but difficult to say exactly what is wrong with it. Graeme Quote Link to comment Share on other sites More sharing options...
Wingman Posted November 10, 2015 Share Posted November 10, 2015 Is it normal to block the crankcase vent like that on these engines? Quote Link to comment Share on other sites More sharing options...
.. Posted November 10, 2015 Author Share Posted November 10, 2015 Posted by graeme jones on 10/11/2015 07:02:15: Braddock - I've already checked the mount and its fine, like this - there's not excessive vibration and, as I've said, taking the cowl off made no difference. Also the installation is very similar to the old aircraft in which the Mk 2 ran fine. Justin - one thing I forgot to say is that the exhaust note sounds "wrong", rather like your Saito but difficult to say exactly what is wrong with it. Graeme Why why is the crankcase vent blocked off ? Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 10, 2015 Share Posted November 10, 2015 Because at the time the pic was taken the engine was still full of storage oil and hadn't been run. It was drained and flushed with fuel before use. By the way and before anyone asks, plenty of oil comes out of the breather while running. Makes a mess on the canalizer. Graeme Quote Link to comment Share on other sites More sharing options...
Tony Richardson Posted November 10, 2015 Share Posted November 10, 2015 Yes, unfortunately I couldn't really get it to hold steady below about 2500 rpm. it would be great if it idled reliably at the 1500ish revs in the vid but I was trying to get her at about 1800-2100. Just would go there and it varied depending on whether I chopped the throttle from high revs (slow idle) or just blipped it a couple of times, then it would settle at about 2500ish. Pyro I had a Saito 180 that acted the same way, my problem was the tank position ( way too high ) when I came off full throttle it would idle nicely at around 1800/ 2000 rpm but blip the throttle and it would be up to 2500 plus and would not settle down conclusion was that a blip sucked in fuel and loaded the carb and intake so it was running rich for quite a little while then it would settle down, eventually swapped it out for a gas engine with pumper carb and put the 180 in a model with an upright mount and correct tank position, but I don't think this is your problem as the engine on a test stand is a good set up, have you tried increasing the nitro content Saito recommend a higher than normal nitro% I run mine on the YS/SAITO 20/20 fuel exspensive but it works for me, Keep at it I am sure you will get it right in the not too distant future, also I know it is was previously owned but how much running has it actually had the 180 took about four gallons of fuel before it really started to settle in, compression was always very good and got better the more I ran it, could be a snappy beggar to start sometimes. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 10, 2015 Share Posted November 10, 2015 If I'm reading you correctly Graeme, I think you're saying that two different engines are playing up in the same installation? Could you have a restriction in the fuel supply? What is the blue component before the red fuel tube to the carb - a refuelling valve or filter? If so, can you run a plain pipe temporarily from the tank to the carb to eliminate the possibility that it's restricting the flow... BTW, I always like to run the feed to the carb in clear tubing so that I can check for any air bubbles from leaks or frothing easily. Edited By Martin Harris on 10/11/2015 09:29:55 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted November 10, 2015 Share Posted November 10, 2015 I second what MH says in previous post . what's in the fuel line ? It's poor practice to fit filler valves etc in the fuel line as they can introduce air leaks and flow restrictions. With the added info that two engines are playing up in the same airframe suggests that it a plumbing /tank issue . Also might be a good idea to start anew thread as this has effectively hijacked Pyros thread about his Saito. Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 10, 2015 Share Posted November 10, 2015 Martin - it's a fuel filter, since replaced with one of a different make. No blockage since all 9 oz of fuel will run out of the tank under gravity. Engine doctor - see above. That's why I tried with a separate tank strapped to the outside of the fus. Poor practice? Both my Hirobo Shuttles have a filler valve between the 2 pipe tank and the engine and they run OK. A new thread might just be duplication, since the problem APPEARS to be the same. Different engines yes, but both 4 strokes, both not developing full power and won't idle correctly and both sounding wrong. I'm happy to keep quiet for now unless I find the problem and wait for the OP to sort his. Graeme Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted November 10, 2015 Share Posted November 10, 2015 Hello Greame. Sorry if I offended you re the post hijack thing I didn't mean to . My bad practice statement was also not meant to offend , Sorry again . The use of the in-line filler valves on Helis is more common I know possibly due to the two stroke engines running almost turbine smooth compared to a plane and the vibes don't affect the filler valves as much. On a plane the vibes generated by a engine especially a FS can unseat the valve and allow air into the fuel system. I note you say that you use FS fuel . Is that a higher oil content fuel as haven,t heard of that in years. Higher oil content will cause a lower power . The 20% oil fuel is ok on older engines but the modern engine is quite happy on 17% oil and the extra methanol makes a real difference to the power at top end power and better idle . Sorry again If I offended you . Quote Link to comment Share on other sites More sharing options...
