QuestionI just bought a used Craftsman riding lawn mower for $500.00. Model #917270722 Serial# 062698D003730. It has a 17 HP OHV Briggs & Stratton engine, but the serial plate is missing, so I don't have a serial number for the engine. I mowed for the first time last weekend, but my sister checked the oil and gas. This weekend I mowed again, but the engine started smoking really bad. I guess it was a grey color. Anyway, it stopped dead and I had to push it to the garage. I waited a while and tried to start it and it won't start. I checked the oil and it was overfilled and the oil looked very light-weight or watery. Could the person who sold me the mower have put some kind of additive to the oil, so it would run for a time? Just so they could sell it? I'm afraid I've been screwed out of $500.00. Do you think this will be an expensive fix? I've read a lot of your answers in regards to engines smoking and I'm thinking it may be a blown head gasket. Is that expensive to have repaired? PLEASE HELP
AnswerKathy
If there is a watery looking oil most likely that is gas put your sniffer there and see if it smells likefuel. If it does then you have a carb problem. If you find the oil level over the full mark or higher than it was before, gas may be leaking into the oil due to a flooded carburetor - a stuck inlet needle or bad float. If this is the case, the oil will need to be changed once the underlying cause of the leakage is determined. (This is only likely with float type carburetors such as those used on the Tecumseh engines used in a variety of Sears/Craftsman models equipment.
4 stroke engines should produce virtually no smoke while running. At first startup of the season, there may be a few seconds of white/blue smoke resulting from the oil squirted into the cylinder at the end of last season (you did the preventive maintenance, right?) burning off as well as white smoke/steam from accumulated moisture. If you tip the mower on its side routinely (to clean out grass clippings, for example), oil may seep into the cylinder resulting in white/blue smoke at startup as well.
White or blue smoke while running may be an indication of an excessively worn cylinder or rings or a clogged or inoperative breather (the breather assures that there is always negative pressure in the crankcase - if not, oil can get forced up into the cylinder). Or, you may be using the fuel mixture for your 2 stroke weed whacker by mistake. I think the seller just sold you a mower with out knowing the problems with it.
Next time you want to buy a mower follow these guidelines
A used mower at a bargain price may not turn out to be such a bargain if you have to do extensive repairs. There are two types: the living and the dead.
If the owner claims the mower will start and is prepared to demonstrate, this is usually a good sign! However, first, take a moment to check the following:
(Disconnect the spark plug wire, and tie it safely away from the spark plug terminal to prevent accidental starting if you are doing anything more than looking.)
Check for significant oil leaks particularly around the main bearing at the blade/PTO end. This could indicate a defective oil seal or extremely worn main bearing.
Check the oil both for level and condition. If the oil level is low and/or really black and icky, the owner probably did not follow the recommendations in this document! The oil should also not smell of gasoline.
CAUTION: the oil will be hot if you check it after the engine has been running for more than a couple of minutes.
If there is gasoline in the fuel tank and it will start without undo effort, then there is an excellent chance that the engine is in good condition.
How much effort does it take to start? If 10 pulls on the starter cord are needed, this probably means that some maintenance, at the very least, will be required.
Check for unusual vibration and noise which could indicate an unbalanced, bent, or broken part. The blade of a rotary mower can be replaced easily and inexpensively if it is bent but any internal problems will be costly or time consuming to remedy.
Check for any unusual unevenness, surging, or sputtering. If there is more than one speed, see how smoothly the engine switches between speeds. Put it under load if possible (offer to mow some foot tall weeds) to see how well the engine deals with actual conditions that will be encountered during normal use. Problems here usually indicate at most that the engine needs some long overdue maintenance but it might help your bargaining position.
In most cases, if the engine starts reasonably easily, there will be no really serious problems. The ignition system may require a tune-up or the carburetor may need cleaning and/or adjustment. Even a hard-to-start mower may very likely restored to tip-top shape with this type of intermediate level maintenance. Of course, the blade may have to be sharpened or replaced.
If the engine doesn't work - no gas in the fuel tank and no handy gas can is usually a tip off of this - how can you be fairly sure that there are no major mechanical problems? Note that the objective here is not to identify **the** problem but to have a good idea of whether repairs will be really expensive or difficult. Thus, we won't even bother checking the carburetor or spark as problems in these areas are minor compared to those caused by internal mechanical damage. Here are some simple tests you can do without tools and without overly upsetting the people running the sale or junk yard:
WARNING: disconnect the spark plug wire and tie it safely away from the spark plug terminal if you will be doing anything under the deck. Yes, I know, there is nothing in the fuel tank but it doesn't hurt to be safe. Use a rag or proper work gloves if you attempt to rotate the blade directly.
The single most important test is to determine if the pull starter will rotate the engine without binding or unusual noises. If it doesn't turn at all or with great difficulty - and there isn't a clump of grass stuck between the blade and housing, there may be severe internal damage including broken parts or seized bearings. However, make sure that the blade brake is disengaging before walking away - it could be that simple (you did remember to grab the dead-man bar or set the throttle control to RUN, right?). There is also a very slight possibility that the starter itself is simply tangled or rusted and that the engine itself is fine. In this case, you should be able to rotate the blade and it should rotate the crankshaft.
For a 4 stroke engine, you should feel the resistance of compression once every two rotations of the crankshaft (blade). If there is a tough spot every rotation, the valves are not working probably due to broken teeth on the crankshaft gear or camgear. (For a two stroke engine, there should be compression on every rotation.)
If it turns too easily with minimal resistance (and the blade is actually rotating, not just the starter) - you should have an idea of the effects of proper compression on a typical mower - then there may be stuck valves, worn piston rings, or other internal mechanical damage.
If possible, perform this simple compression test: Spin the crankshaft is the opposite direction from normal. A sharp rebound on the compression stroke indicates decent and probably acceptable compression. Little or no rebound means that the compression is probably low. (This is actually the only compression test Briggs & Stratton recommends.)
If the cord pulls out with no resistance and doesn't rotate the blade, the starting clutch may just be broken - a very minor repair. Then, you will have to check for binding by rotating the blade itself (carefully).
If you found the starter cord broken, this could be minor and simply due to wear or forgetting to engage the safety bar once too often - or major resulting from attempting to start a broken and seized mower.
