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Poorly OS40 repair

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Jon - Laser Engines17/02/2020 19:00:24
5507 forum posts
268 photos

Very kind Malcolm

My plan is to do as little to the engine as i can in terms of replacement parts. I mean, its not really fixing it if i replace all the parts, but equally if something is beyond repair then it needs to be changed. Bearings, piston ring, valve springs. These are my main worries and i know the throttle arm is also broken. Beyond that i have not looked at it closely as i didnt want to start the video already knowing the story.

What i will do is try and get myself organised and see what it is we have, are the parts any good, can it be saved. If i can get a video of that lot done then i will see where we end up

Wingman18/02/2020 10:12:36
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1148 forum posts
405 photos

Jon,

While a video would be great can I suggest that in order not to get trapped in it that you video yourself doing all the repairs/refurbs until complete and you have a running motor and then upload it after editing. That way the thread won't stall because you can't get a part or have insufficient time available to do the job etc. etc. and you will be a

herolaugh

Jon - Laser Engines18/02/2020 11:08:25
5507 forum posts
268 photos
Posted by Wingman on 18/02/2020 10:12:36:

Jon,

While a video would be great can I suggest that in order not to get trapped in it that you video yourself doing all the repairs/refurbs until complete and you have a running motor and then upload it after editing. That way the thread won't stall because you can't get a part or have insufficient time available to do the job etc. etc. and you will be a

herolaugh

I did think about that but i would like to stay away from the 'here's one i prepared earlier' style. If someone is watching the video and trying to learn something about fixing an engine then the video needs to be as they will see it themselves and will be, more or less, completely unedited. If i have all the answers before i begin then i can miss things in the video that i take for granted when looking at a damaged engine.

I dont want to go in with the whole project figured out and a script of what needs to be done as this is not representative of trying to fix an engine yourself. You open the thing up and you evaluate it, that will be the focus of the first instalment. If during that process we learn that the engine is dead, then fine, its dead, but at least we all now know what to look for in a dead engine, how to evaluate the parts you have, and when to decided its done and not go spending loads of money on replacement parts.

At the end of the whole thing the engine might still be a failure. It might not run very well, compression might be poor, whatever. That is not really the point.

Its like in a maths test at school. If you got the answer wrong but showed your working you still get most of the marks.

Cuban818/02/2020 11:27:45
2956 forum posts
1 photos

Not a mullered engine - but a good video showing four stroke assembly here. OS FS Rebuild

Jon - Laser Engines19/02/2020 23:13:06
5507 forum posts
268 photos

i had a brief go at getting the video started this evening and immediately came to the realisation that i did not have the equipment or setup to really make it work. I am going to try again in a few other locations but i am not holding out too much hope. The real issues are lighting and camera mounting as i dont have any tripods or anything like that. Looking through the camera it was impossible to see anything inside the engine as the light was so poor and trying to use a torch (all i had to hand) just washed out the image.

I will try again in the workshop at work as the light is much better than my living room but i am still stuck on ways to hold the camera. If i cant work it out then a step by step blog might have to do.

Jon - Laser Engines08/04/2020 08:48:43
5507 forum posts
268 photos

Following a few failed attempts i have abandoned the video idea for this one as i lack the time, facilities and equipment i need to do it and have actually mean something.

So, instead we will have to live with the photo version.

A quick inspection of the parts reveals a few problems.

The crankcase is generally intact but the camshaft bearing is rusted into the case. There is no way that is coming out with heat as normal so its going to need a drill.

os40 (1).jpg

Somewhere down the line someone has welded or otherwise melted the front bearing portion of the case, and has mangled the cam chest a little as well.

os40 (2).jpg

Other than dirt/rust and general grime the head seems ok

os40 (3).jpg

Although the exhaust port is clogged with who knows what

os40 (4).jpg

Jon - Laser Engines08/04/2020 08:51:34
5507 forum posts
268 photos

Minor rust staining on the liner, nothing major here

os40 (6).jpg

Crank needs a bit of wire brush action

os40 (7).jpg

Broken cam cover. Repair or replace?

