Can it be done?

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mojoe
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Can it be done?

Post by mojoe » Mon Nov 23, 2015 8:55 pm

I got a buddy who is looking at a boat. AC 470. This will be his 3rd airboat and 1st A/C. He is taking his brother-in-law with him to help check out the motor. Concensus on here is to perform a leak down before buying any AC motor. I mention this to my buddy, he mentions it to the Bro-in-law. The Bro-in-law says he can spin the prop by hand and tell. I am a newbie, bro-in-law is a lifer, so I move on in the conversation. But I gotta ask:

Can it be done? I get the theory(I think), 6 distinct points of compression in 2 rotations. But can someone with enough experience actually feel the variance in compression enough to give the ok to buy with any certainty?
Mark 7:9

Afflicted
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Re: Can it be done?

Post by Afflicted » Mon Nov 23, 2015 9:06 pm

No. U can tell if they have compression but not how much. They all need to be within % of each other, a muscley throwing arm don't read true most of the time!
I assume he's an older guy an back in the day that's how they/he did it but there's better ways to know for sure

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scottyroll
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Re: Can it be done?

Post by scottyroll » Mon Nov 23, 2015 9:09 pm

Sure, a worn out engine with hardly any compression won't give up much of a fight but I think it would be worth it to have the actual #'s for each cylinder.

If the motor is shot it might give the buyer a good amount in leverage to go ahead an purchase at a steep discount.
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John Fenner
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Re: Can it be done?

Post by John Fenner » Mon Nov 23, 2015 9:48 pm

Absolutely, crank it up, do a mag swap at idle, then at say 1500 rpm, watch the breather(s) and get her hot beforehand, then let it cool for a few "20" minutes and pull it safely through knowing that engines are loaded like a gun, if she loads a hard pull on each one, go for it!
I never finish anyth,,,.

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kmr0290
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Re: Can it be done?

Post by kmr0290 » Tue Nov 24, 2015 7:06 am

Get it hot. Oil pressure,oil pressure,oil pressure,see how much it drops from cold to hot. Cyls and rings r easy to replace. Crankshafts and rod n main bearings,,not so easy.
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kwanjangnihm
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Re: Can it be done?

Post by kwanjangnihm » Tue Nov 24, 2015 7:51 am

a lot of good input! can you guys take the boat out and drive it for an hour or so?

get everything up to temp, run it hard, check the vitals, shut it down, crank it up and drive it some more!!

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" I don't care who you are back in the world, you give away our position one more time, I'll bleed ya, real quiet. Leave ya here. Got that? "

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mojoe
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Re: Can it be done?

Post by mojoe » Tue Nov 24, 2015 12:26 pm

Thanks for the info. I hope it helps him out.

I just sent this thread to my buddy.
Mark 7:9

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Re: Can it be done?

Post by jeepinocala1111 » Tue Nov 24, 2015 12:29 pm

Do a leak down test it is the best way to be sure or good luck cause I don't see to many ac motors for sale that are good unless your price is way up there in price even then do a leak down test.

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