Interference fit

[MG David]

I have some hardened exhaust valve seats to fit or have fitted into an old cast iron head to use with unleaded fuel.

My guess is that these are intended to be an interference fit. So how much smaller than the incert should the hole be? The seats have a small chamfer on the face that would go into the hole machined in the head.

Is there any majic version of loctite that is used in this application?

 

[MrFluffy]

Dont use loctite as a sole bond, just stick to making the fit right
From :-
http://www.aa1car.com/library/ar993.htm
" recommendations range from .003 to .006 in. for valve seats up to 2 inches in diameter."

He also says not to use loctite as it can create a thermal barrier between seat and head. And I agree if you get the fit right, you wont need it...

 

[MG David]

That was a great link. Thank you.

 

[pidgeon chit welder]

Are you changing the valve seats on a old engine so that you can run it on unleaded petrol?

If so investigate a product called Broquet by David Locke it is a catalyst that aligns the molecules and allows you to use unleaded . He is indeminified to many millions of £'ss incase of failure ..as far as I know no one has ever claimed .

It comes in the form of moulded tablets in a stainless type wire mesh cage and is lowered into the fuel tank ( I put mine on a nylon string and each car change removed it and put it in the new car. . The tablets do not appear to dissolve away. I ran an old citroen for years using Broquet and did something like 150,000 miles .

It was originally developed in WW 2 to allow the Russians to fly Spitfires using their unleaded petrol.
It is also good for keeping fuel exhaust emissions cleaner than average in modern petrol and diesel engines . I found that my modern cars also seem to have far better fuel consumption figures .

 

[MG David]

Unleaded is only part of it.

I also want fresh seats so I can cut triple angle seats to enhance flow.

 

[gaz_moose]

is in not in the workshop manual?
i seem to recall seing a picture of a head in something hot and the valve seats just drop in.

 

[pidgeon chit welder]

Unleaded is only part of it.

I also want fresh seats so I can cut triple angle seats to enhance flow.

Preheat the head once it is immaculately cleaned ( don't forget to clean and degunge the valve guides ), by using 2 x 100 watt light bulbs under it whilst it is covered in a wooden box /cabinet for at least five hours this gentle heating will expand the head without localized stress, meanwhile bung the seats and their corresponding valves in the freezer .

When you are ready simply put a valve in a seat and using a 9 inch cut off a broom stick & gently with a 2 pound hammer & the stick persuade the seat and valve to slide in the hole ..the valve stem acts as the guide to keep things trued up

Make sure the seat is fully down , then sort out the rest before you do the seat & valve grinding.
Interference fit.. usually 0.5 thou of an inch is OK but like most precise things you need figures especially where heat is in the equation.

Try a website for your type of engine /car and ask if anyone has the manufacturers technical data for that vehicle/head and the valve inserts etc.