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Briggs and Stratton Assistance :)

3835 Views 17 Replies 6 Participants Last post by  mbaker9105, 
M
Need some help or advice troubleshooting. I have attached some pics for reference

I have an Ariens riding mower with a Briggs and Stratton 31P677-1373-B1 (Parts list and diagrams here Home

The engine began surging a few weeks ago, no smoke or anything. So I cleaned the tank, replaced the fuel filter, and sprayed out the carb and checked the plug. No difference.

So last week when I started it, it blew a ton of blue smoke, and at idle evetually turned white and quite (looks like fuel flooded it out). You could let it set awhile, and the same thing would happen.

So I pulled the plug, lots of fuel came out, no sign or smell of oil, and plug smelled like fuel and no indication of fouling.

Looked at carb, seemed ok, but since I didn't know about the solenoid and why it was surging, etc, ordered and put a new carb on. Same result. So I did a compression check twice, 140 PSI...that seems ok right?

So I pulled the head. Lot's of oil in the valve tappet/rod chamber (think it's supposed to be there right?), a little oil in the cylinder. But the cylinder doesn't look all that bad, and he head/valves have some coking, melting or whatever, which I asseume to be the sealant, but I don't think it's that bad. The seal before cleanup was MAYBE showing a little area over at the rod chamber that looks a little different than the rest of the seal (not as much gunk, so maybe oil coming over from there, not sure).

But after wiping the seal down, the seal looks pretty good. When I rotate the engine, a little bit of oil around the piston from the ring, but then again the compression had already checked fine. Checked the crankcase breather, it seems ok and pretty clean, but hard to tell with those.

So I have a new head gasket, and new breather with flapper, I haven't reassembled everything yet.

So I'm wondering how much oil is too much coming by the piston ring, why the compression is good, and why all the fuel....a little stumped. I'll replace the plug again, but I just checked it a few months ago, and it does run, and no fouling, so I think that's ok.

Also, there appears to be some oil seeping from the engine sump gasket, but how would that matter to the smoking?

So what could be the answer?

2 more general questions:

I'm wondering is if I buy a new head that comes fully assembled (about 100 bucks), is it already adjusted for the valves? If I have a head/valve issue, I'd pay the 100 bucks not to mess with the adjustments)

Also, the two pushrods are different (see picture, item 1026 on the parts list), the parts list shows 2 different part numbers, 692011 Rod-Push (Exhaust) and 692003 Rod-Push (Intake
how can I be sure which side to put them on? One has more of a rounded ball end, the other is just rounded on the end with no ball appearance.

Any help appreciated...:thanku:

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3
No way the valves could come preadjusted. The intake push rod is aluminum. The exhaust is steel.valve adjustment must be done as per manual. Bit tedious but straight forward.
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T
Have you checked the oil in that engine? Possible it's contaminated with fuel and over full.

Mike
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M
Tencubed said:
Have you checked the oil in that engine? Possible it's contaminated with fuel and over full.

Mike
Click to expand...
I just checked it again, it appears to be on the upper limit, and there IS a slight angle leaning away from the dipstick, so maybe a little much, but it's VERY clean, like new looking, no blackness at all to it, I changed the oil and filter last October and I've been running it at that level for months with no problem. And no fuel I can see or smell in the oil, even in the oil that came out of the rod chamber when I took the head off. But even if it was slightly overfilled, wouldn't that wet the plug with oil, and not have just a clean plug that smells like gas and dying out with white smoke?

Then again, is it maybe blowing the blue smoke, and not firing the fuel enough to where eventually it's just too much fuel built up and that's why it blows the white smoke before dying?
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3
Do you inspect the head gasket for damage in area about centre of the pushrod galley .had you noticed any oil in the air filter housing? Your smoke is typical of a blown head gasket. Common on those engines.
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M
38racing said:
Do you inspect the head gasket for damage in area about centre of the pushrod galley .had you noticed any oil in the air filter housing? Your smoke is typical of a blown head gasket. Common on those engines.
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Yes, you can see by the pic that the one I took that still had the "gunk" buildup looked a little different over by the chamber, but on the other picture once I cleaned the gunk off the gasket looked great. Maybe the gunk buildup in the other areas was allowing a bit through that other area?

And there was a slight bit of oil in the breather housing.

I have everything on hand and about ready I think to just replace the head gasket, the breather flap and cover, filter, and drain the oil and refill ensuring maybe at the lowest level possible.

