TDC, PISTON STOP and NGK BR9ES spark plug ???

Middle age crisis. Trying to become mechanical. Synching up. Am I trying to find a consistent point or am I trying to get an average of TDC ? I am not forking over the money for that piston stop tool but have tried the NGK BR9ES long reach spark plug which when put in all the way stops the piston BEFORE TDC as compared to my other method of measuring which is with a pencil, erasure end first. So am I just looking for an AVERAGE spot at some common point of piston head or am I trying to get TDC ? I could see maybe when piston is stopped by spark plug I could loosen plug out a little then move flywheel a little and so on until I figure out where TDC is. The pencil method is a bit rough because it is all by eye. So what should I be doing ? How often when you mark it twice they are virtually the same spot ?

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

Bump !!!

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

You don't find TDC directly. You must use a dial indicator or a piston stop of sorts, and find/mark either side of TDC, then split the difference. At TDC, you will get a little rotation w/ no piston travel.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

In order to make the process work using the piston stop technique is to start when piston is AFTER TDC.

That allows you to rotate the crank in its normal direction(clockwise) WITHOUT moving/disturbing your piston stop.

Since the process begins on the downward stroke ensure the piston is tight to rod and crank for the start of process. Make your flywheel mark.

Rotate clockwise until piston stops, make your 2nd mark. Between the marks will be TDC.

If your plug doesn't work well, you can buy a usable tool as low as ~$10 delivered.

Hope that helps.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

And to expand a little, basically what you're doing is finding a point on the flywheel after top dead center where the piston is x disance from the head, then go through a little less than a full revolution and finding the point on the flywheel before top dead center where the piston is the exact same distance from the head. The midpoint of these two locations is top dead center.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

So the NGK plug, if I put it in all the way, stops the piston about an inch + BEFORE the TDC mark. It hits this same mark consistently. If I play with the plug by loosening a little and turning flywheel a little and then tightening up to snug the plug to piston I am getting to about 3/8" BEFORE TDC mark consistently(?). Two questions:

1) Is it possible to get CONSISTENT marks, in other words there is no in between ?

2) If CONSISTENCY is OK then wouldn't a mark where I put the plug in all the way and it stops the piston a little before TDC work since it marks a specific time in the revolution which TDC really is, at least to me ? I would like this to be true because there would be no question that I was marking it right.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

dazk14 said:

In order to make the process work using the piston stop technique is to start when piston is AFTER TDC.

That allows you to rotate the crank in its normal direction(clockwise) WITHOUT moving/disturbing your piston stop.

Since the process begins on the downward stroke ensure the piston is tight to rod and crank for the start of process. Make your flywheel mark.

Rotate clockwise until piston stops, make your 2nd mark. Between the marks will be TDC.

If your plug doesn't work well, you can buy a usable tool as low as ~$10 delivered.

Hope that helps.

Click to expand...

So as long as I make sure it is AFTER TDC, I turn the plug until contacts piston firmly, MARK, turn fly wheel until makes contact with plug again and MARK. Find the equidistant point between marks and TDC.

The 1.5" after TDC that the manual mentions does not work with NGK plug method. In my case I think it will be a hair past TDC mark. I got to do something with the tip of plug, maybe some heat shrink tubing so as to not scrape piston.

I think I got it now.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

Yep, you got it. Good luck.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

Couple of things...

You need more than "a hair past TDC". You have to have some "range"; that's why the book says 1.5". Than 1.5" is totally arbitrary, but you need a good wide distance between the contact point that is AFTER TDC and the contact point that is BEFORE TDC.

You have to have some distance to divide in half to locate TDC.

Just to be on the safe side, disconnect your battery. I was doing TDC with a piston stop tool on my V6 looper, went away from the job for a few hours, came back to it, and for some STUPID reason, hit the key. Engine spun one partial revolution, hit the stop tool, punched a hole in the top of the piston, and knocked the stop tool hard enough to ruin the spark plug hole threads in the head.

I had to replace the head, and piston. Just wasn't thinking....

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

That plug is not long enough to make contact at 1.5". I THINK my REAL TDC is about 3/8"-1/2" before TDC cast in mark. I am contacting piston with plug all the way in at about 2" BEFORE TDC cast in mark, so about 1" PAST TDC mark is my estimate where I'll get piston as it moves in.

Re: TDC, PISTON STOP and NGK BR9ES spark plug ???

As daselbee said, you need some range. If you haven't already, remove the plug washer.

Unless you're a gorilla, you don't need to pad the plug electrode - Pistons aren't that fragile.