<VV> Seat Life WAS Valve Seats

[Mark Durham]

Ken, you are correct in your last statement, it is the skill of the
machinist in using the tools needed to replace the seats. To remove,
I've always used a water injection tool. You heat the head and insert
the tool into the guide and shoot water on the seat, it shrinks and
comes out with the tool. Where the skill comes in is measuring the
machined hole in the head and figuring the interference fit to the new
seat. I always go to the tighter side of the limits set by the
engineers using a oversize seat if necessary and have never lost a seat
in engines up past 375 hp (aircraft). To install, freeze the seat for a
couple of hours, heat the head, put the seat on the chilled tool, slip
it into the guide until it seats in the hole, they drop right in with
no damage. Mark Durham

Sent from my Windows Phone
From: Ken Pepke
Sent: 5/5/2012 6:22
To: Vair Views
Subject: <VV> Seat Life WAS Valve Seats

Lon's thinking is still correct.  Inserted valve seat failure is
neither an age nor a mileage condition.  A newly inserted valve seat
starts its life from exactly the same place as an original that has
not moved.  That is to say the newly installed seat has the same odds
of failure as the unmoved original which it replaced.  Seat failure
comes with excessive heat [or poor installation of a replacement.]
If a seat is replaced, it really needs to be of the higher press
variety because removal of the original seat damages the head in the
seat area.

Heads on a 140hp engine run hotter because they make more power, use
more fuel while doing so, and produce more heat, so they have a
greater chance of seat failure.  This frequently [but not always]
happens on vacation such as a long trip to a Corvair meet.  These are
times when the car is loaded, running faster than usual for prolonged
periods of time and getting hotter than usual.

Bottom line:  The single most important factor in longevity of
replacement valve seat inserts is the skill of the machinist.

Ken P
Wyandotte, MI
Worry looks around; Sorry looks back, Faith looks up.

************************

> From: Bruce Schug <bwschug at att.net>
> Date: May 4, 2012 12:33:46 PM EDT
> To: VirtualVairs <virtualvairs at corvair.org>
> Subject: <VV> Valve Seats
>
> While I don't have the experience driving scores of Corvairs, or
> building dozens of engines, some of you do, I'm in the "replace 'em"
> camp.
>
> When I built my engine in '86, I sent the heads to Bob Coffin. This
> was when he was still in MA. I had him replace all the seats. Now, a
> distinction must be made here. These are the "high press" seats that
> some of the folks install, not just new seats. I did "everything" to
> this engine and wanted it to be completely reliable as well as
> powerful on the street. I didn't want to be tearing it down in a few
> thousand miles to replace a seat.
>
> I understand the idea of inspecting a head to see if a seat has
> started to move. I wasn't worried about that. I was worried about a
> seat that hadn't started to move yet, but would start in 10,000 miles,
> then let go in another thousand.
>
> Since then my engine has been driven in every kind of condition
> possible. It has run thousands of miles on interstates running an air-
> conditioning system. It was the fastest car driven to VIR in 2002. It
> is unbeaten in three convention autocrosses. It has made scores of
> other autocross runs with an MSD chip ranging from 6,200-6,800. At
> times, it has been driven on the rev limiter to the next corner, when
> an upshift wasn't worth it. It has scored more than 50 mpg a few times
> in economy runs. It has won rallies. It has been driven on the
> "Corvairs Drive the Tail of the Dragon" three times. It has run up and
> down the mountains of Western North Carolina for miles and miles. What
> more could you ask from an engine? Last year, I rebuilt the carbs
> after all these years and over 60,000 miles, but nothing else has been
> apart.
>
> Build it right once and enjoy it.
>
>
>
>
> Bruce
>
> Bruce W. Schug
> Membership Chair,
> CORSA South Carolina
> CORSA member since 1980
> '67 Monza, "67AC140"
> bwschug at att.net



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