OS camshaft bearings

[Nigel R]

These look like fun.

I have two old 40 surpass motors to spruce up a bit. They are both externally quite tidy, show good compression without much evidence of valve leak, and I believe they really just need a bearing swap and a quick clean up.

The first one has been run on castor and although all the moving parts move perfectly freely some of the less mobile bits are a bit stuck. I've stripped it down all the way - barring the usual piston pin problem it came apart ok, on the piston pin I ended up using a tight fitting machine screw to pull the pin through that daft little crankcase hole.

I'm a bit stuck on the camshaft bearings though. How the deuce do you get these out? They're just sunk into a blind hole so can't be pressed out from the rear and whilst a dose of heat got the main bearings out the cam bearings are staying put. Any ideas welcome.

[Dad_flyer]

There was a big thread on something like this last year. I think I found it on Google, but the link come to a blank on the site. Maybe someone else can find it. I have never had a model with an IC engine, but the ingenious solutions to bearing removal were a good read.

[Bob Cotsford]

Nigel, I used to do it by dripping candle wax through the bore of the bearing until it was full, then tapping a close fitting pin punch into the wax filling the inner race. The wax gets pressed between the rear of the bearing and the case pushing the bearing out.

[Nigel R]

ok, that sounds workable

I assume the usual heat cycle is applied at the same time as pushing the wax?

[Nick Cripps]

That sounds an interesting idea, Bob. I've got a couple of OS four-strokes that need refurbishing and I'm struggling to remove the cam bearings.

Laser Jon's thread here showed a couple of alternative methods. One was to drill a hole through the crankcase behind the bearing and press it out, the other was to make up an extractor tool. I don't fancy the 1st method and I don't have the facilities to make a tool so I'll give the wax method a go.

[Engine Doctor]

The camshaft bearings can occasionally be removed by heating the crank case and tapping it against a wooden block; however our known enemy corrosion can make this method impossible. An expanding tool that fits the bearing center snugly then tightened is really the only other option to remove these bearings without damaging the case. The tool can be easily made if you have a lathe or know a friend/clubmate who has one.

Edited By Engine Doctor on 27/01/2021 10:45:57

[Bob Cotsford]

I wouldn't apply heat with the wax method, it would most likely just melt the wax allowing it to run out between the balls though the more solid red sealing wax used on documents might be ok with it. I only heated the case to get the new bearings in.

[Jon H]

Yep, my hole through the crankcase method works a treat but i did upset the natives

If you want it out fast, and dont mind sticking a small litho plate disk over the hole you made when you are done then by all means drill a little hole.

In my case on that 40 it was mostly a time constraint thing. The engine was scrap anyway, the bearing was rusted into the etched aluminium, i had 5 minutes of the tea break left and i wanted the bearing out. There are ways of doing it that would not damage the case, but i needed a quick fix and that is what i got. After i repaired it and covered the hole you would never know it was damaged and it will certainly make repairs easier next time!

[Cuban8]

The old heavy grease or candlewax trick can work but is a bit variable in results although I have used it at work from time to time.

Usually heating the bearing seat to expand it and and then shrinking the bearing with a freezer spray is useful, or if you haven't got that, a degreaser aerosol does get cold enough. Obviously timing is of the essence to get the heat and cold in the right place but it does work and usually the bearing will drop out with a swift tap providing its not jammed with crud.

Alternatively a puller or extractor will have to be made up so the race can be tapped out in the fashion of a 'slide hammer'. Can be tricky with very small bearings though. Only as a last resort and really if all else fails, a small hole can be drilled in an appropriate place in the back of the bearing housing and the race drifted out. The access hole can be filled with a dab of epoxy - did this with an old ASP fourstroke that I wasn't too bothered about, but I still have the rebuilt engine in a model and it continues to run OK. TBH, with patience and cunning you can usually work around the problem.

Edited By Cuban8 on 27/01/2021 10:58:20

[Rich Griff]

I don't know this engine or the sizes involved, a picture would be good.

