implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Good morning All:
This is a question for all you automotive guys.
I've been asked to make replacement valve guides for a customer who apparently makes and runs antique race cars.
The original guides are cast iron (based on what he's told me...I have no idea what motor this is going into)
He wants replacements in 660 bronze.
He gave me a sample (a "good" one) from the ones he pressed out of the head and I'm supposed to make the new ones "the same" as the old.
Here are my questions:
Do I make the press fit for the bit that goes into the head the same as it was (0.7515" ) which assumes a press fit of 0.0015" if the bores in the head are nominal 3/4" diameter.
Do I bore to +0.002" clearance for the valve stems as per the sample, assuming the bores will collapse when the guides are pressed in and can simply be honed back to size after fitting.
Can 660 bronze be easily honed with the standard tools you'd use in this application or is this going to be miserable to do?
I'm a bit concerned about the consequences of just making and putting these new guides in without thinking this through first.
I ask because the coefficient of thermal expansion for 660 bronze is almost double that for cast iron...with too hefty a press fit, is there a risk of cracking the head when it all gets hot?
Is there a risk of the bushing collapsing onto the valve stem and making the valves stick?
The customer can't answer any of these questions and the mechanic downstairs (I'm directly above an auto restorer) won't stick his neck out so I'm kind of just going with the best consensus I can get here.
I was hoping one of you would have specific experience to point me to any pitfalls.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
This is a question for all you automotive guys.
I've been asked to make replacement valve guides for a customer who apparently makes and runs antique race cars.
The original guides are cast iron (based on what he's told me...I have no idea what motor this is going into)
He wants replacements in 660 bronze.
He gave me a sample (a "good" one) from the ones he pressed out of the head and I'm supposed to make the new ones "the same" as the old.
Here are my questions:
Do I make the press fit for the bit that goes into the head the same as it was (0.7515" ) which assumes a press fit of 0.0015" if the bores in the head are nominal 3/4" diameter.
Do I bore to +0.002" clearance for the valve stems as per the sample, assuming the bores will collapse when the guides are pressed in and can simply be honed back to size after fitting.
Can 660 bronze be easily honed with the standard tools you'd use in this application or is this going to be miserable to do?
I'm a bit concerned about the consequences of just making and putting these new guides in without thinking this through first.
I ask because the coefficient of thermal expansion for 660 bronze is almost double that for cast iron...with too hefty a press fit, is there a risk of cracking the head when it all gets hot?
Is there a risk of the bushing collapsing onto the valve stem and making the valves stick?
The customer can't answer any of these questions and the mechanic downstairs (I'm directly above an auto restorer) won't stick his neck out so I'm kind of just going with the best consensus I can get here.
I was hoping one of you would have specific experience to point me to any pitfalls.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining