Timing a RCexl without degree wheel
12-08-2011, 09:23 AM
#26
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RE: Timing a RCexl without degree wheel
It really does not matter what method you use to find top dead center as long as you are happy with it.
I use the top dead center rock of the cylinder most of the time just like in the video I made but have found that sometimes it is hard to do with some engines.
Was going to use the top dead center rock in the instruction I posted but knew I would get a lot of slack if I did. You have to have a good feel to do it.
For a person that has never did it before the piston stop is the best.
I had planed for a while to do a instruction sheet like the video I posted on U tube and someone ask how to do it on another forums, I posted instruction how to do it finding top dead center with top dead center rock, Well some certified aircraft mechanic posted that I was nuts and called me everything you could think of from a idiot to a moron, If I said I could do it more than once I was a lair. That is why you see me do it two times on the video and then check the reading with a piston stop. They were all with in 1/2 degree.
Like Ralph said a degree one way or the other really does not mater.
Milton
I use the top dead center rock of the cylinder most of the time just like in the video I made but have found that sometimes it is hard to do with some engines.
Was going to use the top dead center rock in the instruction I posted but knew I would get a lot of slack if I did. You have to have a good feel to do it.
For a person that has never did it before the piston stop is the best.
I had planed for a while to do a instruction sheet like the video I posted on U tube and someone ask how to do it on another forums, I posted instruction how to do it finding top dead center with top dead center rock, Well some certified aircraft mechanic posted that I was nuts and called me everything you could think of from a idiot to a moron, If I said I could do it more than once I was a lair. That is why you see me do it two times on the video and then check the reading with a piston stop. They were all with in 1/2 degree.
Like Ralph said a degree one way or the other really does not mater.
Milton
12-08-2011, 11:21 AM
#27
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RE: Timing a RCexl without degree wheel
Piston stop = cheap LONG reach 14mm plug or long reach 10mm plug. Paper degree wheel on a piece of scrap wood. Paper clip. Total cost $2. It times as accurate as $50 worth of dial indicators and dial calipers.
Ya pays yer $$ and makes yer choice, any method will work. BUT the more accurate your TDC is the more accurate your timing is.
Ya pays yer $$ and makes yer choice, any method will work. BUT the more accurate your TDC is the more accurate your timing is.
12-08-2011, 11:39 AM
#28
RE: Timing a RCexl without degree wheel
Hey, I made myself a fancy piston stop years ago that I still use. I knocked the guts out of a spark plug, and brazed a piece of tubing into it. The tubing acts as the stop, and also lets air in and out so I am not fighting compression while using it.
Properly used, a dial indicator can find TDC, but it is faster and easier with a piston stop. Every race engine builder I have ever known or seen, (including myself), uses the "positive stop" method to find TDC, though as mentioned, one should just use whatever they are comfortable with. It is not that critical on engine timing a small engine.
AV8TOR
Properly used, a dial indicator can find TDC, but it is faster and easier with a piston stop. Every race engine builder I have ever known or seen, (including myself), uses the "positive stop" method to find TDC, though as mentioned, one should just use whatever they are comfortable with. It is not that critical on engine timing a small engine.
AV8TOR
12-08-2011, 12:58 PM
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RE: Timing a RCexl without degree wheel
Every race engine builder I have ever known or seen, (including myself), uses the "positive stop" method to find TDC
12-08-2011, 02:34 PM
#31
RE: Timing a RCexl without degree wheel
We use a positive stop to find TDC even with the heads off when we build race or hot rod engines. The problem is that when the piston reaches the top of its travel, that is not TDC. The crank has several degrees of dwell, whereas the crank moves across its arc, and then starts pulling the piston back down. Halfway across that arc is where true TDC lies. Just bringing a piston to the top of its travel and assuming that is TDC can introduce an error of several degrees. How much depends on the rod/stroke ratio, etc. An engine with a large rod/stroke ratio has more dwell time, where the piston is sitting still at the top of its travel and the crank is still moving.
