Valve seat material for B&S lawn mower engine

[Bazzer]

Before long I have to overhaul a Briggs and Stratton lawnmower engine.

Specifically, I have to get the valve seats tight in the case again, it is an alu case side valve engine and the valve seats rattle around in their pockets in the case.

I think I need to make some new seats with a slightly larger OD to get a good fit into the case.

So what is the right material to make the valve seats from?

Thanks

Barrie

 

[welderskelter]

I would throw it and get a different one. The camshaft is just floating in a hole drilled in an aluminum block and so is crankshaft. The rod is just a piece of aluminum with a hole drilled in it. The little hole that the point rod works in gets to big and leaks oil into the points. Good way to spend a lot of money. Buy a new one and spend the extra cash on machinists tools.

 

[Bazzer]

I would throw it and get a different one. The camshaft is just floating in a hole drilled in an aluminum block and so is crankshaft. The rod is just a piece of aluminum with a hole drilled in it. The little hole that the point rod works in gets to big and leaks oil into the points. Good way to spend a lot of money. Buy a new one and spend the extra cash on machinists tools.

If you saw how many tools I have you would not be telling me to buy more !!

 

[MRA]

Make them out of whatever bit of pipe you have which is nearest to the size you need?

(Well, unless it's nylon pipe, I guess). I'm not taking the mickey; that's what I would do, it's not going into space and from the sounds of it something else will wear out pretty soon anyway!

Or - pull them out, indent the ID of the ali bores they are meant to press into with a centre punch all over, and then push them back in tight (for a while), to give you some time to think about it!

Or - go through your tubes of out of date Loctite (is this just me? I seem to inherit this stuff, which is great as it is mind-blowingly expensive to buy and appears to work even 40 years out of date) and wonder which one might cope with the most heat?

 

[mcostello]

The way I have seen it in aBriggs and Stratton manual to fix it is to take a flat punch and go all around the seat staking it into place.

 

[bluejets]

Specifically, I have to get the valve seats tight in the case again, it is an alu case side valve engine and the valve seats rattle around in their pockets in the case.

Centre punch around the edges of the valve seat, in the aluminium, perhaps 1mm from the edge of the seat, with the seat in place.
Go all way around, perhaps a dozen or more locations.

 

[Nerd1000]

Ductile iron is often used for car engine valve seats. I'd give that a go. Keep in mind that these engines are disposable so don't spend too much money on one. They burn oil by design and have numerous dubious 'value engineered features' like aluminium cylinder bores, no bearing shells, etc.

By sheer coincidence I just fixed up a similar B&S engine with valve trouble. In my case the valves themselves were worn so bad that there was a groove you could catch your nail on all around the sealing face of the valve. Seats (inexplicably) were fine. I machined the valves until the grooves cleaned up and re-lapped them to the seats.

After that you have to grind the valve stems to re-establish clearances, taking care not to make them too wide because the B&S solution to a compression release on the sidevalve motors was to hold the intake valve about 0.01" open on the compression stroke. Make the clearance wide enough and this 'controlled leak' won't work anymore, making the engine difficult to crank.

Then you spend an hour fighting the valve spring keepers trying to get the darn thing back together.

 

[lathe nut]

Bazzer, I have been working on small engines for over 50 years and owned a lawnmower shop, sales and repairs, over the years it was only the Briggs&Stratton that would have the seats come loose and only on certain models, if you put the seat in and take a center punch, (small one) and sharp, put the valve in with the spring, that will seat it, light pings across from each other then get them closer and closer together, it will seat perfect and won't come loose again, another thing that will probably be a carbon built on the stem of the valve do not remove it, like with a wire wheel grinder, that is caused by the block wearing and the oil coming through to the firing chamber, if you leave that it will cut that down it makes a seal, if you remove it when you start the engine you will get a puff of smoke, so leave that alone, I am in my Seventies retired and still have a repair shop at home, it hard to get away from that kind of work and like you, tools, tools and more tools, I started work on them when I was about 9-10 years old (when they were extremely simple and they were old) I made several of my tools, like to remove the valve spring with plyers the handles would grasp the spring, crude but it worked, think it trough, you will overcome every time, Lathe Nut​

