B412 Combining Gearbox - 2 metal particle incidents 1,800hrs TSN

[aseanaero]

On the question of B412 gearboxes making metal I've got a question for mtoroshanga and other B412 'old hands'

I looked at a T3 combining gearbox for sale here in Indo with TTSN 1,800hrs

At 1,000hrs TSN the gearbox was making metal particles and was completely overhauled by the factory (Pratt and Whitney and parts cost alone $180,000 10 years ago) then 800 hrs later it starts making metal particles again !

So it's up for another overhaul the question is why would it make metal particles twice well short of TBO and if there's a major problem with the gearbox casing not being machined or aligned properly why wouldn't that be picked up by the inspection procedures during overhaul ?

I offered them $15,000 for the gearbox as-is and they wanted $30,000 but with 2 metal particle incidents in less than 2,000hrs it's possible that even $15,000 was too much as if there's a problem with the casing also it's a boat anchor.

Has anyone else had a low time problem gearbox and what would cause 2 metal particle incidents in such a short time ?

[Matthew Parsons]

What happened to the rest of the helicopter that the gearbox was attached to? If its still flying, then why don't they want that gearbox. If its not flying, then find out what happened to it.

In the end, I'd check with P&W to see what they have to say. We've been dealing with P&W tech reps lately and they seem to be focused on getting things running than on selling more parts for no reason. Quite impressed.

[Oldlae]

The two occurrences may not be connected. The CGB was overhauled and new bearings almost certainly installed. Chips on the magnetic chip detectors are normally from failing bearings not the casing which is non-magnetic. The latest chips may have come from a new bearing with 800 hr TSN. Do you know which of the three chip detectors on the box now indicate the chips compared to the detector at 1000 hrs?

[mtoroshanga]

412 cgb

Would be inclined to stay clear without more history. Considering effort to fit cgb will be a pricey business if you have to pull it early. They do have spates of metal making from time to time but without knowledge of previous tasking advise against it.

[Eng AW139]

I'm I to understand that in 10 years the C box only has 800 hours. If this was the case low usage and poor preservation might cause a 2nd chip.

[aseanaero]

I'm I to understand that in 10 years the C box only has 800 hours

No , it was rebuilt 1998 and I'm guessing 12 mths use then 2nd chip incident and they replaced the CGB with a new gearbox , it's been in an air conditioned store for 9 yrs

I don't know which chip detector sensed the metal particles , the logs just say making metal and the engineers there now weren't around when it happened.

The main reason for the post is to get a feel why it would happen so soon after a proper rebuild , it maybe one of those quirky alignment and clearance issues where everything is within spec statically but something is off when the gearbox is run.

Gut feel is something was wrong with this gearbox from day 1 and still is.
My guess is if it was rebuilt a second time a similar occurence would occur and it would be a headache for an operator in the future

The operator must have come to a similar conclusion and put another new CGB in the 412 it came out of.

[widgeon]

From what you say it is probably worth its weight as scrap metal .

You could probably tear it down and put it on a CMM machine to check out if there is any warp in the casing . If you had the results of the SOAP oil analysis you could probably identify where the metal was coming from .

Too many ifs , I would steer clear of this one,

[Matari]

aseanaero:

Finding chips after an engine, c-box or transmissions rebuild is not that uncommon. As others have noted, usually it is new wear and break-in.

The maintenance manual will provide you with the proper guidance, but the relevant factor is the size, quantity and type of chips that your c-box is making. As others have mentioned, a SOAP analysis is best, but if you are in a remote location there are other ways to understand what is happening.

The maintenance team can do some basic things like pull the filter(s), clean and capture all debris. I can't remember if the 212/412 c-box had a paper or metal filter, but if paper you can cut it open and clean carefully between all the folds with solvent, and drain the cleaning solvent and debris through a paper towel.

Then run a small magnet on the underside of the paper towel and check for ferrous and non-ferrous metals. Use a magnifying glass to see if there are flakes, fragments, fuzz or specks. Note approximate size of the larger type (ferrous or non-ferrous) you find. Take digital pics. You can also do a ground run for a period of time, and repeat the process. If you continue to get chips, or if the amount is increasing, you (probably) have a problem. If the quantity, size and type is decreasing, then you might have break-in wear.

Again, follow the maintenance manual. But all the data above will help the maintenance team and OEM (if needed) troubleshoot your problem.

Hope this helps.

[aseanaero]

Thanks for the responses

The engineers still there can't remember or don't know the specifics of the metal particles (which happened 9 yrs ago) but their action at the time was to buy a new gearbox and they didn't attempt to fix this one so it must have been pretty bad.

I'll leave this one for the moment