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-   -   OS 1.20 Surpass wrist pin removal (http://www.rcuniverse.com/forum/glow-engines-114/11286808-os-1-20-surpass-wrist-pin-removal.html)

bigphil 11-04-2012 05:27 PM

OS 1.20 Surpass wrist pin removal
Looking for tips on getting a stuck wrist pin out of a OS 1.20 4 stroke. This engine was laying around for quite a while when turned over to me for some TLC. Everything was stuck solid when I got it. Caster goo-ed up pretty goodl I've torn it down to the bare case except the crank, piston, rod, and bearings. Cleaned it in the crock pot and then soaked it 24 hours in alcohol. All pretty clean and the piston is now free on the wrist pin but the wrist pin is still stuck in the piston. I've never had one this stubborn to get out and I'd like to check the bearings.

If there is an actual proceedure for removing the wrist pin I'd be interested in that. The similar Webra designs have the wrist pin threaded inside so you have something to get a hold of, OS didn't seem to have that much foresight. :(

I've tried making an L shaped tool to slip through the wrist pin and hook to the opposite end to try to pull it out but no go.

Maybe there's an easy way that I just don't know... Anyone?

w8ye 11-04-2012 07:11 PM

RE: OS 1.20 Surpass wrist pin removal
I've had pretty good luck with a #6 deck screw into the center of the wrist pin. It gives you something to grab onto

You might try working it back and forth some?

Eventually it comes out and you wonder what all the big fuss was about?

Bax 11-05-2012 06:54 AM

RE: OS 1.20 Surpass wrist pin removal
We use screw extractors, also known as "Easy-Out's".

earlwb 11-05-2012 07:59 AM

RE: OS 1.20 Surpass wrist pin removal
It could also be gunked with with old congealed castor oil residue too. I would suggest heating it up when you try the screw method to pull it out. Do double check and make sure that there isn't a locking cir-clip or snap ring in there you didn't see.

I do remember some engines in the past where the wrist pin only came out from one side, not the other. But I forget if it applies to your engine or not.

buzzard bait 11-05-2012 12:23 PM

RE: OS 1.20 Surpass wrist pin removal
Same problem on my OS 40 Surpass. There are no locking clips of any kind. Tried the Easy Out after treating the piston/pin overnight with PB Blaster and then heating with a torch...it was not easy and nothing came out. Easy Outs are really not designed for this. The pin is hardened steel and the Easy Out does not grip very well.

Do a search and you will find some very creative and often rather drastic solutions, including boring a hole straight through the crankcase or cutting the con rod. And occasionally you'll find someone who got one out.

This was an incredibly bad design choice by OS. If there is corrosion, it will lock up the wrist pin and you can be left with no non-destructive way to get to the bearings.


bigphil 11-05-2012 02:31 PM

RE: OS 1.20 Surpass wrist pin removal
Right, there are no clips on the removal side, there is one on the opposite side. If you haven't torn down an OS 4 stroke before, you have to remove the liner and then fish the wrist pin out through a hole barely larger than the pin in the cylinder casting. The rod will not come off the crank pin until the piston is freed from the rod.

I had already tried the easy out too and had the same experience as Buzzard, pin is too hard for easy out to grip. I had already tried the torch too with no help. I'm going to give W8ye's suggestion a try. Gotta find something to get it to twist in the piston and get a hold of it.

Like I said in my original post, there are Webra engines that use a similar disassembly technique but they have the wrist pin threaded on the inside. This might be an excellent suggestion to make to OS Bax! The threads need to go only part way through the pin so the screw will bottom and tighten in the threads to help twist and thus free the pin.

Thanks all. I'll report back...

bigphil 11-05-2012 02:55 PM

RE: OS 1.20 Surpass wrist pin removal
Well still no luck. The screw method still won't bite good enough on the hard wrist pin to get it to break loose. The good news is I've had it soaking in old fuel since I first posted and the bearing now feel pretty darn smooth.

I shot it full of PB Buster and will let that soak over night and give it one more try tomorrow. Maybe a slightly different screw would help too. I'll check around my junk drawers for alternatives. If I can't get it out tomorrow though, I feel pretty good about the bearings now and it's going back together to give it a try on the engine stand. [8D]

buzzard bait 11-05-2012 03:51 PM

RE: OS 1.20 Surpass wrist pin removal
Yes, it sounds like you can live with the bearings as is. Good luck with it.

I didn't try the deck screw either; mine is the 40 size and the hole is very small, so I don't think I can get one in, and if I did it would probably be the same problem as the Easy Out.

Did OS finally stop making engines this way? The whole experience has really soured me on OS four strokes.


bigphil 11-05-2012 07:22 PM

RE: OS 1.20 Surpass wrist pin removal
I actually haven't had any of the recent design OS 4 strokes apart so, I don't know for sure if the design is still consistent. Actually though, I'm not sure they can get around it with the cylinder/case cast as one piece.

gerryndennis 11-09-2012 02:59 AM

RE: OS 1.20 Surpass wrist pin removal
Hi Big Phil,

It's usually the rod that the wrist pin gets stuck in not the piston.

Try sliding the rod fore and aft on the pin before removing the liner. You should be able to hook a hex key behind the rod as high up as you can and gently pull the rod to the back then push it forward again. Do this after applying heat and solvents etc.

Also try running the engine. This often frees the pin right up.

Keep trying you will get it out

Cheers Dave H

bigphil 11-09-2012 04:49 AM

RE: OS 1.20 Surpass wrist pin removal
It was stuck on everything when I got it Dave but I was able to free it from the conrod with the antifreeze cook and alcohol soak as I mentioned above. I have used a allen wrench to work the rod on the wrist pin in the past as you have suggested. It was completely free on the conrod now but completely solid in the piston!

After the PB buster over night soak I still couldn't budge it even heating it again with a torch. The engine has been reassembled and will be on the test bench when weather permits. Bearings feel fine after alcohol soak and judging by the residue on the valves and piston this is a pretty low time engine. So I've lost interest in getting it completely stripped down. If it runs good it will be reoiled up and returned to the owner as is.

Thanks everyone for your suggestions.

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