425 Tune-up For Dummies.....
May 17th, 2021, 06:36 AM
#1
Registered User
Thread Starter
Join Date: Aug 2019
Location: Western PA
Posts: 69
425 Tune-up For Dummies.....
Thanks to a few of you, I now know the 425 and 455 are interchangeable as far as parts. My question now pertains to a tune-up.....
1. Do these motors like a certain plug over another?
2. What is the proper plug gap (stock motor)
3. Does it require certain plug wires or can I use any for a BB GM motor?
4. Is there a step by step article somewhere on adjusting points? I am only familiar with HEI.
Any help is always appreciated.
1. Do these motors like a certain plug over another?
2. What is the proper plug gap (stock motor)
3. Does it require certain plug wires or can I use any for a BB GM motor?
4. Is there a step by step article somewhere on adjusting points? I am only familiar with HEI.
Any help is always appreciated.
May 17th, 2021, 06:56 AM
#2
Registered User
Join Date: Nov 2009
Location: Red Oak, Texas
Posts: 2,999
My opinion:
What ever heat range plug your engine runs best at. Start with the manual that fits your engine year and adjust from that.
Any plug wires that are for any points type ignition will work.
Set the points with a good dwell meter. Adjust more or less as needed for the performance of your engine.
What ever heat range plug your engine runs best at. Start with the manual that fits your engine year and adjust from that.
Any plug wires that are for any points type ignition will work.
Set the points with a good dwell meter. Adjust more or less as needed for the performance of your engine.
May 17th, 2021, 07:05 AM
#3
Administrator
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 41,053
Thanks to a few of you, I now know the 425 and 455 are interchangeable as far as parts. My question now pertains to a tune-up.....
1. Do these motors like a certain plug over another?
No
2. What is the proper plug gap (stock motor)
.030
3. Does it require certain plug wires or can I use any for a BB GM motor?
7MM, I like Taylor Spiropro wires.
4. Is there a step by step article somewhere on adjusting points? I am only familiar with HEI.
You need a tach/dwell meter. Set the point dwell to 30*. If you don't have a meter, then use a feeler gage and set the point gap to .016 on one of high points of the distributor cam lobes.
Any help is always appreciated.
1. Do these motors like a certain plug over another?
No
2. What is the proper plug gap (stock motor)
.030
3. Does it require certain plug wires or can I use any for a BB GM motor?
7MM, I like Taylor Spiropro wires.
4. Is there a step by step article somewhere on adjusting points? I am only familiar with HEI.
You need a tach/dwell meter. Set the point dwell to 30*. If you don't have a meter, then use a feeler gage and set the point gap to .016 on one of high points of the distributor cam lobes.
Any help is always appreciated.
May 17th, 2021, 07:23 AM
#4
Oldsdruid
Join Date: Dec 2007
Location: Southside Vajenya
Posts: 10,534
You want a plug heat range "hot" enough to burn off deposits but not hot enough to cause detonation. AC R45 or equivalent is a good start. Gap at .030 or .035.
Use a good quality point and condenser set. NAPA Echlin or Standard Motor Parts Blue Streak are good. NOS Delco are even better if you can find them.
You need a dwell meter/tach to set them. Good ones are usually close enough out of the box to start the car. GM spec is 28 to 32 degrees of dwell and most engines run well at an even 30. Use a 1/8" allen wrench to adjust the points if needed. Access is thru the window in the distributor cap. There's a flexible shaft tool available to do this.
Set dwell first, then timing. I think the 425 spec is 5° before top dead center at 500-600 rpm but may need to experiment to eliminate detonation since modern gas is not the 100 octane leaded these engines thrived on when new. Adjust timing same as HEI by rotating the distributor with vacuum advance disabled.
If you don't have a dwell-tach or engine analyzer good working ones often show up on ebay and flea markets. Sears had a line of good ones for years. Dixco were good too and all the tool trucks had their own brands. I'll assume you already own a timing light.
Good luck and have fun!
Use a good quality point and condenser set. NAPA Echlin or Standard Motor Parts Blue Streak are good. NOS Delco are even better if you can find them.
You need a dwell meter/tach to set them. Good ones are usually close enough out of the box to start the car. GM spec is 28 to 32 degrees of dwell and most engines run well at an even 30. Use a 1/8" allen wrench to adjust the points if needed. Access is thru the window in the distributor cap. There's a flexible shaft tool available to do this.
Set dwell first, then timing. I think the 425 spec is 5° before top dead center at 500-600 rpm but may need to experiment to eliminate detonation since modern gas is not the 100 octane leaded these engines thrived on when new. Adjust timing same as HEI by rotating the distributor with vacuum advance disabled.
If you don't have a dwell-tach or engine analyzer good working ones often show up on ebay and flea markets. Sears had a line of good ones for years. Dixco were good too and all the tool trucks had their own brands. I'll assume you already own a timing light.
Good luck and have fun!
Thread
Thread Starter
Forum
Replies
Last Post
