Pond Boss Forums GENERAL QUESTIONS Pond Boss Attn: Sprkplug

Unusual (to me) engine problem.

Today I went to start the B&S IC 10.5 HP engine (1998 vintage red top) on my D-R mower. It wouldn't start, only popped a little, and had almost no compression. Ran fine last time I used it about three weeks ago. I ended up taking it partially apart to get the head off, and found that the intake valve seat had popped out and was holding the intake valve open. I carefully tapped the seat back into place to full seating, cleaned everything up, put the engine back together, and it started on the first pull and ran fine. Got my mowing done.

Is it a common or a very unusual occurrence to have a valve seat pop out? Is it likely to repeat that on this engine, or maybe it wasn't seated well to begin with? I bought it used two years ago and it looks to me like the engine might have been overhauled. The valves looked almost new.

Thanks in advance for any insight.

It's actually pretty common, I saw examples of loose valve seats every summer. It usually became more prevalent when the temperature started going up, and many times was due to engine overheating due to blocked cooling fins,(mouse nest), but I have opened a few up that had come out for no apparent reason.

In the old days of flathead engine design, the remedy was to peen over material to hold the seat in the block after reinstalling it. Sometimes it worked great, other times it fell back out a short time later. If this is an OHV engine, I would probably bite the bullet and get a new head. They come from Briggs with new valves, guides, (which also come loose frequently), complete, ready to bolt on. If it's a flathead, valve-in-block engine, then you've done all you can and time will tell.

One thing for certain, if it's going to come back out it will do so
at the worst possible time. Different expansion rates when you have a steel seat in an aluminum block/head.

It's a flathead, valve in block. I guess a new engine would be in order if it keeps happening. It was about an hour job for me after I decided what to do.

Is it possible it wasn't pressed in well after a rebuild?

Would a OHV engine fit the same bolt pattern on the base? It's a vertical shaft.

Edit: The head bolts were almost loose; came out very easily...looked like some leakage had occurred across the gasket, but gasket still looked good. Could that overheat the valve seat? I got the head bolts tight enough on reassembly. I did not peen the seat.

Bill,
I bought the machine used two years ago.

Sparkie,

1998 machine and now a valve seat lifts 20 years later. Slightly bent valve? The only way an interference fit sleeve will lift is because there is a load in that direction that is significant enough to over come the friction force of the fit. I guess if it is a bent valve, the seat will lift again fairly quickly.

I can also see the scenario you mentioned with operation at temp beyond the spec limits of the equipment. The difference in thermal expansion coefficients between steel and aluminum will cause the seat to come loose at temps above the design spec. If that is the case then the question is why the equipment is running so hot to be operating at temps out of spec.

The bolt pattern is the same. You would need to match crankshaft diameter and length also. And, the OHV engines are physically larger in some aspects, and there can be interference issues with the head or exhaust in some cases. Sometimes they bolt right down...just depends on the application. Briggs no longer manufactures flat heads, so replacement means modernization.

It's possible the engine was rebuilt, and put back together incorrectly, but I would guess if the parts look new it's because it had the same issue in its past, and someone tried a repair. If the only thing holding the seat in now is valve spring pressure, it will certainly come out again.

I agree with everything sprkplug said and I too owned my own small engine repair business for 30 years. Have seen many valve seats pop out over the years. My question is...have you asked DR Company what replacement engine to use in place of the flathead?

I experienced the same problem on a 5hp briggs on a tiller about 10 years ago. I didn't know any better, so I took a hammer to the valve and tapped it back in. That motor outlasted the tiller and a go kart my son outgrew. It was still running strong when we sold the go kart. Hopefully, you will have the same luck.

If the motor on my old DR lasts two more seasons I will have my money's worth out of it. Probably use it ten hours or less a season, but a lot of work gets done in that time and the land keeps improving with every mowing. Less weeds and sprouts and more grass. May get to use a finish mower eventually.

It is good to know we have at least two top notch small engine mechanics on this forum. I am grateful.


Edit: After further reading on the valve seat coming out issue, I think it may have been partially popped out since I got it. The engine starter rope was always hard to pull and harder to start than it is now. It seemed to have excessive compression when starting. Now it starts better and doesn't take both hands and a body pivot to pull start.

Would the intake valve seat being partly popped out lead to high compression during starting on the flathead engine? Is the compression release on the intake valve? It's much easier to pull now that it's fixed, and runs fine.

n the not so old days, the comp release functioned on the exhaust lobe of the camshaft. Emissions concerns caused it to be moved to the intake lobe, so I suppose if the intake valve seat moved just enough to take up the slight movement of the comp release, yet still allowed for a seal, then theoretically what you describe is possible. Now that the seat, and by association the valve, is setting deeper in the block the comp release would have a greater impact.

Thanks sprkplug. Since I got it used year before last, it was always hard to pull (two hands and body pivot) and somewhat difficult to start. Now it seems the compression release is working, and likely starts easier because the starting RPM is greater due to the easier pull.

Back in the old days, we had a 1966 model 40HP Johnson two stroke outboard that my Dad bought new. It had a recoil start in addition to the battery. Boy, was that ever difficult to pull, but at least it started easily. Batteries were not so reliable in those days. I suspect no compression release on that one.

After a few mowings, I suspect the intake valve seat popped out again. I used it a while ago for an hour or so, put it in the tractor shed, shut it off, and after stopping, it backfired through the intake. I pulled the cord, and no compression. I am going to peen it in this time. Do I need to peen it all the way around continuously or only in three or four places around the circumference?

I suspect the backfire blew out the valve seat.

Flat head Briggs 10.5 HP single.

All the way around.

Thank You! Planning to fix it again in the morning.