Briggs twin V OHV problems!

[Bibbyman]

Dad has a Poland rider lawn mower with an 18hp Briggs twin V OHV engine.  This spring we put in new plugs, changed the oil and filters and replaced a leaking fuel line.  Son Gabe mowed his lawn with it a couple of times. 

At least a month ago I went up and mowed a little patch that Dad wanted mowed that Gabe had missed and then I parked it in the shed.  Gabe went up a couple of days later and it would not start so he used our lawn mower.

I went up and checked out the mower.  It would turn over but not hit a lick.  I checked all the interlocks in the wiring I could find.  But the conclusion was that if the interlocks were not working it would not crank over.  I tried gas in the throat of the carburetor and that didn't work.  Dad just knew starter fluid would be the answer so I got a can of that.  That didn't help.  We pulled the plugs and let them dry out.  It was getting gas as the plugs were wet.  We let it set for a week with the plugs out just in case they had got fouled out. Saturday evening we put the plugs back in and cranked and cranked but it never even hit.  I pulled the plug wire and it has fire.  The spark will jump at least a 1/4". 

Dad is very frustrated.  I keep telling him it's getting fire and it's getting gas.  If it won't hit and try to run at all I don't know what it could be.

The only thing I can think of is that it's way out of time somehow.  Or that the cam broke or something like that. 

While I was typing,  I got to thinking...  I can't even find where the muffler exhaust is on the mower.  Would there be a chance that some varmint or something plugged the exhaust? 

[beenthere]

You mentioned new plugs....if they were Champion plugs, I'd suspect them. Can't believe how poor they can be nowadays.

Just a thought.

[John Bartley]

There's a couple of things that you might look for. If you're absolutely sure it has spark and that the cylinders are wet with gasoline, then there might be a timing issue as you already suspect. You could check for a sheared flywheel key or you could also check for a shorted coil isolation diode in the coil wiring harness. Usually a shorted diode will allow the motor to run, but roughly (poorly). I have seen the odd case however where the shorted diode will not let the motor start. The other possibility is that you have no compression? MIght be worth a check with a compression tester and see if the two clinders are close?

cheers

John

[Bibbyman]

As it was running when I parked it,  I kind of dismissed a compression problem - like borke piston, or valves.  But I've thought about checking the compression anyway. 

I have a neighbor that worked on small engines all his life come out and check out the Onan we had on our first Wood-Mizer. He checked the compression by putting his thumb over the plug hole.  "Yep, no compresion on this cylender." 

They are Champain plugs but run one time and then not even hit the next time?

I remember the old Briggs engines for the push mower had a key in the flywheel that if it was even scored, it would not start.  Replaced and cursed the key many times.

John, where would I look for this diode?  Is there a way to test it or is it something you just replace if you suspect it's bad?

[John Bartley]

Diodes are tested with a multimeter set on a high resistance scale. There is resistance one way, but not the other. The resistance value will vary depending on the diode. The diodes (there are two - one for each coil), are in the wiring harness that leads from each coil. The harness is in the form of a "Y". The top wires of the "Y" each have one diode in them and go to the coils and the bottom of the "Y" is wired thru' the tractor harness to the ignition switch.

The order that I would troubleshoot (based on your description of the trouble) is :

1) check compression
2) check flywheel key
3) check diodes.

cheers

John

[Bibbyman]

Thanks !  I'll give it a try. 

If I take the screen off the flywheel, will I be able to see the key?

[beenthere]

..........

They are Champain plugs but run one time and then not even hit the next time?
..............

Had it happen just like that...in fact twice. If once, I'd a figured it was just a chance of getting a bad one. But have heard of others having the same experience with Champ---s.   Still, just a guess.

Both times, managed to get the motors to start with the new plugs, then back to the "no start" problem. Then proceeded to change a lot of things out, trying to chase the problem. Finally replaced the plugs again, and problem solved.
NGK plugs are what I use now.

[Bibbyman]

..........

They are Champain plugs but run one time and then not even hit the next time?
..............

Had it happen just like that...in fact twice. If once, I'd a figured it was just a chance of getting a bad one. But have heard of others having the same experience with Champ---s.   Still, just a guess.

Both times, managed to get the motors to start with the new plugs, then back to the "no start" problem. Then proceeded to change a lot of things out, trying to chase the problem. Finally replaced the plugs again, and problem solved.
NGK plugs are what I use now.

Just in case,  I'll pick up a new pair of plugs - NGK if I can find them.

[Bibbyman]

Well, tried a couple of things.

Went to town this morning and got two new plugs.  They are Autolite brand as they didn't have the NGK equivalent. 

Before I put them in I did a crude compression check by sticking my finger in the plug hole and, when cranked, it blew it out.  I've not done this before so I don't know if I'm qualified but there appeared to be compression and I have no reason to think something happened to the engine that would make it suddenly loose compression.

It still would not hit a lick, backfire or anything.

I took the screen cover off the flywheel but the fan section is plastic and bolted to the top of the flywheel.  I'd have to take off a bushel of shilding to get the fan part off to see the flywheel.  And then it looked like I'd have to remove the flywheel nut.  That didn't look to be a simple task with the tools I had.

So I've got dad convinced that it needs to go to the shop. 

[Gary_C]

The only other thing you could try is to drain the gas and put fresh summer gas in the tank.

Yah, it's a long shot but you seemed to have covered everything else I could think of.

[Bibbyman]

I've used starter fluid on a few attempts. 

We just tried squirting fresh gas I got just last week in each cylinder after I put in the new plugs and that didn't work.

Besides,  I drained the tank this spring and put fresh gas in it and it's had a couple of tanks of gas since then and it's been running on the gas until it flat wouldn't start.   :'(

[Tom]

Not that this is your problem, but it reminds me of the hassles I've had with my Kohler for years. 

