Ed Cesnalis Posted March 10, 2013 Report Share Posted March 10, 2013 When I attempt cold starts, if I have the choke / enricher wide open I will generally get some loud / violent bangs from my gear box. If I advance the choke a bit and find the right spot the start up happens normally. I assume the bangs are the sprag clutch slipping then catching. Can someone explain why this happens when enricher is too rich? Link to comment Share on other sites More sharing options...
Roger Lee Posted March 10, 2013 Report Share Posted March 10, 2013 Hi Ed, The clutch doesn't work nor engaged on starts and stops. What you may feel is the 30 degree free play between the dog gears. You may also get a spark on one cylinder over another then more may fire and all this would depend on when and how much fuel gets dumped into each cylinder, not to mention your engine is firing at 4 degrees before TDC and with the newer soft start system they fire at 3 degrees after TDC. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 10, 2013 Author Report Share Posted March 10, 2013 Roger, Do you have a link for this soft start system? Link to comment Share on other sites More sharing options...
Roger Lee Posted March 10, 2013 Report Share Posted March 10, 2013 Bullyhawk makes an aftermarketet, but Rotax took it a lot farther and changed both modules and the fly wheel. The Bullyhawk works, but not near as good as the integrated and more complete Rotax soft start system. There is literature out there on both and the Rotax system is taught in Rotax school. You could put either system on your plane. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 10, 2013 Report Share Posted March 10, 2013 Bullyhawk only for Experimentals, right? I installed one in my Sky Arrow, and it helps. But on really cold mornings I still sometimes have to go to both "mags" to get her to fire, eliminating some of the advantage. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 11, 2013 Report Share Posted March 11, 2013 Bully Hawk was a good starting point for the idea and does help some, but it isn't near the complete system that Rotax took it to. I don't mean to slam Bully Hawk, but it was more of a band-aid fix. Technically yes it is for the ELSA's or Experimental's. Link to comment Share on other sites More sharing options...
Jeremy MacGregor Posted March 11, 2013 Report Share Posted March 11, 2013 I'm guessing you have low gear box tension and a partially damaged sprag clutch. If the starter is slipping and spinning freely form the crank it's the sprag clutch. Any time the engine is kicking back it's damaging the sprag, kickback is most likely caused from low gearbox tension. I recommend servicing every 500hrs to keep mid range and low idle vibrations to a minimum. The Rotax recommended friction torque test can sometimes be a poor representation of the amount of actual axial play on the the prop shaft. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 11, 2013 Author Report Share Posted March 11, 2013 The Rotax recommended friction torque test can sometimes be a poor representation of the amount of actual axial play on the the prop shaft. Now you tell me. Both Kevin and I sensed a need to look at the gear box after the attempted starts with the stuck float but I didn't know the test was poor. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 11, 2013 Report Share Posted March 11, 2013 Hi Ed, The gearbox friction torque is a contributor to kickback, but not so much a big factor trying to start in cold weather. You may be better served with an engine pre-heater for just cold weather starts. Kickbacks need a gearbox check and most likely a re-shim to tighten it up. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 11, 2013 Report Share Posted March 11, 2013 One other suggestion... BMW airheads have used essentially the same Bing since about 1970. Though the handlebar lever says "CHOKE", we probably all know it's not a conventional choke at all - it a separate starting circuit in the carb - the flow of air to or within the carb is not "choked" at all. I think my Sky Arrow says "CHOKE" as well. So far as I know, that starting circuit Is calibrated to function properly with the throttle closed. Opening the throttle throws off the mixture the engine wants when cold. Of note is that on my Sky Arrow, the checklist says to open the throttle 1/2". I don't think that's the best procedure - wait until it starts with the throttle closed, and only then give it enough throttle to keep it going. Just curious as to what the CT checklist says. If its not freezing cold and you have a strong battery and the planets are aligned just right, none of this probably matters much. But in marginal conditions, having the throttle closed on cold starts may help. If anyone knows different, I'm all ears! Link to comment Share on other sites More sharing options...
Roger Lee Posted March 11, 2013 Report Share Posted March 11, 2013 Hi Ed, How old is your battery? In the summer time a weak, but still good battery will start the engine, but this same battery won't in the cold winter. Link to comment Share on other sites More sharing options...
coppercity Posted March 12, 2013 Report Share Posted March 12, 2013 For the CT, starting without the choke I crack the throttle a bit off of idle, like a 1/4inch. That has the engine running around 1900-2000rpm. With the choke On, I start with throttle all the way at idle and it ends up around the same 1900-2000rpm until the choke is shut off. Link to comment Share on other sites More sharing options...
Doug G. Posted March 12, 2013 Report Share Posted March 12, 2013 When cold (even with a Reiff heater) I use full choke and no throttle. No kickback and it starts quickly - mine has the integrated soft start so after a few seconds the rpm increases. I then slowly take the "choke" off and add throttle to keep the rpm up for warm-up. If the engine is relatively warm I start with the choke off and usually need a bit of throttle (not much) for it to catch. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 12, 2013 Author Report Share Posted March 12, 2013 I have always done cold starts at full en-richer. I don't know how this fuel circuit works but at full I get a lot of kickback until I advance the en-richer a bit. After 7 years I just figured out that my issue is a cold / high altitude start and for that full rich is too rich and my sweet spot for cold starts is a bit leaner. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 12, 2013 Report Share Posted March 12, 2013 You could have a valid point on your elevation and richness idea, but it still shouldn't kickback. Allowing that to continue over a long time will damage the starter sprag clutch and then the engine has to come off and lots of things pulled off to get into that area to replace it. Better to make sure the battery is top notch and send the gearbox in to get it re-shimmed. Even if an engine won't start it should kickback. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 12, 2013 Author Report Share Posted March 12, 2013 Looks like I have sprag clutch damage. My recent fuel issues made starts much worse. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 12, 2013 Report Share Posted March 12, 2013 Hi Ed, here are the items to rule out before you claim sprag damage. These things can and do affect the start and can cause kickback. Low battery, too much fuel to start, carbs poorly synced, Most common the gearbox needs to be re-shimmed, bad plug gaps. All or a combo of these can cause your kickbacks. Address these and what's left would be the sprag. These other items are easy to check and a whole lot cheaper to correct. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 12, 2013 Author Report Share Posted March 12, 2013 Jeremy is going to come buy and shim the gear box and do some test starts and take it from there. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 24, 2013 Author Report Share Posted March 24, 2013 The gearbox was tight after 600 hours, new sprag clutch coming up. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 24, 2013 Report Share Posted March 24, 2013 Hi ED, Why do you need a new sprag clutch? It should last a long time unless it gets damaged. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 24, 2013 Author Report Share Posted March 24, 2013 We believed the sprag clutch was damage but proceeded to shim the gear box 1st. The gear box is tight, no need to shim so again we believe the sprag clutch is damaged. The hard starts and rough running due to stuck float and rubber debris along with long term full rich (full choke) starts at 7,100' and a warp drive prop to boot. Don't forget my timing too, BTDC for starts! We talked about Bullyhawk but I'm thinking if I change my cold starting procedure to restrict the enricher to territory where it doesn't want to kick on cold mornings at 7,100' and combine that with a new battery and more use of my pre-heater that my new sprag clutch will last till overhaul. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted April 21, 2013 Author Report Share Posted April 21, 2013 New sprag clutch installs today, or today and tomorrow. Perfect weather for Jeremy to cross the sierra. 1 hour flight vs 5 hour drive. Link to comment Share on other sites More sharing options...
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