The International Cessna^® 170 Association

What kind of life can be expected from spark plugs? I thought that as long as the electrode/centerpost wasn't too eroded,they're good. But I was talking to an A&P/IA today,who indicated 500 or maybe 600 hours was all you can expect,due to resistance build-up in resistor-type plugs* (resistor,as in the R of REM40E Champions) as the innards begin to break down. I tested my plugs in a tester,with about 450 hours on them they seem to have plenty of spark.
In a related vein,anyone ever have any trouble with new Slicks? I have a pair of 6364 Slicks with about 400 hours on them since new,& I seem to be having ignition troubles. I've having the mags checked at a local mechanic's shop tomorrow--hopefully,we can diagnose the trouble. The magnetic resistance as I rotate the mag gear (opposite normal rotation,so I'm not dealing with the impulse coupling) seems very low compared to a couple other mags I checked. Possibly the permanent magnet of the rotor is defective,so it's not generating the voltage it should? Both mags seem to be similar with regards to lack of magnetism,& weak spark. Anyone ever experience this sort of problem?

Eric

Eric,

You'll have to forgive me for asking this, but did you dig
way deep down inside the plugs (with a dental pick, whatever)
to remove all the lead "clunkers"? Only reason I ask is I thought
kinda the same thing... which is if the electrode / core-tip isn't
too worn (oval) the plugs should be OK. The error of my ways
was pointed out to me by digging a dental pick way down in the
bowels of the spark plug(s), and up came big ole' clunks of lead.

I bought a new set of plugs recently, but probably didn't really
need them..... (there was approx. 225 or so hours on the old plugs
since new). Running these engines on 100LL will foul them up....
no doubt about that....

On a side-note, I tested each of my old plugs with one of those
tester doo-hickeys (where you can put pressure on the plug and
fire it to see what it does). The old plugs were dismal in performance,
but much to my surprise, brand new plugs didn't register very much
higher on the dial (in other words, they wouldn't take too much more
air pressure before they quit firing than the old plugs).

Remember when I mentioned I was having ignition problems?
New set of plugs = problem went away.

Something else I was told to do, is if you're cleaning / re-gapping
used plugs, set the gap at the lower end of the tolerance (smaller
gap), as the gap will increase with time/wear. Also, every time
you pull the plugs, swap the uppers & lowers (some guys with
large bore Continentals do this at every oil change).

Bela P. Havasreti
'54 C-170B N170BP

Yup,dug out the clinkers,of which there were very few. No doubt due to the amazing properties of the glorious gar gas which is my preferred fuel.
Plug tester indicates good spark. We tried reducing the gap on the lower plugs to approx .011",to help out the apparently weak spark produced by the mag. Seemed like a good idea at the time (desperation),but maybe not so smart after all,cuz now how do we make the gap bigger-- back to .016" or so? The spark on the smaller-gapped plugs doesn't look as good as on the regular-gapped ones in the tester.
Been rotating the plugs top-to-bottom at annual.
I hate to pony up 20 bucks each or so for new plugs if I don't really need them. I might buy 6,to replace the ones we de-gapped,just to see if they improve things.
I hope to know more tomorrow after paul neunhaus (sp?) at AIR at Arlington tests the mags on his bench-tester.

Eric

Hope it's something simple to fix.

FWIW, when I checked around recently, National (BFI) had the
best local price on plugs $19 & change each), and they had a
mess of them in stock.

You going to PAE tomorrow? Might swing by for a free
hot-dog <grins>.

Bela P. Havasreti
'54 C-170B N170BP

Is, .016" the correct gap for REM40e. Im going to regap my plugs, i think theyre not well gapped

.016" is correct,the gauge a friend of mine lent me is a go/no-go type with .014" and .018" feelers.
I'm gonna give the new Unison plugs a try,they're a couple bucks cheaper than Champions--it adds up when there's 12 of them!

Eric

PS--Bela,how was GA Day at Paine? I went a couple years ago & all they had going on was young eagle rides--no fly-in type action at all.

Well, at the risk of sounding like a party pooper, it was
kinda a waste of time....

There was maybe 15 airplanes there.

