twoturnspin

Hi,

I have a OS70 which needs to have it's bearings changed. Does anyone know where I can access instructions for this job? I'm told it is prettty easy but I sure would like some instructions to make sure I get it right.

I also notice there is rust on the top of the piston (looking in with a torch when the glow plug is out), should I just ignore this or do something about it?

All help much appreciated.

Best regards, Simon

William Robison

My Feedback: (3)

Simon:

No rust on the piston, just discoloration. Not to worry about.

Searcch "Bearings" here, many posts about it.

Bill.

twoturnspin

Thanks Bill, appreciate the response.

I have read heaps of the posts but there doesn't seem to be a step by step guide which is pretty much what I am looking for. I'll keep looking through the files as you suggest.

Regards, Simon

William Robison

My Feedback: (3)

Aussie:

Is yours a two stroke or four? Disassembly and reassembly are different, for obvious reasons.

Two stroke:

1) Pull the head and back plate, mark the cylinder liner and con rod so you can get them back in the same position.

2) (A) If your engine will allow you, slide the con rod to the rear and disengage the crank pin, pull the rod and piston out through the top of the engine. Do not remove the cylinder sleeve.

2) (B) If the rod wont come off the crank pin pull the cylinder sleeve, then the rod will come off.

3) Pull the prop drive washer, press the crankshaft out to the rear. You may have to use a hardwood block on the end of the crank and start it out with a few light taps from a hammer.

4) Find a wooden dowel that's a fairly close fit through the rear bearing, and long enough for you to push on the inside of the front bearing.

5) Set your oven to 275F, cook the crankcase for about 20 minutes while you find a hardwood block 6" square or larger.

6) Using suitable protection for your hands take the case from the oven and tap the rear on the hardwood block, the rear bearing will come out. Stick your dowel in and push the front bearing out.

7) Clean everything, being careful to retain the marks you made on disassembly.

8) Reheat the crankcase and install the new bearings. Finish in reverse order of disassembly, observing your match marks.

If yours is a 4s engine it's mostly the same, adding the camshaft and valve gear. On a 4s put the push rods, tappets, and rockers back in their original positions also. Be sure the cam shaft is out before pulling the crank. I use two separate baggies, mark one as intake and the other exhaust, for the valve gear parts.

Bill.

twoturnspin

Hey Bill,

Thank you for the excellent advise, really good, I will get started on this tonight.

All the best, Simon

twoturnspin

Hey Bill,

Got most of the engine apart but have two issues currently:

(engine is a OS 70 Surpass 4 stroke)

1. Can't get the con rod off the crankshaft. I have removed the linerand can get con rod about half way off the crankshaft but no further. I was concerned about damaging the copper bushing that lines the hole in the con rod and so didn't want to lever it off too hard. Any ideas here?

2. I got the cam shaft out but slipped and are now unsure as to the exact position it should go back relative to the crankshaft location.

Any ideas?

Simon

JimTrainor

You need to pull the piston pin. Look for a hole in the back of the crank case just behind the carb. You need to lift the liner then pull the pin through that hole. The one time I did it I used a tap to grab the pin and pull it out.

OS have an entry in their FAQ list concerning cam timing: http://www.osengines.com/faq/product-faq.html#q15

w8ye

My Feedback: (16)

Be careful removing and installing your bearings. Our model engines are actually very delicate

Enjoy,

Jim

twoturnspin

Thanks all for the excellent advice, I will battle on and get it all back together!! (fingers crossed)