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Thread: Overpriced starter motors

  1. #11

    Overpriced starter motors

    I've watched people struggle to start DCDI engines many times. In fact, unless the 12v battery is well charged, even electric start can be useless.
    As an electronics type, it occurred to me that the plug 'gap' on the dual ignition types is actually twice the physical setting - it has ignition HT coils that have a plug connection at either end (rather than one end going to earth, as in single ignition systems), so two plugs are effectively in series. So Wally's setting gaps to 15 though instead of 16 makes a 2 thou improvement (and as an inspector myself, I couldn't give a stuff - the engine is merely an 'accessory').

    So here's a novel, but possibly impractical solution. Have a shorting switch on one plug in each cylinder (you'd choose plugs on different systems, of course). So you'd short one plug on each system to earth, reducing the effective gap on each system to just 16 thou (or whatever) for starting. Once running, you'd remove the shorts and continue to benefit from a dual plug engine. The impracticality is making a shorting switch that would function at up to 25kV, and could be opened remotely after start-up. At the simplest level, it would be like the sprung metal tab used to short out an open topped plug on an old lawnmower, in order to stop it.

    Thinking about it, another way might be to run a really close gap on one plug on each system. Say 10 thou. It wouldn't affect ignition timing as it is in series with a normally gapped plug. You'd also still have the redundancy of a second plug, even though it wasn't most efficiently gapped.

    Dave

  2. #12
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    Overpriced starter motors

    Dave - are the plugs of the twin lead coil really in series? This means that if one plug cap drops off, or the HT is severed (or any other HT open circuit failure occurs) then both plugs on that coil fail to fire. This is not the failure mode I would choose.
    There is (was) a common 'dodge' for bike engines, which involves adding an extra series gap in the HT lead to raise the voltage at which the coil discharges and preventing the coil charge from leaking away across a fouled plug. Reducing the gap reduces the discharge voltage and therefore reduces the spark energy, which is crucial to cold starting when fuel form larger droplets and may wet the plug.

  3. #13

    Overpriced starter motors

    Ok that's my weekend sorted.

    Well if all else fails I can always resort to Wally's yanking method.

    Because after all, everyone enjoys a good Yank. :lol:

    Cheers

  4. #14

    Overpriced starter motors

    Hi Peter, It's one of life's compromises: wide gap = lots of energy, but the risk of either the generator failing to rise to sufficient voltage to spark (usually at starting cranking revs - not such a problem with battery/coil ignition), or insulation elsewhere breaking down and diverting the energy away from the plug gap.

    Yes, the plugs really are in series - earth-plug1-HTcoil-plug2-earth. Yes, if one cap comes off, you lose both plugs. But it's got a second independent (almost) ignition system, so there's redundancy, so who cares?
    Used to fly with Fuji Robins that had a similar (but more robust) arrangement - but that did only have single ignition. We always had a bungee over the plug caps then...

    Dave

  5. #15
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    Overpriced starter motors

    Simon used to be the agent for the M4 sys...thats what I have on my 503DI.

    http://ecclestonaviation.co.uk/

    Maybe worth having a chat.

  6. #16
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    Overpriced starter motors

    Bryan,

    No-one's actually asked you yet whether your 503 is a DCDI or a points engine, or whether you've got two plugs per cylinder or single plugs, and whether you've got a single or twin carbs? All these things make a difference to the starting technique. Also, is your engine upright or upside down? If it's upside down then you'll need to take the plugs out every time you start it for the first time each day. I used to have an inverted Robin 440 on one of my XL's and I found that if I didn't take the plugs out and clean them before trying to start it for the first time, it just wouldn't go. The plugs filled up with oil over time, and this had to be removed so that the engine could start. What I did in the end was kept two pairs of plugs, and for the first start per day I'd change the plugs, so that it was a fresh pair that went in for that vital first start of the day.

    As to Ginge's comment about me sorting out the starting ritual on my current engines (462's on both my Peggy trikes), yes I did, but it took me a while to get it right. The secret was to treat the engine as though it hadn't been started for a year. So the first thing I do is take off the float chamber from the single carb, and empty it. Then, as I have plastic tanks on my trikes, I refill the float bowl from the drain valve at the bottom of the tank. This serves two purposes. If there is any water I'll see it in the bottom of the bowl, and can discard it. So having checked to see if there's water in the bowl, if it's clear then I fill the float bowl to the very top, then carefully reattach it to the carb.

    My engines have separate breather tubes from each side of the carb, so I put my thumb over one and blow into the other. This has the effect of pushing some of the fuel from the float bowl up the main jet and needle jet and into the venturi of the carb. I then make sure the ignition is turned off, and pull the engine over slowly on the prop about 3 or 4 times, then quickly for 5 or 6 times. This pulls some of the neat mixture into the crankcase. I then climb into the trike, sit on the back seat, turn on the ignition, make sure the throttle is shut and the choke is off, shout 'clear prop' very loudly, count to 5 and then imitate an olympic rower by giving an almighty pull up and back as fast and as far as I can. The engine normally bursts into life on the first pull, but usually by the second or third if not the first.

    After this I know the engine will always start first pull for around the next hour. After that I have to treat it as a totally cold engine again and go through the whole rigmarole of making sure the float bowl is full, blowing through the breather tube, etc.

