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B&S 18.5 Intek OHV (Craftsman)


wallydog's Avatar
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07-23-08, 04:56 PM   #1  
B&S 18.5 Intek OHV (Craftsman)

While mowing, and without prior symptoms, the engine just died. When I tried to restart it, the engine turned over very fast as if it had lost all compression. I figured it was a valve issue. After describing it to the mechanic, he agreed, saying that the cam and/or valves on the OHV Briggs engines only last about three to five years before failing. At least he'd seen quite a few of them and he wasn't surprised. Any comments? I've searched the threads and couldn't find anyone with a similar problem. If I'm going to be looking at the same problem a few years down the road, I'd rather buy a new mower with a more reliable engine. Kohler, maybe?

 
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07-23-08, 07:43 PM   #2  
I rarely see the camshafts fail on these engines. The valves on engines with solid lifters require periodic maintenance (adjustments) regardless of brand, or you can have issues with the valves. If they get too loose the push rods can fall off the rockers, if the engine oil is not changed often enough or if you run old fuel, valves can seize in the guides.

Before you pass judgment on this engine, you may want to determine what happened to it, then you can decide if you should replace it or repair it.

You may want to remove the valve covers and inspect the valve train to see if its operating.

 
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07-23-08, 07:49 PM   #3  
Sometimes valves will stick open for other reasons, the most likely being a buildup of deposits in the valve guide.

Remove the valve cover and turn the engine over.

You may be able to see that a valve is stuck open, and its rocker is very loose.

Hold down on the end of the rockers over the pushrod to see if the cam is actually pushing the rods up as the engine is turned over.

 
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07-23-08, 09:18 PM   #4  
I agree, pull the valve cover and look to see if the valves are operating. If not, go from there. If the valves are operating, you've probably got a broken connecting rod (was the oil good and full?).

As far as the camshafts and valves giving problems....not under normal operating conditions with proper maintainence. If you never adjusted them, then they can get loose as 30yt said, and the pushrod fall out of the socket on the rocker arm. The valves should generally be adjusted yearly. The camshafts rarely ever fail. There were some that had compression release problems on the camshaft that caused excessive compression during startup, but that's about it. There are several of these single cylinder OHV engines out there that are 10-15 years old now...still running well.


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07-24-08, 01:59 PM   #5  
Thanks guys! It's in the shop right now, I'll let you know what happenned as soon as I find out. I'll have to admit, I never adjusted the valves but the oil & filter were changed regularly & it was full of rather clean oil. I did notice that, during this season, the engine seemed difficult to start at times because of the compression release problem that cheese had mentioned. How does the camshaft work to release the compression during startup and what might cause it to fail? I'll heed your advice; if there is anything I can do to prevent this from happening again, Ill do it.

 
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07-24-08, 03:26 PM   #6  
"How does the camshaft work to release the compression during startup and what might cause it to fail?"

The compression release I'm familiar with has a section of the cam that can be moved by a centrifugal weight/spring arrangement. At cranking speed, the spring pushes the movable piece so it'll open the intake valve when the piston is near top dead center. At higher speed, the weight moves so the piece so it doesn't open the valve.

There's a picture of teh mechanism in this thread:
http://images.google.com/imgres?imgu...en-us%26sa%3DN

 
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