Skywatcher primary - a cautionary tale

[acey]

After a few years of regular use I finally decided to wash the grubby primary of my Flextube 300. As I began removing the screws that hold the primary cell in place in the tube I realized they had suffered slight corrosion from dew exposure, and were very stiff. The worst two were the pair at the bottom of the tube (as seen horizontally), presumably because of the tendency for moisture to drip round the tube. One of them yielded to firm force, but on the other I found myself left with a stripped screw.

I tried various standard tactics (e.g. cutting a new slot in it for a flat-head screwdriver, supergluing a nut on it) but in the end I had to drill out the head, after which the primary cell came out easily. The stuck screw is the only one that goes fully into a hole in the primary cell - the others just go through thin wall, hence are less liable to get stuck.

I can manage fine without it, but a good preventive measure would be to replace the screws with stainless steel ones, or at least make sure that they get a turn every year or two, especially the one that caused me so much bother. It's the one on the lower right as you look at the cell from the rear with the tube placed horizontally.

[swamp thing]

Very useful heads up. May well prevent anyone else saving this problem.

[estwing]

i bet many have over looked this one...cue lots of people checkin screws!

[NGC 1502]

Some grease on the threads should help to prevent corrosion stopping easy removal of any screw.

So when replacing a screw, a moment to put a small dab of grease on the thread could save a lot of grief in the future.

You can get dedicated anti-seize stuff which would be better than ordinary grease.

Regards, Ed.

[scarp15]

Thanks for that, and good to learn that you have no lasting concerns. Yes, a bit of multi purpose greese (such as LM2 carlube) on the screw threads looks to be in order - prevention certainly is better than cure.

[crashtestdummy]

I coated all the screws on my flextube housing with a teflon coated grease but as i take my mirror cell out every 3 month or so i doubt for me it would be necessary.

Great heads up though

[kirkster501]

I coated all the screws on my flextube housing with a teflon coated grease but as i take my mirror cell out every 3 month or so i doubt for me it would be necessary.

Great heads up though

Why do you take the cell out so often may I ask please?

[earth titan]

Why do you take the cell out so often may I ask please?

I'm glad you asked. I was wondering the same myself.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[Mr Fiery Jack]

I'm glad you asked. I was wondering the same myself.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

Yeah me too, I would be interested to know.

[JonF]

I'd use copaslip rather than grease. Grease tends to encourage things to come loose, copaslip doesn't, but enables easier dissembly than dry fit. Last for ages.

[earth titan]

I'd use copaslip rather than grease. Grease tends to encourage things to come loose, copaslip doesn't, but enables easier dissembly than dry fit. Last for ages.

CopperGrease is wonderful stuff - if a little pricey from what I recall. Used to use it on car brakes to prevent them ceasing up.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[russ.will]

Indeed it isn't cheap, but on the plus side, a moderate sized tube is a lifetime purchase. I'm still using the tube I bought for lubricating the slide pins on the brake calipers of my CB125 Super Twin in 1989. That was the first of twelve bikes and as a once all year round two wheel commuter, that meant having the brakes apart a couple of times a year minimum.

I used it when reassembling my 300p FlexTube, as indeed I do with anything that has an aluminium/steel interface exposed to weather and I've still got about 2/3rds of a tube left. £20 well spent I'd say.

Russell

[Moonshane]

great heads up. I tend to only use stainless on my builds and mods etc. so cheap from ebay these days it's really quite ridiculous.