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#36686
Something else is wrong or changed. Random: Turn off DFCO. Turn off EGO/O2 corrections if they are on. Use your MAP as a diagnostic. A better running engine will show lower MAP, so that's wonky, plus it has a cyclic pattern that is especially noticeable at initial idle and shutdown. Sticking/mis-adjusted valve, vac leak, etc. Misfire, Ignition, dead injector, etc, possibly at idle, but I'm looking to mechanical as it jerks around at shutdown as a clue.

David

4A084_shutdown-no-spk-fuel.jpg
4A084_shutdown-no-spk-fuel.jpg (40.48 KiB) Viewed 1495 times
#36695
PSIG wrote:
Wed Jul 24, 2019 9:08 pm
Something else is wrong or changed. Random: Turn off DFCO. Turn off EGO/O2 corrections if they are on. Use your MAP as a diagnostic. A better running engine will show lower MAP, so that's wonky, plus it has a cyclic pattern that is especially noticeable at initial idle and shutdown. Sticking/mis-adjusted valve, vac leak, etc. Misfire, Ignition, dead injector, etc, possibly at idle, but I'm looking to mechanical as it jerks around at shutdown as a clue.

David


4A084_shutdown-no-spk-fuel.jpg
thanks for giving me a few places to start looking, I took the head of the #2 cylinder last night, and am just looking at all the possibilities, of where I messed up.
I have turned off the DFCO,
it is a simple little motor, "what could go wrong" and only takes 10 minutes to take a head off, but I am looking at everything, and when I put it back together, I will take a little more time and look at all the things you mentioned.
I may not have had the head seated correctly. which would have thrown out the alignment for the intake flange. It is always the little things that are overlooked, that are always getting me. I need to figure out why I am getting such a high map reading at idle. just taking my time, stepping back and looking at the big picture.
thanks again
#36697
+1, it is a simple engine, so that just makes it more frustrating. :lol: "Simple" could be a loose spark plug, sticking ring, incorrect valve lash, etc. I think if I were attacking this, I'd go first to a leak-down test. If not available, a compression test or a simple cylinder-pressure test with high-pressure air to listen for leaks and where they are coming from. Use a threaded compression tester hose to pump the air into the cylinder at TDC or BDC so it doesn't spin the engine. That may give some clues to chase. Good luck!

David
#37217
I may have found the problem, at least this one was kind of obvious. the pinned exhaust valve seat on cylinder #4, had came loose and was holding the exhaust valve open. I will be getting another head coming, and see where it goes.
Attachments
162 exhaust valve seat.jpg
162 exhaust valve seat.jpg (315.53 KiB) Viewed 1368 times
#37242
Suckage. :( Well, that explains your odd MAP data. I cannot tell if that head has been overheated, and it does not appear to have run lean recently, but that shouldn't be an immediate problem anyway. What I know of seat issues centers simply on that seats drop when the seat is smaller than the rabbet/recess it is squeezed-into. This is more common when there is overall chamber and head overheating than lean run, because lean exhaust heats the seat quicker, which just makes it fit tighter - though in some cases it can expand the rabbet and loosen the press-fit upon exhaust and seat cooling or do it after many cycles. Long-term lean can lead to overall head overheat just like any overload, and though this isn't a rule - it should be relatively balanced assuming the seat remains similar or hotter than the head. Maintaining proper ignition timing is important whether running rich or lean in order to help avoid overheating, seat cutting or erosion, etc. Running too rich can lead to erosion, pitting, and valve recession or "sinking seats".

Head overheat may expand the head more than the seat, which is generally related to poor head cooling (e.g., poor airflow), insufficient heat dissipation (e.g., excess paint, corrosion, bugs, etc), or excess generated heat or power for the existing cooling capacity. An example of the last case is VW Type 1 engines that are limited to around 90hp continuous, as they simply cannot shed more heat at higher sustained power levels. Of course, this assumes the head was machined properly for the press-fit seats, and there is no other damage such as cracks that can reduce the press-fit holding it in, or other valve train issues such as weak or broken springs or valve bounce causing "seat pound-out". I can't go into every case scenario or how some effects tie into others, but I hope that helps.

David
#37611
I took your advice and put some air in the cylinders and there was just a little air getting past the rings. :o
that would explain all the soot that has been showing up, and everything being so erratic opened the motor up last night, and 3 of the jugs are just a little tired, and worn out in the center of the stroke.

when I had picked up the motor, the gentle man mentioned that the person who sold it to him had just rebuilt it. well. if that is how a rebuild goes, I would hate to see what else he has done... :lol: :roll:

so give me a couple of weeks to get the parts, and put it back together, and we will start again. hopefully with better results. all in all I have been having fun and enjoying the learning curve. :D
#39884
a little update, I have been going on a few different directions on this motor, I got new pistons, jugs, 2 heads, & bearing and did an inline rebuild , It started up. but I haven't ran it much,
where this is and air cooled motor, I came to realize that even though I had the stock fan that is built into the flywheel. with out any shrouding, there was not enough air movement past the heads, so anything over an idle, the heads were getting on the hot side of things.
eventually I will be changing the flywheel and back housing for a redrive and prop. where this prop will be in the pusher mode, many times there still might not be enough air flow going across the heads.
so I have came up with this solution, to install a 16 in. fan on the front pulley, and build my shrouds to fit. I just need to finish them up.
I know that ones I get this air flow problem fixed, my head temps should get to be normal. and then I will be able to go forward again.
Attachments
275 finished pieces.jpg
275 finished pieces.jpg (250.78 KiB) Viewed 710 times
281 finished the adaptor.jpg
281 finished the adaptor.jpg (271 KiB) Viewed 710 times
285 one side fitted .jpg
285 one side fitted .jpg (238.86 KiB) Viewed 710 times
284 scroll saw to cut shroud.jpg
284 scroll saw to cut shroud.jpg (266.63 KiB) Viewed 710 times
283 fan shroud in plasce.jpg
283 fan shroud in plasce.jpg (256.16 KiB) Viewed 710 times
#39898
Nice. Good analysis to overcome hurdles in application, in both lack of cooling airflow, and lack of directed cooling in specific areas.

David

Crank-driven and electric fans have been used on countless air-cooled engines, but the engine-driven versions were common in aircraft. One of the most often-noted of the type is the WWII FW190:
FW190_fan_cooling.jpg
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#39943
a question about the location of the intake air temp sensor?
does it need to be before the throttle body?
I am changing the throttle body from a 50mm to a 36mm
I picked up one from a 2015 polaris 325 4 wheeler, it comes with the goodies a tps and 4 wire air idle valve.
the stock throttle body was close to 30mm, and i found even though it was running with the 50mm body. At a 1/4 throttle, the rpms were maxed out. granted I had no prop on the motor to work as an governor.

anyway on this new style. this is a port where the stock injector went. and at the moment I just put a plate/plug over it..
looking at it, to me it looks like a grand location for the intake air temp sensor..
any thoughts??
Attachments
7 side view.jpg
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7a top of motor.jpg
7a top of motor.jpg (250.73 KiB) Viewed 597 times
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