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motor act like its locking up?


thegoat's Avatar
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05-16-06, 08:39 AM   #1  
motor act like its locking up?

Hello all,

I dont have the model # with me, Im at work, but here goes;
I have a Murray lawn tractor. 17hp Briggs & Stratton motor.
I have had mower for about 7 years, no problems with engine ever. I got her out of building to cut (1st time this season) I tried to start mower and acted like battery was dead, replaced it of course. Anyway after alot of troubleshooting and reading I watch the starter engage the flywheel, it turns the flywheel about a 1/2 a turn and then the motor acts as if it is stuck. I can free it with my hand and try again but motor seems to be sticking? Where should I start?

 
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05-16-06, 09:02 AM   #2  
Take the spark plug out and try cranking it,if it spins over real fast like it should then it's the compression release not working.

And thet's on the cam gear on the inside of you engine.

realy back with results and the modle,type and code of your engine and we will be able to help you more.

 
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05-16-06, 04:29 PM   #3  
Ok Heres the motor info:

17 hp Briggs & Stratton Twin II
Model: 42A707
Type: 2653 E1
Code: 99030958

Ok, pulled both plugs, It still would partially turn flywheel then stop.

 
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05-16-06, 07:30 PM   #4  
Ok,sounds to me than like you're still having battery problems.
When you replaced the battery did you claen all of the connections good (+ and - cables going to the battery,and also the two going to the solenoid,and the one to the starter itself)??
Electrical current doesn't want to flow through rust or other debres.

Thak an ohm meter to see if your battery has 12 volts coming out of it.

 
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05-17-06, 12:50 AM   #5  
This sounds like another problem. Check your belts on the engine pully. Sometimes they stick to the pulley, and don't allow the engine to turn. If that's not the case, you may have a magnet loose under the flywheel, or the coil may have come loose and is hitting the flywheel. Can you rotate it a full turn by hand?


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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05-17-06, 03:05 AM   #6  
I can rotate it by hand all the way around by hand, and I installed a new battery when I 1st had problems, every connection has been cleaned and tightened twice.
I have tried starting it with hood up, I can see my starter
engage the flywheel, Its just like it dosent have enough to turn flywheel.

 
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05-17-06, 03:19 AM   #7  
If the engine will spin over as it should by hand it sounds like it is time for a bench test of the starter motor. I doubt you have the test equipment (special bracket, DC shunt, Vibratory tachometer, Proper wiring, Test switch and Mulitmeter) nedded, so, you'll want to remove the starter and take it to a Briggs repair shop for them the perform the test.

 
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05-17-06, 04:11 AM   #8  
Thanks guys, I am going to pull starter and get it checked.

 
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05-21-06, 05:03 PM   #9  
I have same issue with same motor. Repair Guy, talk about the compression release again please ("Take the spark plug out and try cranking it,if it spins over real fast like it should then it's the compression release not working.")

 
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05-21-06, 05:21 PM   #10  
Change to first message: Motor spins fine w/ plugs out.

 
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05-21-06, 10:34 PM   #11  
Adjust your valves first before condemning the compression release. Usually a valve adjustment fixes the problem.


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05-22-06, 02:23 AM   #12  
Will do. Does this mean the compression release is hard to check and fix? How do I know it has one and how does it work? The engine runs great but just has trouble starting w/out assistance, both electrical and mechanical.

 
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05-22-06, 02:57 AM   #13  
The only way to check if the Mechanical Compression Release (MCR) is functional is to first set the valves to proper clearance and then watch for the exhaust valve to open slightly on the compression stroke. Bear in mind though that not all opposed twin Briggs have an MCR and it is these that we have found to be troublesome at cold start up. On such engines it is critical that the valve clearances are spot on and that the engine in general is well tuned.

 
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05-22-06, 07:18 AM   #14  
Where do I find a document that covers the MCR, it's components and how they operate?

