using piston stop

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j.d.duggan

j.d.duggan

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I have never used one.found enough on some threads to build one.need to know how use it safely.any chance of piston damage? is it easy to tell that your at stop?
 
I Guess you are talking about a screw-into-the-plug-hole, stop.
Here's how I make mine safe to use , while doing an in-frame measurement, where I cannot see the piston.
Firstly; the adjusting pin you made or have, has to be very sturdy. If it bends, EDIT; or if it wobbles or in any way moves; then you are screwed.Then remove all the sparkplugs.
So what I do is put the piston either #1 or #6 at TDC-compression. Then I back it up to 10* advance on the factory timing tab. Next I back up the adjuster to simulate a projected-nose RN12Y plug, then install the tool and tighten it down. Next I screw in the adjuster until it hits the piston and lock it down. Now you are ready to go hunting.
But first, familiarize yourself with how it feels to hit the stop. Back the crank up some more and then crank it into the stop gently, cuz you know about where it's gonna stop. Do it several times to get the feel of it. And while doing that, watch to see the exact # of degrees that the balancer stops at, and how repeatable it is.If it ain't repeatable; find out why and correct it. Finally, make a mark on the balancer exactly where it stops, compared to the TDC indicator.
Next, turn the engine over backwards about 3/4s of a turn, then slow down, cuz you are coming up on the stop. Gently nudge up to it. With your breaker bar go back and forth a couple of times to prove repeatability; then make your second mark on the balancer, again compared to the TDC mark.
Finally, remove the stop and rotate the crank to where you can see both marks, then make a third mark to bisect the other two, and this third mark is exactly TDC; well it would be if you did perfect work. In the real world, if using a Sharpie, the line it draws is about 1/2* wide. So, depending on how careful or how sloppy your work is; you could be out by up to 1 or even 2 degrees.
_______________
Since the cam is already in and degreed at this time, this small error only becomes important when setting your power-timing. So instead of targeting 36* which everybody "just knows" is where a Mopar makes peak power; instead, target 34* and sneak up on the perfect power-timing over the coming weeks or months. With aluminum heads target 30/32*, and you can sneak up on 34 a lil quicker.
Now, in a streeter, my advice is that you are better off with 2 or 3 degrees sub-optimum power-timing than even 1 degree too much. Two or three degrees short,on a 360, represents perhaps 7 to 10 horsepower. But one degree two much can put your engine into detonation, and depending on circumstances and parts used, can cost you an engine in just a very short time.
Now, with an automatic, you are only gonna suffer this 7 to 10 HP loss once on the way to 65 mph, and you will probably be spinning the tires anyway, plus this power loss will only last for a fraction of a second. The racier your rear gear, the shorter the fraction. So unless you have 2.76 geared Low-C, teener, IMO, this is a non-issue
And finally; if you can notice that loss of 7 to 10 horsepower at peak output, with your butt-dyno, in first or second gear where a streeter lives; then you are light years more sensitive than me,lol.
ok so that was more of AJ's 2cents worth.
 
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The commercial ones are not very well thought out. You need a jam nut on the rear of them to lock the plunger. As above it must be rigid this is the one I made for a SB in the 70's and (miracle) LOL still have it

stop2-jpg.jpg


It's not very important how long it is except that you don't want it too close to TDC. You want the piston to stop "down a ways"
 
AJ/FormS said:
I Guess you are talking about a screw-into-the-plug-hole, stop.
Here's how I make mine safe to use , while doing an in-frame measurement, where I cannot see the piston.
Firstly; the adjusting pin you made or have, has to be very sturdy. If it bends, you are screwed. Then remove all the sparkplugs.
So what I do is put the piston either #1 or #6 at TDC-compression. Then I back it up to 10* advance on the factory timing tab. Next I back up the adjuster to simulate a projected-nose RN12Y plug, then install the tool and tighten it down. Next I screw in the adjuster until it hits the piston and lock it down. Now you are ready to go hunting.
But first, familiarize yourself with how it feels to hit the stop. Back the crank up some more and then crank it into the stop gently, cuz you know about where it's gonna stop. Do it several times to get the feel of it. And while doing that, watch to see the exact # of degrees that the balancer stops at, and how repeatable it is.If it ain't repeatable; find out why and correct it. Finally, make a mark on the balancer exactly where it stops, compared to the TDC indicator.
Next, turn the engine over backwards about 3/4s of a turn, then slow down, cuz you are coming up on the stop. Gently nudge up to it. With your breaker bar go back and forth a couple of times to prove repeatability; then make your second mark on the balancer, again compared to the TDC mark.
Finally, remove the stop and rotate the crank to where you can see both marks, then make a third mark to bisect the other two, and this third mark is exactly TDC; well it would be if you did perfect work. In the real world, if using a Sharpie, the line it draws is about 1/2* wide. So, depending on how careful or how sloppy your work is; you could be out by up to 1 or even 2 degrees.
_______________
Since the cam is already in and degreed at this time, this small error only becomes important when setting your power-timing. So instead of targeting 36* which everybody "just knows" is where a Mopar makes peak power; instead, target 34* and sneak up on the perfect power-timing over the coming weeks or months. With aluminum heads target 30/32*, and you can sneak up on 34 a lil quicker.
Now, in a streeter, my advice is that you are better off with 2 or 3 degrees sub-optimum power-timing than even 1 degree too much. Two or three degrees short,on a 360, represents perhaps 7 to 10 horsepower. But one degree two much can put your engine into detonation, and depending on circumstances and parts used, can cost you an engine in just a very short time.
Now, with an automatic, you are only gonna suffer this 7 to 10 HP loss once on the way to 65 mph, and you will probably be spinning the tires anyway, plus this power loss will only last for a fraction of a second. The racier your rear gear, the shorter the fraction. So unless you have 2.76 geared Low-C, teener, IMO, this is a non-issue
And finally; if you can notice that loss of 7 to 10 horsepower at peak output, with your butt-dyno, in first or second gear where a streeter lives; then you are light years more sensitive than me,lol.
ok so that was more of AJ's 2cents worth.
Click to expand...

Thank you - bookmarked!

Jeff
 
j.d.duggan said:
I was planning on building me one like 67dart showed.
Click to expand...
If you build one, like that, I threaded the bolt all the way to the HH, then installed it from the top with a nut under the head about an inch down, with which to jam the assembly solid. Then I machined a few threads off the end that touches the piston and rounded the end. This does not have to be accurate, cuz you are not using it for anything but to stop the piston. By tightening the jam-nut it takes all the wiggle out of system, that come from using a de-porcelained plug shell.
With the jam-nut, now it is adjustable and works in frame with all the accessories bolted on. What I mean is you can get both initial marks visible on the balancer at the same time, making it simple to bisect them. If you make the plunger too long, you may have to extend your initial marks closer to TDC and then bisect. Of course that introduces two more possible errors, er, probable errors.

Notice how 67Dart gives you a measurement. I'm assuming he built it specifically for an SBM, so the plunger is likely fixed in place. That would be OK too.
 
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