Valves & seats

Had a closer look at my -73 850 head, having some work done, and noticed the exh valves seems to sit very deep in the seats.


And I don't quite like the look of the valve either, the aligning surface shouldn't look like this, or? And I don't just mean the pitting, but the way the angled surface looks.


Is this a poor job done by PO? Are there different sizes of valves that fit the 850? And as seen in this pic the seat looks to be a smaller diameter than the exhaust channel, there's an edge showing pretty well here. Normal?

fiatfan said:

Had a closer look at my -73 850 head, having some work done, and noticed the exh valves seems to sit very deep in the seats.

And I don't quite like the look of the valve either, the aligning surface shouldn't look like this, or? And I don't just mean the pitting, but the way the angled surface looks.

Is this a poor job done by PO? Are there different sizes of valves that fit the 850? And as seen in this pic the seat looks to be a smaller diameter than the exhaust channel, there's an edge showing pretty well here. Normal?

Click to expand...

The seats are way too wide. The spec is 1mm wide for intake and 1.5mm wide for exhaust.
They can get this way from high mileage but it looks like someone has cut your seats very wide.
If they are run this way they will pack up with carbon and fail. They show signs of pitting now. Jim

Thanks Jim, my concern was that I think the valves seem to sit very low in the seats, but that's not the case? Do I need to buy new valves, I suppose you shouldn't grind them? Is there a specific maximum length of the valve stem that protrudes from the top of the guide? (Before it starts messing up the geometry of the rockers.)
Tommy

fiatfan said:

Thanks Jim, my concern was that I think the valves seem to sit very low in the seats, but that's not the case? Do I need to buy new valves, I suppose you shouldn't grind them? Is there a specific maximum length of the valve stem that protrudes from the top of the guide? (Before it starts messing up the geometry of the rockers.)
Tommy

Click to expand...

I would not be concerned about geometry changes from valve stem length. The affect is minimal.

It is hard to say by looking at pictures but often if the correct three angles are used to make a proper seat the seats can be saved.
If you have to get into the aluminum around the seat to get the correct angles then the seat will need to be replaced. Jim

Thanks again Jim, sounds good. I'll take the head to a shop who has done good work for me before.
Tommy