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"Problem" with an MECOA OS FP 40 Head

Old 11-01-2010, 07:22 PM
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goggijo2
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Default "Problem" with an MECOA OS FP 40 Head

Wondering if there is anyone out there who has used this head and / or might be able to give me some advice. I've put on the head and even with the contra piston right at the top, there seems to be too much compression. No fuel line connected, one drop of fuel in the carb and I get a bump after a few turns of the prop. A really good flick and she fires but almost immediately seems to lock up. And sometimes she really bites (now my non diesel buddies know why I wear that big red rubber thing on my flicking finger ). I have quite a load of diesels and it really feels like trying to start an over compressed engine.

Any thoughts ?

Thanks,

John
Old 11-01-2010, 07:34 PM
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Recycled Flyer
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Default RE: RE:


ORIGINAL: goggijo2

Wondering if there is anyone out there who has used this head and / or might be able to give me some advice. I've put on the head and even with the contra piston right at the top, there seems to be too much compression. No fuel line connected, one drop of fuel in the carb and I get a bump after a few turns of the prop. A really good flick and she fires but almost immediately seems to lock up. And sometimes she really bites (now my non diesel buddies know why I wear that big red rubber thing on my flicking finger ). I have quite a load of diesels and it really feels like trying to start an over compressed engine.

Any thoughts ?

Thanks,

John
I think that the guy you want to speak to is Jim Thomerson as he has had a few of these if I am not mistaken.

But are you using any head shims? And is the engine new and tight?

And here are the instructions for use -

http://www.mecoa.com/acc/diesel/40die.htm

Cheers.

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Old 11-01-2010, 07:47 PM
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erik58
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Default RE: RE:

you might put some shims in it.had the same promblem with a davis head on a os46. I put 4 shims in it to make it work. after a bit of running it lost some compression I pulled some of the shims and it runs really nice now. Erik
Old 11-02-2010, 12:51 PM
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Lou Crane
 
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Default RE:

Jim T had one - or a Tower 40 FP clone - in which I seem to recall either he, or someone else in a related thread, had the lower 'land' - below the O-ring that seals the contra - break. I think he also had the shaft's crankpin shear off. Diesels can be a bit more demanding than glows...

Jim knows engines very well. If his MECOA conversion head sat too deep into the sleeve, I'm sure he'd have shimmed it correctly. I haven't flown a MECOA conversion head for the OS/or clones, but it looks to be a well made part.
Old 11-02-2010, 05:13 PM
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goggijo2
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Default RE:

Thanks all. Got the engine used on ebay and assumed it was run in. Now I check the listing I see it was "only run twice". Think I'll get it a lot more loosened up on the glow head and give it another go. It does look a very well made part.
Old 11-02-2010, 10:47 PM
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Recycled Flyer
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ORIGINAL: goggijo2

Thanks all. Got the engine used on ebay and assumed it was run in. Now I check the listing I see it was "only run twice". Think I'll get it a lot more loosened up on the glow head and give it another go. It does look a very well made part.
So the problem was actually in the engine and not the head?

Just be wary about the long term survival of the crankshaft, they seem to break in front of the flywheel (again ask Jim about this) and there may not be much you can do about it but simply enjoy it while it lasts!

Good luck with it.
Old 11-04-2010, 08:13 AM
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goggijo2
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Yes, the head is fine, I think it's just that the engine is still very tight.
Old 11-04-2010, 09:44 AM
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Mr Cox
 
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Default RE:

One should be able to back off the compression to a level where the engine doesn't fire. If that is not possible you need to shim or shave some material off from the counter piston. Otherwise it will be very dangerous to run the engine as occasionally you'll manage to overprime etc.

Be sure to use fresh fuel, with ignition improver, and the safest prime is also to prime the side of the piston, no way to overprime it that way.
Old 11-04-2010, 05:13 PM
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fiery
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Default RE: RE:

Just in case anyone is interested, if you have an old OS 40 FSR or Royal FSR 40 (OS 40 FSR clone) these heads bolt right on.

So, you can use them on these ball-raced 40's.

Old 11-05-2010, 04:09 PM
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Jim Thomerson
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I didn't have any problem with the head fitting a Tower 40. It extended into the liner the same distance as the Tower 40 glow head. I had a problem with the shelf under the O ring breaking off. I bought the head at least 20 years ago, so this may no longer be a problem. I had crank breakage problems, which may be related to running a heavy hub. I now have the head on a Magnum Pro 40, with a homemade contrapiston, no heavy hub, and It seems to work fine.
Old 12-18-2010, 02:17 AM
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NM2K
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I tend to be Mr. Cautious in that I run the minimum amount of compression necessary for a good run and I creep up from the low side compression wise.
As was previously mentioned, but not expounded upon, fresh fuel will help preserve your engine. Why? Because chances are good that fresh fuel will have plenty of ether, which requires less compression to start and maintain running. If in doubt, get new, or add ether/ignition improver to what you have. Much cheaper than buying a new crankshaft.


Ed Cregger

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