No valve seals - is this normal?

[PiratePast40]

Having a head rebuilt and noticed that there are no valve seals listed on the parts list. The manual says that some of the earlier models had seals on the exhaust valves but that they should not be reinstalled. Just curious as to why and if this is typical for a marine engine.

Engine is an early 70's OHV Volvo 4 cylinder. The automotive version does use valve seals.

 

[mkast]

Re: No valve seals - is this normal?

The manual says that some of the earlier models had seals on the exhaust valves but that they should not be reinstalled.

Without knowing what manual this is from, rarely does the factory maintenance manual send you in the wrong direction.

 

[PiratePast40]

Re: No valve seals - is this normal?

It's the Volvo manual and I'm not questioning the validity. I'm just wondering why they would want to NOT use seals in the marine version of the engine. I know that Volvo switched to hardened valves and seats in the fuel injected versions for cars and this was about the time leaded fuel was being phased out in the US. Just wondering why no seals and wondering if perhaps valve seat lubrication was a consideration.

 

[mkast]

Re: No valve seals - is this normal?

wondering if perhaps valve seat lubrication was a consideration.

Valve guide seals are on the other end of the valve, under the valve spring, seals have nothing to do with the valve seat.

 

[PiratePast40]

Re: No valve seals - is this normal?

Yes - I understand that. The valve guide seals on this engine sit on top of the valve guides and are shaped like little umbrellas. The valve stem passes through the seals.

This was not a question about assembly, simply a question to satisfy my curiosity as to why they would use valve guide seals on an engine for one application but not for another. My thought leap to valve seat cooling by allowing oil to be sucked into the valve seat was just a thought and was wondering if that might be a reason behind the lack of seals.

 

[mkast]

Re: No valve seals - is this normal?

Think about the seal, the first time the valve opens, the seal is stuck above the valve guide.
All that seal is for is to minimize oil entry into the combustion chamber, not eliminate it.
Racing engines sometimes use Perfect Circle seals. To use that seal, the valve guide boss has to be machined for the seal, which now sits on top of the valve guide forever.