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B&S 14.5 hp ohv valve problem.


redhead_men's Avatar
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Join Date: Apr 2007
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04-08-07, 09:01 AM   #1  
B&S 14.5 hp ohv valve problem.

My farther has MTD mower with a B&S 14.5 hp OHV engine. The engine will rotate freely with the spark plug out but it will not rotate with the starter when the plug is in. It will partially rotate and stop until the the compression leaks off and then will rotate until the compression stops it. My dad always keeps the oil clean and now it is very black after just 3 or 4 hours of running this year. When I took off the valve cover on the front of the engine I noticed that the valve rocker arms were very loose with a visible gap between the rocker and the valve stem. I also noticed that there was no oil under the valve cover. Could there be a problem with the camshaft and the oil pump? Could it be a valve adjustment nut problem since I saw some post about them working loose? Is it worth tearing this engine apart to check since it is 10 years old, but has only mowed one yard all those years. (3/4 acres) Model 287707 Type 0224-01 Code 9603124A

Any advice would be greatly appreciated. Happy Easter holiday to all.

 
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04-08-07, 09:36 AM   #2  
I would expect your engine is still good. The high compression is likely due to oil getting up into the cylinder. If the machine has been tipped, etc. oil can easily get to places it isn't supposed to and increase compression to the point where the engine can not turn over.

You could put a couple of tablespoons of gas into the cylinder, then try to start it. The gas will thin the oil out enough to allow the engine to turn over and you will get a big cloud of smoke that should go away quickly as the oil is burned out.

If you continue to get blueish smoke from the exhaust, as the engine warms up, you may well have an oil burning problem, seized or bad rings, bad valve guides, etc.

 
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04-08-07, 02:17 PM   #3  
Yes, the oil in the combustion chamber is possible, as backyard indicated, but it doesn't sound as though that this is your problem. Have you had the battery load-tested to determine the strength? Are all the battery cable connection (six total) clean and not corroded? And, related to your valve train, have you checked the valve clearances? They should be .004"-.005". You then need to confirm that the mechanical compression release (MCR) is functioning properly whereas when the pistion is approaching top dead center (TDC) on the compression stroke the bottom most valve will open slightly to relieve pressure for the starter. If the clearances are excessive the MCR will not function as needed. This series engine has had issues with the MCR camshaft wherein you will need to replace the cam if the MCR is not functional AND you know you have the clearances set properly.

 
redhead_men's Avatar
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04-08-07, 04:26 PM   #4  
puey61

I put a brand new 360 amp battery in the mower on Saturday. The visible gap on the exhaust valve was 3/16", the lower valve; which I believe is the intake, was also real loose but not as much. I did not adjust either one for fear of doing something that would damage the engine. If you could tell me how to adjust the valves to the .004-.005 clearance I would be very great full. When adjusting the valves should I have the piston at the TDC or slightly before? How do I make the correct MCR adjustment. Thank you and all who have and will reply.

 
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04-08-07, 09:09 PM   #5  
Wow! That's too much valve clearance, and definitely will cause your problem. Take a straw, put it in the spark plug hole until you feel it hit the top of the piston. Now, rotate the engine by hand clockwise until both valves are closed, and the piston is traveling towards the top of the head. Continue to rotate the engine until the piston begins to travel back down. Let the piston go about 1/4 of the way back down, and then set the valve clearances here. Use feeler guages to set the valve clearances. The nut is a 10mm, and there is a torx set screw in the center of the nut. Obtain the proper clearance with the nut, then tighten the set screw. Then recheck.


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04-09-07, 05:04 AM   #6  
FYI, there is no MCR adjustment, other than having the valve clearances set properly, that is. Also, setting valve clearances can be tricky and may take several attempts so be patient and be sure to get them set properly! By all means, before you button the engine back up, rotate the engine by hand and watch for the valve lift as I previously indicated, once you have the clearances set correctly.

 
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