You say races, so the bearing in question is a ball race bearing ?

Grease method and close fitting shaft idea can and does work, application dependent.

A hole so as to drift the outer race, again works, maybe the hole can then be tapped and a plug screwed in place ?

You know iff raw plugs and similar, to act like a slide hammer or extractor perhaps ?

A rear good clean down before bearing removal attempts is a must.

Warmth is good for bearing removal as alloy expands at a different rate to the steel of the race.

A cold spray can also help.

Please post some pictures and parts exploded views 😀

[Nigel R]

Posted by Bob Cotsford on 27/01/2021 10:48:48:

I wouldn't apply heat with the wax method, it would most likely just melt the wax allowing it to run out between the balls though the more solid red sealing wax used on documents might be ok with it. I only heated the case to get the new bearings in.

ok, I can see how that could go wrong, just cold wax forced in through the middle then.

think I'll try this as first port of call

[Nigel R]

freezer spray, good thought c8

[Martin Harris - Moderator]

Posted by Rich Griff on 27/01/2021 12:25:06:

I don't know this engine or the sizes involved, a picture would be good.

Please post some pictures and parts exploded views 😀

Best bet is to have a look at the thread linked to earlier in Nick Cripps' post - all should be clear from that.

[Martin Harris - Moderator]

Off topic post moved to relevant thread.

[Bob Cotsford]

Rich, cam bearings in our size engines are typically 12-15mm OD and 4-8mm ID with the OP's engine at the bottom of that range, and they fit in blind bores. Internal pullers at those sizes are rare beasts and usually home made, hence the need to use alternate methods.

[Nigel R]

12mm 5mm 4mm is the size, I think (common to all OS glow four strokes?)

[Martin Harris - Moderator]

Although I have the luxury of a lathe and made an expanding puller, a simple claw type slide hammer made from a small bolt or length of studding and a lump of steel or brass with a hole drilled in it would be within the capability of many modellers.

[Sheepish]

Another vote for the candle wax method, worked a treat for me on an OS 40 Surpass and an SC52.
Both the bearings out in minutes with no damage and no stress and no need to heat the parts either.

[Rich Griff]

How much room left in blind hole ?

A plastic raw plug and long screw and sliding weight for a slider hammer perhaps ?

[Nigel R]

Not much, the bearing is right up against the bottom of the hole.

Rawl plug plus long bolt might do it, if the end of the plug is cut off square?

I shall try wax first though. I think I'm only fighting against some castor goop, not rust.

Is it worth an overnight soak in thinners to see if it dissolves the goop?

[FlyinBrian]

This is how I removed a stuck camshaft bearing on an ASP 120 FS, they were brown with rust and stuck fast. - I had tried heat without success.

This relates to the bearing opposite the removable plate.

I thoroughly washed out the bearing with cellulose thinners, then left a pool of thinners covering the bearing overnight. I emptied the thinners out the following morning and let the bearing dry. I took a length of studding about 30cm long (5mm I think) and ground the threads on the end to be an interference fit into the inner race of the bearing. I then put a drop of cyano around the end that had been ground and inserted it into the bearing and left it about a half hour. At the other end of the studding I put an oversize washer and nut. With the crank case supported by a vice with the studding pointing down I heated the area around the bearing with a heat gun the put an adjustable spanner above the nut and closed the jaws till it was just touching the studding the gave the jaws a solid tap with a hammer. The bearing came out on the first tap.

[Martin Harris - Moderator]

There's a little room behind the inner race. The flange on this tool locates behind it.

[Nigel R]

that's a very professional looking gizmo, martin

brian - another option to try after the wax I think

 

Edited By Nigel R on 29/01/2021 12:39:04

[robert chamberlain]

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.

[Chris Walby]

How about a take on Flyinbrian's suggestion

Instead of ca use a very strong Loctite (602), glue the dowel and then use a puller to remove the bearing