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arhick

Briggs twin has me baffled.

arhick
12 years ago

It is a model 406777 type0139. The engine seems to me to be losing power and it even sounds weak. One cylinder is weaker sounding than the other when I ground 1 plug, then the other there is a definite power difference. The compression is 180 on 1 and 150 on the other. Installed new plugs with no help. Others were not fowled out or anything.

Comments (15)

  • rustyj14
    12 years ago

    I'd say it is time for a re-build, or a new engine. You can only whip a dying horse for so long, until you find he has croaked, and you have to get a new horse!
    there are no magic bullets, nor magic additives that you can pour into the gas tank, or the crank-case to rejuvenate the engine you now have!
    This from an old guy with many years of experience with internal combustion engines, of the auto type!
    Ohh--way back after WW II, when folks couldn't buy new cars, and the old ones they had stored away looked like a wild garden inside, from the beans we kids shot at passing cars, as Daddy drove us on a trip., The automotive scally-wags came up with a product name of "Piston Seal"! It came in a lead tube, similar to a tooth-paste tube, and the idea was to remove the spark plugs, squirt a worm of the product into each cylinder, replace the plug, and VOILA! No more oil burning!! MMMHHH!! It worked , especially after dark, as you couldn't see the oil smoke!
    That was a one-time deal, but they made money! As Old P.T. said:" Well, you probably know what he said!

  • walt2002
    12 years ago

    " The compression is 180 on 1 and 150 on the other."

    Both of those are too high, perhaps indicating you have a gage problem. Not enough info to really help otherwise. What makes you think things are bad? Sounds weak?

    Walt Conner

  • arhick
    Original Author
    12 years ago

    Mr Rusty, I hope that it isn't ready for the boneyard yet! The sound is most off Walt. It isn't crisp sounding as my tractor engine, or I believe as this once was. Not a true miss as I would describe it either. Seems that it isn't as snappy as it was too. I don't run this particular tractor a lot. Others made a comment that it could use a tune up, so I grabbed new plugs and filter type things before I went to the property.

  • tomplum
    12 years ago

    If you don't have a valve opening on 1 side, you will get a high reading. Pushrod bent, possible loose valve guide, loose rocker type thing.

  • walt2002
    12 years ago

    "If you don't have a valve opening on 1 side, you will get a high reading. Pushrod bent, possible loose valve guide, loose rocker type thing."

    Good point, I suggest you remove the valve cover on the weak cylinder at least and see what is going on in there, see if everything is in place. Suspect you will find a pushrod off.

    Walt Conner

  • arhick
    Original Author
    12 years ago

    Interesting. Does it pay to pick up new pushrods and gaskets? I didn't have a way to bring the rider back with me. Walt, I still have instructions that you sent me for the valve procedure! So if there are parts and tools that might be out of the ordinary that I should bring then let me know. I will return this weekend with the trailer in tow in case I can't fix it there.

  • tomplum
    12 years ago

    Those parts are cheap, but you may need more- or none. Gaskets are a good idea to replace. Could this engine be run so occasionally that you are dealing w/ lots of deposits on the valve stems? have some carb spray with you and give some blasts into the carb throat as you are running it up. Do the valve inspection and lash setting first though as it needs to be cold.

  • arhick
    Original Author
    12 years ago

    I brought the rider home. We may be on the right track here, but now I am very puzzled. On the left cylinder (as I sit in front), the exhaust valve moves 1/3 as much as the intake valve- yet everything is tight. ??

  • mownie
    12 years ago

    ***"exhaust valve moves 1/3 as much as the intake valve- yet everything is TIGHT"***
    Tight before....or after the valve adjustment?

  • arhick
    Original Author
    12 years ago

    Sorry. Meaning that it has .006, maybe .007 clearance- no adjustment was done. The bolt is tight in the center rocker, jam nut tight- just poor valve action. The valve opens 3/16". The push rod is not bent. I can't help but think that a poor lift distance = a worn camshaft. But how can be a bad camshaft?

  • mownie
    12 years ago

    Briggs has had some bad experience with poorly heat treated camshafts at times, but I don't recall your engine being in that group.
    You have pretty well eliminated other problems by your description of the state of things.
    I guess the next step in proving would be to get the cam out and "mike" the lobes to compare to B&S specs.

  • tomplum
    12 years ago

    Has this been worked on before? Worn cam normally should show a large gap...

  • mownie
    12 years ago

    ***"Worn cam normally should show a large gap"***
    If the "wear" was only on the CAM LOBES due to poor heat treat or other defect in the metal, the valve lash would not increase. Valve lash or clearance is the result of the rocker arm NOT TOUCHING the valve stem, and thereby not placing any pressure on the camshaft at that time in the 4 stroke cycle. So the base circle (when the valve has clearance) does not experience additional wear and clearance does not increase.
    The high point of the cam (lobe) does experience accelerated wear and so the effective LIFT of the worn lobe decreases.
    Wear to the cam shaft bearing journals or the cam shaft bearings WILL cause an overall increase in valve clearance, but wear to those surfaces is seldom seen except in cases of lube oil failure or gritty contamination of the lube oil.
    But in those circumstances, there will be wear to all other engine parts as well.

  • arhick
    Original Author
    12 years ago

    It has to be unfortunately a camshaft. Not what I was looking forward to doing. Thanks!

  • tomplum
    12 years ago

    Mownie must be right that some cams wear that way. The only thing that I would add is to look close at where the valve guides come out of the head. Compare the distances between all 4 valves guide ends. There are enough issues on these to warrant an inspection whilst you are getting ready to fix things up. Not that this related to the other problem. Just watch closely as things come apart, mark where the springs come off or take a pic. Take your time on clean up. Good time also to remove the carb bowl and give a quick clean before flipping it all the way over.

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