OutdoorKing Repair Forum Forums Repairs and Maintenance Questions On Ride On Mowers Questions On Ride On Mowers Frames Not had this happen before

B&S 13.5HP 28T707 motor on the ride-on

Running OK - every time I switched off it would backfire - wasn't worried about that -happens on other motors.
This time I stopped the motor to remove sometime that had got caught in the blades - it popped on stopping like usual but when I went to start it wouldn't - just span and gave encouraging chugs every now and then. Started to smell fuel and it was getting dark so chucked it in for the day. This morning the same so pulled the plug - OK (new anyway) Knew I had an old air filter so took that off and noted the inside of the carby throat was wet. Tried to turn it over and it coughed and shot 6" of flame out of the carby.

Any idea on the problem ? timing? but how can that be it's fixed isn't it?

It sounds as if it hasn't been backfiring (exploding in the exhaust system) but spitting (exploding in the intake system). There are three common causes of that: grossly wrong ignition timing, lean mixture, and leaky inlet valve. In the case of a B&S engine an ignition timing error seems unlikely. If it were lean mixture, it would be spitting as much while it was running as it did when you were starting or stopping it. Hence it sounds like it needs attention to its valves.

I agree with grumpy but I would check one other thing which has happened to me a few times when a machine has been on a farm or in a country area.

Check the exhaust / Muffler for a wasp nest first before you go for the valves.

Thanks guys- an update

1.. checked keyway - true and square
2.. with cover off noted oil mess on one side of cylinder head - bolts loose -one by 1/4 turn others about 1/8 - tighten all but some hard to get at cause some cowboy had welded the muffler bracket to one of the cover bolts
3..liquid fuel spraying out off air intake for carby on cranking -beginning to think valves but will check for wasp nests - lot of activity in that area lately

Good point on checking the keyway, I should have listed that as a likely cause of wrong ignition timing on a Briggs.
If your head gasket has been leaking oil, it sounds as if its likely to be blown. Tightening the bolts properly may not fix that, and if it leaks air/fuel it won't run properly either.

Speaking of keyways... funny story along similar lines last weekend.

Mate was mowing with a rideon last weekend, he did the usual, engage the blades, drop the deck and started mowing away, after only getting 5 meters the thing just ground to a halt.

he kept trying to start it only to have the same symptoms...

He calls me, and I do one of the best jobs I have ever done on a set of valves, they came up beautiful, lapped perfectly and a perfect gap, the machine now had more compression than before and they were sealing 100%

So I bolted everything back together a,d proceded to start... same issue as before! would pop and fart but no actually start.

After several beers the penny dropped and I thought to check the key. I quickly took a new key from a scrap motor and it fired right up on th first pull.

Long ago I had a 2 stroke lose power. It was an ancient 250 single motorcycle engine and gearbox in a gokart. We warmed it over pretty extensively, but it would only go 62 mph and we wanted more. We finally ran a lot of bronze into the cylinder head (block and head were cast iron), checked it would turn over OK, and took it back to the test track. After a while it lost power, went slower and slower until it wouldn't pull itself along. I was scratching my head a bit - it still ran OK, just no power output - but my father pointed out that the cylinder head was dead loose, which had a bad effect on the compression due to extreme leakage. When we took the head off, there was a contact mark from the top of the piston, which had knocked it loose. The problem was pretty obvious after that: although the piston cleared the head when you turned it over slowly, at maximum rpm the momentum of the piston and rod at the top of the stroke stretched things a bit, so the piston hit the head. It was only over a small area, and luckily the aluminium piston was pretty strong. We ground a bit of bronze out of the head, and went right back to running it. Result: top speed was still 62 mph, didn't gain a thing.

With the B&S engine is it 'engine out' to do the valves or can they be done with the engine in place on the mower? What are the chances the seats will need cutting? Do I need the special valve spring compressor tool or are there ways to 'improvise'

David L,

Two flat screw drivers will do the trick to compress the spring so that can remove the colar but the valve tool is a great advantage. As to the seats, unless they are pitted then I would only lap the valves in with some valve cutting paste after you reface the valves.

As for valve spring compressors this is what I use with great sucsess is.

On the inlet valve the retainer is usually a washer with a enlongated slot that is relatively easy to push down and flick off.

The exhaust valve is a bit trickier, you need to compress the spring with the valve closed while at the same time pushing the valve shut will pop the little collets out, use a magnetic screwdriver with your 4th hand to fetch them out.

As for putting them back in, compress the springs using 2 small-med sized cable ties, this makes it tons easier to reassemble, get the retainers in order while keeping a little pressure against them from coming loose with a flathead screwdriver and cut the cable ties. All going well you should be able to pul out the parts of cable tie and straighten out the springs if they have released on an angle.

There is an official gap to set the valve clearance at I have always done it to the thickness of the cardboard on a cereal box/cigarette packet/business card...

Great - thanks for all that - can I do it with the engine still in the mower or do I have to take it off?

most times you can do it with the engine on the mower, sometimes it can be easier if you take the bonnet off though

Bonnet already off

This is what greeted me when the head came off. Seat has come out of the head. Is this a job for the experts or something a DIY car restorer who has a bit of gear and good at improvising could takle?

Note also the amount of oil at the bottom of the cylinder (right side of pic) Normal or a ring job as well?

The replacement-or just reinstallation-of inserts isn't rocket science but there are a couple of special tools that you won't have and perhaps don't want to buy. Extracts from B&S manual follow.
To Drive In New Valve Seat Insert
Select the proper valve seat insert and the correct pilot
and driver according to Table 3 & 4. You will note that
one side of the seat insert is chamfered at the outer
edge. This side should go down into the cylinder.
Insert the pilot into the valve guide. Then drive the valve
insert into place with the driver, as shown in Fig. 17.
The seat should then be ground lightly and the valves
and seats lapped lightly with grinding compound. Clean
thoroughly.
NOTE: Aluminum alloy cylinder models. Use the old
insert as a spacer between the driver and the new insert.
Drive new insert until it bottoms. Top of insert will be
slightly below cylinder head gasket surface. Then peen
around the insert as shown in Fig. 18.
NOTE: Replace Cylinder if a .005" (0.13 mm) Feeler
Gauge enters between Valve Seat and
Cylinder.

I am used to seeing some oil in B&S combustion chambers and around the rings, because their oil rings are not highly effective, like those in a car. What matters is the ring gap.

Well - rough and ready fix. Rotated the engine until the insert was free sat it square under the valve and rotated engine and the valve pulled the seat partway into the head and a soft faced hammer finished the job. Now to prean over the lip as above and lap the valve in.

There may be dirt/carbon under the seat. First, this may make it come loose again. Second, obviously the seat is not guaranteed to be square to the bore now if there is dirt under it, so when you try to lap the valve you may find you can't get continuous contact all the way around.
If the engine hadn't been run with the seat loose, the odds would be pretty good. However it has obviously been loose from some time (the spitting on shut-down that went on for a while before it quit working completely) so I think there will be garbage under that seat. It might work anyway, though - time will tell.

being a bit of a redneck, I have done this repair before without even lapping in the valve, used the valve to hold the seat in nice and firm and just peened it as pictured.

I cannot reccomend my repair methods due to the nature of them, but for older equipment if tools and time is not available I just use what I can.

As for the oily patch, I would not be that concerned, maybe the rings are leaking a little, but just keep an eye on the oil level and she'll be right