21 hp Briggs with issues

13 years ago

So last season I had to take my Craftsman YS4500 to a shop to have it repaired as it was smoking badly while under any kind of load and the guys at the shop said it was the head gasket, fixed it and off I went. About three months later the mower became very sluggish and stalled in the middle of cutting grass. I promptly replaced the battery, spark plug, and fuel filter in hopes of a quick cheap fix. Not so much the case. I was able to get it started again, but at full throttle, the engine was barely above idle as though it was starved for fuel. I blew out the carburetor and tried again with no luck. Next I replaced the carburetor, again with no luck. So I began reading forums including this one and felt that I was more than likely dealing with maladjusted valves. So I decided to do the work myself. Upon removing the valve cover, the intake valve tappet fell into a vertical position, still connected to the stud which had begun to back its way out (yes, the stud not the nut at the end or the lock screw), but was no longer touching the push rod or the valve. Disturbed by the sight I decided to turn the flywheel by hand to see if everything else moved as it should. The exhaust valve and push rod appear to be fine and cycle while turning the flywheel, however, the intake push rod does not cycle at all. Not even a small nudge. My questions are, what would cause this and would I be better off buying a new mower/engine? The engine numbers are 331877-0805-E1, code 070316ZD

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Comments (8)

roadbike
13 years ago
I think you should take your lawn mower to another mechanic with a good reputation. He should be able to diagnose and fix the problem and save you from replacing more parts.
walt2002
13 years ago
Well you have a sort of strange engine. It does not appear on my IPL CD but have run across it before and finally managed to get close to it on the B&S site but not the type numbers you have but not important.

I would carefully inspect the rocker arm, push rods and the stud and threads in the head for damage. IF all appears well, I would reinstall the stud torquing to 85 INCH Lbs. using some thread lock which is relatively expensive but not nearly as expensive as taking to a repair shop. Also check that the valve guide has not worked up. Should not be more than 1/8" above the head casting.

B&S went thru some "Identity crises" around this period. The 33 engine appears to be a "stretched" version of the 31 series engines which had a letter in the model number. The 31C--- has considerable differences from a 311--- for instance.

I MAY have torque settings for that and I do have detailed instructions for valve adjustment for the 31 which I would use for the 33. IF you would like them, contact me at address below, put in proper format and remind me. Note that I am experiencing computer trouble at present so don't think I am ignoring you.

Walt Conner
wconner5 at frontier dot com
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I take it the warranty out by years? IMO that's why they put time limits cause they know most people won't put to many hours or do any maintenance on or in two years. When it won't start that's when you need to troubleshoot it. IMO first I would do would pull the plugs see if you getting fire at the plugs (pretty blue spark, no orangish and of course no spark) It you got spark spray carb. cleaner down the spark plug holes and see if it will start up on the carb. cleaner. If it fires of the carb. cleaner and dies you still have carb. issue or compression lost. I afraid you going to have to take the heads off and look in the comb chamber at the cylinder walls, valves and head gaskets. seems like your problem occurs after the engine heats up and of course that would be the ideal time to take compression when it quits also. my guess would be cracked head, or something causing it to loose compression, that;s why you need to take the compression when it dead, if you got 130 PSI or more then IMO the bottom end, valves are good but that IMO don't over rule the head gasket or cracked head. I would also take the cooling fin covers off and see if I see any sign of leakages before I go tearing it apart. there alot of engines that will fit Based on the shaft size and length Course it easier to get the same type engine (HP number not that important but hookups are. if they are the same then HP don't matter as long as it close to what you've got. Most problems with going with different brand are the muffler and starter setup and throttle cables arrangement and brackets and of course if it will fit under your hood cowl. For the price of honda you can get you another used mower. and fixing the old one if you can do it yourself would be the best choice money wise IMO.
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hdh3
12 years ago
I had a bent intake push rod so I replaced both intake and exhuast rods but now am having trouble adjusting the valves. I have set them to .010 because that is what I was told by a old timer but just cranks and back fires. Getting good spark and good fuel if I choke it when cranking it will kick back or back fire from to much fuel. model 331877 type 0805
tomplum
12 years ago
.004 is best for both valves. Check that the rocker studs are secure in the head and not loose. Also look closely at each of the valve guides inside the spring. They should protrude similarly from the top of the head. If not, you have a loose valve guide. I bring this up as that can bend the push rods.
walt2002
12 years ago
hdh3,

I have detailed instructions on adjusting your valves IF you would like them. Address below, put in proper format and remind me, model number of engine. The instructions include a compression release test along with other helpful hints.

I have the utmost respect for tomplum but do not agree that it is best to set both valves at .004".

My regular computer is off line for a couple more days, so if I don't respond promptly, it is because this back up computer has a problem.

Walt Conner
wconner5 at frontier dot com
homegrown55
12 years ago
The Briggs Check Chart states that Intake and Exhaust valves in that model range have both valves adjusted @ .004"-.006". The chart, however does NOT specifically list the 331877 model. Isn't it better to have the exhaust valve adjusted with a little larger clearance than the intake valve on these engines?
bill_kapaun
12 years ago
I know this is a bit old, but this MIGHT help with ID.
The 331877 uses the same crankshaft (but not piston or counter weight) as a 31C series.
From that, I'd call it a "bored" 31 series vs "stretched".

Same cam, tappets & push rods, but not head.
tomplum
12 years ago
I thought maybe hd responded. He's probably never to be heard from again. Yes, the 28's, 31's, 33's intake spec can actually be .003" which is desirable in the long run. The singles also for some reason have ex spec slightly greater than the twins. .005 by the chart is as tight as the engineer's like. If I remember right, repair manuals tell you to make the setting in the middle of the spec, maybe not all. BTW I believe the 33's head is the same actually as a 31 -when you get a new kit, it has both gaskets, which could be interchanged inna pinch anyways. Thanks for the kind words Walt.Check's in the mail... ;)

21 hp Briggs with issues

Comments (8)

roadbike

walt2002

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tomplum

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