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Garden Tractors / Mowers / Scooters

Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods


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  #1  
Old 12-16-2018, 06:48:44 PM
R Davis R Davis is offline
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Default Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

The 10 HP OHV Briggs is off an older Simplicity snow blower that's been "fixed" a couple of times, but as soon as it's fired up, it backfires and breaks things again.

A buddy's asked if I'd try to fix it and from what I've read, it's either a valve seizing in the guide, or a valve guide that's come loose and causing the piston to hit the valve

I'm no expert at this and that's why I'm here, I can buy a new head with valves and guides already installed, but it's not cheap and I want to make sure there's nothing else that could cause what's happening so I don't waste this guy's money.

Thoughts? And thanks!
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Old 12-16-2018, 07:08:38 PM
Heins Heins is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

It sounds like a valve in head engine. Make sure the valve clearance is adjusted properly. Does it have valve clearance when you turn the engine by hand? Can you turn the engine over by hand with out the piston hitting the valves? Is this a V-2 cylinder engine. Take the valve covers off and check the valve clearance. With the valve covers off, turn the engine over and watch the valves move.

Last edited by Heins; 12-16-2018 at 07:11:04 PM. Reason: add a line
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Old 12-16-2018, 07:20:53 PM
R Davis R Davis is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

The motor's apart with busted lifters already removed and adjusters back out, so there's no way to check anything. The motor's a single cylinder, model # 20G414 - 0111E1.
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Old 12-16-2018, 08:17:03 PM
K-Tron K-Tron is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

While it is apart, check the timing of the engine. If the problem continues after replacing broken parts, the root of the problem has not been properly addressed. The good news is that that engine is nothing special. You can literally put any horizontal shaft engine on that snowblower with a 3/4" shaft and make it work by simply swapping the pulleys.

Chris
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Old 12-16-2018, 08:22:59 PM
Pat Barrett Pat Barrett is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

I had a 5 hp flat head go kart engine drive me crazy. It would start and idle but do what you describe. I tore that thing down 5 times and finally found the problem, The pin/Key that held the crank timing gear on the crank had sheared and a nub was sticking up and the gear would hang on it turning it slow, but when the crank sped up,it would slip. Check that as it's cheap to look at.
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Old 12-16-2018, 08:35:02 PM
R Davis R Davis is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

Ok, K-Tron and Pat Barrett answered my question, I can't just blindly order another head without digging further to make sure the timing's right. The head cover's off, but that's it.

Not sure where this will go from here, I'll check with the owner and see what he wants to do. He's at least looking at the expense of new lifters, rocker arms and valves, maybe he'll just opt for a new motor.

Either way, I'll come back and finish the discussion I started here...

Thanks guys...
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Old 12-16-2018, 09:29:23 PM
FlJim FlJim is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

With the valve cover off and rocker arms removed, you should be able to see the top of your valve guides. Easier done with head removed and valves removed. See if one of the guides is noticeably higher than the other. That can actually be repaired with loctite and set screw after you tap back to proper height. I think there are you-tube videos of the repair.
I encountered this on an ohv Briggs v-twin a year or so back. I replaced with used head.
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Old 12-17-2018, 12:00:54 AM
Heins Heins is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

You should be able to check to see if the cam is in time. When the piston is at top dead center, both of the lobes on the cam shaft will be up (one to one side of the engine and the other to the other side of the engine), the next revolution the lobes will be down. When the lobes are up, that is valve overlap.
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Old 12-17-2018, 02:51:13 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

Does that engine have a plastic cam gear - lobes? If so, hold the shaft and see if the cam gear or lobes are floating on the cam support shaft. I have seen several B&S OHV engines where the plastic cam gear has loosened on the support shaft, which in turn puts the valve timing out, allowing the piston to contact the valves. Not pretty for the engine. EBay has all steel replacement camshafts for these engines. I never liked the plastic crap cams, not only do the gears slip, but if you use automotive oil in the engine, the lobes will wipe out, sending abrasive plastic grit thru the engine If the valves have been bent, look at the piston for damage to the ring grooves. Also look for damage to the valve guides. If the hit is hard enough to pretzel the pushrods, there is liable to be damage to these items as well.

Checking for a loose cam gear - put the support shaft in a vise with a towel between the vice jaws and the shaft. Try to turn the cam gear on the shaft. If it moves, you have your answer. If the gear itself is tight, check the cam lobes.

If the clearances are too tight, it may cause contact between the valves and piston. if you don't have specific specs - .004" and out the door comes to mind!
Andrew
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Old 12-17-2018, 06:18:49 PM
R Davis R Davis is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

Ok, the valves are out. The intake valve guide is centered in the head, with just as much sticking out above surface as below. The exhaust valve guide is sticking out more on the lower side and maybe 1/8 inch below on the top.

The timing looks right, but it looks like the pieces that drive the push rods are damaged. I need a parts breakdown to know what they're supposed to look like, but haven't been able to find one on-line yet. It doesn't look like the valves are bent.

I'll look at the cam gear and lobes tomorrow to see if they're plastic, but given the quality of the motor and value of the snow blower, if it is, it's probably a game changer.

Should have an update tomorrow. Thanks Andrew Mackey
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Old 12-17-2018, 08:27:21 PM
radiodoc radiodoc is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

Here is a link to the B&S parts breakdown for the 20G414-0111-E1 engine. https://www.briggsandstratton.com/na...20G414-0111-E1
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Old 12-18-2018, 09:20:46 PM
R Davis R Davis is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

After taking a closer look at the valve guides, I made a mistake thinking the exhaust guide was where it belonged, it's actually been pushed up at least 3/8 of an inch.

After explaining that and the expense of a new head, plus the possibility of problems with the plastic camshaft and lobes, the owner decided to cut his losses and start fresh with a new snow blower.

As usual, the info shared by members here was a big help. Thanks again to all!
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Old 12-19-2018, 07:34:00 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Briggs & Stratton 10 HP... backfires, then breaks / bends valves & push rods

Replacement cam is relatively cheap . A head is not so much - expansive item. Not so good a design by B&S, if the engine runs hot or the wrong oil is used, the head warps and the guides work loose. You can try staking the aluminum by the guide, to try and keep it in place, but that is a 50-50 proposition if the guide stays in place. Common problem with them
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