Changing spark plugs! (Part 1)
Ok a simple one!
All outboards (except the Yanmar diesel ones) - require a change of spark plugs from time to time!
Now back in the good ol days - spark plugs were built to last basically the life of the engine...and came in a series of "parts" that could be dissassembled, as the cathode (+ve) part wore down...and replaced / changed, re-adjusted, insulator replaced, whatever!
You had the ceramic (porcelaine in those days) insulator and the body of the plug plus the cathode rod and a fitting at the end for the lead to either press fit over or screw to, with a washer etc...
They had their problems, a insulator might crack with heat and cooling and then spark would take the least resistance path to earth and they would short out and not fire or misfre etc etc
If they came undone and the cathode rod dropped into your cylinder they could seize the rings / piston and destroy the engine etc!
These days, due to mass mechanised manufacture we are much better off - spark plugs are a cheap, throw away easily serviceable unitized part that does not come apart (hopefully)!
That said - they aren't manufactured to the typically high standards they once were, (with the exception of aircraft spark plugs which still are, for obvious reasons!)
Course a boat that don't go can get you into plenty bad water - so choose GOOD brand spark plugs of the type (heat range / reach and cathode type) specified by your engine manufacturer!
You can see these are the same brand and type.
(new against old)
Always compare to make sure before screwing a new spark plug into an engine. A 'long reach' plug might actually contact the top of a piston if it's not meant for that engine etc! Don't 'trust to luck' or 'believe the spare parts guy' (Coz often he might be an idiot or not care less!) - get your service manual or owners handbook and find out and compare with what you take out!
Can't be too carefull!
A wrong heat range plug, can cause all sorts of funny symptoms to a engine and might not be good in the long run!
One we KNOW we have the right ones - then comes 'gapping' them.
Sadly I didn't take photos, but it's a very simple proceedure! Most plugs these days come 'pre gapped' with a cardboard tube over the end to stop the gaps getting closed up by the plug banging against the cathode end while in storeage / transit.
All the same check it with a feeler gauge anyway!
If necessary re-gap it!
You will find that the manual states 2 settings.
One is smaller than the other!
They are the max / min gap plug perameters that the engine should run at!
You GAP your plugs to the narrower (smaller numerical) setting!
Why?
Because - when they spark - the +ve cathode rod wears away slowly (as does the -ve anode)! As they wear away the gap widens, eventually to maximum designed gap (the second larger measurement) and then beyond!
Eventually the gap will get so wide if you don't change plugs at the recommended hours interval that spark has difficulty jumping such a large gap! So it will go anywhere in preference - past the insulator (particularly if it's cracked with age / repeated heat / cooling cycles or covered in salt and moisture, dirt, oil, etc!).
Sometimes that spark will jump from the plug lead to the engine body in preference to jumping an excessive plug gap if the leads damaged in some way and coated with salty wet moisture..
These things lead to all sorts of engine problems at sea - best to avoid them at all costs and keep good correct type / brand plugs properly gapped in your engine!
When you pull the old ones out that were still working fine, re-gap them, clean them up, put the cardboard tube from the new ones over the old one so it doesn't lose it's gap and keep them inside a oily cloth in the cardboard boxes the new ones came in, inside a small sealed waterproof lunchbox / tupperware container in the boat!
If you ever get a 'bad' plug (and it does happen)- you will have a spare thats already gapped, that you know already works, on hand to get you home! ;o)
Theres something else to know about spark plugs!
The crush washers!
So, to part 2!
Fly
Posts: 485
Date Joined: 04/02/06
Crush washers!
OK.
Cylinder heads on most modern OB engines today are aluminium which is a soft metal!
That aluminium has a thread cut in it into which we screw the spark plug!
If we overtighten the spark plug - we MIGHT 'tear out' that aluminium thread with the harder steel thread on the spark plug body!
Also - if we cross thread the plug, when we get it started in the hole - we might bugger up the thread in the alloy for the remaininng life of the OB!
We don't want to do this - so how the heck do we know how much to tighten the plugs?
And - how do we get the plug 'started' in the hole, such that it won't cross thread???
First lets look at crush washers!
Not the greatest of photo's but it will do!
You can see that the washer on the old plug is 'thinner' than the washer on the new plug!
This is because the washer is designed to "crush", ONCE as it is tightened down into it's hole..with a spark plug socket wrench, such that the washer seats on the plug seat around the spark plug hole and then squashes flat to create the gas tight seal!
The idea is - that with a NEW spark plug, you tighten down the plug by hand until the crush washer seats on the spark plug hole seat friction tight by hand only!
THEN you fit a spark plug socket wrench, and tighten the plug 2/3rds of one whole turn.. It should come up reasonably tight, as it crushes the washer down to make a good gas tight seal!
Starting from 'hand tight' in the above position with a NEW plug with a previously 'uncrushed' crush washer, we then tighten....
2/3rds of a turn in the clockwise direction!
There is definitley NO NEED to heave down on it like 'a he man, hero - gorrilla' - you WILL strip out your soft alloy spark plug hole thread!
If you do - then you are looking at having the engine stripped down by a mechanic - the head removed, the damaged thread drilled out and somethig called a steel 'helicoil' threaded in to the head to allow spark plugs to be re fitted after it's all reassembled!
This is NOT cheap - heave on your plugs like Arnie Schwartzenegger if you have something to prove, if you must, but don't come whining to me if you strip out the thread by being heavey handed!
