Jump to content

Unofficial Home of Old Simplicity & Allis-Chalmers Garden Tractors

Sign in to follow this  
rich_kildow

Briggs L-head needs a rebuild

Recommended Posts

rich_kildow

This is engine out of my 88 Craftsman II 12hp and it is being replaced with a Vanguard 14hp single OHV, so no hurry to get it back in operation. This will be my first teardown/rebuild and I figure it will be a learning experience. Worst case, I screw it up beyond repair and am out a spare engine laying around. I'm hoping you guys can talk me through what I need to do to this thing.

It started smoking like mad occasionally last fall and it seemed to be random. I would be mowing with it and then no power, clouds of blue smoke, and extremely rough running. After a few seconds, it would return to normal and run like a champ for a good long time. Started getting more and more frequent until I could barely get it running. It started spitting an oil gas mixture out of the exhaust.

I have it out of the mower and partially opened up, I just need some longer bolts to pull the flywheel. The head gasket looked intact and the breather appears to function, but there is oil on the air filter. Combustion chamber appears to be uniformly covered in soot and the valves move properly (they don't rotate, not sure if they are supposed to) but are going to need to be lapped...tool is on order. The big thing I noticed is the oil must have had quite a bit of gas in it as it was way to thin and smelled strongly of fuel.

I know it needs the following:

Carb kit

Gasket kit

Valves lapped/checked for clearance

rings

new key on flywheel

Anything else to do while I'm in there or take a look at? I have the repair manual for it and other than a valve spring compressor, it didn't seem like I needed any particularly specialized tools.

Share this post


Link to post
Share on other sites
timflury

Thinned oil?? You just described bad piston rings. The smoking would indicate the same.

You won't really notice the valves rotating when turning the engine by hand, they will at speed. Check the valves while they are open and try to wiggle them side to side to see if oversize stems and reaming the valve guides is needed.

Inspect the cylinder wall for scratches and galling.

Take photos for your reference, LOTS of photos!!

There's reference charts and repair instructions you can download. You can never have too much paperwork!

Keep us posted!

Share this post


Link to post
Share on other sites
dentwizz

You will need a hone for the cylinder most likely and a feeler gauge for the measurements. Even when replacing the ring set(which will be a ring set and piston unit), I like to take one of the old rings and set it in the middle of the bore to find the ring gap. Some engines are more tolerant than others as far as displaying symptoms of smoke. One I just did had a ring gap of .5 inch when reject is .024sm00 It barely smoked at all. Depending on how much you would like to spend on tooling you could get bore gauges and a micrometer of appropriate size to measure for roundness, but most of the time it is not a big deal in my experience. Check the gap of the new piston ring set carefully after honing lightly since that is an aluminum block engine, just to make sure the gap is within tolerance as it may fall between sizes indicating the need to size up to the .020 oversize.

Share this post


Link to post
Share on other sites
rich_kildow

I have my calipers for reloading, so I'm guessing those will work. Let me make sure I understand this right...if the new ring gap is beyond the reject size, I need to go to an oversize setup, right? Is there a way to determine that before I order new rings so I can just order oversize if I need it? Does going to oversize require boring the cylinder or do I just go up to the correct size needed?

Share this post


Link to post
Share on other sites
dentwizz

The difference between standard and oversize is only .02" so precision counts. What I would do if accessable is take the block minus piston/rod to a machine shop and have them measure it. Some shops would do this for free or a low rate. If it is within the charted tolerance of the manual then go for standard. If it is past tolerance it will need to be bored and oversize piston/rings ordered.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Who's Online (See full list)

    • plastikosmd
    • NandoG
    • rbstuartjr
    • BLT
    • Bear
    • Baja24
  • Today's Birthdays

    1. Peter Hitchcock
      Peter Hitchcock
      (55 years old)
  • Recent Status Updates

    • F.U.N.

      F.U.N.  »  sandyhillbill

      Dear Sandhillbill
      Can you please copy me on this data, for Sun Star parts list.
      :
      September 12, 2004 Mike I sent you a PM and have all the mfgs. available for the tiller/hitch/pto/liftgroup if you need me to send them to you. Let me know. Thanks, F.U.N.    
      · 0 replies
    • gwiseman

      gwiseman

      Club banners are available  for members use during show season https://simpletractors.com/forums/topic/57849-simpletractors-club-banners-available/
       
      · 0 replies
  • Adverts

×