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Discussion Starter #1
I own a Toro CCR 3650 that is 7 years old. It has been flawless up until now.

The machine runs fine and throws snow a decent distance for a single stage machine.

Recently a hiss noise is developing. When you shut the machine off you can hear the hiss noise happen as the machine is winding down. It is not a constant hiss, but it goes hiss, hiss, hiss at a very rapid rate in conjunction with engine speed. When the machine is on you can't hear it.

When the machine is off, and you pull the starter rope just to turn the machine over without starting it, you can hear the hiss. As the pressure on the pull cord increases, so does the hissing noise. I am not a mechanic but enjoy tinkering. Is this a compression issue? What would the fix be? Thank you for your time.
 

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quick guess would be head gasket/loose headbolt/loose sparkplug

pull off engine covers/shrouds and spray on or brush on a soap and water mix. pull starter cord and see if you have bubbles
 

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Found at least one source of the leak. As you suspected the head gasket is releasing air. I haven't removed the head yet but after I sprayed it with the solution it wasn't even bubbling, but rather spraying the liquid out.

I just bought a new head gasket, along with a new exhaust gasket, and some other parts.

My winterization procedure consisted of running the machine dry. I think the gasket probably blew due to a lack of moisture in there. I will be fogging it in the future.

I will post back with what I find after tearing down the engine. I am saying my prayers.....

td5711, thank you for your guidance. I wouldn't have even tried the soap bubble technique without your suggestion.
 

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i think your engine has 4 head bolts, regardless of how many it has make sure you tighten them in a criss cross pattern tightening them a little each time around. if you can look up the engine manufacturer, see if you can look up a service manual so you can possible get the torque spec for the head bolts to see how tight they should be.
 

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Discussion Starter #5
I just found the engine service manual on the web. Thanks again. When my parts arrive I will keep this forum posted.
 

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Update:

I took off the head and exposed the gasket. The gasket had a "channel" burned through it that caused gases to escape when the piston moved back down the cylinder. I removed the gasket and replaced it. I used SeaFoam to clean the carbon off of the top of the cylinder and so far have replaced the head. The torque specs were 140-200 inch feet, not pound feet, according to the service manual. I will be reassembling the rest shortly. Once the pull start is back on it I will attach my compression tester and report back.
 

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Discussion Starter #7
Final update:

I replaced the head gasket, and while it was torn down I also replaced the muffler gasket, fuel filter, and spark plug.

Once fired up and warmed up I attacked a pile of snow and it performed like new. I want to thank you all for your help.

Attached are three photos of the head gasket. In the first photo you can see a channel on the left side halfway between the two screw holes. The next two photos are close-ups of the gasket. Any ideas what went wrong for this to happen?
 

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glad I could help

Probably nothing special. machines (even though computers are used) are not made to the same quality as the days of old. computers can get the tolerances exact but sub-par materials in the metals or the gasket could have created a hot spot or where the different materials in the gasket itself were not adhered to each other perfectly.

Couldn't hurt to re-torque the head bolts at the start of the season as well as maybe midway. there is a good deal of vibration in any motor. if you didn't put lock tight on the threads I would not take it apart but keep it in mind for anything on engines.

If it happens again get a new gasket and you will have to flatten the surfaces by hand or bring them to a machine shop to get rid of the low spot. chances are it was just the gasket.
 
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