fc911c

I broke in the engine on the bench his weekend after running a good half gallon. I noticed that the engine didn't seem to tight when new and now there is no pinch at TDC when cold. I broke in engine following directions. Any ideas what happened? Piston and liner look good.

fuel S&W 15% with 4 oz caster added for breakin
Prop APC 11X4

Thanks
Frank

alan0899

G'day Mate,
First off, not enough prop, start with a 12x6, & fly it, I bet it screamed with the 11x4, & you may have over reved it for too long.
As long as it has good compression, the lack of pinch, doesn't mean anything.
Don't use too much castor, as it will cause varnish build up, a small amount is ok, if you are a needle tweeker, to help with lean runs.

babenson

How much did you spend on the .55? I just bought two OS .50 SX engines this year at $155.00 a pop. I just saw the new .55 on the OS site today.

fc911c

thanks for the quick responce

I am now running a 12X8 prop now, I does have compression , but feels a little soft. I think it was running around 14.800 when I tached it.

Why would running at that RPM cause that? Manual say 2,000-17,000 RPM could you explain?

I am running 21% oil after I ran the 2 first tanks with 23%.


Thanks
Frank

fc911c

149.00 at Tower

Thanks
Frank

Rudeboy

If it wasn't tight when new, it will not get any better over time. You'll just have to live with it... these things aren't hand fitted after all.

You will not hurt that engine by running it at 15000 rpm... lugging it down with a 12x8 on the other hand, doesn't sound too healthy. A 12x8 is a .90 size prop in my book.

alan0899

G'day Frank
If it starts & runs sweet, no problem, just because the maufacturer say it will rev to, whatever doesn't mean you can't damage the motor, if it is too lean, especially when new, I run between 18 & 20% Coolpower oil in all my motors, I don't use castor at all, I use 160FX, 61FX,2 x 46AX & FS120, put simply, don't run em lean, make sure, before you fly, that when the nose is raised, the motor pick up some revs, then it is rich enough to fly.
If it won't fly at this setting, then you need a bigger motor.
Enjoy.

alan0899

G'day Mate,
Get another book, that is a recomended prop for the 55 AX. I run one on my 61 FX.
If you ran a 12X8 on a 90, now that IS under propped.

DarZeelon

Frank,


If you ask Dub of Jett Engineering, he will tell you that for practical racing purposes, your engine has bitten the dust...

But for most people, if the engine puts out good power, idles well and starts easily; it is still good.


It just seems too soon for the pinch to be lost.
I have an engine with over 70 hours on it that still has a strong TDC pinch.


Don't do any break-in with less than 6" pitch. Cooling is impaired and reducing the diameter lessens the load without hampering the cooling. In this case, a 10x6 would load the engine like an 11x4.

speedster 1919

My Feedback: (3)

Are you sure your tach is working right? 12x8 is the perfect speed prop for a 90-91 size and at 14,800 to boot. I need to get rid of my 90's for a 55AX. I don't think an 11x8 would tach 14,800.

speedster 1919

My Feedback: (3)

ALAN you better get another book . OS website says 12x7 and 13x6 is the largest rec. prop not 12x8 and your 61FX is being held back with a 12x8 I bet a 12x7 and 12x6 would be a better match . OS has the breakin prop for a 61 at a 11x7

NM2K

My Feedback: (14)

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Castor oil only turns to varnish when the engine is ran too lean, which is precisely when the benefits of castor oil are needed.

If you are seeing varnish build-up, you are running too lean.

An 11x4 is a prop suited for a .32 or weak .40. NOT a .55.


Ed Cregger

Kostas1

Dar,
yesterday i tached my OS 65LA and can spin an MA 11x8 arround 12500.
What OS 55AX can do with the same prop?
Fuel was 10% heli.
Kostas

DarZeelon

Kostas,


I have not run this engine yet, but telling from the ~12K Guy was seeing on his engine, with a 13x4W, I would guess 12K is a good estimate for an 11x8 also.

downunder

Some engines will keep a pinch and some won't and it doesn't seem to make any difference to how they run. And as Ed said, castor only goes to varnish (a lubricant BTW) if you run too lean and hot. My break in fuel is 25% castor and then I drop down to 20% castor. The 11x4 would have been fine for running in and cooling is not impaired by it.

Sport_Pilot

The amount of pinch the engine has varies due to how well it cools, what fuel it was made for, how thick the sleeve, what material the sleeve is, etc. Some engines just do not have much taper and OS is one of them. Just because you cannot feel it by hand does not mean the taper fit has worn out, or that the engine is worn out. Many of my engines including those that had considerable pinch when new, have lasted longer and run better after there was no noticeable pinch left.

DarZeelon

I don't agree, Brian.

And this, for the same reason many engines in 3-D planes suffer from overheating while hovering.
Sufficient cooling is a result of higher pitch.

This is why people like Dub Jett, Dave Shadel, the late George Aldrich and several others including myself, tell you to use a prop with 1" less diameter, not less pitch, to reduce load for break-in.

JettPilot

My Feedback: (6)

Check your engine again, maybe your O.S. is starting to peel its cheap nickel lining like many OS engines do very quickly.

JettPilot

Iflyglow

My Feedback: (79)

That does not sound to good.[X(] Even my Tower .75 ($95.00) is allmost as tight now even with 10 trouble free gallons through it. With out the plug it still cannot beturned over by hand with the drive washer if you stop it at top dead center.
It still runs like a scolded cat.

NM2K

My Feedback: (14)

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I don't claim to have the answer. I do know that none of my OS non ringed engines ever had much pinch at the top, but they all seemed to run just fine. None were true ABC.


Ed Cregger

Flyer95

My Feedback: (1)

I have had a few both new and used OS non ringed ABN and true ABC engines and none of them had much pinch at TDC and all of them could be turned over by the prop washer. They all ran great and where very powerfull and I would not worry at all about it.

Harry Lagman

I second what Flyer95 and others are saying. OSs just don't usually have much if any pinch. For example, low use AX .46s have very little pinch yet have great compression even when hot.

I have a brand new, never run OS VF .61 that I can turn over through its "pinch" by thumb and forefinger on the prop washer. My lightly used VF .61 has no discernable pinch at all and yet has superb performance and compression at all operating temperatures.

alan0899

G'day Mate,
Maybe your book is out of date, mine came with the motor, not a web site.
Mine says, Sport 12x6~8 or 13x6~7. so I used a 12x6, 12x8, 13x6, & 13x7, on my Diablo, the best prop for the PLANE, not the engine, it didn't care, never heard it complain once, was the 12x8.

speedster 1919

My Feedback: (3)

Hi Alan it was the OS web site and mft's prefer web sites because in case of mis prints they can be corrected 12-7 And are you quoting a 55AX or a 61FX book ? On the high side of props it might be fine for a cub!!!!
http://www.osengines.com/engines/osmg0556.html

alan0899

G'day Speed,
I was talking about a 61FX, I said it was a good 61 size prop. OK.
And as far as the web site goes, in the Suggested propellor sizes section, it doesn't mention the 46AX, 55AX or the 120AX.
Catch ya.