The Ford Barn

vilanar · 01-26-2016, 12:45 PM

Hi folks,
I did take off my Offy 400 heads from 8BA , and looking the spark plug electrodes they seem to be rather deep in the pocket. Combustion chamber shrouds them quite a bit so that spark don´t have a
straight shot....
I have used NGK 6L and Autolite plugs .
Have you modified the combustion chamber or machined the head so that
plugs goes deeper in the head ?
What is the safety margin from plug to valve ?
I tried to search but didn´t find anything for this subject.
Thanks,

Ari

Ol' Ron · 01-26-2016, 03:38 PM

you can use a longer plug or use a powertip plug. I also use a large 45 Degree end mill to clearance down to the first thread. Yes some hi lift cams can hit the spark plug in the older style heads, However Offy and Edelbrock both began moving the plug up. To bad they didn't move it into the transfer area.

BillM · 01-26-2016, 04:41 PM

Here is a drawing I did that shows some alternatives:
https://www.fordbarn.com/forum/attach...7&d=1449085666

Ol' Ron · 01-26-2016, 07:11 PM

Excellent drawings. It shows how a power tip plug might fire the chamber with a 45 degree relief

tubman · 01-26-2016, 07:35 PM

I agree with Ron, "excellent drawings", but it troubles me that all of them show the plugs recessed in the heads. That can't be the way the manufacturers designed them can it? I am going with "Edmunds Custom" heads that have the spark plug moved enough so that the electrodes miss the valves. This seems to make a lot of sense to me; why didn't the other manufacturers figure this out? It seems to be another case for using 3/4" reach "surface gap" plugs in this application. There was a thread on this a few days ago; I for one, will be interested in what that poster finds out. I will repeat again that I had a very successful experience using surface gap plugs in a 276" Merc with a Isky Max-1 15 years ago.

vilanar · 01-27-2016, 12:15 AM

Sponsored Links (Register now to hide all advertisements)

Thanks , guys.
Now I know what to do.

Terry,OH · 01-27-2016, 07:21 AM

I did not like the recess of the electrode even though the plug was between the valves on my Eddie Meyer, 21 stud heads. I too used the chamfer but used blank plugs in each hole and found the depth of chamfer does vary from hole to hole. I did not cut all the way to the first thread but to the end of the NGK plug body (minus the electrode), which does not have a thread.

tubman · 01-27-2016, 08:24 PM

Quote:

Originally Posted by vilanar

Thanks , guys.
Now I know what to do.

I don't know what you mean by this, but I think $20 spent on a set of plugs to try beats the hell out of pulling your cylinder heads and doing some irreversible modifications.

Kray_Z-1 · 01-27-2016, 08:59 PM

Is the machine work on the OFFY heads complete crap like my manifold? I opted for Edelbrock heads after seeing the crap quality of the OFFY product. The Edelbrock's are beautiful. The one I got are good to .400 lift. my cam is .375 but the deck was milled a little so I had trouble closing the gaps on Champion rc12yc's . I replaced them with autolites that have the same reach, but the electrode is about 1/16 shorter, then I added Moroso indexing washers to shim the plug out a little more. Now she runs gRRRReeeaaT!!

01-26-2016, 12:45 PM	#1
vilanar Senior Member Join Date: Jan 2011 Posts: 163	Spark plug reach Hi folks, I did take off my Offy 400 heads from 8BA , and looking the spark plug electrodes they seem to be rather deep in the pocket. Combustion chamber shrouds them quite a bit so that spark don´t have a straight shot.... I have used NGK 6L and Autolite plugs . Have you modified the combustion chamber or machined the head so that plugs goes deeper in the head ? What is the safety margin from plug to valve ? I tried to search but didn´t find anything for this subject. Thanks, Ari

01-26-2016, 03:38 PM	#2
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Spark plug reach you can use a longer plug or use a powertip plug. I also use a large 45 Degree end mill to clearance down to the first thread. Yes some hi lift cams can hit the spark plug in the older style heads, However Offy and Edelbrock both began moving the plug up. To bad they didn't move it into the transfer area.

01-26-2016, 04:41 PM	#3
BillM Senior Member Join Date: May 2010 Location: Everett, WA Posts: 504	Re: Spark plug reach Here is a drawing I did that shows some alternatives: https://www.fordbarn.com/forum/attach...7&d=1449085666 __________________ My web page: http://myplace.frontier.com/~wgmumaw/

01-26-2016, 07:11 PM	#4
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Spark plug reach Excellent drawings. It shows how a power tip plug might fire the chamber with a 45 degree relief

01-26-2016, 07:35 PM	#5
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 11,638	Re: Spark plug reach I agree with Ron, "excellent drawings", but it troubles me that all of them show the plugs recessed in the heads. That can't be the way the manufacturers designed them can it? I am going with "Edmunds Custom" heads that have the spark plug moved enough so that the electrodes miss the valves. This seems to make a lot of sense to me; why didn't the other manufacturers figure this out? It seems to be another case for using 3/4" reach "surface gap" plugs in this application. There was a thread on this a few days ago; I for one, will be interested in what that poster finds out. I will repeat again that I had a very successful experience using surface gap plugs in a 276" Merc with a Isky Max-1 15 years ago.

01-27-2016, 12:15 AM	#6
vilanar Senior Member Join Date: Jan 2011 Posts: 163	Re: Spark plug reach Sponsored Links (Register now to hide all advertisements) Thanks , guys. Now I know what to do.

01-27-2016, 07:21 AM	#7
Terry,OH Senior Member Join Date: May 2010 Posts: 5,187	Re: Spark plug reach I did not like the recess of the electrode even though the plug was between the valves on my Eddie Meyer, 21 stud heads. I too used the chamfer but used blank plugs in each hole and found the depth of chamfer does vary from hole to hole. I did not cut all the way to the first thread but to the end of the NGK plug body (minus the electrode), which does not have a thread.

01-27-2016, 08:59 PM	#9
Kray_Z-1 Junior Member Join Date: Jan 2016 Posts: 17	Re: Spark plug reach Is the machine work on the OFFY heads complete crap like my manifold? I opted for Edelbrock heads after seeing the crap quality of the OFFY product. The Edelbrock's are beautiful. The one I got are good to .400 lift. my cam is .375 but the deck was milled a little so I had trouble closing the gaps on Champion rc12yc's . I replaced them with autolites that have the same reach, but the electrode is about 1/16 shorter, then I added Moroso indexing washers to shim the plug out a little more. Now she runs gRRRReeeaaT!!