I recently replaced my spark plugs and wires so I decided to just go ahead and replace my cap/rotor too. Upon installation I noticed the new distributor cap was loose, meaning it had movement side to side if I twisted on it.

I thought it was just the clips on my distributor so I bent them to apply more tension on the cap, and still the cap was loose. I then measured the I.D. of both caps and realized the new cap was about 1/16" larger than my old cap.

I go back to Napa and voice my concern, they replace it with another cap and I go home and install it only to have the same issue! I start/drive the truck anyway and it drives great, no apparent issues that I'm aware of.

My old cap fit very tightly and I was expecting the same with a new replacement. Is the loose fit of the new cap any concern, or should I just go with it?

 

It definitely sounds like cheap parts but I have 3 ford trucks with loose caps that have been just fine for years.. Just drive it a few hundred miles and look under it to make sure you dont have corrosion from a weak button/cap connection and be sure to avoid getting water in that area

 

I ran into a similar issue recently with a BWD cap adapter that I bought from O'Reilly's.

The adapter was loose/sloppy took it back and looked at another new in box adapter.
Same issue, out of spec parts. I ended up re-using my old Motorcraft adapter until I can
find one that fits correctly.

 

I use the MSD Cap-a-dapt kit with the same issue. Between the distributor flange being slightly loose and the cap- to-adapter surface being slightly loose, I have a good bit of play. Maybe a full degree or two.the spring clips don't hold it down very well either.

 

OP failed to mention what year the truck is.

Ford changed the V8 dizzy cap and rotor in 1977 (shown as % in pic). Dizzy cap has male ends plus a plastic adapter below that has the clips to retain the cap in place.

 

You know China uses different measurement system, as evident by poor fitment of their products.

 

I went back to Napa this morning and opted to pay the additional $12 for the Echlin Premium cap.

While there we measured it against the cheaper Mileage Plus cap and sure enough there was nearly a 1/16" difference between the two.

I guess the old adage "you get what you pay for" certainly applies in this case.

 

Agreed GLR, I run metric and standard lathes every day at a chinese copper plant and they tend to round EVERYTHING up.. Our standard system is by FAR superior for tolerances hence .01M vs .001S