I am not familiar with the particular machine you are working on. But I have seen some problems arise after overhauls that had similar symptoms. In all of these cases, we had higher shaft deflection in the vertical and lower in the horizontal. We may have shown some signs of looseness in the vibration on these events, as well. These could be relevant to your problem.
We replaced the rotor and bearings in an Elliott barrel compressor. Following the overhaul, there was higher vibration in the vertical and lower in the horizontal as measured with proximity probes. When the machine was shutdown, they found that the tapered dowel pins for the inboard and outboard bearing housings had been reversed. The pins were similar but not identical. When the IB pins were placed in the OB housing cover, they did not extend all the way through the top cover and engage the bottom of the housing. As a result, the outboard bearing housing cover was not properly positioned. It was setting off to the side creating a bearing clearance that was squished side to side, but full clearance up and down. We added a dowel pin check to our repair procedures. We place the pin in the top cover and mark where it protrudes. Then we place the pin the bottom half and mark where it protrudes. The two marks should be very close side by side.
We had another machine with unusual orbits and higher vibration than expected. We found a similar problem with the tapered dowel pins. We did a blue check of the pins to the holes and found that they were getting tight in the holes in the bottom housing when they were still loose in the top. We believe that at some point in the past, someone reamed the pin holes in the upper cover while cleaning it on the bench. Since they only reamed the upper part of the hole, the pin was no longer properly locating the cover.
We had a new gearbox for a large fan that had higher vibration in the vertical and lower vibration in the horizontal. We found that the original construction of the gearbox had missed a step. In this particular gearbox, new bearing liners are made with excessive crush in the vertical. They are supposed to be dressed down at the split line to achieve the target housing crush. The factory had failed to do this. As a result, there was excessive vertical clearance in the bearing and very high crush in the housing. The bearing was actually holding the gearbox cover up. We found this with a lift check in the field. The vertical lift was over 0.012” and should have been about 0.007”. When we opened it up, we expected to find the bearing wiped. But it was not. The manufacturer makes this gearbox with bearing liners that have to be custom fit each time. Or, as an alternative, they will make it with precision bearings that do not require hand fitting. We converted to the other bearing arrangement.
I would add the following checks to the next repair:
Check the dowel pins for proper engagement in the upper and lower housings.
Bolt up the housings with no bearings and no rotor and check the bores for out-of-round, taper or offset at the split line.
Check the crush between the liner and the housing.
Install the bearing liner with no rotor and check the installed bearing bore for out-of-round, taper or offset at the split line.
Blue check the shaft to the lower half bearing liner to verify bearing housing alignment
Johnny Pellin