graeme jones Posted November 10, 2015 Share Posted November 10, 2015 Engine Doctor - no offence taken, I'm just hoping for a solution to the problem for me and for Justin and Pyro. I've been so frustrated by this one and I'm sure they are as well. Fuel is Model Technics Special Four Stroke 5%. That's 5% nitro. 9% EDL and 9% castor. Southern Modelcraft do an identical mix which also works well (see fuel info. at Just Engines). I standardised on it some years ago and use it in all my engines now except the old ones like HP40's which don't like synthetic oil and run very well on castor straight. I don't think Justin and Pyro have said which fuel they use, just that both Saito's use the same. What we need of course is someone to say " I had that problem and cured it by XYZ"!!! Graeme PS if it's not raining tomorrow Plan A is to run some engines. Quote Link to comment Share on other sites More sharing options...
Pyro Posted November 10, 2015 Share Posted November 10, 2015 Posted by Tony Richardson on 10/11/2015 09:25:35: Pyro I had a Saito 180 that acted the same way, my problem was the tank position ( way too high ) when I came off full throttle it would idle nicely at around 1800/ 2000 rpm but blip the throttle and it would be up to 2500 plus and would not settle down conclusion was that a blip sucked in fuel and loaded the carb and intake so it was running rich for quite a little while then it would settle down, eventually swapped it out for a gas engine with pumper carb and put the 180 in a model with an upright mount and correct tank position, but I don't think this is your problem as the engine on a test stand is a good set up, have you tried increasing the nitro content Saito recommend a higher than normal nitro% I run mine on the YS/SAITO 20/20 fuel exspensive but it works for me, Keep at it I am sure you will get it right in the not too distant future, also I know it is was previously owned but how much running has it actually had the 180 took about four gallons of fuel before it really started to settle in, compression was always very good and got better the more I ran it, could be a snappy beggar to start sometimes. Hey Tony, good tip. I shall check that next time I'm out there running it. My rig has the tank centreline dead online with the centre of the carb barrel. This is almost exactly an inch above the crankcase centreline. Should I have lined it up with the crankcase centre? Quote Link to comment Share on other sites More sharing options...
Tony Richardson Posted November 10, 2015 Share Posted November 10, 2015 Pyro your tank position is sounds perfect, have you tried running the engine without muffler pressure? Quote Link to comment Share on other sites More sharing options...
Pyro Posted November 10, 2015 Share Posted November 10, 2015 Posted by Tony Richardson on 10/11/2015 20:27:52: Pyro your tank position is sounds perfect, have you tried running the engine without muffler pressure? Nope, but I'll give it a shot if you think it worth while. Quote Link to comment Share on other sites More sharing options...
Tony Richardson Posted November 10, 2015 Share Posted November 10, 2015 It's worth a try, nothing to loose at this stage of the game, I am far from an "expert " on engines just sharing things that have worked for me in the past, you may need a one way check valve in the fuel line to the carb if you have no tank pressure as with some engines air can tend to syphon back into the tank from the carb at certain throttle settings mostly when coming down from high to low, in all honesty I have found some engines to be problematic when inverted but fine when fitted sideways or upright, same make same size I have no explanation for why, maybe I am just impatient Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.