OS camshaft bearings

[cymaz]

Posted by robert chamberlain on 31/01/2021 04:57:28:

Hello, My experience with removing bushings from a blind hole was to simply use a wooden dowel. Maybe this would also work with a bearing.-----I would fill the hole with a little oil and then take a tight fitting wooden dowel, push it in by hand, and then hit the dowel with a hammer. Hydraulic pressure had no where to go but behind bushing and drive it out. Always worked for me, but then again I am talking about bushings and not bearings. I guess it depends on how far the bearing is in the hole. Just a thought and am trying to help out.

I’ve heard either clay or silly putty will work as well

[Bob Cotsford]

One point to bear in mind when using hydraulic action to pop a bearing out of a blind hole, whether using wax, oil, clay or whatever, is that you need to support the back of blind bore face which may only be a thin wall of cast alloy. You don't want to pop your punch straight through!

[Jonathan W]

The way I do this, which I have described previously, is best if you have access to a lathe. Otherwise, you could improvise manually with a drill and filing I suppose.

I take some aluminium round bar, say around 3/8" or 7/16" diameter and turn a spigot on the end which is a close fit inside the cam bearing. The closer the fit (interference), the better. Push the spigot into the cam bearing and then heat the whole thing up with a heat gun. Due to the aluminium expanding more than the steel bearing, the crankcase loses its grip on the bearing while the spigot on the end of the round bar grips harder. Wearing thick leather gloves, you should then be able to pull the round bar out with the bearing held on the spigot end.

From memory, the OS 40 cam bearings are 5mm bore, so that is the size of spigot you should need.

[robert chamberlain]

I guess I was way off on my thinking. I pictured pilot bushing in crank shaft of car engine.

[Nigel R]

Gents

Success with wax!

First motor now runs sweet as a nut; second yet to be checked, but this only needed main bearings to be swapped the cam bearings were fine.

 

[Nick Cripps]

Good news!

I'll have a go at this when it warms up a bit in my workshop - probably sometime in March...

[Denis Philippe]

Hi Nigel, I did a refurb on an OS 46 AX last summer and found that once everything was stripped other than the bearings, a quick stint in the oven at 160 expanded the case a little so you can tap it out gently with a dowel. 

Whole process took less than 20 mins, including explaining to the wife that it would not ruin the Sunday roast!

Same process for fitting new ones after in reverse order.

Hope this helps.

[Dave S.]

I've just removed all four bearings from an OS 52 four stroke I acquired recently. The engine was basically in good shape, but hadn't been run for some time and the bearings were showing signs of rust. Crankshaft bearings came out easily - heat gun and tap the crankcase on a block of wood and bearings just fell out. 

I read this thread and decided to try the wax method to remove the camshaft bearings, and it worked very well. I used a 5 mm dowel that was a close fit into the bearing, dripped wax in and then tapped the dowel with a hammer. I had to replenish the wax a few times as it spread out behind the bearing, and supported the outside of the casting on a piece of wood. Both bearings came out fairly easily with no collateral damage at all (unless my wife checks her candles!)

New bearings ordered, and then I can 'remantle the engine back together again'.

[Geoff S]

... and then, of course, the engine will be perfect ?

Geoff

[Nigel R]

I've run the second now. Both go lovely.

Denis, I agree changing the main bearings is usually straightforward given some heat and a few taps on a block of wood. I seem to need a dowel to tap out the front bearing from inside, about half the time though.

You can make your life even easier on reassembly by popping the crank and the new bearings in the freezer for five minutes before you drop them back in.

 

Edited February 15, 2021 by Nigel R

[Dave S.]

2 hours ago, Geoff S said:

... and then, of course, the engine will be perfect ?

Geoff

I'm sure it'll be purring like a kitten with a bowl of cream once I've reassembled it - and bought some fuel!

Looking forward to getting it back to work in the 4 Star - been far too long since I last flew one of them. My last one had an ASP 61 FS, a Saito 62 and an Axi 28226/10 (a different one!) with a vast number of NiMH cells at different periods in its long life. It flew with skis from frozen lakes in the winter, and conventional gear from the club field in the summer.