3 Thread Heads and Reliabilty/Maintenance/Prevention

[WhatsUpDOHC]

OK - I tried to search if this has been discussed and came up with nothing (not a search expert).

But, I have read a few responses concerning heads with 3 threads for spark plugs.

I know that many of our motors have reached multiple 100K mileage milestones and have been S/C-d (why no issue with combustion chamber pressures?) but I wonder about this weakness.

Can anyone elaborate on this design (seems kind of short-sighted) and what can be done to avoid issues?

Also, what is the frequency when plugs should be changed?

Thanks,

Mark

[1stMerc]

Oem plugs on stock motor were suppose to be good for 100k.

i usually change plugs at 15-20k

Don't know which heads i have, but have been boosted for a little over 5k from 80.

[Shaijack]

What you have to change the plugs?

[RF Overlord]

The primary cause of flying spark plugs is not the lack of threads per se, rather it's improper installation. Overtightening plugs on an aluminium-head motor can damage the threads easily. Of course if you have enough threads the problem is not as severe, but is still there.

Many people claim to have "the touch" and that they don't need to use a torque wrench; others will use anti-seize and not realise that anti-seize is a lubricant and will change the torque value by approx 10%. Both of these together can result in significant overtightening and subsequent thread damage.

Use a torque wrench set to 11 ft/lbs (10 if using anti-seize) and you won't have anything to worry about.

[fastblackmerc]

The primary cause of flying spark plugs is not the lack of threads per se, rather it's improper installation. Overtightening plugs on an aluminium-head motor can damage the threads easily. Of course if you have enough threads the problem is not as severe, but is still there.

Many people claim to have "the touch" and that they don't need to use a torque wrench; others will use anti-seize and not realise that anti-seize is a lubricant and will change the torque value by approx 10%. Both of these together can result in significant overtightening and subsequent thread damage.

Use a torque wrench set to 11 ft/lbs (10 if using anti-seize) and you won't have anything to worry about.

Correct, I change plugs once a year and have never had a problem.

Anti seize & proper torque is the key.

[na svt]

Anti seize & proper torque is the key.
along with not changing the plugs when the engine is at operating temp.

[fastblackmerc]

along with not changing the plugs when the engine is at operating temp.

Yes, change when cold.

[ImpalaSlayer]

i believe it was 4 threads and not 3 IIRC, the 04s have 9. that goes with any 4.6 dohc motor i believe

[LANDY]

i believe it was 4 threads and not 3 IIRC, the 04s have 9. that goes with any 4.6 dohc motor i believe
yes is 4 thread. change your plugs when engine is cold and you will be fine.

[WhatsUpDOHC]

Is there a cast numbering/point when the castings changed to the heads with higher threads?

Anyone out there with 03 head cast numbers?

Mark

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[MitchB]

The primary cause of flying spark plugs is not the lack of threads per se, rather it's improper installation. Overtightening plugs on an aluminium-head motor can damage the threads easily. Of course if you have enough threads the problem is not as severe, but is still there.

Many people claim to have "the touch" and that they don't need to use a torque wrench; others will use anti-seize and not realise that anti-seize is a lubricant and will change the torque value by approx 10%. Both of these together can result in significant overtightening and subsequent thread damage.

Use a torque wrench set to 11 ft/lbs (10 if using anti-seize) and you won't have anything to worry about.

Antiseize changes the torque requirement to reach a given preload by much more than 10% - had this discussion with the founder of ARP many years ago...

Mitch

[Marauderjack]

The primary cause of flying spark plugs is not the lack of threads per se, rather it's improper installation. Overtightening plugs on an aluminium-head motor can damage the threads easily. Of course if you have enough threads the problem is not as severe, but is still there.

Many people claim to have "the touch" and that they don't need to use a torque wrench; others will use anti-seize and not realise that anti-seize is a lubricant and will change the torque value by approx 10%. Both of these together can result in significant overtightening and subsequent thread damage.

Use a torque wrench set to 11 ft/lbs (10 if using anti-seize) and you won't have anything to worry about.

I have changed the plugs in my Marauder about 15 times and never used a torque wrench Bob......been doing it MANY years in aluminum heads on outboards.....the key is that the engine has to be COLD......dealers screw 'em up more than anyone by doing them HOT!!!:argue::mad2:

I would not use a ft. lb. torque wrench at 11# but use and in. lb. one.......most ft. lb. torque wrenches will be pretty inaccurate at low settings!!:shake:

"Touch Method" rules!!;)

[RF Overlord]

I would not use a ft. lb. torque wrench at 11# but use and in. lb. one.......most ft. lb. torque wrenches will be pretty inaccurate at low settings!!I use an inch/lb handle set to 132.

I don't necessarily dispute that some people DO have "the touch", but I would wager that it was only achieved after lots of practice. I think if someone has little experience changing plugs they would be better served using a torque wrench than finding out the hard way on an early Ford 4V head with 4 threads exactly HOW little extra it takes to ruin them.

[Marauderjack]

I use an inch/lb handle set to 132.

I don't necessarily dispute that some people DO have "the touch", but I would wager that it was only achieved after lots of practice. I think if someone has little experience changing plugs they would be better served using a torque wrench than finding out the hard way on an early Ford 4V head with 4 threads exactly HOW little extra it takes to ruin them.

I would never suggest that someone with NO experience ever change ANY spark plugs in anything of value and yes the in. lb. wrench should be much more accurate and safer!!

I still contend that most thread damage is the result of yankin' 'em out HOT Bob??:confused:

A rule I have used since the 50's was to hand tighten them then 1/8 turn and stop........so far it has worked well.......so I'll probably screw my Marauder up next plug change since I've bragged about it??:(

Happy Labor Day Weekend folks!!:beer:

[RacerX]

Some more info on the different 4v heads: http://www.svtperformance.com/forums/engine-tuning-214/877204-how-identify-heads-you-have.html

[WhatsUpDOHC]

Sweet and timely, thanks!

Mark

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[Black bart]

Over the past 3 years had 2 plugs blow out, one from each bank.

Yes I use an inch pound torque wrench set at 12lbs, anti size compound while the engine is cold.
Over the past 50 years have changed plugs countless times w/o any problems..whoops once on my GP bike during a race event!

according to my local auto servcie center the 4.6 modular engine is noted for the blown plug issue. So this is a ford design weakness.

fred

[WhatsUpDOHC]

Verified 4 thread heads.

Build date 04/02/03.



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