Poorly OS40 repair

[Jonathan W]

Posted by Martin Harris on 08/04/2020 23:34:46:

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...

That's a very neat bearing extractor, Martin. I think all the OS 4 strokes have the same size cam bearing, so I can see why you took the time to make it.

Ref the OS FS40 con rod, it is quite likely to be the same con rod as also used in the OS 2 strokes of the era, i.e. the Max 40 H and 40 FSR. That might open up more possible secondhand sources.

[Nigel R]

I believe it might be 40H. The piston ring is the same (I think!). So maybe OS borrowed the whole rod/pin/piston/ring assembly and removed the lump from top of piston?

[Former Member]

[This posting has been removed]

[Jon H]

Jrman, yep they are, but given the nature of the project i dont want to spend loads of money just it case it ends up a dud.

Alan, the bushes are ok its the ali that has been munched by the acid it was exposed to.

ED, Thanks very much for the offer but i already bled another chap for an ASP 52fs rod i knew he had spare. If its no good or something else happens i will let you know.

I have made a little more progress on the engine but didnt take photos as it was really quick work. The cam followers, gudgeon pin, pushrods and valves got some abrasive treatment to polish them up. The crank and cams were wire brushed and came up nicely. I shot blasted the valve springs to de rust them but if the engine runs well i will replace them later.

I rebuild the head and the valves appear to seal so all in all its not going too badly. It might actually work!

[Martin Arnold 1]

Just fitted bearings to two of these old OS40FSs in my Super Trouper twin, went stainless steel this time in the hope they won't rust quite so quickly !!!

[Jon H]

Since my last post i have received two care packages. One contained the bearings i needed for the rebuild and the other a conrod kindly donated to the cause.

All that remained was to put it all back together.

I am currently still missing the O rings for the pushrod tubes so i left them off. I also need a new cam cover as my plan to repair the old one wont work. I drilled a big hole through it so i can rescue the new bearing without cooking it. The prop driver is also pretty shot and the head shim was shredded so we are going without for now. there is no point replacing these parts unless the engine runs ok so we will see what happens.

I am still quite confident it will run. The exhaust valve is leaking but im hoping it will settle down with a run. It will then be a case of working out if its worth adding those other new parts and making good the hole in the crankcase.

Depending on how things pan out, i might even try running it later this evening

[Martin Harris - Moderator]

What was your failed plan, Jon? I would have thought you should be able to epoxy an aluminium plug in the hole if you don't want to heat the case high enough for aluminium solder. I'd be tempted to turn up a thin brimmed top hat plug for increased glueing area if originality isn't more important than function.

[Jon H]

The o/d of the bearing part of the cover is 15mm so i was going to drill a 15mm hole through a strip of 3mm ali i have. I was then going to put the cover in the hole, drill through the remaining mount lug, and then flip it 180 to pick up the other side. I could then file away to get a new flange which i would then press over the current bearing housing after i turned it to remove the current lug.

It would have been fine, but my ali strip was not wide enough

[Martin Harris - Moderator]

Ah - I thought it was the drilled holes that needed repair. I'd imagine that you'll be able to pick up a spare housing/cover from any of a multitude of engines if you can't repair yours but the single bolt should retain the housing sufficiently for test running as long as you don't overtighten it. (Granny and eggs come to mind!)

[paul d]

What a bodge job Jon! working where you do surely you have access to bearing pullers or a lathe to make one? you didn't even acknowledge Martin's suggestion.

So you've "rebuilt" it complete with a hole in the crankcase, a leaking exhaust valve and no shim on the head.....hmm!

[Martin Harris - Moderator]

Posted by paul d on 16/04/2020 18:40:45:

working where you do surely you have access to bearing pullers or a lathe to make one?

I'm guessing that CNC machinery used for production runs isn't the most suitable for a one-off...

Edited By Martin Harris on 16/04/2020 19:17:49

[Jon H]

Posted by paul d on 16/04/2020 18:40:45:

What a bodge job Jon! working where you do surely you have access to bearing pullers or a lathe to make one? you didn't even acknowledge Martin's suggestion.

So you've "rebuilt" it complete with a hole in the crankcase, a leaking exhaust valve and no shim on the head.....hmm!

 

Its always hilarious to me when people criticise my work.

Not sure why you are so outraged Paul and had no idea you were such an expert on these things. The idea here was to have a little fun with some old junk, nothing more. The engine is ruined make no mistake. The castings are all shredded, the valve seats are shot and the head shim is virtually dust. Just shot blasting the crankcase obliterated the areas of damaged aluminium. Frankly, im surprised its not crumbled apart like a biscuit.

The hole in the crankcase? Its completely irrelevant really, and once plugged it wont matter a jot and it makes changing the bearings so much easier. As for bearing pullers we dont have any as we dont bury bearings in blind holes so have never needed one. Had it been possible i would have heated it up and bashed it out as normal, but it wasnt...so i didnt. Again, the objective is important. Old junk, can it be saved at all, bit of fun...?

Anyway I am well aware of the remaining issues the engine has, but if its dead why would i spend money/time on a new cam cover and all the other parts? As for making one, you clearly dont quite understand how this all works. My job is to build Laser engines, not faff about with an old OS. I have been doing this work all during 15 minute tea breaks and whatever part of my half hour lunch is left after i stuff my chops. Spending half a day getting one of the guys to write a program and make a cam cover is not really an option.

