I just thought I would post my story about all that I went through to get my engine to run in my Hummel Bird, (Little Loosie). I first saw a classified ad in the back of Kitplanes magazine for a 1/2 VW engine with 3 Hrs run time on test stand for $1300 (the gods were smiling down on me!) I called the gentleman on the phone and he informed me that the engine was built by a machinist in Georgia as a for fun project and it only had ground time on it. The fella that had purchased from him was in Missouri, he was 85 years old at that time and working on his 13th homebuilt! Wow! The engine had bed style engine mounts, a deep oil sump extension, an oil pressure gage,and a 54X22 Culver wooden propeller. Sounded like a good start on an engine for my plane although my project wasn't ready for an engine yet. I asked him if he wanted a cashiers check and he told me no a personal check would be fine because he trusted me! (A very rare sort of man these days!!) I sent him a check and he called me to tell me crated and shipped the engine about two days after we talked before the check got to him. I told him "the check is in the mail" and he said that was fine.You don't meet people like this very often,I wish I had stayed in touch with him. That was quiet a few years back and I suspect he is not with us any more, GOD BLESS YOU LARRY, I HOPE YOUR READING THIS. The reason for the sale was he buggered his shoulder up and couldn't prop the engine so he needed one with electric start. So the freight truck delivered the engine and I stuck it in the corner of the garage for a couple of years until it was time to install it on my plane. So thats chapter one of this novel. to start with I needed to change the Engine mounts from the bed style mounts to rear mounts so it would fit into the H.B. cowling. This involved removing the back plate from the engine and drilling & tapping the two holes for the lower mount bolts (3/8"),removing the old mounts from the sides of the engine case, drilling & tapping the four holes on each side, epoxying plugs in and grinding them down flush. A little paint and all evidence of the old mounts was gone. I fabricated the new engine mounts and hung it on the plane.after completing the rest of the firewall forward plumbing and wiring and a new 46X34 propeller I was ready to test run the engine. I did my first test run on memorial day 2003,it seemed to run O.K. but I had 100Lbs. of oil pressure. I checked the relief valve and found it was stuck. After cleaning it up and reinstalling it I tried another run. This time I had about 60Lbs of oil pressure when cold. I thought I had the problem solved. NOT! :depressed When I reduced the RPMs to idle my oil pressure droped to 0 and did not come back up when RPMs were increased or if engine was restarted. had to pull the relief valve plunger and turn engine over to prime the pump and reinstall the plunger. It had oil pressure until RPMs were reduced below 1500 and it would zero out again.onder: I went to Hummel Aviation and logged onto there forum. I posted my symptoms and got a reply from Scott Casler of Hummel aviation. (I think that the thread is still there.) He told me he had the same trouble with a couple of engines, one he solved by installing a cup on the bottom of the oil sump and he never did get the other one to work. He suggested that I change to a 26mm oil pump instead of the 29mm(high volume) pump. His theory was that the case volume of the 1/2VW allowed the oil to foam up or it could not return to the sump fast enough to keep the pump from starving. I was getting desperate, I thought I might have a $1300 boat anchor! My next move was to pull the engine and tear it down to change the oil pump. because the 26mm pump drive is shorter I also had to buy a new camshaft and cut it off . I used my friends small metal lathe (he owns a bicycle shop,I felt like Orville Wright making airplane parts in a bike shop). After that I fabricated a new cup to replace the flat plate on the bottom of the oil sump and a new extended oil pick up tube. I reassembled the engine and put it back on the airplane. All this took me about another year to complete. I was sure I had the problem solved this time. When I did the next run nothing had changed! :mad2: Not being one to give up easily I thought about what Scot had said about the oil foaming because of the small crankcase volume and the crank spinning. so I had the bright idea to fabricate a baffle plate from thin aluminum and slide it in under the camshaft and crank to separate all that whirly stuff from the oil sump. So off with the engine again for another tear down I put in the baffle plate and reassembled the engine again, Put it back on the airplane. about this time I was glad it was a 1/2 and light in weight! But i was getting good at taking it off and putting it back on. :tired: O.K. this time for sure! another test run and It was still the same. The thread on the Hummel Aviation forum was silent nobody was even making a guess! so it sat while I pondered my dilemma. It was probably another 8 months that passed and I would occasionally pull it out to the back yard and try it again.(I was hoping it would fix itself)? LOL. one day I had done this and had the same results, I was standing there looking at it and it came to me like someone had turned on a light switch! DUH! the return line from the oil separator/breather was connected to the bottom of the oil sump about an inch from the oil pick up tube location. to test my theory i disconnected the return tube from the breather and plugged it off. I started the engine again and SHAZAM! it had good steady oil pressure. :roll: But I wasn't done yet. Because of all the runs that the oil pressure zeroed out for 15 or 20 seconds I thought I should change all the engine bearings. So off came the engine again for another tear down! I posted my findings on the Hummel Aviation forum and still got no response and no one has posted anything further on the subject of oil pressure. If you remember when I bought the engine it came with a deep sump extension, it was welded up from heavy gauge steel and it weighed about six pounds! Ugly!!! Not for my air plane, to heavy and not enough room, I still have it if any one wants it they could have it cheap! The flat plat I replaced it with was per Morry Hummel's engine planes. I always wondered why it worked for his plane? it shows the return line right were I had mine. When I replaced the fllat sump plate with the cup type I put the return line to the bottom again,(dumb). Ultimatley the fix was to remove the return tube from the bottom of the sump and weld the hole shut(aluminum)in the cup then drill & tap the back of the engine about four inches up from the bottom. I had to pull the engine one more time after that due to a planes revision that called for the engine mount to be four point mounting and made from 1/2" X .058 tubing instead of three point with 3/4" X .035 tubing. I kept a three point mount but I used 3/4" X .058 tubing. So thats the whole story, I hope it wasn't to boring and maybe helps someone else so they don't take the same trip as me. Are we there yet? Good luck and may it always be C.A.V.U. with the wind up your tail. A.P.