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Which spark plug 1/2" or 3/4" shaft

F

floatin radio

Regular Contributor
1991 3.0 info on air cleaner calls for an Ac mr43lts, the cross reference NGK plug is Bpr 6efs, which is a 3/4 inch shaft. Current plug is a NKG with 1/2 shaft. Been in there 4 years. Which one is correct and why the different lengths?
thanks in advance
 
Ayuh,.... I believe a '91 uses the shorter spark plugs,.... MR43T,....

Only the Vortec heads use the long plugs, 'n they didn't exist til '96,....
 
Ok, I'll get the 43t or the equivalent Nkg. I wonder why my air cleaner says 43lts? May not be original cleaner. Can you tell by looking if the heads are vortech heads? Any reason someone might have changed heads? If they did, would short plugs work in the vortech heads? I'm assuming it has non vortech heads and just the wrong air cleaner cover.
Thanks
 
Both arrangements might cause trouble:

Too long a plug might contact the pistons, and the exposed thread will heat up excessively, causing pinging under load. Also, that extended thread will carbon up, making removal a problem and possibly tearing the threads out!

Too short will probably not cause overheating, but the threads ahead of it will carbon up so, when the right plug is added, it will jam up and possibly break off--I've seen that happen.

I suggest you find a serial number on the block (or ?) and be sure. You might also be able to eyeball the plug threads and see how long they are.

Jeff
 
The plug info on the flame arrestor is correct for your year 3.0L. The AC # reads like this: MR- marine, resistor style. 4- 14mm thread. 3- the heat range. LTS- long reach (.715") with a tapered seat and extended tip. The NGK # reads about the same: B- 14mm thread. R-resistor style plug. 6- the heat range. EF- tapered seat with .708" reach. S- standard (2.5mm) center electrode.

Just out of curiosty, what is the NGK# of the plugs that you are replacing?
 
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Existing plug is NGK bpr6fs. ( short shaft)

im really confused now as to what is the correct plug. What I have read says that LX motors use the extended shaft plug. As far as I know mine is a non lx motor, pics of other lx motors say it on the air cleaner. It's running of the old plugs, but I want to make sure correct ones are in it.
How do you know if it's a LX motor?
 
You should be able to determine the engine model from the serial #- if not, you can use the engine block model code, located on the block just above the fuel pump, aft of the distributor. The last 2 digits should be RM if it's a 3.0, RN if it's a 3.0LX
 
Well, guess what? Air cleaner says 43t, I don't know how I misread it! Guess I should have had my reading glasses on. Sorry about that. Motor is definitely a 3.0
Thanks
 
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