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Onan b43g rebuild (fuel pump)

8081 Views 20 Replies 5 Participants Last post by  rustifer
Im getting to the point of being able to order parts for my onan rebuild project. One question I have is, when I was taking the fuel pump off I broke one of the barbed hose connectors. Do you think that would be fixable? My neighbor gave me a universal pulse fuel pump, would that work on the onan? Last question, to remove the pto I first took off the crank bolt, now I need to take off the three nuts that are retaining the springs?? Any help would be greatly appreciated. And I will be following up with some pictures!!:thanku:
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Yes, you can use a vacuum pulse Mikuni pump or Briggs 808656 but will need the barb to allow fuel into the carb

Take the bolts out that mount to the engine block and the pto will slide off
ive got the bolts out that hold the pto to engine and I have the bolt out of the crank. the pto does not slide off. Ive taken off other pto's the way you describe, but something is still holding this one on. I thought I remembered reading a post the described a different method for removing the pto on a 318, but cant find anything with the search function.
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It is just rusty,might have to get a puller,usally they come off good,it is 25 + years old so you might find a few things tough to get off.I use a 2 wheel drive Gator pump if I have to replace one.
thanks, i just didnt want to damage it. I sprayed it with some pb. So i'll try with the puller!:thanku:
You want hurt it once you break it loose it will slide off.Once yo get the coil off you will sr the rotor for the pto,it is supposed to be free to slide on the crank if it isn't you will need to free it.
What all you going to do to the motor?
well i got the pto off and looking at the field coil the red plastic is cracked and kinda bulged in a few places. Is this something to be concerned about?
Sign of being hot,way to check them is apply battery voltage to the wires coming out of coil,lay a screwdriver over the coli and if it sticks it is ok.Just use till it quits,140.00 to replace it.
as far as what Im going to do to it, I plan on getting some new rings, decarbon, and get a complete gasket set. first some measurements ! Ive downloaded the onan service manual and plan on going step by step. I bought the tractor with a bad starter. So i was gonna buy a new starter and try her out. Then I removed the engine and notice a broken engine mount that someone tried to jb weld. So i bought an oil pan off of ebay. Then pulled the pan and started to think that I was this far might as well get it done right. So I asked here on mtf and most said at the least some new rings. The tractor has 1400 hrs on it. I'm obviously going to read more, but one area Im not to sure on is the valves. In small engines class i remember lapping the valves, is that common practice for an engine like this?
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Lapping is fine.while you have the valves out put a new seal on the intake valve,keeps it from sucking oil thruogh the valves.Conan parts has them.check your pm
lapping is fine ONLY, if the valve face is flat.
if there are grooves etc. on the face you should have the valves and seats ground.
then most shops will still lap them.
clean the faces of your valves,then PLEASE post some pics. of them.
thank you boomer ( the used onan engine parts guy )
P/S deglase the cyl. walls.
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boomer thanks for the heads up on the valves, and i just bought a stone style deglazing hone for the cylinders. I just removed the pistons and measured the top ring clearance. I read on a thread about rebuilding onan's that the allowable clearance is .003-.008. I can fit .009 feeler in snug, wont fit .010 . Man does that mean I need new piston's? ughh:banghead3
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No you don't need new pistons but new rings,really that is not much wear considering the age of the tractor,I had 2 Onans that the rings would drop through the cylinder after I took them off the pistons and still ran,they had 016 -020 end gap.Did you push the top ring about an inch down in the bore?
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I was talking about the the clearance between the ring and groove on the piston. For the top groove.
That ring is worn thin I suspect,mic it and poat he dimention s/b .057? not sure what ring you have
Top: .058" 1/16 or 1.5 MM
Second: .058" 1/16 or 1.5 MM
Oil ring: .125" 1/8 or 3.0 MM
Here's what they should be.
On the fuel pump issue. The two barbs are identical, except that only one is open to the inside. I've reused some that were broken like yours. Plug the broken one, I drill and tap for a little screw. Then drill the other one out so that it goes into the inside, Install the fuel hose on that one and it's good to go, assuming the diaphragm and check valves are good.
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thanks i'll check it out in the morning, thanks for all the help
the top ring measures .078 . This might be a dumb question, but the feeler gauge Im using has 2 measurements on it. Could I be using them wrong. I found a link on amazon that shows the feeler gauge I've been using. I assumed the measurement indicated is for one side of it, and vice versa. Is that the correct way to read it?
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That feeler gauge is two thicknesses, one at the end (shaded in the picture)and thicker farther up. It is used to measure the minimum, 'go' and maximum clearance 'no go'. Not ideal for what you're doing, but can be used.
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