Mower turns once then stops

[ThatBadMechanic]

Hey everyone I have a 20 hp Briggs engine (model 460707-2278-E1). It's a really old engine that had bad compression on one of the cylinders. I took it apart 3 weeks ago in hopes of changing piston rings, after installing the new piston rings and putting it back together I tried to crank it and it would turn once and then stop if the spark plug is on. if the spark plug isn't in then it would continue to turn as normal. I looked up the issue and found out that it's likely an issue with the valves being out of adjustment. So I took the valves out, cleaned them up, and did my very best to get them back into spec. then I reseated them and used grinding compound etc etc. I put everything back together and the issue remains. I finally decided to take a look at the camshaft to make sure it was timed correctly today, and all was good. Put everything back together after cleaning it again, and still... the issue remains, I'm worried that this might be a starter issue however it doesn't make sense since when I took everything apart it was functioning fine. So my question is: are piston rings the cause of my issues? or is the starter at fault, since compression on both sides of the engine jumped up quite a lot after re-seating the valves.

 

[hlw49]

Did you adjust the valves?

 

[ThatBadMechanic]

Did you adjust the valves?

yes, as far as I can tell both sides were up to spec, the weird thing is that when I take out the spark plug on the right side cylinder the mower is able to turn over, so I'm guessing it's an issue with the right side.

 

[sgkent]

Doesn't anyone start with the simple stuff first anymore?

 

[StarTech]

460707-2278-E1 is a vertical Briggs opposed twin cylinder engine.

Going to be a little hard to take the rocker cover off as this engine does not have rockers. Second as far as I know there is no ACR on the this.

The op will need go over his assembly as it appears to an error made during reassembly. Also getting a copy the Briggs Opposed service would be advisable if he hasn't already done so.

 

[Tinkerer200]

Yes, of course this is a flat head horizontally opposed engine. It is possible that the new rings increased the compression enough that the starter could no longer turn the engine over. Start with the simple stuff. Make sure all battery cable connections are good with special attention to where the ground cable attaches to the frameand battery is good as well. Use a good set of jumper cables to bypass the mower cable system, this will show a mower cable problem. This problem is sometimes caused by carbon build up in the cylinder heads of these engines but assume you cleaned up any when doing rings. The starters on this series engine were taxed to the limit when everything is good. They had a habit of wearing the top bushing oblong so that the armature rubs the field magnets reducing the torque. It is also possible that the starter was held too long in non starting condition and over heated the windings reducing the torque of starter to the point it would not handle the increased compression of the new rings. Good luck, I can send you a Service Manual for this engine IF you like. Address below, put in proper format an remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

PS: This engine does have what I call a Passive Compression Release System. The camshaft Intake valve lobes are ground in such a way that they hold the valve slightly open well into the compression stroke releasing compression back thru the carb. Typical of B&S Flat Head engines. This has little affect on operation at operating speeds according to B&S. You might be interested in knowing this system was used B&S OHV twin cylinder engines as well, perhaps this has changed now.

 

[hlw49]

I guess we are so use to working on the V-Twins that no one really caught that it was an opposed twin. Except Star Tech. Only way to adjust the valves is to take the valve cover off and check the clearance between the lifter and the valve. Only way to adjust is to cut the valve stem if there is not enough clearance. If there is too much you will have to replace the valves and adjust from there. Which is really uncommon since as they wear the clearance gets less.

 

[ThatBadMechanic]

I guess we are so use to working on the V-Twins that no one really caught that it was an opposed twin. Except Star Tech. Only way to adjust the valves is to take the valve cover off and check the clearance between the lifter and the valve. Only way to adjust is to cut the valve stem if there is not enough clearance. If there is too much you will have to replace the valves and adjust from there. Which is really uncommon since as they wear the clearance gets less.

460707-2278-E1 is a vertical Briggs opposed twin cylinder engine.

Going to be a little hard to take the rocker cover off as this engine does not have rockers. Second as far as I know there is no ACR on the this.

The op will need go over his assembly as it appears to an error made during reassembly. Also getting a copy the Briggs Opposed service would be advisable if he hasn't already done so.

Did you adjust each cylinder when the piston for that cylinder was at TDC on the compression stroke ?
Take the rocker cover off and look for the decompression bump
Should be on the inlet .

yes, the adjustment was done correctly, I was able to get a service manual from a briggs dealer, my assumption at this point would just be to retest clearance when springs are in place and hope for the best. before adjustment was done there was literally no clearance at all. If I remember correctly I set exhaust to .009 and intake to .006.

Yes, of course this is a flat head horizontally opposed engine. It is possible that the new rings increased the compression enough that the starter could no longer turn the engine over. Start with the simple stuff. Make sure all battery cable connections are good with special attention to where the ground cable attaches to the frameand battery is good as well. Use a good set of jumper cables to bypass the mower cable system, this will show a mower cable problem. This problem is sometimes caused by carbon build up in the cylinder heads of these engines but assume you cleaned up any when doing rings. The starters on this series engine were taxed to the limit when everything is good. They had a habit of wearing the top bushing oblong so that the armature rubs the field magnets reducing the torque. It is also possible that the starter was held too long in non starting condition and over heated the windings reducing the torque of starter to the point it would not handle the increased compression of the new rings. Good luck, I can send you a Service Manual for this engine IF you like. Address below, put in proper format an remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

PS: This engine does have what I call a Passive Compression Release System. The camshaft Intake valve lobes are ground in such a way that they hold the valve slightly open well into the compression stroke releasing compression back thru the carb. Typical of B&S Flat Head engines. This has little affect on operation at operating speeds according to B&S. You might be interested in knowing this system was used B&S OHV twin cylinder engines as well, perhaps this has changed now.

So yes, the starter gear is basically fried at this point just from trying to get it to turn so many times, I skipped basically all the wiring and hooked up a jumper to the starter directly, this had no effect at all. I'll send you an email to make sure the service manual I received was the right one. thanks!

 

[ThatBadMechanic]

also if it's of any use, originally after using the mower for a bit and having it warmed up, if it turns off or runs out of gas it wouldn't start unless the mower is completely cooled off. which if I remember correctly indicates a valve issue, however with the compression I was getting on one of the cylinders while cold it's not far fetched to say it's just caused from the mower having to run on one cylinder.

 

[bertsmobile1]

My bad for not checking the engine IPL first before writing the reply
I shall go to bed without any dinner and stand in the naughty corner for an hour after removing my incorrect post.
If the engine has been running for a long time with zero valve clearance then there is a really good chance that the cam &/or follower has also worn excessively.
The valves are identical as is the cam grind
So the valves on each side should move the same distance in & out and open & close at the same positions of their respective cylinders
I put a run a masking tape around the flywheel & mark the opening & closing points with a sharpie against the side of the magneto
Left & right should be almost the same variations in the actual valve lash will vary the opening & closing times a little so it is "same" not identical .
You can go one step further and stick a timing disc to the top of the flywheel