Head reworking

[chitwnvw]

What do they do when they recondition a head?

Do they replace this whole area when reworking a head?

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I thought it had something about going from leaded to unleaded gas. I don't recall seeing any seated ring for the valve to seat into. What is it that they have to heat the head up for and work in, is it that ring that dropped out of Sluggo's head? What is it that they three way grind then? That ring?

[vdubyah73]

Valves and valve seats were made unleaded freindly in the late 60's
The valve seat is under the closed valve when looking at the head. Kinda hard to notice if you don't know what your looking at.

They heat the head and chill the valve seat and press it in. it's what is called an interference fit. The seat is a scosch bigger than the hole it fits in.

Yes that is a dropped seat on Sluggo's head. Running too hot can do it and just plain bad luck with an old head casting. That is why the guru's reccomend brand new AMC castings and a rebuild with all ne seats and hardware. Pricey!

A thre angle valve job is when the seating interface of the valve and seat is three seperate matching angles machined and ground on both the vale and seat. Promotes better airflow and sealing.

Bill

[Amskeptic]

A three angle valve job is when the seating interface of the valve and seat is three seperate matching angles machined and ground on both the vale and seat. Promotes better airflow and sealing.

Bill

Well, that's what they tell you at any rate.
A three-angle valve grind is not a "performance enhancement"
or "better airflow and better sealing" deal.
It is a necessary and factory demanded operation
to insure that the valve seat contact width is dead-on accurate.

The contact surface itself is at 45º. When you have ground the surface smooth, it will be wider than it was. So you kiss the outer edge with a 15º stone and that narrows the 45 at the top. You hit the inner edge with a 75º stone to narrow the 45 at the bottom. You pick which one to emphasize based on how far up or down on the seat the valve sits.

The surface area of the contact patch is critical. It needs to be big enough to transfer heat from the valve to the seat. If it is too big, carbon can build up between the valve and the seat. This promotes incandescent carbon pocking and then a nice a nice burnt valve. Too narrow of a seat width hampers heat transfer, but the pressure goes up enough to not allow carbon build-up.
Colin
(p.s. ask for a three angle grind to give 2.2-2.5mm contact width. Don't let them poo-poo you, aw that's racing crap. . . air-cooled VWs are harder on valves than any water-cooled engine)

[chitwnvw]

Thanks. Just trying to understand what happened to Sluggo. Rimco told me they've never had one of their seat drop yet. Don't know whether to believe that, but that's what the guy on the phone said. Hopefully they knew what they were doing, because when I had the work done, I sure didn't have a clue to ask for a certain surface area for the seat to get proper heat transfer, while minimizing carbon build up. Hopefully, there won't be a next time, but if there is, I'm filing it away.

[Sluggo]

Thanks. Just trying to understand what happened to Sluggo. Rimco told me they've never had one of their seat drop yet. Don't know whether to believe that, but that's what the guy on the phone said. Hopefully they knew what they were doing, because when I had the work done, I sure didn't have a clue to ask for a certain surface area for the seat to get proper heat transfer, while minimizing carbon build up. Hopefully, there won't be a next time, but if there is, I'm filing it away.

Rimco is one of the best. But that is crap. Seats drop. They may have very few. But after 100,000 miles?

[CASEY79WESTFALIA]

Rimco is lying to you becuase my last heads were done by Rimco and they dropped a seat at 10k miles. Junk rebuild! Go with Adrian at Headflow Masters or Raby heads if you can afford it!