Hello,

I'd like to solicit your opinions on the following problem...I bought new, cast iron, aftermarket heads for my small block 350 from my local machine shop. Unfortunately I did not do any research about these heads before I shelled out $600 for them. The owner assured me they'd fit my engine, that they'd use a 5/8" 14mm tapered plug for a little bit later model than my 1970--he said to use plugs for about 1975 onward.

The parts store showed one size for all 350s from 1975 onward, so I bought a set. They are NGK V-Power UR4. They have a reach of 0.460" I installed one and took a couple pictures before installing the heads.

http://memimage.cardomain.com/member_images/7/web/3091000-3091999/3091107_2_full.jpg
http://memimage.cardomain.com/member_images/7/web/3091000-3091999/3091107_3_full.jpg


As you can see, I have a problem...these plugs come up about 2 threads short. What I need is a plug with about 0.55" reach. The only plug that I can find that is the next size up is a 0.708"...which would make me about .158" too long--about 3 threads.

Removing the heads for machining is not an option. I need to either find a non-standard plug that will fit, or go with one of the two standard lengths.
Anyone know where I could find a 14mm plug with 0.55" reach? If not, would it be better to run this with the plugs shown, or with the longer .708" plugs? I don't "think" piston clearance would be any problem--and the longer plugs would actually increase my compression ratio slightly due to taking up more space in my combustion chambers...

Can valve clearance be a problem with a plug that's too long? It looks fairly close in the photo, although the angle is not clear.

If anyone has any advice they can offer, I will appreciate it. (I know, I know, if I had it to do over again, I'd have looked a little closer at these heads before buying them) I AM learning from my mistakes, though, and have appreciated everyone's time and input on this forum.
Thanks!
Scott

I think the UR4's crosses to the AC Delco R45TS. Grab a R45TS and see if there is any difference which I doubt. That should be the correct plug, everything looks normal to me.

Dave

everything looks normal to me.

Dave

Dave,
That certainly does not look normal to me :(

Scot,
What brand heads are they ? Can you post a picture from the other side, where the plug seats ? The way they are in the picture is definitely not correct. There was a batch of Dart aluminum heads a few years back that were machined incorrectly from the factory. The plugs looked the same as yours do and that is definitely not right.

Scot,
They might be one of the Vortec head "knock offs" If so, they probably need the same plugs as the Vortec heads, which are longer than the usual taper seat plugs. Take a look at this link http://198.208.187.182/internet/PartImage.jsp?mfgname=ACDELCO&prodlinecd=41&acpartnbr=41-993 That is the plug for a 99 Chevy Tahoe 5.7 vortec engine.

What I need is a plug with about 0.55" reach

Heres the ACDelco Spark plug ID table:
http://www.acdelco.com/parts/sparkplugs/identification.jsp

You might need the F or FF suffix plug.