 
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05-22-06, 11:17 PM   #15  
I don't know of any publication that covers it in great detail. The camshaft has a flyweight on it that when it is turning slowly, adds a few more thousandths to the lift on the backside of the cam, to keep the exhaust valve from fully seating. When the engine starts and centrifugal force slings the flyweight out, it disengages from the lifter and allows correct valve operation. This keeps the compression from being too high during startup. If the valves are too loose, this will not operate as it should, because instead of the MCR holding the exhaust valve open a hair, it just closes the gap in the valvetrain and is ineffective. There are some known problems with the MCR on some briggs engines, but most of the time it's just a valve clearance issue that needs an adjustment.


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06-03-06, 03:08 PM   #16  
engine just won't start

I've got a the same basic Briggs & Stratton Twin II engine (it says it's an 18 hp Briggs & Stratton Twin II, Model: 42A707) that has some of the same symptoms but not all.

It was running fine, then is suddenly started to run rough, and then died, sort of sounding as if it were choking out on too rich a mixture. It hasn't started since.

When I try to start it, the first time it cranks it almost always turns about 1/2 revolution and stops - it sounds just like the battery was low and it didn't have enough jiuce to run it through a compression cycle.

But the second time I try to start it, it will crank for as long as I want. I've checked all the obvous things - there is spark, compression, fuel, the coil is clean, and so on. If I pull the spack plugs out, the engine cranks a little easier, but there is no tremendous difference. The plugs are wet when I pull them out, but I can't tell if they're too wet or just normal with unburned gas.

I pulled the cover off the carb, and it looked like gas was blowing back up the carburetor when I cranked it.

If this were a car, I'd think the timing belt had jumped and the camshaft was out of synch with the crankshaft.

Any clues on where I might start looking? Any help would be greatly appreciated.

 
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06-06-06, 02:11 AM   #17  
How did you check spark/compression/fuel?


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06-06-06, 06:31 AM   #18  
I checked things by pretty simple means.

For fuel getting to the cylinders, I just guestimated by the fact that when I pulled the spark plugs out after cranking the engine for a while, you could see that there was a film of gasoline on them. Had they been dry, I would have felt I found something worth looking into.

For spark, I pulled the spark plug wire off, pushed back the cover and held it close to the spark plug while I cranked the engine with the starter motor. Nice bright blue spark. Managed not to shock myself this time, so I was happy with the results.

For compression, I actually have a compression gauge (leftover from my Triumph days) and it read 120-125, which seems pretty good to me.

Again, any suggestions on better ways to diagnose are welcome. I am truly stumped.

 
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06-08-06, 12:23 AM   #19  
Try shooting a bit of automotive type spray carb cleaner, or a squirt of gas in each spark plug hole, reinstall the plugs, and see if it will start up for a second.


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08-15-08, 11:26 AM   #20  
how do I adjust the valves on briggs 42A707. I cannot find any adjustment

 
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08-15-08, 12:29 PM   #21  
Posted By: holywood how do I adjust the valves on briggs 42A707. I cannot find any adjustment
Please begin a "New Post". This is a thread that is two years old and of a different subject.

In addition to your engine model number include the type and code number.

What type of problem are you having that makes you want to adjust the valves?

 
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12-18-08, 07:01 PM   #22  
17hp briggs&straton/313777.compression release

i have the same problem. starter will not turn engine past the compression stroke. good battery,new solenoid,set the valves for.oo3-.005 on intake and .005-.007 on ext.but still the same.will turn over fast with spark plug out.i put my finger on hole till i feltair being forced out.then put screwdiver in sparkplug hole,and moved the piston to tdc and 1/4"more, then i set valves. but still same.heard about compression release system. if this is my trouble,what can i do? thanks [email protected]

 
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12-18-08, 09:22 PM   #23  
Double check your valve clearances. Make sure they are correct. Set them both to .005". If still no joy, and the battery and connections are good, the compression release may be at fault. If the comp release is at fault, it normally requires replacement of the camshaft.


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