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Discussion Starter #1
I'm sure I'll feel dumb when someone answers this but, here we go.

I have a K301AQS in a 1250. If the motor has "automatic compression release" how am I supposed to do a compression test on the motor to see if the rings and what not are still good?
 

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Thanks Jroy,

If I'm understanding this correctly. The 25 PSI I got with the throttle down and a battery that needs charged, on a 12hp motor with stock cam, means I probably have at least 50psi if not a little more.

I took the head off and see on the gasket where I believe there was some blowby. My buddy is getting a new gasket and putting it on this week (Thanks Steve) and after doing that and charging the battery I should be able to have a pretty accurate psi just by multiplying what the guage reads by two?
 

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I read that turning the engine backwards by wrapping a wrope around the pully or something and pulling would get an accurate reading.

I never tried it myself though.
 

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i wouldnt spin the motor backwards myself ...they are made to go clock wise for a reason ..If you spin it backwards it sucks the oil into the carb and the cyl you will get a higher reading yes but is that really accurate
 

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i wouldnt spin the motor backwards myself ...they are made to go clock wise for a reason ..If you spin it backwards it sucks the oil into the carb and the cyl you will get a higher reading yes but is that really accurate
What?

No it doesn't. It will suck air through the exhaust, compress it, then shoot the air out the carb. It can't suck oil from anywhere when you spin it backwards.

But yes, wrapping a fairly long rope around the PTO pulley, and giving a good hard pull backwards should give you a reasonably accurate compression number. Just make sure the ignition is off and the throttle is at max.
 

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What?

No it doesn't. It will suck air through the exhaust, compress it, then shoot the air out the carb. It can't suck oil from anywhere when you spin it backwards.

But yes, wrapping a fairly long rope around the PTO pulley, and giving a good hard pull backwards should give you a reasonably accurate compression number. Just make sure the ignition is off and the throttle is at max.

yes it can i have done it some motors if you spin them bark-wards will pull the oil out of the crank case ,,,not saying all them will but i have done it ...I always thought it was BS to till i tried it ..I did to a Tecumseh and a honda filled the carb full of oil and the breather ..it smoked like a pig for about 15 min after i got it going again ...Why they did that i dont know but they did it not up for a debate here just telling you what happened to me ..I dont care if he dose it or not ..It wont hurt it but he wont get a true reading if it dose back up
 

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I've got to call Marlarkie on this one.

The only way it is possible to suck oil out of the crankcase is if the rings, specifically the oil ring, have gone bad. This in and of itself would be an indication and result of poor compression.

So even if you were to get a little oil in the carb, it will be dispersed by the fuel and burned through the combustion process (assuming the compression isn't so low that combustion isn't possible).

In any event, I prefer a leak-down compression test as it provides the source (rings or valves) of lost compression.
 

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i think i figured out why it happened i had to think about had to go back threw my repair logs .It was about 5 years ago this happened ..I think it was the vent on the T.C it was a rubber hose and it was kinked a little as for the Honda i have no clue as of why it did it ..I have been in the trade for 10 years and haven't spun very many backwards to be honest and the 2 i have did this ...i will say i have shot a touch of oil in the cyl to do a comp test tho
 

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i wouldnt spin the motor backwards myself ...they are made to go clock wise for a reason ..If you spin it backwards it sucks the oil into the carb and the cyl you will get a higher reading yes but is that really accurate


I retract this info as i was not thinking proper i went back threw my repair logs and found why ..Not sure what i was thinking ..I will admit my mistake on this matter ..Opps ....I would do a comp test on it myself
 
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