Loose valve seat in 8HP Briggs aluminum

[Kent]

My neighbor wanted me to ask you guys if the valve seat in an 8HP Briggs aluminum block (vertical crankshaft) is replaceable. He's been having problems getting this engine to run -- it'd fire, but not run. When he pulled the head, he found a lose exhaust valve seat. Can these be replaced?

[ehertzfeld]

I'm not sure, but the same thing happened to one of mine out of a 717. I would think if you talked to a machine shop, they should be able to do something. Elon

[dads707]

A friend of mine replaced one in my 6216. It has the alum block and cast iron sleeves. Heated the block to expand it and froze the seat. When he put it back it snugged up nicely. The repair shop fix is to take a punch and hit around the seat to force the alum snug.

[richp]

I know Loctite make that bearing mount stuff that will lock it in good if prepped right. It's the green colored stuff. Loctite makes a primer that helps it adhere better.

[firefoxz1]

Yes if the block area around the seat is not to messed up. I had it done once. The local machine shop here found one that he could machine to work, machined the block and then the seat once in, but as always what's he willing to pay.

[Doll]

Pinging with a round punch is the way to repair this. With the valve in place and seated firmly and you go slowly trying to make sure to keep it centered. If you can seat it, then remove the valve keeper and spring. Lap the valve and or use dye to see if your still centered. Have the seat ground to center if not. If the area is to worn to make this repair then have the aluminum built up and cut back down for a strong sweat fit on a new seat.. BTW, check the old seat very carefully for a crack. Happens a lot .

[jdm]

Doll is right. This works. I did this several years ago on one of my Dad's engines. Go ahead and peen the other valve seat while it's apart. It will save you pulling the head off again, as I had to do, should the other come loose.

[bud119195]

Ihad a valve seat pop out on a 8 hp about 2 years ago and I pushed it back in and peaned around it and it has been running since.

[MrSteele]

Doll and Bud have the solution for a loose seat. Keeping it centered is the hard part, but it is not impossible. The seat can be ground once it is pinged, or piened in place. if it is so far gone as to be tightened where it is supposed to be, a machine shop can make it work. Cost of that, versus replacement with a short block, will determine the cost of the job.

[Al]

HI, I have peened them. Use a pin punch about 3/16 dia. I start on one side, punch aluminum, go across the seat and peen once. Go 90 degrees and once, then across This gives 4 first steps 90 deg apart. Then go 1/2 way between a 90 quadrant, then directly across, then 90 from the line between these 2. The key is to do one hit, then 1 directly across, them one 90 and one across then keep halving the quadrants, until the total area has been covered. Then repeat. The key is to upset or swag the metal all the way to the base of the seat so it is gripped all the way up the side of the seat. If you do not keep going back and forth and then 90 degrees you will "move" the seat and distort it. Use a heavy hammer, but don't kill it. Repeat the cycle 3 or 4 times depending on how loose it was. A light hammer won't move the metal far enough down. Do not use a center punch as it will only move the metal at the top of the seat. Failing to get the metal swagged all the way down, leaves the seat with little metal to metal contact and then the seat doesn't transfer the heat to the fins and it will run very hot and fail again. After the seat is reinstalled, it must be re-cut with a hard seat grinder or a New Way cutter. More importantly BRIGGS STRESSES THAT THERE ONLY 3 THINGS THAT CAUSE VALVE SEATS TO COME LOOSE! 1. Mowing, or working the engine at 1/2 OR PART throttle instead of recommended governed top speed. or 2. Plugged fins or fins that are covered with grime. 3. Heat recirculation, the engine fan pulling hot air in and cooling it with air from the outlet side. At part throttle the engine block absorbs and generates more heat, and the blower fan (which operates on a square law function) only provides 1/4 the cooling air at half throttle. Every time the fan speed is doubled the output is 4 times what it was. A four time speed increase gives 16 times the air flow. This is how turbochargers are able to generate so much flow from a small turbine. With the extra heat the aluminum expands too much and then when it cools it contracts, but not as much. This continuous over heat cool cycle causes the aluminum to no longer grip or retain the seat. About 5 years ago we got a Vanguard v twin 16 in, in a 9 year old Grazer. It was running on 1 cyl. Pulled the head and a valve seat was out. Called the customer and quoted new head and install. Asked him if they mowed at half throttle. He said, Funny you should ask. We have hired kids to run this for 9 years and they just beat the heck out it. This year we hired and older guy and he just putzes around with it. Run them where they are rated. I just contacted Briggs about a 37 hp big block as a replacement for a 30 hp Wisconsin in a skid loader application. The Wisconsin is rated at 2800 RPM and we would have to keep the Briggs at 2900 to 3000 max. They said there is no way the engine would survive. A it will be down on the torque curve and lugging overheating and wouldn't adequately cool and if I put in this application and there was a failure that showed signs of overheating any warranty claim would most likely be rejected. My thoughts on valve seats. Al Eden