Valve Clearance Questions

[805moparkid]

So after looking around i really had no answer for my questions so i'll ask.

What is the minimum clearance:

between valve margins (int to exh)?

between valve seats, i hear some people say as long as the valves are not touching your fine, others say the seats shouldn't even touch (which probably isn't realistic)

and finally from valve to bore?

 

[805moparkid]

bump

 

[Cudafever]

OK I'll give my 2c
it keep ring in my head .020(i don't know for sure)

As far as the valve seats go i have a head that got damaged by a broken valve. Had a hardened seat put in the intake as well as the exh. The intake and exhaust inserts sightly overlap on the out edge.

 

[OldmanRick]

Seat wise, I have to think there's a difference in spec between a street engine vs race. I've seen some big valve race heads with really close seats/valves. How much heat was transferred from the exhaust to the intake, I don't know. After all, they still occupy the same space. But, from a durability standpoint, especially on a street or a endurance engine, I have to think more clearance is better. I will be watching for other opinions.... Never to late to learn.

On the bore clearance, my thoughts are, as long as a larger diameter valve doesn't get to the point of wall interference, the little lost against the bore, will be made up for, or more, in the rest of the circumference as far as breathing is concerned. Is that correct? I'm not totally sure, but my thinking say's yes.....in my mind...lol.

 

[Cudafever]

Seat wise, I have to think there's a difference in spec between a street engine vs race. I've seen some big valve race heads with really close seats/valves. How much heat was transferred from the exhaust to the intake, I don't know. After all, they still occupy the same space. But, from a durability standpoint, especially on a street or a endurance engine, I have to think more clearance is better. I will be watching for other opinions.... Never to late to learn.

On the bore clearance, my thoughts are, as long as a larger diameter valve doesn't get to the point of wall interference, the little lost against the bore, will be made up for, or more, in the rest of the circumference as far as breathing is concerned. Is that correct? I'm not totally sure, but my thinking say's yes.....in my mind...lol.

I know that adding a bore notch will improve flow as well as power..............But this still, does not make your statement Wrong :-D

 

[OldmanRick]

I know that adding a bore notch will improve flow as well as power..............But this still, does not make your statement Wrong :-D

I agree with you on the notch.

I don't know if there is a definitive answer for these questions. Some of the "uber" pro racers run clearances thru out their engines that would make most of us just shake our heads. In 74'/75', i watched Bill Jenkins dump close to 10 cans of BarsLeak in his radiator during a match race at Maryland International Raceway. I thought it was nuts, but super thin engine specs and a win at all cost mentality make some do crazy things....


P.S. I should add that I didn't see the Grump actually put ten cans in his car. I saw him dump 2 in the trash can and didn't think much of it.....until I went over to throw out a cup and there were about ten in the can. Maybe he had just cleaned out his trailer...lol.

 

[805moparkid]

OK I'll give my 2c
it keep ring in my head .020(i don't know for sure)

As far as the valve seats go i have a head that got damaged by a broken valve. Had a hardened seat put in the intake as well as the exh. The intake and exhaust inserts sightly overlap on the out edge.

im not exactly sure what you mean

Seat wise, I have to think there's a difference in spec between a street engine vs race. I've seen some big valve race heads with really close seats/valves. How much heat was transferred from the exhaust to the intake, I don't know. After all, they still occupy the same space. But, from a durability standpoint, especially on a street or a endurance engine, I have to think more clearance is better. I will be watching for other opinions.... Never to late to learn.

On the bore clearance, my thoughts are, as long as a larger diameter valve doesn't get to the point of wall interference, the little lost against the bore, will be made up for, or more, in the rest of the circumference as far as breathing is concerned. Is that correct? I'm not totally sure, but my thinking say's yes.....in my mind...lol.

i will totally agree on longevity in relation to clearance and heat. I also agree with the shrouding loss vs size gain.

I know that adding a bore notch will improve flow as well as power..............But this still, does not make your statement Wrong :-D

right because your again un-shrounding the valve

I agree with you on the notch.

I don't know if there is a definitive answer for these questions. Some of the "uber" pro racers run clearances thru out their engines that would make most of us just shake our heads. In 74'/75', i watched Bill Jenkins dump close to 10 cans of BarsLeak in his radiator during a match race at Maryland International Raceway. I thought it was nuts, but super thin engine specs and a win at all cost mentality make some do crazy things....

Yea grumpy did what it took!