Bearings clearances limits

I assume you are talking about journal bearings (white metal)

Most probably it is a lobed bearing. How many lobes and at what position will decide where you should check with the feeler gauge.

The lift of 11 (0.27mm) thou looks to be OK, though on a bit lower side where as 77 thou (1.96mm) is too high.

The PSI is not important, did you put the load enough to lift the rotor ? The over load is again going to damage the white metal.

At our place (OEM) we do simply by measurements and Lead wire check since the feeler gaugese themselves are sufficient to scrape off the metal.

The acceptable clearance must be available in the manual.

Thank Sb,

could you please explain what does lobed bearing means?

and what do mean by ....simply by measurements and Lead wire check since the feeler gauges themselves are sufficient to scrape off the metal....

What is confusing is that by using the jack to left the rotor, I have got 11 thou, which it is fine as you have said, but using the feeler gauge on top and bottom exciter end is giving unsatisfactory reading as from top is bigger than from bottom (77/55) thou, which means that the shaft is resting downward a little bit.

what do you think?

Many journal bearings are profiled, that is, not round. Taking leads of these bearings may give false results.

The shaft will anyway rest downwards due to gravity when on rest .

The journal bearings may be

a) Grooved or pocket cut - where a depressed pocket (arc) is cut at the oil entry point. These pockets work to lift the journal and also to uniformly feed the oil and avoid cavitations.

b) These can be made elliptical by machingig with a shim in parting plane and then removing these shims in final assembly.

c) offset machined - the Center of upper half and lower half shifted in x directions

d) Tilting pad where the support pads are on hinges and may tilt to take uniform load.

Some other types also are possible, but I personally have used these 4 types in machines we have manufactured.

A link is here

http://www.gepower.com/businesses/ge_oilandgas/en/literature/en/downloads/tiltingpad_journal_bearings.pdf

however you can go through google and check other types.

In our case we ensure the dimensions of bearings before assembly and as a final check at defined location a thin led wire is put and the journal is closed. Then as the journal upper half is again removed, you get the thickness as the clearance profile.

The feeler gauges being of steel may easily damage by scraping off the white metal.

It would help if you were a little more specific on the generator models (GE AB-20 or ?) but I believe you in fact are dealing with roller bearings here.

Theres really no need to "jack" as long as you can get your feeler gauge in on the top of the bearing.

Rather than just going on with something that may be slightly off track, I'll wait until you send more details.

Tim

Sorry Tim for being late to reply, as I was in the field for 3 days.

Yes, we are using the roller bearing with CAT SR4 , and GE AB -20 and KATO 2500 KVA generators.

And we are using the Jack to duple check the results of the feeler gauge, as I don't have any manufacturer reference for the acceptable differences between the top and the bottom clearances.

Thanks -Salem