siddus74

What do you mean? with center punch or something? can you explain?

Scott.

frema

your back bearing was running with the shaft , the black colouring .
the outer ring of the bearing i mean.
to avoid that , i always do 3 center punch in the bearing seat of the shaft tunnel , nicely divide ,
It makes the o.d of the seat a bitt smaller , so the bearing has a better fitt , and will not run in the seat.
i hope you understand that , my English is not that good you know

siddus74

so you make the 3 center punches toward the side of the flat then? maybe I can use this method instead of the shimming?

Scott.

alan_brinsley

Nice work Scott, my Wren 54 next yeah :-)

siddus74

Alan if I get this going, I cant see why not ... I need to get lathe :-)

Scott.

siddus74

I think I know what you mean, is the phote correct? (red dots :-))

Scott.

frema

No, you have to make the centers in the seat of the bearing , where you slide the bearing in.
maybe you have to sand grind it a little after to get a good fitt.

siddus74

Appologies, I must be thick - I dont understand you ...

Scott.

Xairflyer

My Feedback: (1)

The rear bearing locates in the end of the tunnel, ideally this should be a snug fit so the outer case of the bearing dos'nt rotate.

Wren and a few others experimented with O rings in a groove to help with this but that caused other problems, what frema is suggesting is to make a few centre punches around the inside of the tunnel so it helps prevent the bearing from turning.
If your new bearing is a snug fit and dos'nt seem like it will turn, then it might be ok.

frema

YES thats what i mean with the centers.
sorry for my bad English

siddus74

Thanks guys ... ive ordered the bearings ...

Scott.

basimpsn

My Feedback: (5)

Lets not jump the gun yet, On is first post he said (there is no play side to side) if after he assemble the engine and the turbine wheel is touching the NGV on startup then that's a good fix P.S I need to steal that idea . Now as for shimming, you might have to make them your self using real thin stainless steel material and cut to fit. Call me crazy but even a paper clip fashion to the inner circumference and flatten to adjust thinnest, this would be your last option.

P.S after 6yrs of service my injectors finally clogged up on the second flight. I remember my blowtorch in the back of my truck, Quick disassemble at the field, Then using the torch to clean the injector, Re-assemble the engine, 4 more flight later [8D] Got to love them old RAMS.
My opinion

siddus74

mmm a squashed paper clip behind the rear bearing .... how cowboy yee haa

Im still a little baffled how the rear wheel didnt touch the NGV but the front turbine wheel did? you would have thought that the if the rear bearing is issue that rear wheel would have slipped forward and fowled as well but it hasnt ... or is there a larger gap between with rear face of the wheel and NGV than there is between the compressor and the intake?

Seriously there isnt any movement side to side in the bearings and after exploding the front one I know that the bearings do move front to rear a little because of the design and taper when forced.

Also is the rear nut and shank one piece or the round collar at the end seperate? (its been gripped to death before)

Scott.

frema

it isnt a nut , its a piece of the turbine wheel.
and maybe the previos owner didnt know it was left thread

i have some pictures for you , but i dont know if it will help.

frema

and an interresting link :
http://www.toflyrc.com/Forum/tm.asp?...7&mpage=4&key=

KAON

how do you separate the shaft tunnel from the diffusor? i have a P80 and would like to replace the front bearing but can't
KAON

siddus74

All you have to do to replace the front bearing it to remove the compressor wheel, then the preload assy will push the front bearing out ... my front bearing was ok, the rear one was knackered ...

Scott.

KAON

the preload assy is stuck and so as the bearing. they wouldnt come off. tried heating the tunnel but the same...

Vinceyboy

Very interesting thread Scott, I love to be able to get hold of an old turbine and strip it, but a virtually free one would be better
I am a washing machine engineer, so get to strip motors and do bearing jobs, what Frema was saying about using a punch, I have done on washing machines where the bearing has spun in the housing, just made some punch marks on the side of the housing where the outer shell of the bearing goes into the housing, and as said, maybe a bit tight to get back in but will stop it spinning in the housing. On washing machines, I also put a smear of thread lock around the outer shell of the bearing before putting in back as an extra securing for the bearing, whether this is advisable in a turbine, Frema or Seamus can advise.

Anyway, well done so far, and I hope you get back together OK.
Regards,
Vince.

Xairflyer

My Feedback: (1)

It is a compromise as the bearing still needs to be able to move very slightly fore & aft otherwise the preload wont work

Vinceyboy

AAAHHH I see Seamus, so they need to be able to move, so looks like shimming is the only answer without replacing the part where the housing is, the plot thickens

siddus74

Thanks Vince ... I am enjoying it to a degree and its certainly and eye opener ... The bearing housing is aluminium as far as I can see so I guess if I have to shim behind the rear bearing it to bring back to tollerance after trail fitting it back together with new bearings then any steel / ali washer the correct size would surfice? I guess rubbing it on find sand paper for a while is my future ... worse case is its scrap and I have loads of spares ...

Any further advice would be great ..

PS would the spinning of the outer case when the bearing siezed cause the enough wear on the seat to cause the shaft location to move forward and inturn the compressor to pickup on the intake cone?

Scott.

Xairflyer

My Feedback: (1)

One of the reason wren and others dont use the rear O ring anymore as it would cause the bearing to stick forward, I had a turbine that would do it all the time and used to have to keep freeing it, eventually I rebuilt it with a new tunnel (no rear O ring) and no problems after that.

siddus74

Sorry, not fully with you? define stick forward? is this a possible cause of the compressor wheel picking up?

Scott.

Xairflyer

My Feedback: (1)

Scott we were typing at the same time I think, my reply was not directly about the question you asked.

Yes if the bearing caused wear on the seat in the tunnel the whole thing would have moved forward and so touched the intake, clearance is so small that is why amount shimming/preload is so important.