Spark Plugs

[miked]

Perhpas a numpty question, but..... Can anyone please tell me what is the correct method of fitting plugs is so they are not "dog" tight every time you take them out.

Do you put a bit of oil (or copper slip) on the threads or something. Or do you leave them dry. I need to buy a decent plug spanner as I have broken quite a few plugs with the socket when they suddenly break loose with the ratchet handle. The long box spanner type just bend at the Tommy bar.

I have been fitting them with a very slight amount of oil.

Thanks Mike

[stuartgb100]

Mike,

I always fit plugs that are clean and dry.
I screw them in by hand (to avoid cross-threading) as tight as I can get
them, and then just "nip" them up with a plug socket and ratchet. Use the shortest extension you can.

Regards,
Stuart.

[Dave_Newcastle]

I echo Stuarts views. The spark plugs should not be so tight that you end up with breakages - and its fine to use a plug socket and extension for the final tightening. When tightening do one handed at the socket end of the ratchet, not the handle end and then you can get more feel of when the plug tightens down and there is far less risk to the head threads by over torquing.

[steveww]

Use a torque wrench when you tighten them up. 35Nm IIRC.

[miked]

Thanks guys, will try again.

I am very careful when putting them in when taking up the new crush washer, but they always seem to be tight upon removal.

The plug socket I have has a very shallow reach and I notice there is only slight clearance between the ceramic and a drilling for the top. Hence a slight off centre move and the socket touchs the ceramic. Taken out of service!
Went to Halfords and bought two. One quite tall with lots of clearance and a rubber insert. Also picked up a magnetic one which seem to hold the plug well.

I know it is only a simple subject but if you have road side problem it makes crisis out of small drama if you crack a plug. Did so with recent fuel problem. I was carrying spare plugs, but those ceramic splinter could get in the plug hole.

Thanks Mike

[msd1107]

Steveww,

Why didn't you say to torque them to about 25 ft lbs for us SI impaired people?

Luckily, my torque wrenches read both.

David
1968 36/7988

[steveww]

Steveww,

Why didn't you say to torque them to about 25 ft lbs for us SI impaired people?

Luckily, my torque wrenches read both.

David
1968 36/7988

Here in metric world my torque wrench only reads Nm However 35Nm = 25ftlbs as you stated.

[bill308]

I always put a little dab of anti sieze compound on my spark plug threads. I've never damaged a thread and once broken free, they come out easily.

Bill

[bill308]

Oh yeah, one caveat, be sure not to get the antisieze on the spark plug body, it's probably conductive, so be neat.

Bill

[CBUEB1771]

I always put a little dab of anti sieze compound on my spark plug threads. I've never damaged a thread and once broken free, they come out easily.

Bill

In the early 70s when I was just learning to work on engines I watched the McLaren lads putting new plugs in a DFV before the warm up session on Grand Prix day. I noted them carefully put a little dab of Copaslip on the threads of each plug. I've done the same since then and never had a problem. I use Bosch plugs because they have a very clean thread form and won't carve up the aluminum on the way in. I also have gotten very conservative and use a torque wrench for just about every threaded fastener. Even with all these precautions I find the plugs in a Twin Cam take a bit of torque to break loose after a few months of use. Careful use of a long breaker handle helps for the first loosening.

[ppnelan]

I have read that it is best to avoid using oil/grease/coppaslip near the end of the thread as it will burn, turn to (hard) carbon, and could destroy the soft aluminium threads when the plug is removed.
Helicoil-ing must be the best way....

Matthew

[CBUEB1771]

I have read that it is best to avoid using oil/grease/coppaslip near the end of the thread as it will burn, turn to (hard) carbon, and could destroy the soft aluminium threads when the plug is removed.
Helicoil-ing must be the best way....

Matthew

I agree, any type of anti-sieze should be applied at about the mid point of the threaded body. That is what I watched the McLaren mechanics do. Helicoils add another contact area in the thermal path from the plug to the head and therefore interfere with cooling the plug. The best thing is to preserve the threads in the cylinder head.

[msd1107]

Interesting commentary on spark plugs. There are several things to consider here.

Threading spark plugs.

Whether you choose to thread them in by hand or with a spark plug wrench is up to you. But offer it up to the spark plug hole, give the spark plug an anti-clockwise twist to get to an alignment of the spark plug threads and cylinder head threads. Then with a slight downward pressure, turn the spark plug clock-wise to thread them in. They should turn with just gentle finger torque. If you feel any resistance, stop, reverse them out, and try again. You do not want mangled threads in the cylinder head. You should be able to turn the spark plugs all the way in with finger torque. When you reach the bottom, use a torque wrench or spanner to apply gentle torque to the spark plugs. Remember, you only want to apply enough pressure to crush the copper enough for a gas tight seal, not squeeze the life out of them. I am a bit queasy about Steveww's recommendation for 34Nm, that is enough for a bolt. I seem to remember, through the haze of 40+ years, of reading about 10-12 ft-lbs or maybe 15-20 Nm.

The next thing is the problem of the spark plugs being hard to remove.

This implies that unburned oil or other deposits have accumulated at the end of the spark plug, have not been burned off, and have sat around long enough to harden.

There are several ways to alleviate this.

First, use the proper heat range spark plugs. This means using a hotter heat range than recommended, which is quite conservative and oriented toward touring, not intermittend low speed running. I kept two sets of spark plugs, a warm set for every day use, and a colder set for weekend enthusiasm and trips. It only takes a few minutes to swap a set about, and it keeps the spark plugs from getting frozen.

Second, drive your Lotus every day. A daily driver is a reliable car. It forces maintenance at reasonable calendar intervals so that things don't crack, dry out, or weld themselves to their neaest neighbor. And putting enough miles on so maintenance intervals come up at 3 or 6 or 12 month intervals means the spark plugs do not have enough time to freeze.

And finally, if you are having problems, this may indicate excess oil in the combustion chambers that does not get fully vaporized, either from the valve guides or from the rings. Either of these means maintenance coming up. Toward the end of an engines life, when the oil consumption creeps down past 500 miles/qt, and especially as it heads to and past 100 miles/qt, think of running a warmer heat range just to alleviate these possible problems.

David
1968 36/7988

[steveww]

I am a bit queasy about Steveww's recommendation for 34Nm, that is enough for a bolt.

That is the torque figure from the workshop manual. It is what I have always used and no problems so far.

[miked]

Not been about for a day or two. Some interesting points. Dont have excessive oil use etc but will try hotter plugs. I do think the design of the plug spanner plays a large part. Mine was too close to the plug ceramic.
A lot of socket sets seem to have these type. Very stubby, not much room.
Slightest off centre when breaking the seal and they touch.


Thanks Mike