Rockwell hardness of valve seat insert

OK, my ONAN engine in the Mity Mack scid steer has lost power to the point it is clear it is only working on one cylinder. So I find that one of the intake valves has an insert that fell out after pulling out the valve. There was 0.030 inches of slop between the OD of the insert and the bore of the aluminum block where it existed. OK I can bore out the block.

What rockwell hardness should the new insert have? The valve was Rc

  1. I would think the seat should be in the same range.

Anyone here have a knowledgeable value for what the Rc hardness should be for valve seats.

Searching google gets patents to sintered processes,. but no stated value. Ratz!

ignator

PS. Onan no longer supports this 1972 engine. It's a NTC engine, it may be time to put a new engine in it that is maintainable.

I machined a replacement insert from O2 round stock, currently at Rc

20, will this last a few years without hardening? If I harden it, Rc 55 is around it's peak before tempering, how far down should this be drawn for a reliable hardness?

Thanks to you engine experts for input.

Reply to
sk
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It's been the practice for air-cooled VW engine rebuilders to use Stellite or similar material for valve seat replacements for decades. If you're using unleaded gas, you'll need it. Exhaust gas temperatures will pretty much make a joke of any heat-treating you do to regular steel. Also, you're going to have to have a really good shrink fit for your seats. Usual VW practice is to heat the head up in the oven and freeze the seat inserts with liquid nitrogen. If you try just a force fit, you're going to broach the recess and you get to do it all over again, probably won't stay put past the first part of the first startup. VW rebuilders TIG weld the heads and remachine the recesses to fit the standard seats. Have fun!

Stan

Reply to
stans4

Probably not. The material should be shatter proof and corrosion resistant. Federal Mogul has valve seats (and should have stock material to make your own). If you can't get that, cast iron (not the softest one) should be a fix. If it has nickel/chrome in it, the better.

Nick

Reply to
Nick Mueller

Thanks for your replies.

As this was the intake valve seat, I heated it with O-A torch and quenched in oil, then heated to 400F for a half our to temper. Looks like Rc 50. So far, it's got too much power. Really, I'm digging a 12 x 24 foot hole next to the house with a long sloping trench, as I was backing out, the wheels were spinning and digging out to the point I was bottoming the machine. It's never had this much power since I've had it. Throttle back and I can control this beast. A pig farmer owned it before me, never fixed anything unless it would not move. I can tell from all the abuse it's had. This is a 1972 Mity Mac made in Thief River Falls MN, and packaged for Geil ag. equipment. I'm running out of summer here in Iowa, and it's got's to keep working else I have a freeze and major problem as the water pipe and sewer pipe are now exposed to freeze. I need to get a footing and

11 courses of concrete block laid and capped before the hard freeze gets me.

Sk

Reply to
sk

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