TRUE TDC Questions
04-29-05, 10:28 PM
#26
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Originally Posted by wackyracer
I waited but since no one commented, then I will. The first mark is not a TDC. Read the label in ur hood - usually, timing is 10L.
correct me if i'm wrong but isn't the second one (trailing) set at 0
04-30-05, 01:11 AM
#28
Originally Posted by wackyracer
I waited but since no one commented, then I will. The first mark is not a TDC. Read the label in ur hood - usually, timing is 10L.
04-30-05, 06:59 AM
#29
Originally Posted by nimrodTT
In all that time you spent waiting, did you ever think to check your facts? The first mark (if you are turning the engine in the direction it rotates) is the leading mark and is in fact timed at 0° TDC, the second mark, for trailing, is at 20° ATDC. And is there really any reason to make a personal attack like that?
sorry but I have no intention on making any personal attack; just waiting for someone to chimed in but I gues no one knew about it.
the leading mark is NOT always at 0. the only way to find out is to check the specs decal in in the hood. The only pulley that has a 0 mark is the racing beat one.
Again, Im not putting on the spot. Im just trying to make a point.
04-30-05, 09:23 AM
#31
I just re-read my posts and I think I gave confusing info-thats what I get for not proof-reading my posts. sorry about that. 12-A's are set at 0L. 13-B's are not. I never use stock timing since I prefer a full advance.
Timing mark is in my pre-installation checklist when it comes to receiving an engine. I have seen engines with mis-match parts as in 13-B block with 12-A pulleys OR 12-A's engines with improperly installed stock pulley (separating the belt pulley from the main). I have also seen stock engines that run better by not using the stock timing mark in the pulley.
At any rate, the leading on 12-A motors are different from 13-B. But be sure to check the decal on ur hood. So if you feel that ur timing is properly set but the engine is missing (assuming no issues with carb/spark), double check the timing mark by removing the main bolt and make sure that the key is at 9 o'clock (12 o'clock is 0). Who knows what the previous owner did and never trust someone elses work.
Now, if you wanna set ur timing at full advance, I dont recommend advancing the timing with seeing an actual mark. Do it right the first time may save you $$ in the long run. You have 2 options:
1. Buy the marked pulley from Racing Beat (but you also have to add 1 or 2 marks since it goes 10, 0, 10 and 20.
OR
2. Do it the "YAW" way. Prior to removing the 4 10mm bolts, be sure to turn the pulley til the timing marks are ligned up with the needle and there is no need to remove the main bolt. This is to ensure that it goes back to its original position. Pre-81 pulleys are different as there is a notch/dimple that needs to come off.
Whew, I need to start a habit of using the "Preview Post" button.
Timing mark is in my pre-installation checklist when it comes to receiving an engine. I have seen engines with mis-match parts as in 13-B block with 12-A pulleys OR 12-A's engines with improperly installed stock pulley (separating the belt pulley from the main). I have also seen stock engines that run better by not using the stock timing mark in the pulley.
At any rate, the leading on 12-A motors are different from 13-B. But be sure to check the decal on ur hood. So if you feel that ur timing is properly set but the engine is missing (assuming no issues with carb/spark), double check the timing mark by removing the main bolt and make sure that the key is at 9 o'clock (12 o'clock is 0). Who knows what the previous owner did and never trust someone elses work.
Now, if you wanna set ur timing at full advance, I dont recommend advancing the timing with seeing an actual mark. Do it right the first time may save you $$ in the long run. You have 2 options:
1. Buy the marked pulley from Racing Beat (but you also have to add 1 or 2 marks since it goes 10, 0, 10 and 20.
OR
2. Do it the "YAW" way. Prior to removing the 4 10mm bolts, be sure to turn the pulley til the timing marks are ligned up with the needle and there is no need to remove the main bolt. This is to ensure that it goes back to its original position. Pre-81 pulleys are different as there is a notch/dimple that needs to come off.
Whew, I need to start a habit of using the "Preview Post" button.
Last edited by Siraniko; 04-30-05 at 09:29 AM.
05-01-05, 03:36 PM
#32
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Originally Posted by wackyracer
I just re-read my posts and I think I gave confusing info-thats what I get for not proof-reading my posts. sorry about that. 12-A's are set at 0L. 13-B's are not. I never use stock timing since I prefer a full advance.
Timing mark is in my pre-installation checklist when it comes to receiving an engine. I have seen engines with mis-match parts as in 13-B block with 12-A pulleys OR 12-A's engines with improperly installed stock pulley .
Timing mark is in my pre-installation checklist when it comes to receiving an engine. I have seen engines with mis-match parts as in 13-B block with 12-A pulleys OR 12-A's engines with improperly installed stock pulley .
