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Old Nov 22, 2005, 06:34 PM
seanpcola is offline
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Magnum 91 XL 4 stroke


Can someone provide the specs for valve adjustment on a Magnum 91 XL 4 stroke or a link to the info? Engine was purchased used by a flying buddy, seems to run well but he wants to check everything over before flying it.

Thanks in advance,

Sean
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Old Nov 22, 2005, 06:44 PM
Robert Bauer is offline
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.004" both valves.
Old Nov 22, 2005, 07:17 PM
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Thank you Robert Bauer!
Old Nov 22, 2005, 10:32 PM
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Quote:
Originally Posted by Robert Bauer
.004" both valves.
Are you sure that's inches? I will have to go back and check, but I think that my Magnum 70 called for .04mm, which is roughly .0015". Like I said, I could be wrong...
Old Nov 23, 2005, 06:56 AM
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[B]Hillbilly, You are probably correct on the .04MM but I am sure you will not see any difference or bad effects between .04 MM and .004" in fact every time I noticed a need to adjust valves they were at about .010" or greater. I would rather go to the loose side of error in setting them than tight. A tight setting below .0015" could result in valves not opening enough and poor running. Just my personal experience.
Old Nov 23, 2005, 06:22 PM
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I agree, Robert, it would be better to be a little loose than too tight, leaves room for expansion when operating temperature is reached.
Old Nov 23, 2005, 06:49 PM
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How often do you check valve specs?
Old Nov 23, 2005, 08:42 PM
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Quote:
Originally Posted by Robert Bauer
[B] A tight setting below .0015" could result in valves not opening enough and poor running. Just my personal experience.
Actually, it's just the opposite. The tighter the clearance, the more the valve gets pushed open.........
Old Nov 23, 2005, 08:44 PM
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Chris -- I don't really know how often, but in the 4 years I am running my 91 I am sure I haven't done it more than 3 or 4 times. Some run their engine more often than other, mine has been run a fair amount. I generally run till I feel there is a loss in power, or till I just get the itch.
Old Nov 23, 2005, 11:34 PM
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Food for thought....when you run valves on the loose side in an ic engine,you change the relative timeing of the engine.Loose valves moves the maximum tourqe to a lower rpm.Good for large props that tend to slow engine down anyway.....Guy
Old Nov 24, 2005, 09:24 AM
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Thanks for the great responses from all of you!

Have a happy Turkey Day!!
Old Nov 24, 2005, 01:39 PM
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Hillbilly, the manual for my Magnum .70 specifies the gap should be in between 0.04-0.1mm (0.0015" - 0.004"). A 0.04mm feeler should slide through the gap, while the 0.1mm feeler should feel tight. Those are the 2 feelers included in the OS valve adjustment kit, by the way.
Old Nov 24, 2005, 01:43 PM
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On Magnum 70 and 52 as well as OS FS-70SII a .04mm (.0015") feeler gauge is a GO, a .10mm (.0040") is a NO GO. I'd assume that the .91 Magnum is the same.
Old Nov 24, 2005, 10:40 PM
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Well folks, we got around to doing the valve adjustment today. Set them to .04MM and the thing runs MUCH better.

Again, thanks to all.
Old Nov 25, 2005, 12:40 PM
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good to hear!


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