 

[ignator]

I came to this post to see what sort of heat treat steel should be used to make a valve seat. I'm only seeing recommendations of using common pipe or ductile iron. I understand this is a cheap B&S engine, and disposable. I fix mine also. But a few years back I needed to make a new exhaust valve seat for a 25HP Onan engine, I asked this same question of what tool steel should be used for the seat. And I never found anyone that knew what material is correct and can take hot exhaust gases. The Onan had a cast aluminum block with cast iron cylinder liners cast as part of the manufacturing process. The seat got so loose, that it wallowed the press fit clearance to where peening or staking it back in place was not possible.
So the question is, for an engine you want to operate for hours of duration and at power, what steel alloys that are hardened, would be the correct choices?
I have the valve seat grinding equipment (too many tools) so hardened seats and valves are not an issue.
Seems like the correct material is private intellectual property as to the correct material to use for valve seats. They have to take thermo cycling, and stay put in dissimilar material for very long operating times.

 

[RM-MN]

Stellite seems to be the proper metal for exhaust valve seats. Now you have to decide if the engine is worth the cost and where to get the stellite.

 

[ignator]

Stellite seems to be the proper metal for exhaust valve seats. Now you have to decide if the engine is worth the cost and where to get the stellite.

My understanding is Stellite is a special conformal coating of valves to enable high temp operation. I've never heard of it in a solid form to make valves or seat from.
I'll have to research that.

 

[stanstocker]

Rather than speculate, here's the info on stellite:

https://en.wikipedia.org/wiki/Stellite
I know it was one of the earliest very high temp operating cobalt materials for cutting tools, but wasn't aware of the crazy high amounts of chromium and tungsten. There's a video out there of a huge lathe such as used for ship engine cranks taking massive cuts with the "new wonder material stellite", complete with the entire business end of the cutter glowing away and cutting without any issue. I wish I knew what video it was, probably one of the "Industry On Parade" sorts of videos that were popular in movie theaters and shown mixed in with cartoons and other shorts before the main feature was shown. For cutters I think it's been displaced by carbide or more exotic materials like PCD.

Happy reading,
Stan

 

[SmithDoor]

Before long I have to overhaul a Briggs and Stratton lawnmower engine.

Specifically, I have to get the valve seats tight in the case again, it is an alu case side valve engine and the valve seats rattle around in their pockets in the case.

I think I need to make some new seats with a slightly larger OD to get a good fit into the case.

So what is the right material to make the valve seats from?

Thanks

Barrie

If I remember B&S engines they just casting in later years.
Most I run cross was a high carbon steel like 1060.
I would use a O1 tool steel it is easy to come by.

Dave

 

[mcostello]

I remember seeing a video showing that Stellite was harder at red heat than at room temperature. It was on the internet so it must be true. Also seen that valves only had the valve face treated with Stellite.

 

[Nerd1000]

I came to this post to see what sort of heat treat steel should be used to make a valve seat. I'm only seeing recommendations of using common pipe or ductile iron. I understand this is a cheap B&S engine, and disposable. I fix mine also. But a few years back I needed to make a new exhaust valve seat for a 25HP Onan engine, I asked this same question of what tool steel should be used for the seat. And I never found anyone that knew what material is correct and can take hot exhaust gases. The Onan had a cast aluminum block with cast iron cylinder liners cast as part of the manufacturing process. The seat got so loose, that it wallowed the press fit clearance to where peening or staking it back in place was not possible.
So the question is, for an engine you want to operate for hours of duration and at power, what steel alloys that are hardened, would be the correct choices?
I have the valve seat grinding equipment (too many tools) so hardened seats and valves are not an issue.
Seems like the correct material is private intellectual property as to the correct material to use for valve seats. They have to take thermo cycling, and stay put in dissimilar material for very long operating times.

There are lots of options for valve seat material depending on severity of service. Many older cars used seats cut directly into the grey iron cylinder head. Later as specific power outputs increased and leaded fuels were dropped they had to be hardened, either by induction hardening the iron around the seat or putting in a hardened insert. These days the 'bog standard' option seems to be ductile iron or tool steel hardened 40-50 Rockwell C, this is still machinable using carbide tools. There are higher end options like various powder metallurgy materials.

