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Old May 08, 2010, 08:21 PM
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Joined Apr 2010
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Compression? How to check?

Miss Elam is my first nitro boat. I think I got her broke in, but not sure.

Local hobby shop told me this, and I quote:

If you don't know what you're doing, maybe you should unload the boat before you do damage since one small mistake could do alot of damage. If you do screw something up, and decide to sell it, someone who knows about boats can simply check the compression and see the boat is worthless.
Ok, fair enough. I took my time, broke in the engine I think. 1 tank on pond, 2 tanks with homemade water cooling system, 2 more tanks on pond. It seems to scream for RTR out of box.

But I would like to learn about this "compression". What is it, how do I check it, and what calibrations should I expect for my boat???

Thanks, I really appreciate your advice!
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Old May 08, 2010, 10:57 PM
RC boat Rock Star
Kalamazoo, MI
Joined Apr 2004
3,008 Posts
Simple enough and you don't need any tools or gauges. Just turn it over and if it feels tight at TDC it should be fine. You'll feel that pop when it's good.
If you wanted to get all fancy about it then you could use a pressure gauge then check for leak-down/blow-by but the problem is that most boat engines have a tapered bore which can throw a wrench in the works.
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Old May 11, 2010, 10:18 PM
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Joined Apr 2009
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Do some searching around 1/8 scale nitro car sites, I've seen a compression gauge for sale but can't find it now. Don't know what a good reading (number) would be though.
The worst thing you can do is run your engine in a lean condition, that will kill compression quicker than anything due to over heating.
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Old May 13, 2010, 07:53 PM
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After much searching on this subject, I cannot find any relevant information - which leads me to one conclusion:

Not something I need to know about right now.

Thanks Ron, Thanks PAINLESS.
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Old May 22, 2010, 09:25 AM
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Joined Apr 2008
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You need a compression gauge to tell the exact compression. Every size engine has a different number. Smaller engines like yours has a low number and when the engine has gone past that number it will be junk. You can tell buy turnning the motor over the feel of the compression but you don't know the numbers when it was new to junk.
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Old Jun 10, 2010, 05:03 PM
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Joined May 2010
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I have pinched many sleeves mostly for 1/8 scale racers, my best advice to you is check the pinch when the motor is hot like rite after you shut it down. Just after you shut it down roll the fly wheel in the same direction the motor would run when started. At TDC you should feel a good amount of resistance if you can even get it through TDC, that's a good pinch. If you roll through TDC with very little resistance your pinch is going, a good sign your pinch is gone is when the motor is idling and shut down for no reason. Also keep in mind that you can have a good pinch and no compression, this can happen if you drop the element out of a glow plug and score the piston and sleeve I have past over a few of these in my time. I do have a compression guage but only used it once and thought that it was hurting the motor with out any fuel and oil running through it.

Good luck...
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