I just this hour found that I had a 12a pulley on a 1987n/a using the method described in this article (bottom of the articles page) http://www.teamfc3s.org/info/articles/demystifying.html
When using the method in the article it seemed that something was way wrong, either with my pulley and its marks or the method described in the article. So I got another pulley that was laying in the shed and installed it in place of the existing one. Then I found top dead center using the articles method and lo and behold the TDC mark WAS within 5 degrees of the LEAD mark on the pulley (series four the LEAD is 5 degrees ATDC). Then I held both pulleys up against each other and it was obvious I'd been using a 12a pulley on my 87n/a .
11-08-11, 05:56 AM
#33
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I know this is a old thread but the same question really is still unaswered. I have to prove the TDC on a blower pully with out being there when they biult the engine. Lost a lot of sleep over this problem, but this is what I came up with and may help a lot of people. My misses came home from work with a Repco pamflet just like TOOLTOPIA in the US. In that panflet was a top dead centre finder. I have never seen them before. So all that happens is you screw the end of this tube into the leading plug hole and slowly turn the engine over. When it comes up on Comp the gauge will rise up as the rota gets to TDC and start to fall as the rota falls away. So the highest point is TDC and mark your pully in accordance remembering that the mark you want is 5 degs from that. How simply is that.
11-08-11, 07:02 AM
#34
I know this is a old thread but the same question really is still unaswered. I have to prove the TDC on a blower pully with out being there when they biult the engine. Lost a lot of sleep over this problem, but this is what I came up with and may help a lot of people. My misses came home from work with a Repco pamflet just like TOOLTOPIA in the US. In that panflet was a top dead centre finder. I have never seen them before. So all that happens is you screw the end of this tube into the leading plug hole and slowly turn the engine over. When it comes up on Comp the gauge will rise up as the rota gets to TDC and start to fall as the rota falls away. So the highest point is TDC and mark your pully in accordance remembering that the mark you want is 5 degs from that. How simply is that.
11-08-11, 06:37 PM
#35
Huh that is cool. From what ive read pull the inspection plate off the pmotor line the flat part of the flywheel up parralel to the engine and thats TDC. Pull the pully off and mark accordingly.
11-09-11, 02:21 AM
#37
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Can any one tell me the settings on this Forum as to how long you have writeing about a subject before it loggs you out. Just spent time showing how to mark your timing marks only to be logged out and loosing all that work.
11-15-11, 02:37 AM
#38
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Update on the TDC Gauge. Used the new gauge yesterday, and how easy was that. Just rotate the engine by hand and when the little float drops that is TDC. The old mark was out 5degs set while biulding the engine with a dial indercator. 
11-15-11, 02:44 AM
#39
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Next I measured the drive pully dia and scribed the circle on to a cam degree wheel. From there you pull a line from the centre of the cam degree wheel to the degrees that you want on the outside. Then go back to were your pulley dia is make a mark. Then transpose those maks on to your pully. No need to take anything of your car. To easy.
11-15-11, 05:04 PM
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These gauges are available on eBay for US $38.00. Made in England by DAT Equipment and sold as a TDC Finder. I also have orded a 18 inch Moroso cam degree wheel to be able to mark any pulley size I want. Hope this sorts the TDC problem for all Rota heads.
11-15-11, 05:51 PM
#42
Just my opinion, but I'm having a hard time visualizing how that 'finder' could work accurately with a rotary engine... seeing as it works off of registering maximum compression within the combustion chamber.
In a piston engine, in finding TDC you're looking for the point where the piston is closest to the top of the bore, which is also the point of maximum compression.
In a rotary, you're looking for the point where the plane of the working rotor face's apex seals is perpendicular to and equidistant from both spark plug bores - which is to say, when the e-shaft lobe is lined up with the housing lobe between the plugs. It's the point of maximum compression, same as for a piston engine... but unlike a piston engine, a rotary won't hold compression for more than a brief period of time if it's not running. Compression bleeds down rapidly without rotation, because the engine design uses both centripetal force and compression rise to make the seals 'seal'.
Seems to me in theory that this tool would tend to respond too early... how early depending on how slowly the shaft was rotating.
Leastwise, based on my understanding of how these motors work.
In a piston engine, in finding TDC you're looking for the point where the piston is closest to the top of the bore, which is also the point of maximum compression.
In a rotary, you're looking for the point where the plane of the working rotor face's apex seals is perpendicular to and equidistant from both spark plug bores - which is to say, when the e-shaft lobe is lined up with the housing lobe between the plugs. It's the point of maximum compression, same as for a piston engine... but unlike a piston engine, a rotary won't hold compression for more than a brief period of time if it's not running. Compression bleeds down rapidly without rotation, because the engine design uses both centripetal force and compression rise to make the seals 'seal'.
Seems to me in theory that this tool would tend to respond too early... how early depending on how slowly the shaft was rotating.
Leastwise, based on my understanding of how these motors work.
11-16-11, 03:46 PM
#43
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Air is a wounder full thing and can be a tool for testing all manner of things. You need to forget about compression, its disipation of air which this tool measures. As soon as the rota stop diplacing the air the tell tail drops. When you watch the dvd that comes with the tool you will understand the logic.
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