QuestionQUESTION: The B&S 18.5 in my JD1100 started smoking suddenly last summer when we were just about finished mowing the lawn. JD dealer wanted to replace the head for 500 bucks. I pulled the flywheel and checked the reed valve in the breather and it looked great, clean and tight to crankcase. I pulled the head and found some small cracks around spark plug hole, one in the exh port outlet and a possible one on the outside of the intake port. Other than the smoke the engine starts great, runs well, sounds good, no scratches on the cyl walls. But there was carbon build up on one side of the intake port near the valve. My gut feeling is that since I found a number of cracks on the outside of the head it could be cracked inside too. Are B&S heads really that bad or is there something I need to check before I drop 100 bucks on a head.
ANSWER: We have not had very many heads cracked on B&S engines. When you checked the breather and pulled the flywheel were the engine fins clean from dirt/debris/grease?
Are you using SAE-30 weight oil? Too much heat could cause the head to crack. Did you check Ebay for a used head? I'd be careful buying a used on as it may be cracked as well. Have you considered taking the head to a machine shop to see if they have seen any cracked head or may be able to provide some advice?
Eric
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QUESTION: yep, the fins were clean, under the breather cover was clean. The last time I ran the engine, a few weeks ago, I let it warm up for a few minutes, and had the air cleaner off and the breather hose was dangling. I didnt see any blow-by or oil come out of the hose. But I was running it at half-speed, and when I would rev it up or slow it down, it would puff a good amount of smoke out Running at half speed, there was no heavy smoke, just a hint of burning oil smell. The fact that it started smoking so badly, just all of a sudden, is odd. If a piston ring was broken, wouldnt the cyl walls be scored? Although it was very hot last summer, and yes I run SAE 30 in it,
ANSWER: I have seen rings crack without scoring or scratching the cylinder wall too bad. I have seen broken piston, above the wrist pin, not cause any damage to the cylinder. Do you suspect a cracked ring?
Eric
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QUESTION: well the cracked head theory isnt really looking like its correct, what else would cause a sudden amount of oil smoke ?
AnswerLoss of crankcase vacuum can cause mass oil consumption. Leaking dipstick o-rings have cause a loss of a vacuum...any significant crankcase seal leaking can cause a loss of vacuum. Briggs does not publish vacuum specs but vacuum is similar on most small mower engines.
Check out this video:
http://www.youtube.com/watch?v=AKaemaXp6gY
Eric
