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Compression with plug removed??

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I’m perplexed and need need to be educated apparently on 4t dirt bike engines
While checking my valves for the first time on my ’15 500exc I attempted to turn the engine over using the kick starter. Realizing it was too difficult to turn over I removed the plug to make it easy and it didn’t make a bit of difference! I still struggle pushing down on the kick starter and I hear air hissing just like the plug is in.
So please tell me what’s going on here
Signed,
Very confused

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Just to be clear; you are referring to the spark plug I assume?

Also check your crank case vent, make sure it's not kinked or blocked. 

 4T motors will have some resistance even with the spark plug removed, the oil rings, opening the valves and turning the oil pump adds drag that you don't get with a 2T.  But hissing air sounds like you're still building pressure somewhere. 

Edited by sirthumpalot

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you'll still have to fight the spring pressure from the valves, but is should be markedly easier to turn over.  Check the bike over for anything obvious...

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7 minutes ago, sirthumpalot said:

Just to be clear; you are referring to the spark plug I assume?

Also check your crank case vent, make sure it's not kinked or blocked. 

 4T motors will have some resistance even with the spark plug removed, the oil rings, opening the valves and turning the oil pump adds drag that you don't get with a 2T.  But hissing air sounds like you're still building pressure somewhere. 

Yes, spark plug removed, and hissing air like building pressure

I can see the valve springs playing a part because the cranking gets easy just before TDC but the hissing is nuts. Is the valve cover the vent your referring to?

Bike runs fantastic btw

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Yes the vent from the valve cover to the air box on the EXC models. Does it still hiss with the valve cover removed or loose?  
 

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9 minutes ago, sirthumpalot said:

Yes the vent from the valve cover to the air box on the EXC models. Does it still hiss with the valve cover removed or loose?  
 

Yes

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7 hours ago, gitenby said:

I’m perplexed and need need to be educated apparently on 4t dirt bike engines
While checking my valves for the first time on my ’15 500exc I attempted to turn the engine over using the kick starter. Realizing it was too difficult to turn over I removed the plug to make it easy and it didn’t make a bit of difference! I still struggle pushing down on the kick starter and I hear air hissing just like the plug is in.
So please tell me what’s going on here
Signed,
Very confused

put the bike in 6th gear, and bounce the rear wheel around, unless you installed a rekluse, then you have to go a different route  hissing is normal

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Had this great explanation in KTM talk. 

 Originally Posted by DJH 

"Hissing is likely the crankcase venting. Piston goes down air under it has to go somewhere, if my memory is correct the 500 has a very small hole to the ignition area to allow air to flow (the crankcase is under vacuum created by the left side oil pump when the engine is running. By having it in a vacuum it eliminates the need to rapidly move air out as the piston goes down which would cause a parasitic loss)"

Thanks guys! Appreciate all the feedback 

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It's a huge piston with a tiny spark plug hole. How many hours? If it's running great and not high hours, I'd forget about checking the valves. I've ridden many bikes with 150 to 200 hours that have never had the valves checked.

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