I guess at this point the reason I'm holding up is thoughts about the ring....I know it's not a for sure test and have heard that it may not mean much, but does the 140 PSI kind of indicate that the ring was probably ok, and the little bit of oil I do see when I hand turn it is ok?
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3
Actually 140 is high. It is hard to get accurate readings because of the compression release .gasket damage commonly on the cylinder side. Do you have the repair manual for proper head bolt torquing and valve adjustment?
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M
38racing said:
Actually 140 is high. It is hard to get accurate readings because of the compression release .gasket damage commonly on the cylinder side. Do you have the repair manual for proper head bolt torquing and valve adjustment?
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No, every where I've looked, about the only place I see it is the B & S site, and they want money for it...I was a Helo maintenance guy in the Army for 20 years, and I still have some of my maintenance references, so I was thinking about looking up what's known as "standard torque" for those type bolts, unless you know where I can find the toque and the pattern....
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tomw0
At no charge, go here:

http://www4.briggsandstratton.com/miscpdfs/RNT/Engine Specifications Chart_ms3992.pdf

Engine Spec chart for a bunch

Mymowerparts.com has one for older engines

This file has a lot of B&S stuff, but I may have fiddled with the actual file name:
B&S276781OHV.pdf ... I down loaded it from somewhere on the web. Maybe even here.
It covers the OHV engines, and a google for the digits found this and more...
http://www.google.com/url?q=http://...eDRCws&usg=AFQjCNHscq-ib2qfqplp2DrBhl8hKOzPdQ

tom
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M
Thanks for all the help so far gents, the Parts manual and torque specs help. I'm re-assembling now, taking care to clean all the mating surfaces and checking everything twice....I'll post on the end results....if after all this it's still mucked up, I guess that would leave the rings....fingers crossed...
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A
It seems to me like the engine could be filling with fuel when sitting. The best solution if you don't already have one is a fuel cut off, about 5 bucks and that will stop fuel entering the carb and then the cylinder. It is quite common.
The other item that could cause it is the small vacuum value that connects to the carb. If you remove it and be careful to apply a little sucking pressure, don't get excited and suck hard, gas is not a recommended beverage you will find out if it is sealing, that works to remove back pressure from the engine. If it is bad it could be sucking gas into the motor.
The valves are easy to set, just watch you don't over tighten the adjuster cap. They have changed these from the old ones which were quite light to a heavier version.
Make sure the rods are seated they bend easy.
Check the float valve for sealing while you are at it.
Hope this helps , just an observation.
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M
Here's the results of todays mainteneance:
1. Carb (previously replaced
2. Replaced breather housing and flapper
3. Cleaned up head mating surfaces, new gasket, inspected rods, reinstalled head with rods and torqued per specs in pattern
4. Cleaned up valve lifter interior, very slight adjustment on the intake and exhaust valves per the manual, ensured rods properly seated and correct (metal rod on exhaust, hollow aluminum on intake), reinstalled cover with new gasket and torqued.
5. Reassembled flywheel.
6. changed plug, filter, and oil

Attempted to start, now getting loud backfires, at first it had some some oil blue smoke, now not so much. Just won't start. Ran carb adjustment screw all the way in and backed of in 1/4 turns and retried, didn't seem to make much difference, hard to tell but still backfiring. After a while the backfires had very little blue smoke, a bit of white smoke, and some residual smoke burning off the muffler. Will not start but seems to try.

So now this is seeming like a timing issue, key sheared off? But if the key was sheared off would it fire at all? Would the rods and valve even move?

Getting flumoxed. After the maintenance now the problem has changed.

suggestions?
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3
you mention putting the flywheel on. Not sure why you would have removed it for the smoking issue. What did you torque the flywheel nut to? A 31 engine spec is 100 ft lbs. Did you R&R the magnetron coil as well? Just another thought on the original problem. If you put the new carb on without draining and refilling with fresh oil you may have still been getting a gas/oil mixture past the rings to produce the smoke. And they may be some in the muffler to burn off. Hopefully new carb is not flooding unless there was a lot of crap in your fuel supply line.
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M
38racing said:
you mention putting the flywheel on. Not sure why you would have removed it for the smoking issue. What did you torque the flywheel nut to? A 31 engine spec is 100 ft lbs. Did you R&R the magnetron coil as well? Just another thought on the original problem. If you put the new carb on without draining and refilling with fresh oil you may have still been getting a gas/oil mixture past the rings to produce the smoke. And they may be some in the muffler to burn off. Hopefully new carb is not flooding unless there was a lot of crap in your fuel supply line.
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Had to pull the flywheel to access and remove the breather cover underneath. Did torque to 100 ft lbs or best I could, hard to hold the flywheel but it's probably close.

