Os max 61 4 stroke.....help!! - RCCanada - Canada Radio Controlled Hobby Forum
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Old 09-07-2016, 07:49 AM   #1
Mytmerc83
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Os max 61 4 stroke.....help!!


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As the title says I'm look for help with my old OS max 61 4 stoke. It's a sf of fs can't remember I have both 2 and 4 stroke anyways the carb o-ring is leaking nitro and I can find the o-ring but no one has one. Is it ok to just use a regular black o-ring that will fit?? Thanks
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Old 09-07-2016, 09:59 AM   #2
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Re: Os max 61 4 stroke.....help!!

The stock O-rings are standard Buna-N so should be fine. Just make sure if it has sat for a while that none of the original material has bonded to the inside of the tube.

You may be able to find them at a local hydraulic or industrial supply, but I found they seem to be of non-standard thickness and more difficult to locate.

For a quick fix you may be able to use a piece of fuel tubing that fits over the threaded portion and also over the outside of the tube.
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Last edited by Cougar429; 09-22-2016 at 07:06 AM.
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Old 09-07-2016, 10:07 AM   #3
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Re: Os max 61 4 stroke.....help!!

Thanks Gary, I've got a fair selection of standard and metric o-rings plus a/c o-rings and the a/c ones are all kinds of wierd sizes. As for the threaded part I'm not seeing any threads it's a straight tube into the top of the carb?
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Old 09-07-2016, 10:12 AM   #4
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Re: Os max 61 4 stroke.....help!!

I meant on the needle itself. If you can fit a piece of tubing that covers the needle and receptacle tube it should seal it for now.
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Old 09-07-2016, 10:18 AM   #5
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Re: Os max 61 4 stroke.....help!!

The high side needle is dry no leak there. Just the intake tube into carb. It runs ok....ish just leaks a little. I did a valve adjustment on it to don't think that had ever been done the valves were pretty close to double the clearance they should have been. Should get a little more power now and be easier to start. Will try to carefully remove the o-ring and try to match it up. Thanks again Gary.
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Old 09-07-2016, 10:32 AM   #6
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Re: Os max 61 4 stroke.....help!!

Ah, misunderstood your OP. If the O-ring between the carb and intake tube is faulty you would normally see a lean condition due to the air leak downstream from the carb. If serious enough you will be outside the adjustment range of the needles.

ps. If that intake tube has been off check where it seals to the head as the same aging condition can occur there.
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Old 09-07-2016, 10:41 AM   #7
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Re: Os max 61 4 stroke.....help!!

It is touch to adjust for sure. I pick the motor up in a rc lot I bought, threw it on and went now I'm trying to get it right. I have one more question if I may. I've run nitro cars lots, one of the guys at the field told me not to run pink nitro in the plane motors put blue in?? I know heli nitro is better then most be is there that much of a difference? I will also be stepping up to 20% for my saito 125. Just not sure which nitro to buy?
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Old 09-07-2016, 11:01 AM   #8
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Re: Os max 61 4 stroke.....help!!

I would be less concerned with colour than nitro content and lube percentage.

Helis normally run more nitro to increase the power/weight, but I have lived by the rule for planes that if you require higher than 15% to have enough power to fly you have mismatched the engine and airframe.

As for lube, unless specialty such as YS, 4-strokes normally require less due to their lower top end RPM. For years I have successfully run a fuel that contains 18% lube in both 2 and 4-strokes throughout the fleet. At first it was a mix of synthetic and castor, although the maker switched to all synth recently.

The difference is castor can tolerate higher temps and is insurance against lean run or inadequate cooling air conditions. It's messier and more work to clean.

If you have a tach, match the prop so your OS and Saitos peak at the mid to high 9K range on the ground. Do not go above that.

ps. I have a pair of the Saito 125's and they are very strong performers. You will notice some serious consumption until broken in so consider that when estimating flying duration. The second burned close to twice that of my first with more time on it and has since settled in.
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Old 09-07-2016, 11:34 AM   #9
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Re: Os max 61 4 stroke.....help!!

Again picked it up in the lot on a showtime 90. The showtime flys great just pull out of a hover is not there, the fuel also came with the lot so I'm assuming it's as old as the airframe. A valve was stuck open on the saito due to gummed up but fixed that adjusted valves it runs great, smoked like crazy with the old fuel so time to buy some new stuff and see how it flys, after I re-tune it of course. All the LHS has it 15% green for 4 stroke so I guess that made it easy. Thanks again Gary. If the weather holds by the time I'm off work I will pull the cowl, tune, and fly.
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Old 09-07-2016, 01:50 PM   #10
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Re: Os max 61 4 stroke.....help!!

Ryan, are you saying that your OS 61 fs is flying your showtime 90? If so you are way underpowered for that model.
If you don't find the correct o-rings and it is difficult because of their slender profile just seal both ends of the intake tube with silicone.

Also remove the backplate and check the bearing for rust. If the main bearing is rusty the front bearing will be as well. They should also be changed and will make a huge difference in the way the engine runs.



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Last edited by williame3590; 09-07-2016 at 01:52 PM. Reason: spell
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