Packard Forum Index » Post-War (1946-54)

Hello im just wondering if it's ok to use lm49 ac Delco plugs in my 53 clipper 327 I've already purchased them and they are shorter then the ac46 that's in it now

I believe Packard in those years used a spark plug with a 3/8" reach (the length of the threaded portion). Your car may have been fitted with spark plugs of 7/16" reach. The old Champion designator for the shorter plugs was the "J" type and the longer plugs were "H". Js and Hs came in the same heat ranges, but differed in reach. Of course the designation of spark plugs has changed over the years and new numbers are now being used. Someone will come along to advise you on the correct plugs for your Packard.

(o{}o)

I have no idea what a lm49 (or is it LM49?) AC plug is or what it was intended for, but finding the correct plug for your car is as simple as going to the major spark plug websites and seeing what's currently recommended for your car. I have a preference for Autolite plugs; their current recommendation for your 53 327 is #308. I have great experience with the Autolite 308, use it in my 34 and have many friends using them in most any Packard engine with 14mm plugs (other than the V8s, of course). If correct appearance is important to you, they also have the black oxide shell which is correct.

Good advice from O_D and one more comment. Using a spark plug that has a longer reach than the one specified, even if it is in the correct heat range, can cause problems. The longer thread will be exposed to the combustion chamber where it will accumulate carbon deposits. Removing one of these longer than specified plugs could damage the threads in the head as the carbon deposit will not allow the plug to unscrew easily.

(o{}o)

Yeah, i'd like to know what that "lm49" designation is too. Does the spark plug actualy have "lm49" on it????

Lots of hits on LM49 spark plugs on Google. Here are some of it's equivalents:


Autolite 358
Autolite 456
Autolite 458
Bosch W9EC0
Bosch WR9EC
Bosch stk 7515
Champion CJ14
Champion J19LM
Champion RJ12C
Champion stk 592

Thanks Owen. I went and cchecked my 1976 AC Delco book. The PREfix "LM" indicates Lawn Mower.
However, the "49" (4 = 14mm, 9 = very hot heat range) does not appear in my book. Only 42 thru 48.

Maybe 53 Packard (se post 1 above) will post a picture of the LM49 and measure the overall leength.

ok. I found an LM49 in my AC book. For Jacobson lawn mower, something called a snow queen and a Lawnboy mower.
That "49" really threw me. So apparently the heat ranges can exceed the 42 thru 48 as listed in my book.

That 49 ahould be one hell of a hot plug tho.

On my plug conversion chart, Autolite #308 corresponds to NGK B2. That is very hot.
Might owners of 51-54 models comment here on what plugs they have in their cars?