The sight glass on my K75's overflow tank is full of fatigue cracks. I ran an ad a few months ago chasing a replacement to no avail. A mate has got four of them in much the same condition. I was waiting for Motorworks to reopen. However I got a bit bored today and decided to have a crack at milling one out of a piece of round 25mm clear acrylic. I have access to a turret mill when the Trades Guild is open but they are currently closed for Christmas New Year.

So I reverted to my trusty drill press with it's cross slide vice. I have previously milled aluminium and wood on it. I used router bits in the drill press and finished it off with files and a bench grinder with buff wheels and polishing compound. I will give it a bit more buffing tomorrow and will eventually remove the tank and replace the old one with the new one. I'm pretty happy with how it came out, I did pick up a couple of tips from a couple of guild members. When milling acrylic there is no need for high speed and keep spraying it with WD 40. This will stop it sticking to the tool and the job and helps in keeping it's clarity. One of the guild guys did offer to make one on his small CNC machine but where's the fun in that.
Happy New Year regards Martin.

That's some pretty impressive DIY.

Thanks Duck but once I got going it wasn't that hard. The cross slide vice is one of my better investments, and the tip with the WD40 really helped. It stopped the swarf from melting onto the tool and the job, which was a problem when I previously tried to cut acrylic. I just have to make slight adjustments to make the ends equal and uniform. Then I can carefully cut off the old sight glass and glue on the new one. I'm thinking of using black Sikaflex but that will have to wait till tomorrow as it's New years day and the shops are closed.

Happy New year regards Martin.

Instead of Sikaflex try Bostic "seal n flex" it is exactly the same and half the price

Thanks Rick I have just looked at the price $19.00 Au for a small tube.
Happy New Year regards Martin.

Rick I ended up with Selley's polyeurethane Flexseal $11.30 Au a tube from Bunnings. Sight glass all finished and installed. I used a mini cut off disc saw and a 1/4" air burr grinder to remove most of the old sight glass. The tank is recessed into
sight glass so care is needed trying to grind off the edge of the glass. So as not to damage the body of the tank I hot glued pieces of an old hacksaw blade to the tank. This made the hole process a lot easier and safer. I started off gluing the hacksaw blade at an angle eo do the ends but ended up just holding the blade while grinding off the excess. The blade can be lifted off the tank easily and the glue easily removed.

As I was unsure of what to expect once the old sight glass was removed I had left the of the new one just flat. I ended up just milling it out to a depth of 3mm with a 2.5mm rim. A bit more polishing with a 1/8" air burr and mop ensued on the recess which probably wasn't needed. After making sure it was a good fit I cleaned up both bits with wax and grease remover . I ran small bead of sealant in the corner of the recess smoothed it out evenly with my finger and stuck it on. I'm very happy with he end result and hopefully it will out last me.
Regards Martin.

I wonder if clear Silicone tubing can't be used as a replacement. Several manufacturers rate their silicone tubing as coping with 200C temperatures with short term max temperatures of 260C. Anyone tried clear silicone tubing as a replacement?

There are two types of sight glass one is the tube type and can be replaced. The other is the built in clear acrylic type built into the tank which is deemed non replaceable. My home made one is still going.
Regards Martin.

Thanks MartinW for your excellent earlier posts on making a replacement sight glass for the later model radiator overflow tank. My 2 overflow tanks are the earlier types with the clear tube used. I've decided to proceed with clear silicone tubing as replacements on the basis of their superior heat tolerance. I'm still interested in tube type used by those who have done a replacement:- type of tube used, how long ago, how the replacement is performing.

I replaced LFB's tube with silicon about eight-nine years ago. You can still see the coolant level pretty clearly but the tube is getting slightly clouded from the crap that's come off the inside of the radiator. You're never going to avoid that.

I have some tube in my shed and have done some but I have two more now to do.

No idea what the tube is though, 88 [Will Crean] gave it to me a long time ago.

92KK 84WW Olaf wrote:I have some tube in my shed and have done some but I have two more now to do.

No idea what the tube is though, 88 [Will Crean] gave it to me a long time ago.

So long ago I cant remember Olaf but I think it came off a drain cleaning kit. Either way the hose only works for those later type expansion bottles. The one above is the sight glass type.