1 or two warbirds (bunch of guys wearing flight suits with
dozens of patches sewn on). An RV-8, some spam cans....

I was the only 170 there (I think, other than 1 warbird
an AN-2 and an RV-8, I was the only taildragger there).

It was still better than sitting at home in front of the boob
tube though....

Bela P. Havasreti
'54 C-170B N170BP

As an aside on the spark plug topic - what's the difference between a REM38E and a REM40E? I've got REM38Es in mine, but I hear of a lot of folks running REM40Es.

I have 500 - 550 hours on my plugs and believe that I am starting to have problems with them. Have done the dental pick and rotation top to bottom twice a year. Noticed a whitish clinker with avgas and a darker and less hard clinker with mogas.

doug8082a wrote:As an aside on the spark plug topic - what's the difference between a REM38E and a REM40E? I've got REM38Es in mine, but I hear of a lot of folks running REM40Es.

The designation of Champion Plugs is:
R = Resistor Plug (vs none, no resistor)
E = Shielded 5/8" -24 Thread (vs none, non-shielded or H Shielded 3/4"-20 thread)
M = 18mm thread with 1/2" thread, 7/8" hex (vs lots of other thread/depth/hex options)
38 = slightly cooler running plug than 40
E = Two massive Electrodes (vs N,S,B,R,Y,P,W which designate 4, single, twin, wire, projected core, twin Platinum, and twin Iridium plugs.)

Well,the old ragwing's running like a top once again. I pulled off the mags (2 year old Slicks with 400 hours on them) and took them to a local shop. He adjusted the points gap/e-gap ( sounds like an online clothes store,don't it?),checked the condensors & coils with an ohmeter,and checked the spark performance on his bench-tester. All within spec. When I told him there was 450 hours on my plugs,he said "there's most of your problem right there!". I was skeptical,they looked good & sparked just fine in the tester at up to 80 psi. But I bought 6 new Unison plugs from him. Reinstalled/timed the mags,put in the new plugs on the bottom,& it fired right up! So tomorrow I'm gonna order 6 more from Spruce.
By the way,Spruce & Chief are about the same on plug prices,about 18.75 for Champions & 15.95 for Unisons.

Eric

Eric,
for what it is worth.
Chamion says that their plugs life is 500 hours.
BTW why didn't you ask me this at 76s the other day.

gahorn wrote:

doug8082a wrote:As an aside on the spark plug topic - what's the difference between a REM38E and a REM40E? I've got REM38Es in mine, but I hear of a lot of folks running REM40Es.

The designation of Champion Plugs is:
R = Resistor Plug (vs none, no resistor)
E = Shielded 5/8" -24 Thread (vs none, non-shielded or H Shielded 3/4"-20 thread)
M = 18mm thread with 1/2" thread, 7/8" hex (vs lots of other thread/depth/hex options)
38 = slightly cooler running plug than 40
E = Two massive Electrodes (vs N,S,B,R,Y,P,W which designate 4, single, twin, wire, projected core, twin Platinum, and twin Iridium plugs.)

Thanks George. So what's are the pros/cons of running REM38Es vs REM40Es (if any)?

REM40E is what is recommended. Some believe that mogas burns hotter than avgas and use 38's for that purpose.
The real answer is found during the inspection. If your plugs have a light tan appearance, then you have the correct heat range. If they are dark then you need a hotter (higher number) plug. Do not exceed the recommended heat range though or pre-ignition becomes a concern.
(Rather than use a plug hotter than recommended, try a fine wire plug in a lower temp range, i.e., a REM38S. This will burn off contaminants better than a massive electrode type, should oil fouling be a problem.)
In any case, don't be mislead into believing that a mere change to a different heat-range plug is going to make more horsepower for you, etc. It ain't so. The best plug in a healthy engine is usually the recommended one.

Tom Downey wrote:Eric,
for what it is worth.
Chamion says that their plugs life is 500 hours.
BTW why didn't you ask me this at 76s the other day.

I wasn't having trouble with it then. Actually,it had been stubborn a time or two about starting recently but I didn't think too much of it. Then all of a sudden it decided not to start at all for two days! Anyway,it's squared away now.

Eric