os40 (8).jpg

The piston ring was rusted into the piston. A little care did have it free and i was able to give it a clean up before refitting.

os40 (9).jpg

The carb is locked solid

os40 (10).jpg

Jon - Laser Engines08/04/2020 08:56:52
5507 forum posts
268 photos

The con rod is a bit of a gonner. There is so much etching damage to the big end that i would not risk using it.

os40 (11).jpg

In order to remove the stuck bearing i took a 4.8mm drill and stuck it down inside the 5mm bearing. I then drilled right through the case before opening up the hole to 6mm from the outside with a reamer. This allowed me to then press the bearing out using an old laser gudgeon pin. The hole can be fixed later

os40 (12).jpg

os40 (12).jpg

I had a bit of a go at removing the mess of melted material from the front of the case. A futile exercise as it turned out (more on this later)

os40 (14).jpg

After a date with the sand blaster the case is nicer colour, but the damage caused by the acid etching is really evident now. That mangled welding was also as bubbly as an aero chocolate bar so the shot blaster made a right mess of it.

os40 (15).jpg

Jon - Laser Engines08/04/2020 09:01:19
5507 forum posts
268 photos

More of the same here on the other side

os40 (16).jpg

The head, carb and rocker cover were also blasted. The head looks pretty decent so i wonder if it is made from a tougher material than the rest of the engine. It seems to have less etching damage than all of the other parts.

os40 (17).jpg

To back track slightly, getting the carb apart was a right pain as one of the screws holding the spray bar refused to play. I had to drill it out in the end and that involved trying to keep a 2mm drill right down the core of a 2.5mm screw and not mangle the threads in the aluminium body. Clearly the gods of engineering took pity on me as i was able to drill out the old screw without totally messing up the carb body. I then pressed out the rusty barrel, cleaned it all up and put it back together. I think it will work ok

os40 (18).jpg

 

So. Looking at the parts i think there is a chance the engine can be saved. The only real problem is the conrod and i need to work out if its worth buying a new one. Bearings are not massively expensive so i think there is hope for a rebuild. in the meanwhile i will keep fiddling and returning individual parts to 'airworthy' condition. 

If anyone has a spare conrod, even if its a bit worn, let me know as it might be the solution i need. 

Edited By Jon - Laser Engines on 08/04/2020 09:03:52

cymaz08/04/2020 09:29:52
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9253 forum posts
1195 photos

I admire your tenacity Jon.....seriously, I would have thrown it away.

I know I did a rebuild a month or two back for a couple of SC 2t. That was easy, £5 on bearings and a very kind and generous gift of parts.

Ron Gray08/04/2020 09:53:10
2166 forum posts
940 photos

Let's face it Cymaz, Jon hasn't got anything else to do!! smile pwink 2

Jon - Laser Engines08/04/2020 10:20:20
5507 forum posts
268 photos
Posted by Ron Gray on 08/04/2020 09:53:10:

Let's face it Cymaz, Jon hasn't got anything else to do!! smile pwink 2

Im still at work luckily as it means i have access to all the tools i need to fix this thing!

As for throwing it away, the important parts like the liner, valves, head etc are all ok. The front bearing fit in the crankcase seems ok as well so in theory there should be nothing stopping it.

In truth it would probably run with the existing rod but i doubt it would last long as there is no point rebuilding it only to blow it up after a few runs.

Piers Bowlan08/04/2020 10:37:12
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2141 forum posts
53 photos

A series of short narrated videos would be an extremely useful resource Jon and probably reduce the number of 'butchered' engines that get trashed unnecessarily?

Paul Marsh08/04/2020 11:02:58
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4024 forum posts
1217 photos

I've got quite a few original OS 40's I bought one off a swapmeet cheap, saying it wasn't running. Needed a new piston ring and fully working.