The coils/alternator seemed fine visually, and the magnets on the flywheel were in good shape, 1 of about 12 was chipped a little, blew all the dust and debris out of it that was caked on around the magnets.

Fuel line and tank is clear, so after glancing at the repair book a bit, I'm going to go through the full carb and governor settings and see if that does anything....

The dang coil/alternator is 53 bucks, the regulator is 50 bucks, and the flywheel is 150 bucks......getting to cost point now I should have just bought a new riding mower for 1200 bucks....

But the shear pin should be fine right? Otherwise the piston, valvess, and rods wouldnt move right?

The carb was replaced before I did all this latest work, it was the first thing I did, and it was still having the original problem with starting and smoking until flooding out and dying. Now, with the latest work, it's backfiring and won't start and I left the carb on there....baffling to me how the problem changed....:dunno:
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3
Check the flywheel key. If it sheared then flywheel is shifted a bit but everything still turns but the spark timing will be off. 100 ft lbs is a lot of torque. I use the cotton rope in the cylinder trick for tightening those.
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MrGiggles
If the head gasket was blown you should have been able to tell, there will be a dark streak on the aluminum and the gasket will be eroded away. Almost always in the 3:00 position, leaking into the pushrod valley.

When mine blew, the first symptom was the oil getting dark very quickly. Prior it stayed pretty clean, once the head gasket started leaking it was stained within 15 hours. The next symptom was smoke (oil getting pushed through the breather and into the carb), and occasionally it would start to surge and stall, then would pick up again after a minute or so. I believe that oil was getting blown into the fuel pump. For the most part it ran fine though.
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tomw0
As a suggestion, I would do two things: 1) R&R the flywheel and check the shear key to insure proper timing. Feed some rope into the spark plug hole and rotate the crank to jam the rope against the cylinder head. You can now torque the flywheel nut without worrying about the crankshaft rotating. A standard business card between the magneto and the flywheel should be close to proper clearance. 2)re-check the valve adjustment, plug out, rotate the engine until you see the intake valve open and close, then as Walt suggests, put a pencil in the plug hole and rotate more until the piston reaches TDC, and continue to rotate until the piston goes down 1/4" more. Adjust intake & exhaust valves.
For the carb, suggested 'generic' turns is 1.25 turns from being the needle being gently seated. If this thing sat for a while, it wouldn't hurt to drop the float bowl and inspect for crud in the bowl that worked its way from the fuel tank or decomposing fuel line.
tom
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M
38racing said:
Check the flywheel key. If it sheared then flywheel is shifted a bit but everything still turns but the spark timing will be off. 100 ft lbs is a lot of torque. I use the cotton rope in the cylinder trick for tightening those.
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:drunkie: I'm calling this one mission complete! So yesterday when cleaning up I did spot a part (see pic) which was a miracle because I have an aggregate driveway, and spotting anything small like this, especially on an oil soaked area, is almost impossible. So I was smart enough to keep it and took the pic.

So this morning, I pulled the flywheel, and sure enough, the slots were not aligned. And magically, the key I found fit right in there...so reassembled, it started, no blue smoke, but was surging a bit with very little white smoke.

So I broke it in a bit at different speeds, and then engaged the blades and took it around the yard. Made it twice before it stalled out. Ok then.

Went and got another air filter and fuel filter (both of which I'd already replaced back in may) and emptied the tank, cut a new filter to carb hose, blew in the hose to tank line, seemed ok and it was hard to change so left it alone. Now that filter didn't have a "forward" on it, but I reversed it from the other filter, not sure it mattered. Pulled the plug, it had a light white grey coating. That was good, meant fuel issue, no sign of oil (rings) on it. Primed the chamber with a little fuel, verified the card mixture screw out about 1 1/4 turns.

Filled 1/2 with fuel, cranked up, steady freddy! Went though break in again, good to go, smooth as silk. Cooled down, shut down, started right back up. So did the front yard, smooth as silk. let it set a bit, checked for oil leaking, nothing. cleaned up and put all cowlings back on, and mowed the back yard.

Runs like new now.

So it was probably a little bit of everything culminating in the problems. Anyway, I'm now more confident doing that type of maintenance, and valve clearance doesn't scare me anymore.

So I'll watch it the next few times I mow, but I think I'm good now:thThumbsU

Said and done with, I'm out about 150 bucks, and about 12 manhours.

Thanks to all for all the guidance and references!:thanku:

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