Re: WARNING!!! To all VRO users
My new pump hasn't shown up yet, so I've taken some more time to closely examine the old/failed one. Here's what I've found.
First, a big "thank you" to Seahorse5 for referring me to the site with the cutaway drawing of the pump and description of how it works. This is the first time I've ever cracked one open, and that was a big help.
Since the oil gets mixed with the gas as soon as the gas enters the pump, there should be no way that raw gas could find its way into the #6 Crankcase. I guess I haven't developed a taste for oil. But quite certainly, fuel/oil mix was running down the pulse line into the crankcase and fouling the plug.
Neither the cutaway diagram nor my Factory Service Manual describe the tiny double-lip seal that I found on the pushrod between the air motor and the fuel pump. There was also an undescribed concave stainless washer between the seal and the pump diaphram. The seal obviously fits into a recess in the intermediate housing. It appears that the washer was pressed into a slightly larger recess to retain the seal, and provide a guide for the pushrod. As I mentioned previously, the inner lip of one side of the seal is torn half-way around. Both the washer and seal had left their homes and were riding on the pushrod between the intermediate housing and the fuel pump diaphragm.
Looking more closely, I noted that the pushrod hole in the intermediate housing is worn out-of-round by about 0.020". If I'm correct about the function of that concave washer, the wear most likely ocurred after the washer became dislodged. Then, the side thrust on the seal caused it to tear and slide out of its recess.
With no seal between the chambers and a badly worn hole, fuel/oil mix was pumped into the air motor. I couldn't find any perforations in the air motor diaphragm, so I assume that the intermediate side filled up with enough fuel that it migrated thru the poppet valve in the center, and traveled down the pulse line into the #6 crankcase.
At lease, I'm relieved to learn that it wasn't raw gas entering the the crankcase. So, I'll pull down the WARNING flag. But it may be helpful to people to recognize the signs of a failure like this. Apparently I'm not the only one with this experience. I've also learned that replacing diaphragms would not have solved the problem.
I'm thinking that a light pressure conical spring between the seal retaining washer and the fuel pump diaphragm would have kept them in place, thereby preventing this failure.
My new pump hasn't shown up yet, so I've taken some more time to closely examine the old/failed one. Here's what I've found.
First, a big "thank you" to Seahorse5 for referring me to the site with the cutaway drawing of the pump and description of how it works. This is the first time I've ever cracked one open, and that was a big help.
Since the oil gets mixed with the gas as soon as the gas enters the pump, there should be no way that raw gas could find its way into the #6 Crankcase. I guess I haven't developed a taste for oil. But quite certainly, fuel/oil mix was running down the pulse line into the crankcase and fouling the plug.
Neither the cutaway diagram nor my Factory Service Manual describe the tiny double-lip seal that I found on the pushrod between the air motor and the fuel pump. There was also an undescribed concave stainless washer between the seal and the pump diaphram. The seal obviously fits into a recess in the intermediate housing. It appears that the washer was pressed into a slightly larger recess to retain the seal, and provide a guide for the pushrod. As I mentioned previously, the inner lip of one side of the seal is torn half-way around. Both the washer and seal had left their homes and were riding on the pushrod between the intermediate housing and the fuel pump diaphragm.
Looking more closely, I noted that the pushrod hole in the intermediate housing is worn out-of-round by about 0.020". If I'm correct about the function of that concave washer, the wear most likely ocurred after the washer became dislodged. Then, the side thrust on the seal caused it to tear and slide out of its recess.
With no seal between the chambers and a badly worn hole, fuel/oil mix was pumped into the air motor. I couldn't find any perforations in the air motor diaphragm, so I assume that the intermediate side filled up with enough fuel that it migrated thru the poppet valve in the center, and traveled down the pulse line into the #6 crankcase.
At lease, I'm relieved to learn that it wasn't raw gas entering the the crankcase. So, I'll pull down the WARNING flag. But it may be helpful to people to recognize the signs of a failure like this. Apparently I'm not the only one with this experience. I've also learned that replacing diaphragms would not have solved the problem.
I'm thinking that a light pressure conical spring between the seal retaining washer and the fuel pump diaphragm would have kept them in place, thereby preventing this failure.