    Now tell us what your starting routine is, and we'll see if there's anything you should be doing that you're not, or whether your doing something that you shouldn't.

    Oh, there is also the thing about timing. Is your timing correct? If you've got the DCDI then it will be, but if you've got a points engine then one of the sets of points could have worn slightly and put the timing out to the extent that the cylinders aren't firing exactly on the 180 degrees apart that they should. This will make the engine difficult to start as well, so it's worth checking the timing if you can.

    Best regards,

    Bob Hood

  7. #17

    Overpriced starter motors

    If its DCDI, don't expect the starter to solve your problems. Anything less than a fully charged, good condition battery will still fail to get sufficient revs to give a decent spark (M4 experience).
    Points - Bob is correct. Another point about points (!), both must be nigh perfect contact as each relies on the other to provide continuity to earth at the point of its opening.

    Bob: I've never had starting problems with 462s. Usually on the third or fourth pull. I have seen them if the throttle isn't fully closed, or if the gearbox dog clutch pre-load has gone out of spec. (evidenced by a sound like the prop being struck by a hammer at starting and low revs). As for inverted Robins, if you took the plugs out before starting, they were usually dry. Then, on starting, it would fire just a couple of times to let you think all was okay, then it would splutter to a stop and refuse to start again, until you pulled the plugs and found them full of oil. My theory: the pistons gather a bit of oil inside the cup. On first starting, the oil is splashed out, down the transfer ports, and drown the plugs.

    Dave

  8. #18
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    Overpriced starter motors

    Dave,

    In my case I flew the Robin powered aircraft on average around once a fortnight, so the fuel in the cylinders tended to evaporate away, leaving the oil behind to coat everything. However, as the engine was upside down, this oil then ran down into the cylinder heads and invariably filled the plugs. So before attempting to start the aircraft after it had been standing for a week or fortnight, I'd take the oil filled plugs out, use a cloth to try and get out any more oil that was sitting around the plug hole and then replace the plugs with clean dry ones. The plane would then start easily, but blow out a lot of oily smoke for the first few seconds. I then cleaned out the oil filled plugs and put them aside so that the next time I wanted to start the plane after a lay off of more than a few days, I'd replace the fitted plugs with the nice clean ones I'd taken out the last time. That method worked well for the three or four years I owned that plane, and when I sold it on, I advised the new owner to do the same. However, I take your point about the oil in the pistons getting thrown into the transfer ports, and I think that was probably one reason for the clouds of smoke I used to get on starting the engine from cold.

    Interestingly, on 4 stroke engines (that don't have oil in the fuel), the pistons often have small holes drilled from the back of the second or third ring groove into the inside of the piston crown. This is to allow oil to be splashed from the small end bearing into the holes and out around the rings to help lubricate the rings against the cylinder wall. If the inverted Robin engines had this then any oil inside the piston crown would flow out around the rings and down into the cylinder head instead of being trapped inside the piston to get splashed into the transfer ports on starting. However, I don't recall ever seeing any such holes when I dismantled my spare Robin engines.

    As for 462's. I've also seen some engines that start easily without all the rigmarole I go through, but they do seem to be variable in this. I seem to remember Paul Dewhurst saying that the 462's could be very good starters, and that some of them were very reliable, but not all the good starters were the most reliable, and vice versa. So I've found a starting formula that works for me, and I stick to it, and so far the engines have been pretty reliable. However, on one engine I had to replace the magneto end crank oil seal, and on the other one I've had to replace the cross shaft oil seal. Furthermore, when I did FlyUK this year, the coil plate on my engine managed to vibrate itself into breaking at the three corners where it's bolted to the side of the block. This lead to one of the earth wires pulling off and reducing the engine to only running on one cylinder. This happened when I was at Fishburn, and I didn't have a spare coil plate with me, so I had to trailer the plane home to London, and since then I've been involved with other things and haven't got round to replacing the plate yet.

    Best regards,

    Bob Hood

  9. #19

    Overpriced starter motors

    I had a 462 that would accelerate up to 3000rpm and then bog down. If you could nurse it past 3000 it would run fine right up to 6500. But if it dropped below 3000 it would refuse to go up again. After resetting points a couple of times, I pulled the flywheel and found black gunge around the stator, so pulled it to look at the seal. The end of the shaft seemed to have a lot of play, so I assumed a bad main bearing. However, on splitting the case, I found the mag end big-end was loose - the press fit of the journal into the end web had failed. Engine had only done ~150 hours, so I assume it must have been loose from the start.

    Been looking around for a new/old crankshaft for a while (I think Nigel/Conrad still has one, but they want 1600 - yeah, right).

    Dave

  10. #20
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    Overpriced starter motors

    Dave,

    One of the things Paul Dewhurst said was that 462's were very variable in their build quality and reliability, and he should know, as he used them in his training aircraft in years gone by. Seems like you got a Friday afternoon engine! Shame, as the good ones are very good at economy per lb and hp. Seemingly more so than the later 532 and 582 engines.

    Personally I'm quite a fan of the 462, and I wish they'd continued with them instead of the 503. Not that the 503 is bad per se, but being air cooled and piston ported it's not as efficient as the 462, or as powerful, unless fitted with electronic ignition and twin carbs.

    Best regards,

    Bob Hood

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