High Quality Chainsaw Bars Husqvarna Toys

portable generator blues lots of hours already

Chainganger

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Here is exactly what happened.

Generator ran fine then just quit. I though maybe low oil shutoff. Nope.
It is an overhead valve 10 hp Briggs and Stratton engine. It had thrown one of those push rods that runs the rocker arms that works the valves. The other rod was bent some. So I got two new rods, set the lash and it started but ran like crap.
Got a new chinese carb, ran better but still rough.
Got a new magneto, ran a bit better but it is still missing some and is driving me crazy. Set it so it throws around 120 volts but it goes up and down some because of the missing. I can't stand it.

I really do not want to spend $100 or more for an oem carb, but is that the problem or are the valves themselves messed up so I would have to tear it apart?? Should I shoot it???
 

kfd518

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Problem I have noted and fixed mine was the original carb couldn’t keep up with wear on the motor. I drilled out the main jet slowly with a tip cleaning drill by hand and reassembled increasing size each time until I got it running Smooth and no missing or surging again. It was a generator I got for free from a friend who used it in his concrete business for many years before I got it. It runs strong and constant now. With constant frequency as well.
 

Chainganger

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Thanks for the tip, the only other thing I can think of is maybe a valve is sticking.
If it is a sticky valve should I run it and shoot spray sea foam in the carb while running?
Any other tips for a sticky valve?
 

Marshy

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Maybe valve timing jumped. Maybe that is why the push rod bent and now runs but like crap. I'd be checking valve timing.
 

kfd518

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Maybe valve timing jumped. Maybe that is why the push rod bent and now runs but like crap. I'd be checking valve timing.
Hadn’t thought about this, don’t play with 4 strike small engine much though
 

Chainganger

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I thought about timing too, I thought maybe the flywheel key sheared and messed up the timing so I pulled the flywheel, that was not it, key was good.
Enlarging the main jet did not work. In order for the valves to be off that would require a missing tooth in the gears or a jump, they are probably metal and it is not that bad, just occasional missing, like bad gas (no, that is not it wither!) .
I think the valve(s) themselves might be messed up.
 

kfd518

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How does the valve guide look on the head casting? Look like it’s backing out?
 

Chainganger

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How does the valve guide look on the head casting? Look like it’s backing out?

I embarrassed to say I do not know what that means, would I have to take the cylinder head off to see it? Is there a separate valve rod guide made out of a different metal that sometimes comes loose and messes things up and how is it inserted in there so it stays?

I think I may end up having to take the head off and valves out to figure it out. Are those valve spring tools expensive?

Here is another hint. When I start it up cold, there is no missing whatsoever for the first couple of minutes, only after it warms up does it start to miss and then only occasionally but enough to drive me nuts. I have small engine OCD.
 

kfd518

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Look inside the spring w the valve cover off. See if there is a little metal tube backing out inse the valve spring on the valve shaft.
Couldn’t tell you on cost of tool. Don’t own one myself. Just know it’s a common problem on OHV Briggs
 

Chainganger

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Look inside the spring w the valve cover off. See if there is a little metal tube backing out inse the valve spring on the valve shaft.
Couldn’t tell you on cost of tool. Don’t own one myself. Just know it’s a common problem on OHV Briggs

I think we now have a winner!

The cause of the bent push rod is the valve guide thimble is only press fitted, and easily loosens when the engine reaches a certain temp. The thimble then pushes outward, restricting the movement of the valve spring, eventually causing the push rod to bend. This is a design flaw in current B&S engines. I have no idea how long this flaw has been around. but it's quite a problem. They say it's because the engine overheats, due to restricted air flow, or inadequate oil maintenance, or ? But those who've encountered the problem often cite no problems with restricted air flow and always made sure the oil was changed frequently and kept topped off. In my opinion, this design flaw might be solved by removing the valve guide thimble, machining grooves in both ends, countersinking the head on both ends, then reinstalling the thimble with C clips on both ends. This would prevent any future movement of the guide thimble. I've yet to put this to the test, but something along this line needs to be done because this is a real problem, and new heads are currently at least $150. IF someone can solve this issue, I bet there'd be quite a market for rebuilding the heads.

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answered Mar 12 at 19:44

Daniel Earl Keith

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These engines are known for what I call "Bent push rod syndrome". The two most common causes of this failure are;

  1. Bad fuel (I have seen bad fuel cause momentary valve stick in large and small engines causing rocker arms to fall out between cam and valve or bent push rods.) Bad fuel can leave sticky deposit on intake valve.
  2. Poor maintenance (Oil breaks down over time and becomes very sticky). When metal heats up it expands. Valve guides with sticky oily deposits in them create a lot of friction/heat. There are lots of other scenarios that cause this but these two are the ones I have seen the most of in the last 8 to 10 years. I believe the ethanol in our fuel is the root of the problem. Tell your politicians to keep corn on our tables and out of our fuel tanks and there will be a lot less of these types of failures.
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answered Nov 28 '17 at 15:47

Back to you tube!
 

Chainganger

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the exhaust guide was backing out so now I have to fix it, thanks for the hint!
 

Al Smith

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Just a question .Are those valve guides aluminum or iron? I've never had an over head valve Briggs engine apart is why I ask .Having said that it would make sense the difference in thermal expansion would be the culprit and thus the cause it's iron in an aluminum head .Just a hunch .
I might mention on the opposed piston 16-18 HP models,flat head ,they had problems with the valve seats becoming loose .Hard steel inside an aluminum head .The fix was simple .Pound the seat back in place and dimple around it with a center punch then peen the aluminum over the seat .They won't come loose again .
 

Chainganger

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Just a question .Are those valve guides aluminum or iron? I've never had an over head valve Briggs engine apart is why I ask .Having said that it would make sense the difference in thermal expansion would be the culprit and thus the cause it's iron in an aluminum head .Just a hunch .
I might mention on the opposed piston 16-18 HP models,flat head ,they had problems with the valve seats becoming loose .Hard steel inside an aluminum head .The fix was simple .Pound the seat back in place and dimple around it with a center punch then peen the aluminum over the seat .They won't come loose again .

Yep, that is the exact problem. A steel guide inside an aluminum head. Now on these the guides stick out of the aluminum, both sides, by say 3/16 of an inch. One guy on you tube dimpled around the outside of the guide around the aluminum, nothing to fold over, I think I will try that.
 

Larry B

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The guides backing out is a common problem. On some heads you can drive the guide back in and peen around with a center punch. On others you can drive the guide out and use a center punch to dimple the outside of the guide to upset the metal and then drive it back in. I open my vise up enough to set the guide on top the jaws and slip and old valve in and then put about a dozen dimples in it and then drive it back in.
 

Chainganger

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Yep, but let me tell you when you do not ever work on a Briggs ohv engine and these symptoms show up it is tough to diagnose! I have a new carb and magneto that probably were not needed, but I learned alot anyway.

There have to be hundreds and hundreds of generators, lawn tractors and the like sitting dead in garages because of this problem
 

Larry B

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Yup. I run a small one man mower shop and see them a lot. All the Briggs have valve train issues and all the Kohlers have ignition issues.
 
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