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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

Rockwell hardness of valve seat insert



 
 
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  #1  
Old August 30th 07, 03:49 AM posted to rec.crafts.metalworking
sk
external usenet poster
 
Posts: 16
Default 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
45. 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.

Ads
  #2  
Old August 30th 07, 06:00 AM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 954
Default Rockwell hardness of valve seat insert

On Aug 29, 8:49 pm, sk wrote:
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
45. 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.


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

  #3  
Old August 30th 07, 10:26 AM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 344
Default Rockwell hardness of valve seat insert

sk wrote:

I machined a replacement insert from O2 round stock, currently at Rc
20, will this last a few years without hardening?


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
--
The lowcost-DRO:
http://www.yadro.de
  #4  
Old September 3rd 07, 12:57 AM posted to rec.crafts.metalworking
sk
external usenet poster
 
Posts: 16
Default Rockwell hardness of valve seat insert

On Aug 30, 4:26 am, Nick Mueller wrote:
sk wrote:
I machined a replacement insert from O2 round stock, currently at Rc
20, will this last a few years without hardening?


Probably not.
The material should be shatter proof and corrosion resistant. Federal Mogul
hasvalveseats (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
--
The lowcost-DRO:
http://www.yadro.de

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

 




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