If you want to get into real exotica, racing engines often use seats of beryllium copper, chosen for its combination of hardness and thermal conductivity (helps cool the valve). If you want to put lipstick on a pig by using this in your B&S mower, beware as the dust produced by machining it is poisonous and carcinogenic.

Personally I'd use ductile iron in the as-supplied hardness of about 180 HB. Briggs engines don't run fast and hard enough to require hardened seats, and if you're really worried about seat recession regardless a bit of lead replacement additive in the fuel is probably cheaper than the time involved in going all high tech with heat treated valve seats or exotic alloys.

 

[ignator]

There are lots of options for valve seat material depending on severity of service. Many older cars used seats cut directly into the grey iron cylinder head. Later as specific power outputs increased and leaded fuels were dropped they had to be hardened, either by induction hardening the iron around the seat or putting in a hardened insert. These days the 'bog standard' option seems to be ductile iron or tool steel hardened 40-50 Rockwell C, this is still machinable using carbide tools. There are higher end options like various powder metallurgy materials.

If you want to get into real exotica, racing engines often use seats of beryllium copper, chosen for its combination of hardness and thermal conductivity (helps cool the valve). If you want to put lipstick on a pig by using this in your B&S mower, beware as the dust produced by machining it is poisonous and carcinogenic.

Personally I'd use ductile iron in the as-supplied hardness of about 180 HB. Briggs engines don't run fast and hard enough to require hardened seats, and if you're really worried about seat recession regardless a bit of lead replacement additive in the fuel is probably cheaper than the time involved in going all high tech with heat treated valve seats or exotic alloys.

Thank you for your post. I'm not wanting to fix a B&S as the OP is doing. I was looking for general information for the repair of the Onan engine. It's a very old design. Cummings bought them a few years back and stopped all parts deliveries. So it's make the parts or scrap it. But I was asking more for in general valve seat should I ever repair a engine that needs to work full time. My Onan was installed in a Hydra-Mac Skid Steer, of ~1972 vintage. It puts out lots of low RPM torque. Which seems perfect for hydrostatic drives.
I certainly am not interested in racing or exotic materials. I certainly understand Beryllium toxicity. Where I worked it was used in springs, and they worked darn good with that material in the brass.

 

[RM-MN]

Now that we have beat the subject to near death, instead of Stellite I would probably just go with mild steel as it would be easier to work with and still probably outlast the rest of the Briggs & Stratton.

 

[Nerd1000]

Thank you for your post. I'm not wanting to fix a B&S as the OP is doing. I was looking for general information for the repair of the Onan engine. It's a very old design. Cummings bought them a few years back and stopped all parts deliveries. So it's make the parts or scrap it. But I was asking more for in general valve seat should I ever repair a engine that needs to work full time. My Onan was installed in a Hydra-Mac Skid Steer, of ~1972 vintage. It puts out lots of low RPM torque. Which seems perfect for hydrostatic drives.
I certainly am not interested in racing or exotic materials. I certainly understand Beryllium toxicity. Where I worked it was used in springs, and they worked darn good with that material in the brass.

I'd probably still use unhardened iron seats in your Onan. Industrial engines are usually much less stressed than auto engines at their rated power, and us home gamers usually don't run our stuff too often. Even if the seats have shorter lives than the originals they'll probably last long enough.

 

[Bentwings]

I would throw it and get a different one. The camshaft is just floating in a hole drilled in an aluminum block and so is crankshaft. The rod is just a piece of aluminum with a hole drilled in it. The little hole that the point rod works in gets to big and leaks oil into the points. Good way to spend a lot of money. Buy a new one and spend the extra cash on machinists tools.

Haha I was just ready yo say the same thing. He would spend more on tools just to make new seats and valves for a questionable fix. I have a perfectly good self propelled more I’ll gladly give to anyone that wants it. It’s a one pull starter and cuts grass has a good belt a good drive wheels . I just can’t handle it even for my miscule yard. I’m just getting old and running out of gas. The mower has been run on non oxy premium for the 5+ years I’ve had it. It runs good there may even be a grass bag . I’m probably on the other side ofvthe planet .