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BN1 Ignition question.

catfood

Jedi Knight
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I'm hoping some of our experts here can reassure me over a couple of things.

1) Firing order of the BN1 is 1 - 3 - 4 - 2. I'm assuming 1 is at the bulkhead end and 4 the radiator? I can't find anywhere in the workshop manual that tells me.

2) I need to find TDC as I am fitting a new CSI dizzy. I haven't removed my old dizzy yet so am I correct in assuming that when the rotor is pointing at number 1 cylinder and that piston is at the top it is TDC and not top of the exhaust stroke?
 

Brinkerhoff

Jedi Knight
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Number 1 is closest to the radiator. If the engine has been running then if you find TDC on #1 compression stroke , the rotor will point to the #1 wire position on the cap. A full rotation of the crankshaft would therefore put the rotor 180 degrees off and point to #4 position on the cap also at TDC.
 

CraigC

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While you are at it, with engine at TDC #1, Check for a small hole in the back half of crank pulley lined up with the arrow embossed on the timing cover.
 

vette

Darth Vader
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Also, If you have completely lost the marks and can use the timing mark on the crank damper and bring the crank around till about 10 or 12 degrees before what you think is TDC. Then with the #1 spark plug removed, place your thumb over the spark plug hole and have someone bump the starter. If the piston is on the compression stroke it will blow your thumb off the spark plug hole. It doesn't hurt, it doesn't blow that hard but you can quite easily notice it. Then knowing that you are on the compression stroke continue to place the crank right at TDC.
 

steveg

Yoda
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If you have a compression tester or other hose that screws in or is a tight fit in the spark plug hole, you can cut the finger off a latex glove and tightly attach it to the hose with a rubber band.

With this in place and the engine almost at TDC, you can turn the engine over by hand and tell when you're exactly at TDC on the compression stroke, as you can get to the point where the balloon starts to deflate.
 
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Also, If you have completely lost the marks and can use the timing mark on the crank damper and bring the crank around till about 10 or 12 degrees before what you think is TDC. Then with the #1 spark plug removed, place your thumb over the spark plug hole and have someone bump the starter. If the piston is on the compression stroke it will blow your thumb off the spark plug hole. It doesn't hurt, it doesn't blow that hard but you can quite easily notice it. Then knowing that you are on the compression stroke continue to place the crank right at TDC.

Be VERY careful with this 'technique.' I once knew an aircraft mechanic who was doing this, and either he had his thumb on the plug hole on the intake stroke or someone kept the starter running too long and all the flesh got ripped off the tip of his thumb. I didn't see the wound, but heard it was nasty.
 

vette

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Be VERY careful with this 'technique.' I once knew an aircraft mechanic who was doing this, and either he had his thumb on the plug hole on the intake stroke or someone kept the starter running too long and all the flesh got ripped off the tip of his thumb. I didn't see the wound, but heard it was nasty.

I don't know anything about airplane engines but I have never had ANY issues with car motors. Especially with the Healey engine where the spark plug hole is so openly available and accessible. Now try it on an American V8 with tight manifolds and well......still never had any problems.
 

steveg

Yoda
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This is a little complicated - guess I had a lot of extra small fittings and a grease gun hose lying around at the time.

IMO you could knock the center out of a spark plug, glue a piece of fuel hose in the housing with Goop and attach the "balloon" with rubber bands to the opposite end of the hose.

TDCballoonHose.jpg
 
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I don't know anything about airplane engines but I have never had ANY issues with car motors. Especially with the Healey engine where the spark plug hole is so openly available and accessible. Now try it on an American V8 with tight manifolds and well......still never had any problems.

I suspect, since this was his profession, that this mechanic had employed this technique many times before without being injured as well. Your protest notwithstanding, I'll bet you'll be a bit more careful next time you do this or, if you prefer, stick your thumb in a plug hole--completely sealing it--and crank the engine through a couple intake strokes. Please report the results, and if your thumb is still intact I will gladly retract the warning.

Aircraft piston engines are large-bore, low-compression (usually, around 8:1 ratio, tops), air-cooled, (dual) magneto-fired, fixed timing (usually 20-25deg BTDC) and relatively slow-turning (usually, 2,500RPM is 'redline,' due to the prop tips approaching supersonic*) four-stroke engines (glorified lawnmower engines, really). Each 'jug' (cylinder) sucks and blows a lot of air volume, but their starters are usually very slow-turning (mainly because large batteries are heavy). Most have two spark plugs per cylinder, both of which are readily accessible either through a hinged cowl, or by removal of the cowl (which is usually done when any work on the engine is required).

* some newer engines--notably Rotax, which gained popularity in snowmobiles--turn at higher revs and have gear-reduction to the prop, and are partially water-cooled.
 

CraigC

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Timing Marks? On a BN1? I wish!

You seem to be implying that NO BN1 has a timing mark on pulley or timing cover. Is this a known fact or just an assumption ? If it is a known fact, at what engine number were they added? I can recall others saying their engines had neither the arrow on the t/c nor the hole in the pulley, but no one haas ever stated where their car fell in the overall production range.
 

vette

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Your protest notwithstanding, I'll bet you'll be a bit more careful next time you do this or, if you prefer, stick your thumb in a plug hole--completely sealing it--and crank the engine through a couple intake strokes. Please report the results, and if your thumb is still intact I will gladly retract the warning. QUOTE ]

Bob, I believe you carry the illustration a bit too far. The procedure is not to stick your thumb in a spark plug hole - completely sealing it- and cranking the engine through any number of strokes. The procedure is to lay your thumb on the spark plug hole without any penetration into the hole and then just bump the starter to turn the crank a matter of only a few degrees. If someone thru innocents or ignorance happens to stick their finger or thumb "INTO THE HOLE" the close clearance between the piston and the cylinder head would probably cut it off or mash it considerably in the least. Please don't confuse the procedure. Bob...... I have to tell you that I find it really, really hard to believe that a competent, professional mechanic would stick his finger or thumb into a spark plug hole of any engine and crank the engine.
 
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I didn't see it happen, nor did I see the wound, so it's possible it didn't go down that way. I did see the mechanic's heavily bandaged hand, and either he or someone else told me what happened (it was probably 25 years or so ago). I don't think he made the story up because he was pretty embarrassed by it, and I can't imagine he was trying to cover up an even more embarrassing mistake. At any rate, it's plausible as the jug size on the common/typical O360 engine is 90ci, about half the total displacement of a Healey 3000's 6 cylinders. That's a lot of air being sucked into a small hole. I suspect he had his thumb over the hole and someone else was a bit too zealous on the starter.

A&P (Airframe and Powerplant) mechanics have to undergo intensive classroom training and/or an apprenticeship program, in addition to passing some pretty tough tests (and rightly so). I threw this out there as a cautionary tale; the chance of it happening may be slim, but it's worth keeping in mind IMO.
 

elrey

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It is a good thing to practice caution around machines. Manys the time I have waited for the pfft of exhale with my finger upon the spark plug hole. Never had I given a moments thought to the danger that may await. I have also employed a "balloon" or, a plastic straw in the plug hole riding upon the piston top to find when the piston is at its apex. Danger lurks, waiting to rear its ugly head at any time. Forewarned is forearmed. Most of us would not jam our appendage into the hole whilst giving the starter motor the business, but some might. So... Cautionary tales can well serve the uninformed.
 
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