Is this a blown head gasket?

[jlatenight]

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!

 

[ILENGINE]

Your description of the problem leans very heavily on a blown head gasket.

 

[jlatenight]

Thanks! Researched replacing a head gasket, and it doesn't seem all that difficult, so I think I'm up to the task! Thanks again for the help

 

[keakar]

Thanks! Researched replacing a head gasket, and it doesn't seem all that difficult, so I think I'm up to the task! Thanks again for the help

yep, its a really easy thing to do to replace the head gasket

its a fairly common failure

 

[Tinkerer200]

I can send you a Service Manual IF you like, address below, put in proper format and remind me model number and what you want.

Walt Conner
wconner5 at frontier dot com

 

[StarTech]

Thanks! Researched replacing a head gasket, and it doesn't seem all that difficult, so I think I'm up to the task! Thanks again for the help

Just remember Briggs increase the torque of these engine over what is in the service manual.

Torque increased to 250 in lbs using three stage step torque. So you basically torquing at 7 - 14 - 21 ft/lbs (20.83 if divide 250 /12)

 

[slomo]

Thanks! Researched replacing a head gasket, and it doesn't seem all that difficult, so I think I'm up to the task! Thanks again for the help

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.

 

[slomo]

yep, its a really easy thing to do to replace the head gasket

its a fairly common failure

Don't forget to lap the block and head. Must do or you will be doing this over and over and over.....

 

[jlatenight]

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

 

[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.