================================================================================ MAXIM-X PETCOCK REBUILD INSTRUCTIONS ================================================================================ As always, rebuilding the Maxim-X petcock doesn't always go smoothely. There are some tricks to doing the rebuild right so that it doesn't leak afterward. There are actually two problems to deal with during the rebuild and two tricks to deal with those problems. 0) Buy the K&L (Napco) Petcock Rebuild Kit referred to at the following link: http://www.maxim-x.com/petcock.html#repair http://www.maxim-x.com/pix/petcock/00-petcock_rebuild_kit_18-2699.jpg ================================================================================ The first problem is that the piston valve portion of the K&L (Napco) petcock diaphragm assembly is too short by about 1mm. It might not have been if the original hollow, tapered valve seal had been used but an o-ring was used in the rebuild kits instead. In conjunction with the o-ring, the piston doesn't reach far enough into the seat. So you'll have to start by first making the piston extend a little farther. The trick is as follows: ================================================================================ 1) Remove the plastic square piece from between the two halves of the new diaphragm assembly. 2) Find two 12pt sockets, at least one of them deep, that fit inside each other. If I recall correctly, I used a 12mm-12pt deep socket and an 8mm-12pt shallow socket. 3) Stand the 12mm socket on end such that the open end points up, then bunch up the inner diaphragm around the piston valve portion of the petcock assembly and stuff the piston valve with bunched up diaphragm into the standing 12mm socket. 4) Set the smaller socket (which absolutely MUST fit into the 12mm socket with some clearance) atop the metal disc on the outer diaphragm side. The combined assembly should look like this: http://www.maxim-x.com/pix/petcock/05-diaphragm_disc_adjustment-1.jpg 5) Now use a hammer (nothing too heavy) to tap on the smaller socket, as perpendicular to the metal disc as possible. Depending on how hard & straight you hit the socket, you may or may not have to do it again. Anyway, tap on the smaller socket to develop a depression in the metal disc that looks like this: http://www.maxim-x.com/pix/petcock/06-diaphragm_disc_adjustment-2.jpg It's that depression that adds length to the piston valve because the piston is connected to the disc. It's fairly critical that you use 12pt sockets because they provide an impact ridge that more closely approximates a circle than a 6pt socket. A 6pt socket tends to warp the metal disc while a 12pt socket tends to stamp out a pretty flat circular depression as desired. 6) When the depression in the disc has been formed, simply pull the bunched up diaphragm and piston out of the 12pt deep socket and reinstall the square plastic spacer between the two parts. ================================================================================ That takes care of one problem. The second problem is that some Maxim-X petcocks seem to have been machined a bit crooked and have a skewed alignment of the valve face in the petcock. That can be resolved by using a wooden golf-tee to regrind the plunger valve seat into a more orthagonal alignment. ================================================================================ A) Buy a number of wooden golf-tees B) Modify the golf-tees by cutting the head shorter and adding some definition to the slope of the shaft and the shorter head as shown in this 4-stage progression picture: http://www.maxim-x.com/pix/petcock/01-golf_tee_adjustment-a.jpg The taper of the golf-tee should approximate the taper of the valve seat but it doesn't have to be identical. In fact the repair will likely work better if the golf-tee has a greater taper. C) Create several identical modified golf-tees - it will become necessary to replace them from time to time because aluminum will embed into the wood and will cause scratches in the valve seat (prepare at least 3). D) Insert the modified wooden golf-tee into the disassembled petcock body such that the tapered head of the golf-tee contacts the valve seat as shown in this picture: http://www.maxim-x.com/pix/petcock/02-golf_tee_usage-1.jpg E) Turn the petcock body around so that the tip of the golf-tee shows out the back and insert that exposed end into a cordless drill as shown in this picture: http://www.maxim-x.com/pix/petcock/03-golf_tee_usage-2.jpg F) Use an appropriate abrasive (I used Fast Orange hand cleaner) between the head of the golf-tee and the valve seat, then start the drill and polish the seat. Just pull the drill, and thus the golf-tee, toward you as you continue to run the drill. Be careful however because there are two very important things to remember. First, the angle of attack is critical. You should try to keep the golf-tee as perpendicular as possible to the body of the petcock (not to the skewed seat). The goal, after all is to change the angle of the seat so that it becomes parallel to the surface of the valve body, essentially perpendicular to the direction of travel of the piston valve. So always keep your eye on the angle of the golf-tee shaft and adjust constantly. There's a certain amount of self-righting by way of the spinning motion, etc... but don't let it guide you - guide it. The second, equally important thing to watch for is the condition of the surface of the wooden golf-tee. Because it is wooden, it tends to grab up all the fine bits of aluminum that get ground away. If you grind too long with the same golf-tee, you'll realize that it ends up with substantial buildup of aluminum in the wood in pockets which then end up scoring the valve surface instead of polishing it. The key is to check the golf-tee often and to replace it with another when you see even the smallest buildup of aluminum on its surface. G) When you feel that you've accomplished grinding a true orthogonal seat, you should test for orthogonality. What I did was coat the piston valve o-ring with a thin, uniform layer of black grease. Then I carefully assembled the back of the petcock and took it apart again. If the seat was ground perfectly orthogonally, it will have a ring of grease that shows full contact around it's entire circumference and that ring will appear to be at the same elevation in the tapered valve seat at every point. If there's something not quite uniform about the ring, then you might need to do some more work on the valve seat. H) After you're convinced that the seat is now properly aligned and that the piston valve does indeed reach the valve seat, then you may want to do one more very brief cycle of polishing the seat with a new golf-tee and a finer abrasive just to make sure the surface of the valve seat is a perfect as possible because any scratches or other imperfections could lead to leaks past the o-ring. ================================================================================ At this stage all of the design problems will have been resolved and only two more things need be done before reassembling the petcock: ================================================================================ I) Stretch the diaphragm return spring until it is at least 20mm long (but don't go much more than that). The 20mm length will help apply more pressure between the o-ring and the valve seat without overcoming the force created by the engine vacuum against the diaphragm. J) It's also wise to polish all the mating surfaces of the petcock to make sure there are no vacuum or fuel leaks at those joints: http://www.maxim-x.com/pix/petcock/15-casting_face_polished-diaphragm_side.jpg http://www.maxim-x.com/pix/petcock/16-casting_face_polished-spigot_side.jpg http://www.maxim-x.com/pix/petcock/17-casting_face_polished-diaphragm_cover.jpg http://www.maxim-x.com/pix/petcock/18-casting_face_polished-spigot_back.jpg ================================================================================ Now the petcock can be assembled and tested for leaks. The entire collection of pictures realted to petcock rebuilding can be found here: http://www.maxim-x.com/pix/petcock/ ================================================================================ http://www.maxim-x.com/petcock.html