Valve Seat Question

[North Beach]

OK, we're throwing this around over in the re-builds section and I thought I'd ask here since this is where those that know hang out

I experienced a pushed out valve supposedly due to not having hardened valve seats in my 110 HP mercruiser. The folks at the machine shop did a re-build and only replaced 4 valve seats. Does that sound right? Is it only the intake valves, or only the exhaust valves? If any of you folks could explain it to me I'd be greatly appreciated. I'd like to torque the head back on this weekend but I don't want to have to do this again in the near future.

 

[JustJason]

Re: Valve Seat Question

the valves seats are integral to the head. Not a press in piece that you'd find on an aluminum head. I'm assuming here you tuliped the exhaust valves. If you did then you more than likely have a detonation issue and if you don't fix it, it will happen again. A 110 is a GM 2.5 liter. Those heads will take a beating, even if you tuliped the valves the heads are 90% of the time okay. If the seat was that bad you would have had to replace the entire head. If the valves were tuliped then you would have to replace the valves, and lap them by hand into the seats to make sure the valve got a good seal. Then you flip the head and fill it with acetone or something similar and make sure the valves are leaking.
Hope that helps.

 

[North Beach]

Re: Valve Seat Question

Jason, I'm totally lost now. The folks at the machine shop took one look at the head and told me that the head had a rebuild in the past (in 82) and that the hardened seats were not used resulting in this problem due to us using unleaded gas.

When i took it in the valve looked open way further than the rest and the shaft was setting higher than any of the others.

 

[stonyloam]

Re: Valve Seat Question

Just went through something similar. Took my 470 (iron) head in for a valve job. They replaced all 4 exhaust valve seats and one intake seat (due to pitting caused by coolant leak). The exhaust valve seats are the ones that take a beating. Think about it, the intakes only allow cool fuel/air mix to enter the cylinder, and are closed during the compression and exhaust strokes. The exhaust valves have to pass the hot exhaust gasses when they are purged from the cylinder. Take a look at Bond-O's avatar. I am sure that they checked to see if the intakes were seating properly. Hope this helps a little.

 

[mkast]

Re: Valve Seat Question

the valves seats are integral to the head. Not a press in piece that you'd find on an aluminum head.

How else would you install a replacement seat?

 

[stonyloam]

Re: Valve Seat Question

How else would you install a replacement seat?

I am no machinist, but I believe they use a mill with a valve seat cutter guided by a rod in place of the valve to cut out the old valve seat, leaving a round flat bottomed hole. The new valve seat insert looks like a metal ring and is pressed into the milled opening, the head surfaced and the seat ground.

 

[bigskiohio]

Re: Valve Seat Question

Here is a exhaust with hardened seat installed, it a metal ring like stony says.

 

[Don S]

Re: Valve Seat Question

Replacing valve seats in automotive heads works great. But I have never seen or heard of anyone having sucess doing that in a marine engine. It may be due to the machine shops inability to do the job correctly, I don't know. But we tried getting heads rebuilt at 3 different machine shops (about 10 or 12 years ago) and the seats came loose in all three. Never tried it again after that.

 

[totx]

Re: Valve Seat Question

I experienced a pushed out valve supposedly due to not having hardened valve seats in my 110 HP mercruiser. The folks at the machine shop did a re-build and only replaced 4 valve seats. Does that sound right? Is it only the intake valves, or only the exhaust valves?

My 1986 3 liter only had "loose" valve seats on the exhaust valve.
(valve seat inserts ore whatever is the correct name...lol)

 

[bigskiohio]

Re: Valve Seat Question

sorry wrong link

 

[totx]

Re: Valve Seat Question

Replacing valve seats in automotive heads works great. But I have never seen or heard of anyone having sucess doing that in a marine engine. It may be due to the machine shops inability to do the job correctly, I don't know. But we tried getting heads rebuilt at 3 different machine shops (about 10 or 12 years ago) and the seats came loose in all three. Never tried it again after that.

How long time did it take before the seats come loose?

I had this job done in june this year, but boat is sold already.

 

[mkast]

Re: Valve Seat Question

I am no machinist, but I believe they use a mill with a valve seat cutter guided by a rod in place of the valve to cut out the old valve seat, leaving a round flat bottomed hole. The new valve seat insert looks like a metal ring and is pressed into the milled opening, the head surfaced and the seat ground.

Of Course the replacement seat is pressed in, what don't you understand about sarcasm?