The whole idea of a crush washer is to STOP that from being necessary!
Where you need to use a bit of 'common sense' is in re-fitting already used spark plugs! (Say they just needed gapping!)
These have already had their crush washers crushed once!
With a old plug thats just been cleaned and re gapped - and is being re-installed you DON'T tighten 2/3rds of a turn from hand tight - you ONLY tighten 1/16th of a turn...which is a just a smidgeon tighter than hand tight till you feel it nip up tight, no more - not a poofteenth more - not a nats whisker more, not tight as a nun's whatsit!!!
So - back to getting the plug started in it;s hole without cross threading!!
Baglimitboy
Posts: 39
Date Joined: 11/02/06
Hey Flywest - Crush Washers?
Hey Flywest
Can you buy new crush washers ???
Just a thought
Cheers
BLB
Fly
Posts: 485
Date Joined: 04/02/06
Starting the plug!
Thisis the method I use to get a plug 'hand started' in it's threaded spark plug hole in the alloy engine head, without cross threading!
Make sure you use a spark plug socket with the neoprene plug holding sleeve inside it!
Push the plug deep into the neoprene sleeve, so it's central withi the socket.
Push the socket on a 'medium extension' down into the hole thru the rocker cover on a 4 stroke (or just into the hole on a 2 stroke), and then centralise the whole thing as staright on as you can get by eye and rotate backwards about 2/3rd or so of a turn you will "feel" the plug climb it's thread starting point as it rotates backwards, then it will 'click' or drop back in slightly as it ciomes past that starting point. at this point tring to keep it as straight as possible I rotate gently between thumb and forefinger to get the plug to screw easily into it's female thread!
Any unusualy resistance I stop - back out and try it again till I get it to go easey. If the old one came out the last few turns, the same way between thumb and forefinger - there is absolutely no reason the new one should not go back in exactly the same way! (with no tightness) on those first few turns!
I do put a bit of new oil on the thread of a new plug just to ease it's hand entry into the alloy threaded head!
Last bit to come!
Fly
Posts: 485
Date Joined: 04/02/06
This last pic probably shoulda gone first!
Removing spark plug lead!
Before you can remove or replace spark plugs you need to pull the spark plug lead! I do this by hand and check for any damage while I'm at it!
I ONLY pull ONE lead at a time!!!
That way you can't 'mix up' the firing order of the cylinders by getting the leads crossed over on to the wrong plugs when you put em all back on!!!!!
It's not good for an engine to do this, remember ONLY ONE lead & Plug change at a time OK?
Engine cylinder firing order (on 4 cylinders) are seldom 1.2.3.4. as you might imagine!
Often they are something like 1.2.4.3. or something like that so DO NOT mix up the damn firing order! (not even on a 2 cylinder engine) OK?
Cheers!
Fly
Posts: 485
Date Joined: 04/02/06
Last thing!
One last thing.
Oneof the great benefits of doing your own mechanics in the way of servicing is you can Take your damn time!
Why rush it - if you wanted the job rushed you'd a paid some spanner twister good $ to have done the service quickly for you at a steep hourly rate! (After you waited 3 - 6 weeks for them to get time to work on your boat after everyone elses!)
Now - while you ARE doing simle stuff like changing plugs, cast your eye over the rest of the engine for anything "untoward" that doesn't look quite right!
I've had these two engines just on 11 months and put about 100 hours on them in that time! (They had 420 hours when we bought her, and now have 520 hrs).
I've checked the oil a few times in that period....and just got friendly with em once or twice pulling the covers for a good look inside!
In all that time - I never noticed the loose bolt, on one of the cover plates spotted in the photo above! (With screw driver pointing to it!).
Now I don't know when the last time the engines were serviced by Transport Dept or Fisheries Dept and I haven't been able to track down any Honda Mechanics who remember servicing this vessels engines for either of the 2 departments and they themselves seemed to have no idea or records!
So, was it serviced at 50 hours 100 or 200 or 300 or 400???
No idea - which is why I did a full service (including impellers) at 500 hours.
At least I now know with confidence, that everythings been done!
When I got them at 420 hours the sump oil was still clean so I was betting they MAY have been done at 300 or 400 hours maybe but I didn't know for 100% sure so now I do!
The manuals recommend changing impellers every 200 hours from memory, so they MAY have been done at 200 or 400 hours but I had no way of knowing for 100% sure!
This is ONE good reason to do your own servicing - you WILL know specially if you keep records!!
And if you take your time (something a service mechanic is always short of - you will perhaps find small things like the above loose bolt that CAN be fixed BEFORE it becomes a bigger issue later!
Cheers!
Fly
Posts: 485
Date Joined: 04/02/06
Buy crush washers?
That's a good question!
I have no idea - probably since plugs are so cheap / mass produced - likely not...but i could be wrong!
Probably you'd have to buy the whole new plug to get the crush washer - and throw away the new plug but keep the washer - he he he!
I'm not sure you can even get them off the plug - I think they are sorta manufactured to be a integral part of the plug that doesn't come off, to stop idiots from losing / dropping a crush washer and not being able to find it & just stick the plug in anyway without the crush washer!
They have tabs on the inside of the crsh washer that are 'too small a dia' to even unwind the crush washer up the plug thread to get it off, without a lot of effort - probably for the above very reason!!
Who knows? - some things may be better off not known! ;o)
Cheers!