AV8TOR
AV8TOR
12-08-2011, 03:10 PM
#32
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RE: Timing a RCexl without degree wheel
ORIGINAL: av8tor1977
We use a positive stop to find TDC even with the heads off when we build race or hot rod engines. The problem is that when the piston reaches the top of its travel, that is not TDC. The crank has several degrees of dwell, whereas the crank moves across its arc, and then starts pulling the piston back down. Halfway across that arc is where true TDC lies. Just bringing a piston to the top of its travel and assuming that is TDC can introduce an error of several degrees. How much depends on the rod/stroke ratio, etc. An engine with a large rod/stroke ratio has more dwell time, where the piston is sitting still at the top of its travel and the crank is still moving.
AV8TOR
We use a positive stop to find TDC even with the heads off when we build race or hot rod engines. The problem is that when the piston reaches the top of its travel, that is not TDC. The crank has several degrees of dwell, whereas the crank moves across its arc, and then starts pulling the piston back down. Halfway across that arc is where true TDC lies. Just bringing a piston to the top of its travel and assuming that is TDC can introduce an error of several degrees. How much depends on the rod/stroke ratio, etc. An engine with a large rod/stroke ratio has more dwell time, where the piston is sitting still at the top of its travel and the crank is still moving.
AV8TOR
12-08-2011, 03:37 PM
#33
RE: Timing a RCexl without degree wheel
You canuse any kind of stop to find TDC even with the heads off when building race or hot rod engines. As long as you bring the piston up to the stop or dial indicator from both crank directions. You do this by turning the crank both directions. Each direction make a mark on the flywheel. Now if a third mark is made between the first 2 marks...thats top dead center.In this case a magnetic dial indicator would be more easy. If a possitive stop was used...you would need too do a lot more...fabricating the stop. Capt,n
12-08-2011, 06:40 PM
#35
RE: Timing a RCexl without degree wheel
On auto/boat engines with the heads off I use one similar to this one: http://www.summitracing.com/parts/PO...1332/?rtype=10
AV8TOR
AV8TOR
12-08-2011, 07:04 PM
#38
RE: Timing a RCexl without degree wheel
I tell you what...I sure do admire you for all the RC fun related things you have done and shared. Sure wish it was not so far to fly RC planes together and talk about engines. I think we could start at day-break and go till dark. I maytravel that way some day....if I win the Lotto! 
Capt,n
Capt,n
12-09-2011, 07:56 PM
#39
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RE: Timing a RCexl without degree wheel
A popsicle stick in the exhaust port works fine for a piston stop. Then I use the degree wheel made from scrap wood and a print out from the internet + paper clip for a pointer.
12-27-2012, 10:08 AM
#41
RE: Timing a RCexl without degree wheel
I was going to up load a picture of a degree wheel but RCU is out of business on picture loading right now
I found a way in spite of the broken problem
Print out and glue to a piece of card board, aluminum, plexiglass, plywood, or something?
I found a way in spite of the broken problem
Print out and glue to a piece of card board, aluminum, plexiglass, plywood, or something?
12-27-2012, 11:09 AM
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RE: Timing a RCexl without degree wheel
As pointed out by Ralph, a couple of degrees does not make much of a difference. I just wanted to point out though that Ralph's method assumed that the magnet is a line. Since the ignition fires when the magnet leaves the hall sensor, the width of the magnet needs to be taken into the calculation.
More accurately the trailing edge of the magnet needs to be determined as the gap between the sensor and the magnet determines where the trailing edge is. Just as soon as this trailing edge leaves the sensor, the sensor returns to its not-sensed state and the ignition fires.
More accurately the trailing edge of the magnet needs to be determined as the gap between the sensor and the magnet determines where the trailing edge is. Just as soon as this trailing edge leaves the sensor, the sensor returns to its not-sensed state and the ignition fires.
