18.5 Intek no compression

16 years ago

My father in-law has a Craftsman mower w/ a B&S 18.5 Intek Plus engine. Model 31P777,Type 0348E1, Code 040205ZD. Engine has 118 hours, well maintained. Engine was working fine when he shut it down to drink some water. 15 minutes later he tried to start the motor and it turned over strong without starting and kept backfiring. After thorough investigation, motor has good fuel delivery, good spark. I researched this site and found that I needed to check the valves. Upon inspection I found that the exhaust valve was severely out of adjustment (almost 1/4 inch between valve and rocker arm, pushrods seem to be straight) I figure that this is more than just an adjustment problem. Anyhow, I adjusted valve lash with piston 1/4 inch past (clockwise) TDC. Again turns over strong just no start and lots of backfiring. Using a compression gauge I discovered the motor has 0 compression. Could the comp. release be stuck open, blown head gasket? Any ideas would be greatly appreciated. Thanks, Kent

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Comments (9)

fish40037
16 years ago
overheated, valve seat fell out.

or valve stuck....

Fish
walt2002
16 years ago
Yeah, remove valve cover and see if valve action looks OK.

Walt Conner
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kenter
Original Author
16 years ago
Valve action seems normal. I rotated both push rods in place and they do not appear to be bowed or bent. If the valve seat fell out, would that cause damage? and can I just press it back in? That would certainly explain the lack of compression, but then again the valve action wouldn't be normal would it? Does this engine have a auto compression release? Thanks again for your help.
Kent
fish40037
16 years ago
Do the valve stems come out to the same height when the
rockers are not depressing them?

Does your model have little spacer caps on the valve stem?

Cranking with a stuck valve can destroy your engine, so I
would suggest you stop cranking.

The compression release only reduces the compression a little, you would have some compression.
walt2002
16 years ago
Fish, where the heck have you been? (Or is this a different Fish than I am thinking of)

Walt Conner
kenter
Original Author
16 years ago
Hello Fish and Walt, yes I believe the valve stems are equal in length at TDC. Yes the stems have a small spacer "Shim" on them. I checked the valve operation with the spark plug out and engine cranking over and it appears to be normal. Could the lack of Compression be a blown head gasket?. I don't understand why the exhaust lash would be out of adjustment over 1/4". I'm concerned for mechanical damage, but I don't hear any grinding or clunking noises, everything appears to be normal. I suppose I should take the head off to have a better look! Again, I really appreciate all the help.
Kent
walt2002
16 years ago
"Could the lack of Compression be a blown head gasket?."

No, not NO compression.

"I don't understand why the exhaust lash would be out of adjustment over 1/4". "

Check the Rocker Arm Stud, is it tight in the head? Check Rocker Arm for crack.

Walt Conner
kenter
Original Author
16 years ago
Found the problem. It turns out that the Exhaust Valve was sticking open. In hind sight that makes sense because of the 1/4 inch gap between the rocker and push rod. Got the valve to seat properly and proceeded to properly adjust both valves again and she started right up and purrs like a kitten. I consider myself a parts changer, not a mechanic, so that helps explain my oversight. Thanks again for all the help, my father in-law is very appreciative as am I.
Kent
walt2002
16 years ago
"Found the problem. It turns out that the Exhaust Valve was sticking open."

"Got the valve to seat properly and proceeded to properly adjust both valves again and she started right up and purrs like a kitten. "

You need to use something like Marvel Mystery Oil per instructions on the can for a while or it is likely to stick again.

Walt Conner