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26 GT Problem

Old 11-10-2008, 01:09 AM
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nate1001
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Default 26 GT Problem

I went to start my plane today and noticed it was very rough to turn. Last time it flew about a month ago there were no problems. I disassembled it to find out the pin on the crankshaft was hitting the backplate. It almost seems like the bearing in the connecting rod has moved out a little bit. Is there supposed to be a gasket on the backplate? Mine just has an o ring. If there was a gasket, there would be more clearance. Any ideas? This motor only has about a half gallon through it
Thanks
Old 11-10-2008, 06:15 AM
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Default RE: 26 GT Problem

Nate,


I suppose your engine is an Evolution 26GT.

First, regarding the O-ring; newer engines use it to replace (not to augment...) the back-plate gasket.
So, the fact that your engine does have the O-ring means it neither needs, nor is it designed to use a gasket.

Also, the thickness of a compressed gasket is less than 0.1 mm and it is hardly the type of material to act as 'a spacer'...


It is much more probable that the rear bearing is prevented from being fully seated in the crankcase, by a piece of grit, or a burr.
...Or that the crankshaft is being prevented from being fully seated in the rear bearing's inner race by the same...


Also, there is an unlikely event of the big-end bearing bulging out and its retainer contacting the back-plate...

It would be very helpful, if you could take some good quality close-up photos, of the back-plate and of the open rear of the engine and post them in the thread, for our reference.
Old 11-10-2008, 06:06 PM
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Default RE: 26 GT Problem

You can do 1 of 2 things. 1) remove prop, use a socket that will slip over the crankshaft and rest against engine housing, tighten prop nuts until crannkshaft is reseated. or 2) ship to horizon for warranty repair. This happened to my evolution 26 cc and
i opted for #1. then about 2 weeks later I called horizon and notified them of what had happenned and they had me send it in for repair. I got the engine back in 2 -3 weeks along with a listing of parts that was replaced.. The same problem is also happening on the MVVS 26cc.
Old 11-10-2008, 11:17 PM
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nate1001
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Default RE: 26 GT Problem

Heres pictures. If the crank isnt seated, what would cause the crank to move? Ive been using this motor for a couple of months without a problem
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Old 11-11-2008, 01:56 AM
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Default RE: 26 GT Problem

Nate,


The damage to the back-plate is superficial, but it does prove the crankshaft is not properly placed...

Since your engine is new, I would suggest sending it back to Horizon, even though you can probably overcome this issue by yourself.


This is covered by warranty, while any damage done to engine parts while you disassemble/reassemble it will not be.


You will need to fully disassemble this engine, to make sure everything is correctly assembled, including the removal of the rear bearing.

I suspect it is this bearing's improper seating that causes this rubbing; and if you look at the side of the retainer, diametrically opposite where your arrow point; it shows rub-marks as well.


The front bearing is what axially locates the crankshaft and it is, by design, seated as far back as possible in its seat at the front of the crankcase.

The inner race of the front bearing must be held very firmly between the crankshaft's 'step' and the prop-driver.


The only thing that would allow the crankshaft to slide rearward, is if the prop-driver, which is located on the crankshaft by a Woodruff key, is somehow prevented from moving all the way back against the front bearing's inner race.

This can happen if the rear bearing is held away from its seat, or the crankshaft is very firmly kept off from fully mating with this bearing's inner race...
But this would have happened immediately (not after using half a gallon...).

Once the bearing is seated, it will not pop out... There is no reason for it to.

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