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#11
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Dan Thomas wrote:
The Type Certificate Data Sheets will give minimum and maximum static full-throttle RPMs for that engine/prop combination in that airplane, and if there is valve train wear the RPM will be out of the range. This isn't rocket science. If the crank is eating its way into something, there'll be metal in the filter. That's simple enough, too. If the oil pressure is well into the green, and doesn't drop to zero at idle when hot, the bearings are OK. If the compressions are as high as he's indicated, there isn't much wrong with the top end of the engine, other than perhaps corroded valve stems. Lycomings have been known to swallow valves when the head broke off the stem because of corrosion pitting in engines that have been run for short periods and left to sit. Similarly, the crankshafts in these engines build up water/oil sludge in the crank nose (unless it's driving a constant-speed prop) and this causes dangerous corrosion that can result in propeller departure. Lycomings run regularly on long flights have reached 4000 hours without overhauls. Tell me what airplane it's in and I'll look up the prop RPM range for you. Thanks for answering Dan, It makes more sense what you say about metal in the oil, as I was going to post how would I know what is happening "below the top" without an overhaul. The engine is in a BE 23 (Beech Sundowner). I bought the plane for $38,000 knowing a major overhaul is in my short future, but wanted to get my learning curve behind me in this engine before overhualing it. Right now, I get the oil changed every 30 hours, and the A&P checks for metal every change. I plan to have the compression checked every other oil change. I fly it a minumum of one hour a week (even if just around the patch) weather permitting. (I have been averaging 6 hours a week). Once I get my instrument rating (I am starting ground school next week), I plan to fly much more a week, as my job takes me throughout the state of MS. Any other tips on maintaining this engine and airplane (or what to look for) is surely appreciated. I have not seen any FAQ's on this subject, and I am learning more from this group and hangar talk. Allen |
#12
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A Lieberman wrote in message ...
Dan Thomas wrote: The Type Certificate Data Sheets will give minimum and maximum static full-throttle RPMs for that engine/prop combination in that airplane, and if there is valve train wear the RPM will be out of the range. This isn't rocket science. If the crank is eating its way into something, there'll be metal in the filter. That's simple enough, too. If the oil pressure is well into the green, and doesn't drop to zero at idle when hot, the bearings are OK. If the compressions are as high as he's indicated, there isn't much wrong with the top end of the engine, other than perhaps corroded valve stems. Lycomings have been known to swallow valves when the head broke off the stem because of corrosion pitting in engines that have been run for short periods and left to sit. Similarly, the crankshafts in these engines build up water/oil sludge in the crank nose (unless it's driving a constant-speed prop) and this causes dangerous corrosion that can result in propeller departure. Lycomings run regularly on long flights have reached 4000 hours without overhauls. Tell me what airplane it's in and I'll look up the prop RPM range for you. Thanks for answering Dan, It makes more sense what you say about metal in the oil, as I was going to post how would I know what is happening "below the top" without an overhaul. The engine is in a BE 23 (Beech Sundowner). I bought the plane for $38,000 knowing a major overhaul is in my short future, but wanted to get my learning curve behind me in this engine before overhualing it. Hokay. For the B-23, with Lycoming O-360-A2G, and with either Sensenich prop number M76EMMS-0-60 or 76EM8S5-0-60, the full-throttle static RPM should be not over 2350, not under 2250. You'll want to make sure of the engine and prop models, to be sure there hasn't been some STCd change in the past. The tech logs will have this dope. The tach should be checked for accuracy, too; they're often 100 RPM low. Most current tachs (in singles) are the magnetic type, and the magnet weakens with time. Here in Canada we have to check them yearly, and they can't be off by more than 4% of the midrange cruise RPM. Dan |
#13
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There is a very good group on Musketeers.
http://groups.yahoo.com/group/musketeermail/ The consensus is that most of the carburetted 0-360's require a lot of prime, but like yours, they start well. "A Lieberman" wrote in message ... I have an old tired engine in my plane that requires 7 strokes of prime no matter what, cold hot or warm. No biggie, as it starts everytime within 3 turns of the prop. I don't have to crank for any period of time. A person told me it is better to push the primer slowly rather then quick shots. Mechanically inclined I am not, but does it make a difference? I have not noticed any difference trying it either way. Mag check. On runup, I check both mags by flipping the switch to mag one and mag two. Another person said I should hesitate before going back to both mags when checking the mags. He says that I should let it run on one mag for 3 or 4 seconds. All I am checking for is the drop. Is there a benefit to letting the engine run on one set of mags for a period of time during the runup? Thanks for any input. Allen |
#14
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Les Gawlik wrote:
There is a very good group on Musketeers. http://groups.yahoo.com/group/musketeermail/ Thanks Les for the lead on this group! Allen |
#15
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"Paul" wrote
If there is a bad or fouled plug, you will see a drop as soon as the good mag is switched off. Yes, and the effect will be dramatic. The engine will shake like a wet dog (especially a 4-banger) and the RPM drop will be both immediate (as you noted) and very large. If however there is a timing error which can be caused by the points wearing, or the magneto itself slipping position due to loose hold down nuts---then the drop will be much slower taking several seconds to stabilize. Maybe. It depends on which way the timing is wrong (early or late) and how badly. Even worse, though, is what happens when the timing is wrong because it's late. The common procedure for dealing with a fouled plug is leaning the mixture as much as the engine will tolerate to 'burn the plugs clean.' This actually works sometimes. However, the nature of the ignition event is such that the flame front propagates fastest with a mixture leaned to peak. Normally, the engine is well rich of peak at runup power with the mixture set at full rich. Imagine, for a moment, what happens if the points have started to wear on one mag and it is firing late. Unless that happens to be the only mag with the impulse coupling, starting will not be a problem. At runup, switching off the 'late' mag will produce a slight RPM drop - so that part of the check is nominal. However, switching the good mag off will cause a large RPM drop - probably more than allowable - and some slight roughness. The pilot will then say "Aha! Plug fouling! Let's burn those plugs clean." and proceed to lean the mixture as much as he can. He'll run it that way for a while, then advance the mixture only slightly (if at all) since he doesn't want to foul the plug again. He checks the mag drops again. Now the drop will be a little more on the good mag, and maybe a lot less on the good mag (since it's late firing is somewhat offset by the faster combustion event). Now the engine might just pass the mag check, and the pilot will figure all is well - the rest will burn off in flight. By the time this process stops working, meaning that leaning the mixture will no longer result in a an acceptably low RPM drop, the magneto is firing several degrees late. Not really a big deal in cruise (especially low power cruise) but if the good mag (or even one plug on it) decides to go during takeoff, it could really ruin your day. Michael |
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