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Briggs 18.5 Wont Start - Valve Issues?


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07-20-09, 08:22 AM   #1  
Briggs 18.5 Wont Start - Valve Issues?

I have a 2004 (I'm almost positive on the year) Cub Cadet LT1018 with a B&S 18.5 Extended Life Engine (31Q777). It has 214 hours on it. I got if from my boss when he bought a new one after this one had trouble.

He was mowing and it started making a "tinging noise". He stopped, checked out the deck, blades, etc. then tried to restart it and failed.

When trying to start it either turns over not at all, or very slowly. It sounds like one stroke really forces it to struggle (and possibly stop) then the next spins easily.

The battery is fully charged, the oil is full and fresh this season. He has performed all recommended maintenance.

Recently this mower ate one of the screws from the carb butterfly. He pulled the head and had the valves inspected by a solid local shop. He put it back together and said it never ran quite as well as before. Then, it died as detailed above, about two months later.

I'm thinking that this has a valve issue, but I would be very interested in your comments regarding the probable issue and a suggested course of action.

 
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07-20-09, 09:07 AM   #2  
Sounds like the valves need to be re-adjusted, The mechanical compression release is not functioning properly. Therefore the starter is not strong enough to roll the engine past compression stroke.


Good Luck

 
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07-20-09, 10:38 AM   #3  
Posted By: 31YTech Sounds like the valves need to be re-adjusted, The mechanical compression release is not functioning properly. Therefore the starter is not strong enough to roll the engine past compression stroke.
Thanks for the quick response! My understanding is that the valves being too far out of adjustment can cause the mechanical compression release to fail. Is that correct?

Also, what are the correct clearances for the valves on the 31Q777 OHV engine?

 
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07-20-09, 02:55 PM   #4  
Posted By: mharrison Is that correct?

Posted By: 31YTech Sounds like the valves need to be re-adjusted, The mechanical compression release is not functioning properly.

Yep.....





Good Luck

 
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07-21-09, 07:05 AM   #5  
Thanks for the direction 31YTech! It was indeed a valve issue, but not simply being out of adjustment. Although it wasn't as bad as you might expect after reading that!

The rocker arm stud for the exhaust valve rocker had backed out of the head allowing it to jump off of the pushrod. I tightened it back down (does anyone know the torque settings for this?) and set the clearance on both valves (the intake was loose as well). It fired right up and ran pretty well.

It is burning a significant amount of oil though. I think that this may be a product of the butterfly screw being swallowed as mentioned prior. The previous owner and a qualified mechanic checked the head, valves, and cylinder. They did not notice any particular issues with any although the mechanic did lap the valves. Neither of them noticed or felt any scoring in the cylinder wall. I'm thinking maybe it has a cracked ring.

I'm thinking about tearing it down and installing new rings even though it runs pretty well now. Does this sound like sound reasoning given its current performance?

 
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07-21-09, 05:58 PM   #6  
Posted By: mharrison (does anyone know the torque settings for this?)

Best to remove the studs and spay the threads and hole threads with carb & choke cleaner to remove any oil, Then add a drop of loctite to the studs then torque to 140-160 in. lbs.


If the engine burns quite a bit of oil but runs and sounds good (no funky rattles/knocks) you could throw a set of rings in that may help with oil usage. But.... De-glaze/re-crosshatch the bore before doing so to assure proper new ring break-in.

Also, Don't know if you do but don't use synthetic oil after re-ringing. Use dino for at-least 50 hrs. before going back to synthetic, This will help the rings seat properly.


Good Luck

 
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