If the engine runs well then it might be worth doing a little extra work.

Sooo, does it run?

 

 

 

Bah! i just noticed the camera lost the plot half way through. Sorry for the loss of focus, not much i can do about that. 

Edited By Jon - Laser Engines on 16/04/2020 19:49:01

[paul d]

I'm not outraged at all Jon and just to set the record straight I spent 35 years working on high performance cars and engines including 20 years in F1 so will I'll refrain from calling my self a expert I do know a thing or two.

That cam cover is a half hour job including programming.

glad it runs!

[Ron Gray]

Keep posting your efforts Jon, the majority of us, non experts, enjoy what you're doing despite you not being in F1.

[Andrew Mawman]

I'm with you John, there's no need for comments like that, if it's not constructive why bother saying anything. I for one enjoy your forum comments and admire your engines.

[Jon H]

Posted by paul d on 16/04/2020 19:56:46:

That cam cover is a half hour job including programming.

Half hour is a touch unlikely. It will take that long to do the drawing. And even if it did take half an hour, who is going to pay for that? which machine shall i ask the boss to shut down and reset for a one off that makes him no money? Its a bit of a fantasy im afraid, especially when i have a hard time getting laser parts done as the machines are busy with all the other jobs that actually keep the company open.

I am sure the owners of your f1 team would have jumped at the chance to give the car development a rest and do you a one off for your own personal use :P

Ron, it seems to work rather well for an apparent bodge. Im really pleased with it in general but i am disappointed i was not able to redeem its cosmetic side. In retrospect i should not have shot blasted it but i didnt know at the time how badly damaged the ali was. Although i have not been uploading it i have been doing a similar but more in depth restoration of my SC400 radial. Blasting up those parts has made them look really nice so its clear something has really eaten up the castings on this little OS

Following the run there are some problems. its apparent both valves are leaking quite badly. The needle leaks as does the carb barrel due to the damage to the carb body.

Given that the engine apparently runs well i will track down a new cam cover (nicked from a scrap ASP52 i suspect) and fit it with the new bearing. I might get a new prop driver as the current one is a mess. The valves do need some attention to try and limit the leaks. My normal valve seat tool is too big so i will come up with something else. Given how grotty the seats are its likely to be a bandage on a broken leg mind. I will make a cover plate or plug for the hole in the cam chest and buy some O rings for the pushrod tubes. I wont bother replacing the carb as it seems to run fine even if its a bit leaky. Again this is a rustoration and not a restoration. Its never going to be good as new unless i replace it all!

[Jon H]

double posted

Edited By Jon - Laser Engines on 16/04/2020 21:18:28

[Martin Arnold 1]

Jon, Just out of curiosity what revs did it pull on which prop ? Wondered how it may compare with my two vintage versions !!

[Callsign Tarnish]

Ignore the negativity Jon, I've enjoyed following this second chance at life for the OS and your clear explanations. 20 years in F1 could have been catering for all we know

[Nigel Dell]

I am with the others Jon, keep doing what you are doing, it is relevant to what we do collectively.

Not a willy waving contest 😳🤭🤔🥴🥳😂

Edited By Nigel Dell on 16/04/2020 22:10:47

[Jon H]

Cheers guys.

To be fair there were other ways to get the job done, but i was dealing with scrap and moving for progress. The guy who sent me the engine was going to bin it so even tarted up and left on the mantle its a better ending for the poor thing.

Also if we ignore the shot blaster everything i did could be done by anyone in their garage with only the most basic tools. If that results in a working engine from a heap of scrap then im totally satisfied with that.

If anyone wants to do a full F1 spec rebuild then i will sit back and grab my popcorn for that thread.

As for performance i was seeing 10200rpm peak and holding 10k on a 10x6 apc prop and 5% nitro 15% oil fuel. According to the review i found here **LINK** its right on the money. Idle wasnt bad at 2500 but the leaky valves didnt help it at really low revs.

I will take a look at the exhaust valve especially and see what can be done. I wont be loosing sleep over it though if i cant make it any better.

[john stones 1 - Moderator]

I don't like popcorn, appreciate the extra threads people are posting though.

[cymaz]

Jon, are you in your shed or doing this using work tools. If the former then well done for getting the thing running. A bit of a quarantine project I assume?

Edited By cymaz on 17/04/2020 05:52:57

[Jon H]

Nah im doing it at work during lunch breaks etc but only using 'normal' tools. The only special tool i used is the sand blaster but the rest was done quickly and simply with only the bearings and conrod replaced as they were mission critical so to speak. Everything else is original although it didnt have an exhaust so i dug one out of my boxes of old junk.

There were loads of small jobs i did that i didnt really cover as they were the work of a moment. Cam followers etc were all polished up, as was the crank pin. The rocker shaft, gudgeon pin and cam follwer holes were all tidied up with a reamer.

If i had done the video i would have shown that stuff, but its not something i can photograph.

[cymaz]

I’m sure I’ve seen a piece on drifting bearings out by forcing in strips of cloth through the ID using a hammer and rod.