Should my 1970 have an RFI shield?

[Pat M.]

Hi all. At a recent Regional I got docked for not having an RFI shield on my 350/300 1970. However, my VIN is 9753, built May 19, and the JG says "350s from at least 1970 s/n 14,544 (body build date July 6) have the 1971-style shielding with an RFI shield."

According to this passage, wouldn't you agree that my car should NOT have an RFI shield? I had so many other things to worry about I wasn't aware of this in the JG, and thus couldn't point it out to the judges.

Thanks for any help, Patrick Moresi #45881

[Warren F.]

Re: Should my 1970 have an RFI shield?

Patrick,

There is a 2 piece shield that covers the ignition point set-up under the distributor cap, that is there whether you have the box style ignition shielding or the '71 style ignition shielding cover.

[Bob D.]

Re: Should my 1970 have an RFI shield?

Patrick, I read that passage as you should have it and that 70s from s/n 14,544 should have the 71 style shielding, but yours should have a 1970 style shielding with an RFI shield. I believe the shielding they are referring to is external to the distributor.

[Pat M.]

Still confused on 1970 RFI shield

Warren and Bob - I really appreciate your responses, but I'm still confused. The beginning of the RFI section in the JG begins with wording that seems to imply there is no unique RFI shielding for early 1970s. It begins with (paraphrasing) "All 1970s with 1971-style shielding..." The section then ends with the previous passage I posted. In total this seems to me to suggest that some 1970s have 1971-style shielding, and that those would be 1970s beginning with the VIN 14,544. This would seem to exclude my car with VIN 9,753. Also, I don't have any shielding external to the distributor, except of course the chrome "dogbox."

Are you sure I should have RFI shielding, 197style or otherwise?

Thanks a lot, Patrick Moresi #45881

[Bob D.]

Re: Still confused on 1970 RFI shield

Patrick

You should have RFI shielding. The passage is referring to the chrome external shielding that covers the distributor on the outside. The external shields are different for 70 and 71 and that is what the tech manual is referring to. The RFI shield is inside your distributor and covers the points. If you lift the adjustment/inspection door on the distributor you should be able to see the RFI shield.

[Dick W.]

Re: Should my 1970 have an RFI shield?

Those 1970 standard distributors that are protected by the 1971-style ignition shielding have a radio frequency interference (RFI) shield covering the points inside the distributor. The shield is plated a dull zinc. All 1971 standard and all 1972 distributors also have the RFI shield. It is visible when the point adjusting door in the distributor cap is lifted. Owner must lift window in distributor cap to display RFI shield. 350s from at least 1970 s/n 14,544 (body build date July 6) have the 1971-style shielding with an RFI shield

Basically if you have the full dog box type of distributor shielding you do not need the RFI shield. If you have the abreviated '71 style shielding you should have the RFI shield.

By your VIN I would expect you to have the dog box and not have the RFI shield. And I may be the dummie that made the deduction!

[Pat M.]

One last observation on 1970 RFI shield

Thanks Bob. I'm sure you're right, but I'm now looking at the manual's wording and it sure seems to imply otherwise. It says "Those 1970 standard distributors that are protected by the 1971-style ignition shielding have a radio frequency interference (RFI) shield covering the points inside the distributor. ... All 1971 standard and all 1972 distributors also have the RFI shield. ... 350s from at least 1970 s/n 14,544 (body build date July 6) have the 1971-style shielding with an RFI shield."

By not simply saying all 1970 distributors have an RFI (like it does for 1972), it sure seems to suggest that some 1970s didn't have one. And by specifically saying those with "standard" distributors AND "1971-style ignition shielding" have an RFI, it seems to suggest that a car without one of those features would not have an RFI. Then the manual ends by being very specific in stating what VINs and build dates should be expected to have both features AND an RFI.

My car does has a standard distributor, but it does NOT have the 1971-style ignition shielding; instead, it has the earlier two-piece shielding like earlier 1970s. This, along with the fact that my car's VIN and build date does not match those 1970 cars that should be expected to have an RFI, would seem to indicate mine shouldn't have one.

I'm not trying to be overly technical and argumentative,and I know the manuals can be unclear and simply wrong at times. I just want to know what's correct, and the JG seems to suggest I shouldn't have an RFI. Anyway, I really do appreciate your kind help. Regards, Patrick Moresi #45881

[Pat M.]

Re: Should my 1970 have an RFI shield?

Thanks a bunch Dick. Like I said in my last post, I do have the early 1970, two-piece, "dog box" ignition shielding, so it doesn't seem I should have an RFI shield. In any event, with all your knowledge, I sure wish I was as much of a "dummie" as you are! Patrick Moresi #45881

[Chuck S.]

Re: Should my 1970 have an RFI shield?

What the TIM&JG is trying to say is that the ignition shielding changed at serial 14544. I didn't know that the RFI shield was added at that time...I had a 66 Impala, and it had the RFI shield in the distributor with NO IGNITION SHIELDING.

To clarify the difference between early 70 and late 70/71 ignition shielding, early 70 has the two piece box distributor cover, flash chrome plated vertical channels, boomerang shaped vee channels on the sides of the engine, and four boxes that each cover two spark plugs (1/3, 5/7, 2/4, 6/8). Late 70/71 has everything the early ignition shielding has EXCEPT the distributor cover is one piece, and there are only TWO BOXES that cover the two rear spark plugs on each side.

There was also an air cleaner change from open element to dual snorkel air cleaner about the same time, probably because of the distributor cover change.

[Pat M.]

Re: Should my 1970 have an RFI shield?

Chuck - the JG certainly implies that the RFI shield was added when the 70 ignition shielding changed at VIN 14,544, because it ties the two together twice. If RFI shielding existed prior to that in 1970, you'd think the JG would simply say all 70s had RFI (like it does for 1972), but it doesn't.

Moreover, Dick's post provides a perfect explanation in that 71-type ignition shielding apparently provided less interference protection than existed before. This may also explain why your Impala, with no ignition shielding, needed an RFI shield.

Thanks for your input, Patrick Moresi #45881

[Terry M.]

[Chuck S.]

Re: Should my 1970 have an RFI shield?

"...I expect tying the RFI shield to the distributor shield is at best an oversimplification on our part. If I had to guess, I would think at some point Delco Remy began to install RFI in ALL the distributors they shipped, and Flint dutifully installed them in ALL the engines they built, as did Tonawanda -- wherever the engines were destined."

That was the point I was trying to make with my Impala as an example, Terry...it seems like if they were putting RFI shields in steel bodied car distributors as early as 66, it wouldn't be too much of a stretch that they were putting in them all during those years, BWDIK.

What's the big deal anyway...you don't have to keep it in there just because vendors sell good reproductions. If you can document that the shield is original to the distributor, and that's much more remarkable than it being missing, then present it for judging that way and take the minor deduct on principle. If you have no evidence that it was original to the distributor, then give the judges what they want to see with a clean conscience.