New starter installed but still slow to start...

[Ignition Override]

We had a starter flown in for the old one on a Pratt and Whitney JT8D turbofan, which had been sheared while the previous crew started it (unknown to them). Even with the new starter, we needed about 15-20 seconds just to indicate N2 rotation, then normal oil pressure and N1 etc. Before installing the new starter, the mechanic said that a certain part of the gearbox would not rotatate, when he checked it per Maintenance Control's advice. Good thing that a certain bearing was not out-this has required an engine change on another plane.

Anyone out there ever seen this problem?

[spannerhead]

No matter how good the starter may be, if the start valve does not fully open then you will have slow accelleration. The start valve has a manual override 3/8 drive, ensure that it is fully open during the start sequence.

[Danish Pilot]

Check duct press while spooling up, and compare on both eng. If still no result, get a jetstarter and check press.

[Ignition Override]

Good points: the mechanic had checked that the starter opened completely, and during start there was only about 5 psi decrease in the (crossfeed) duct pressure.

This was at the smallest airport in our system, at the corner of Eglin Air Force Base. They had no ground starter, or it was inop. The ground crew even connected some sort of bottle (?) starter to the plane, but the hose leaked and no pressure was indicated.

[redtail]

Were the other engine/engines starting the same way? Are there any valves upstream of the starter valve?

[Centaurus]

For what its worth, if you are getting slow N2 rotation, try turning off some electrics such as both B pumps and all the fuel pump switches. We often had this problem especially in hot weather on a B737-200. With a reduction in electrical load on the APU from 120A (Fuel pumps and B pumps on)to 70A (all switches as above off)it made a significant difference to speed of N2 rotation. The engine starts OK with no fuel pump switches on.