Also, on timing, it should be thus:

lg-163571.jpg

Jon - Laser Engines08/04/2020 11:30:15
5507 forum posts
268 photos
Posted by Piers Bowlan on 08/04/2020 10:37:12:

A series of short narrated videos would be an extremely useful resource Jon and probably reduce the number of 'butchered' engines that get trashed unnecessarily?

The problem is i dont have the required equipment, time, or expertise in film making. To do it properly it needs to be well lit with a decent mic and ideally in a place with little background noise. I would also need all of the tools required on hand all of the time and half of them are here at work so its not really possible.

Add to that all the editing, and the lack of really suitable software, and it all just becomes a bit of a mess. As i suspect the final result would not be that good its sort of pointless doing it which is why i gave up.

Paul, yep. Pretty much all OS's are the same. I have an OS91 on the go as well for a customer as a bit of a weekend job.

cymaz08/04/2020 11:43:51
avatar
9253 forum posts
1195 photos

The con rod has the same part number as the .52. As does the wrist pin

con rod.....45205000

pin....45806000

 

Tower Hobbies If you can stand the postage 

Edited By cymaz on 08/04/2020 11:46:36

Jonathan W08/04/2020 12:11:25
124 forum posts
11 photos

Since I'm stuck in quarantine, I'll have a go at explaining my method of removing a stubborn bearing in a blind housing, like the cam bearing Jon has shown. However, you do need a lathe to make some simple tooling.

Get a piece of round aluminium bar, say around 10mm (3/8 inch) diameter. Turn a spigot on one end to be a tight fit into the bore of the bearing. It needs to be a good tight fit, such that a hammer is required to (gently) drive it in. Then heat up the whole lot with a blow torch. The housing expands, loosening its grip on the outside bearing. The spigot also expands, increasing its grip on the inside of the bearing. If you hold the ally bar in a vice, you can grab the crankcase with thick leather gloves and pull it all apart. If the rust is causing an obstruction, a couple of heating/quenching cycles should dislodge it.

The time and trouble you took to turn the spigot on the ally bar is saved when you don't have to repair the hole that you drilled in the crankcase!

Personally I now avoid buying secondhand 4 strokes off ebay due to so many clueless butchers have made the engines almost impossible to repair! I only buy if I am able to inspect first. Even then you can be in for a nasty surprise after a full strip down.

Edited By Jonathan W on 08/04/2020 12:12:08

Edited By Jonathan W on 08/04/2020 12:12:39

Jon - Laser Engines08/04/2020 14:05:38
5507 forum posts
268 photos

Thats not a bad method but this one was way past it. I tried getting a photo but it didnt come out. Anyway, the hole in the middle of the bearing, and more or less the whole thing was just one big rusty lump. I had to drill through all the oxide on my way out the other side. It was a bit of a mess.

Doc Marten08/04/2020 22:45:56
579 forum posts
7 photos

There is a trick using Aluminium Sulphate to eat iron or steel screws in Aluminium castings if I remember correctly?

Martin Harris08/04/2020 23:34:46
avatar
9333 forum posts
249 photos
Posted by Jonathan W on 08/04/2020 12:11:25:

Since I'm stuck in quarantine, I'll have a go at explaining my method of removing a stubborn bearing in a blind housing, like the cam bearing Jon has shown. However, you do need a lathe to make some simple tooling.

Get a piece of round aluminium bar, say around 10mm (3/8 inch) diameter. Turn a spigot on one end to be a tight fit into the bore of the bearing. It needs to be a good tight fit, such that a hammer is required to (gently) drive it in. Then heat up the whole lot with a blow torch. The housing expands, loosening its grip on the outside bearing. The spigot also expands, increasing its grip on the inside of the bearing. If you hold the ally bar in a vice, you can grab the crankcase with thick leather gloves and pull it all apart. If the rust is causing an obstruction, a couple of heating/quenching cycles should dislodge it.

The time and trouble you took to turn the spigot on the ally bar is saved when you don't have to repair the hole that you drilled in the crankcase!

I knocked this up to do the job several years ago - it's never let me down but Jon's one sounded like a challenge!

I left the option to use it as a slide hammer but haven't needed to finish it off...

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