intake lift rod not moving that much

Michael_Gee

Michael_Gee

Member
I have a B&S Model 331777 for my Craftsman 917.28822. I noticed the other day that it was running a little rough, mostly at full throttle. Power would dip from time to time. I took off the valve cover, pulled the spark plug, and rotated the crack shaft both lifters moved but the intake was barely moving compared to the exhaust. I checked the lift rods and they were fine. I also checked the gap thinking this was the original issue and they both still seemed fine. My only guess is the intake came lob wore down but I can't imagine that's really the issue so I'm looking for more plausible ideas before I open the thing up.

Thanks in advance.
 
Let me ask a dumb question. You saying the rocker furtherest away from flywheel is barely moving?
 
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The cam lobes are only induction hardened so the hard facing is about 0.002" thick
It does not take much in the way of dust or grit in the oil to grind through it
Once the hard facing is breeched the cam lobe will wear round quite quickly .
Every now & then I see one like that.
However much more common is the inlet valve guide shifting in the head due to over heating .
The valves springs & guides are identical so should sit at the same heights off the floor of the rocker housing .
At the firing position the rockers should be parallel to each other .
 
It more likely the op is referring to the exhaust valve rocker. The 31 and 33 series will run with the exhaust valve barely opening. Take the air cleaner filter and they will sound like there is no muffler. I have exhaust lobe worn nearly round. This week I had one that sounded like but it was not a worn lobe but a rocker stud backed nearly all the way out. It had over 1/2 inch of clearance.
 
From what you are saying you have a worn out cam lobe on the intake valve. You can check the clearance on the valves and when the lobe is worn out it won't effect the clearance. Since there is no wear on that portion of the cam since there is no pressure on it from the valve spring.
 
A lot of these junk built up from segments camshafts had cam lobes which were not properly hardened. This was never a problem with the one pc. forged steel camshafts used for years by B&S. But they no doubt save a few cents with these plus they get a lot from selling replacements.
Walt Conner
 
hlw49 said:
It would cost a lot more to forge the cams and a lot more material.
Click to expand...
I doubt it would cost all that much more when they already had the equipment and the one item verses inventorying 4 different items to make a segmented camshaft. The big savings was having it made in China with Chinese quality.
Walt Conner
 
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