Craftsman Model #917.287121 with a B&S Model #31P977-0635-E1. It smokes like crazy, but not consistently. It will slow down or stop all together for a minute or two, then start back up again especially when there's a load on it like when I start the blades or speed up quickly, but it can start billowing smoke any time. If I pull the dipstick out, a whiff of smoke comes out, but it doesn't smell like gas. The valve lash was way out of spec, so I fixed that but it didn't solve the problem (may have helped tho, not sure). When I took the rocker cover off, a decent amount of oil leaked out. I'd say maybe 1/8th the volume of the chamber or so. Seems excessive, but maybe that's from the mal-adjusted valve lash? Do you think I should go ahead and assume it's the head gasket, and put a new one in? I'm mechanical, but have never done one. Is there a good step by step somewhere? Thanks so much all!
Um, replacing the gasket, as you say it, is simple.
Prepping the block and head takes time. You will need to lap the block and head with 220, 400 then 800 grit wet/dry paper. Let the paper do ALL THE WORK. These parts are soft aluminum. Spray bottle with soapy water and a small sheet of plate glass. Most likely these two surfaces will not be flat. Never seen a flat one yet. Reset the lash, clean up the valve cover and such. Make sure you set the valve lash proper. There are 2 TDC strokes on a 4 stroke engine. TORQUE the head bolts to factory specs is a must.
So I replaced the head gasket, but it's pretty much acting the same way. It sounds really "pingy". Pretty obvious ticking more than other similar motors I've heard. It's starts smoking only after like 15min of running, then it's pretty steady and relatively heavy.
I honestly didn't see these additional posts since #4. I scraped the surfaces to remove as much of the old gasket as much as possible and checked the valve lash. You think I should do it again and lap the block with sandpaper and glass to check for even-ness? Could it be worn out piston rings? Thanks for all the help guys.
Walt, I'm going to take you up on the service manual offer while I have the opportunity
#10
sgkent
the head and block must be flat and all bits of the sandpaper grit removed. I stuff a damp paper towel in the cylinder to catch what it can. As said by another, let the paper do the work. Make figure 8's, rotate it every few passes. That helps keep it flat and not heavier on one side than the other. On the engine, walk around it to sand from different angles. You can make some sharpie marks to show you high and low spots. Last, be sure to torque in 3 steps using the proper pattern, otherwise you may not get a proper seal. I follow the pattern 4 times, then the 5th go around the head in a circular pattern to make sure I hit all the bolts. On the 4th and 5th pass nothing will tighten. Do not over torque either.
So I did the gasket again and I made sure I cleaned the surfaces really well. I torqued it down evenly too. I noticed one of the two valve caps was missing, which would explain why it ran, but sounded horrible. Now, it runs great and sounds great, but it STILL blows white smoke. It comes and goes while it's running, and I notice it always happens when I put it to full throttle, and when I engage the blades, but comes and goes while I'm mowing. I did the head gasket twice, so I'm going to eliminate that as a possibility, so now I'm wondering if it's the piston rings? It's some kind of blow-by, right? Could it be the carb is gummed up and too much fuel is going through? I'm going to see if I can rig up a cylinder pressure test to see if it holds pressure. Any other suggestions?
1.Oil level EXACTLY on the full mark or slightly below?
2.Is this on a rider? Tires aired to proper specs? Trying to get an accurate oil level check here.
3.Compression and leak down on oily cylinder should be looked at.
4.Didn't mention anything about lapping the head gasket areas.
5.Could be rings. Do #3 and find out.
6.A rich carb would blow black smoke. You said white which normally is coolant. Gray/blue is oil burning.
7.Bock and cooling fins clean? Might of caused this entire thing. Lost valve stem cap and leaking head gasket. Overheats strike again.
#14
Fish
Run it a while and keep an eye on the oil level, it takes a while sometimes to burn off excess oil after having an engine off and upside down.
#15
sgkent
Now if you could control the timing of the smoke maybe you could hire yourself out to sky write while mowing yards........