Backfiring was the death of it.  The solonoid in the fuel cutoff valve in the carburator bowl failed.   The Engine would backfire and the pushrods would bend.  From then on out, all that would happen is that the starter would turn the engine over.  If it ran, it ran very ragged with the choke pulled out.   Usually it wouldn't even fire.

It got to the point that I knew what was going to happen if the engine backfired.

We finally determined that the  fuel valve was faulty and replaced it.  The new one was faulty as well.  That really threw us off.  A third has been put on the engine after many years of frustration and now it seems to be running OK.

[Bibbyman]

Yea,  it's likely something quirky like that.  We'd be encouraged if it even backfired or tried to hit.

It may be awhile but I'll update y-all on what the professionals found.  We are lucky to have a good small engine mechanic in town.  He's always been dead on and knows his stuff.

[Bibbyman]

We kind of put this on the back burner for a couple of weeks. 

A while back I stopped in at the local small engine repair place and talked to the guy that fixes stuff.   He's a rare combination of experience and knowledge and pretty good at figuring out what's wrong.  We went through what I'd already tried and suspected.  His comment was that he'd seen one or more valves freeze up and the push rod bend and or the rocker arm comes off.

This afternoon I went back up and give it one more shot with no results.  So I took one of the valve covers off.  Sure enough,  a push rod fell out.  The other one looks like it's still functioning.  I took the cover off the other side and it too had one bent and one that looks good push rood.  The valve on one side could be depressed.  The one on the other couldn't. 

Dad is now all confused as to how this could have happened.   I can't tell him.  It just did.  He suggested just getting two more push rods and putting them in.  I said that may not be the right thing to do as maybe a valve is bent or broken.  I think I've got him convinced it has to go to the shop.





I don't know if its the only problem but it looks like its enough to keep it from running.

[stonebroke]

Some thing caused the pushrods to  bend , Better find out the root cause before you do more damage.

Stonebroke

[olyman]

and when you put he new pushrods in--the tips need to be oiled well--and then the cold clearance set with a feeler gauge--and i cant tell you what it is--but the new pushrod man can--and it has to be indexed right to set them---

[Bibbyman]

and when you put he new pushrods in--the tips need to be oiled well--and then the cold clearance set with a feeler gauge--and i cant tell you what it is--but the new pushrod man can--and it has to be indexed right to set them---

I'm taking it in to the guy who knows what's going on and how to fix it.  That's how smart I am.  ;D

[sawguy21]

I recently saw a Briggs twin with a bent push rod, the valve guide moved in the bore and would not allow the valve to open fully. The other head was replaced earlier because the exhaust valve seat dropped out.
All that tells me the engine is overheating. The cooling fins were not plugged so I suspect the operator may have been working it hard at part throttle. It needs to be run at WOT for maximum cooling air flow.

[mburrow]

my 18hp briggs V twin dropped a intake push rod today and bent it, I have been having problems with the intake valves sticking, had been running a chainsaw mix in it and the valves hadnt stuck till today, I didnt have any gas mixed up and put regular gas in it, I had talked to a small engine shop they told me bad gas was a problem and to use the mix.   

[Bibbyman]

my 18hp briggs V twin dropped a intake push rod today and bent it, I have been having problems with the intake valves sticking, had been running a chainsaw mix in it and the valves hadnt stuck till today, I didnt have any gas mixed up and put regular gas in it, I had talked to a small engine shop they told me bad gas was a problem and to use the mix.   

I talked to the repair man last Wednesday.  He's got the valves unstuck and waiting for new push rods and time to get back on it.  He thinks that's all it needs to get it fixed.

His take is that the gas was bad.  I asked him about ethanol blend.  He suspected the ethanol gas didn't last as long as old "regular" gas.  But we had fresh gas in it.  Or at least I thought it was and we'd had ran it a good little bit this spring.

He recommended putting an additive in every tank of gas.  We have been using Sta-Bil.

[ScottAR]

I've been putting a can of seafoam to a 5gal. gas can for small engine
gas the last few tanks I've bought.  I've also been mixing my 2 stroke
gas out of the treated gas.  The weedeater seems to like it a lot. The power
washer too.  I buy the 93 octane gas and that seems to help as well. 

Seafoam is getting pretty pricey but the weedeater has never ran better so I
guess it's worth it.   ???

[mburrow]

the first time my valves stuck I ran some seafoam through it,it didnt help on the sticky valves, every time I would shut it down the intakes would stick that is when I started using 2 stroke mix in it and havent had a problem till yesterday when I didnt use a mix. I like seafoam and use it every once in a while, I also like the lucas injection cleaner but so far only use in in my truck a Dodge diesel. I think to fix the sticky valves would need to do a valve job on it, as long as the oil mix works for me that is what I will use.
my push rod was bent just like the ones pictured, my rod are solid so I straiten it and put it back in and it runs fine

[Bibbyman]

Well,  I didn't take a new picture but now the Kohler 25 hp Commander-Pro has a bent pushrod.  I hope that's all it is.   :'(

[Bibbyman]

Well,  it's just not the pushrod.  May have started that way but...  I slept on it and went out this morning for another look.  Took out the two spark plugs and dropped a screw driver with an 8" shaft down one hole.  Turned it over by hand and there is nothing there.

I'll talk to our local repair guy tomorrow and probably Blockbuster but I about bet on figuring on a new engine.

The Kohler on there is a CH25S that has been discontinued.  Replaced by CH730S-0040.  Looks like a 27 hp CH740S-0001 would also work.

Best prices I've come up with yet is Opeengine.   

Anybody got a good source for a Kohler engine?

[pineywoods]

Uh oh, bye bye piston. Try www.tulsa-engine-warehouse.