Spark plug help!

[jglover_81]

I need help with which plugs I need. My current plugs are 13/16 and they hit the heads before they are all the way in. It's a 77 motorhome 440 in my 72 scamp with a fresh rebuild. This is the only thing keeping me from firing this thing up. Thanks in advance!

 

[winstoninwisc]

sounds like you need a peanut plug ??

 

[TrailBeast]

sounds like you need a peanut plug ??

The plugs that take a 5/8 socket (peanut plug) probably.
What ever reason a regular sized plug wouldn't fit in the plug boss could really only be that it uses the smaller plugs.

 

[yellow rose]

I need help with which plugs I need. My current plugs are 13/16 and they hit the heads before they are all the way in. It's a 77 motorhome 440 in my 72 scamp with a fresh rebuild. This is the only thing keeping me from firing this thing up. Thanks in advance!

I don't show a motor home plug per se, but the only head I see that take a 5/8 hex is the vin code A and it calls for a RV12YC.

I have never seen this head in almost 35 years of screwing with this stuff. Must be a rare bird.

 

[Dubob]

They are probably a 3751213 motor home head used on a 440-3. They are a 5/8 hex taper seat. If you have a true parts store they should be able to look them up for a m300-m600 truck. Here's some info I found on line maybe help you out but please don't take it as the final word.

Additional info 440-3 plug info:
14MM; .460 reach; 5/8 hex; tapered seat; resistor type; gap = .035"
original plug: Champion BL8Y (no longer available) which is replaced by Champion RV9YC
equivalent plugs:
Autolite: 23 (Traditional), AR23 (racing), AR12 (racing), AR13 (racing)
NGK: 2623 (Traditional), 5034 (Racing), 4449 (racing)


The heads are kind of an oddball one off for Mopar. There were extra cooling passages/ steam holes in them as well as the block. My 440 is a motor home engine and had these features. I didn't use the heads but no issue with the block the extra passages get blocked by the head gasket.

 

[jglover_81]

I guess the important infoni left out was the aluminum aftermarket heads. I had the problem with the steel heads and spark plugs hitting a casting "bump" but the aluminum heads have a smaller hole machined that won't let the bigger plug in all the way. I did some research on the trick flow heads and they require autolite 3924 plugs so I have a buddy getting me a set of NGK's that cross. Thanks for the help!

 

[AndyF]

Yeah you left out the important info in your post! Most aftermarket aluminum heads use a 3/4 reach plug with the smaller hex.