Determining top dead center
From Crankshaft Coalition Wiki
(Format text, links.) |
|||
| Line 1: | Line 1: | ||
{{youcanedit}} | {{youcanedit}} | ||
| − | |||
| − | |||
==Before you begin== | ==Before you begin== | ||
| − | |||
One of the first things that you will need is a degree wheel, this will tell you EXACTLY where you are at when you turn the engine over. You can take this picture of the degree wheel and have it blown up to a reasonable working size by your local photo copy center. A couple of ways to use it is to have it laminated or glue it to a piece of sheet metal or aluminum. | One of the first things that you will need is a degree wheel, this will tell you EXACTLY where you are at when you turn the engine over. You can take this picture of the degree wheel and have it blown up to a reasonable working size by your local photo copy center. A couple of ways to use it is to have it laminated or glue it to a piece of sheet metal or aluminum. | ||
| Line 15: | Line 12: | ||
===The damper=== | ===The damper=== | ||
| − | |||
First off, the large round hub attached to the front of the crankshaft is called a harmonic damper by some and a harmonic balancer or simply "balancer" or "damper" by others. | First off, the large round hub attached to the front of the crankshaft is called a harmonic damper by some and a harmonic balancer or simply "balancer" or "damper" by others. | ||
| Line 26: | Line 22: | ||
There are a multitude of different dampers and timing pointer locations on a small block Chevy. Refer to [[Timing Tabs and Damper TDC Lines SBC]] for more on them. Other engines can refer to a service manual. | There are a multitude of different dampers and timing pointer locations on a small block Chevy. Refer to [[Timing Tabs and Damper TDC Lines SBC]] for more on them. Other engines can refer to a service manual. | ||
| − | The whole reason for doing this operation in the first place is to be able to time the engine with a timing light and know '''''absolutely''''' that the timing is correct. The elastomeric material that connects the outer inertia ring of the harmonic damper/balancer to the inner hub of the damper/balancer which presses onto the snout of the crankshaft begins to break down over time due to ozone in the atmosphere and oil and fuel or other foreign materials which may find their way onto the material. | + | The whole reason for doing this operation in the first place is to be able to time the engine with a timing light and know '''''absolutely''''' that the timing is correct. The elastomeric material that connects the outer inertia ring of the harmonic damper/balancer to the inner hub of the damper/balancer which presses onto the snout of the crankshaft begins to break down over time due to ozone in the atmosphere and oil and fuel or other foreign materials which may find their way onto the material. When this happens, the outer ring may slip circumferentially in relation to the inner hub, rendering any attempt to time the engine with a timing light futile. Even though this operation you are about to do will bring the timing marks back to correct for the time being, there is no guarantee that the ring will not slip further after a while. You also have no idea if the timing pointer matched the inertia ring in the first place if the engine has been disassembled and reassembled by someone else in its lifetime. If you want to bulletproof the operation, then start with a new or rebuilt damper and use the correct timing pointer for that damper. |
| − | + | ===Checking the outer damper ring for movement=== | |
| + | [[File:Damper line.jpg|left|400px]]Draw a sharpie line as shown in the image below. When the timing light is pointed at the TDC line, the sharpie line will also be seen. By revving the engine and running it at different speeds, if the outer ring is loose, the line on the outer ring will be seen to move independently of the line on the inner hub. | ||
| + | <br style="clear:both"/> | ||
| − | + | ==Rebuilt dampers== | |
| + | One noted place to buy a rebuilt damper/balancer is [http://www.damperdoctor.com/ Damper Doctor]. They disassemble stock, OEM production dampers, clock the hub to the inertia ring and reassemble the unit with new elastomeric material pressed together under tremendous hydraulic pressure. An 8" damper for a 350 Chevy can be had for a mere $32.95 (ca. 2012). | ||
| − | The option is a used damper/balancer that may be clocked worse than the one you have or an aftermarket damper/balancer that will cost more money and may not have been correctly machined on the inner hub diameter. Some of these | + | The option is a used damper/balancer that may be clocked worse than the one you have or an aftermarket damper/balancer that will cost more money and may not have been correctly machined on the inner hub diameter. Some of these offshore (Chinese) dampers being sold are bored either oversize or undersize for the production crank snout diameter. The damper/balancer hub MUST BE A SNUG PRESS-FIT on the crank in order to properly transfer harmonics from the crankshaft to the damper/balancer hub and on to the inertia ring, where harmonics are dissipated. |
| − | On a street engine or a drag race engine down to 11.00 E.T. in the quarter mile, an OEM-type damper/balancer may be used legally. At 10.99 E.T., an aftermarket SFI-18.1 damper/balancer is required. | + | On a street engine or a drag race engine down to 11.00 E.T. in the quarter mile, an OEM-type damper/balancer may be used legally. At 10.99 E.T. and quicker, an aftermarket SFI-18.1 damper/balancer is required. Blower motors normally do not use a balancer/damper, but instead, use an aluminum toothed hub on the crank snout to drive the blower. On these blown motors, the large Gilmer drive belt functions as a dampener to dissipate crankshaft harmonics. |
===Damper suppliers=== | ===Damper suppliers=== | ||
| − | |||
*[http://www.damperdoctor.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=DD&Category_Code=HAR Damper Doctor] | *[http://www.damperdoctor.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=DD&Category_Code=HAR Damper Doctor] | ||
*[http://www.atiracing.com/products/dampers/index.htm ATI] | *[http://www.atiracing.com/products/dampers/index.htm ATI] | ||
| Line 58: | Line 56: | ||
If the engine is a short block on the stand, you can determine TDC with a simple homemade piston stop made from a strap of metal bolted across two head bolt holes, with the strap drilled and tapped for an adjustable bolt/nut assembly. A dial indicator can also be used on a fixture that bridges the bore or on a magnetic base. This would be an ideal time to note the piston-to-deck clearance for use in computing the static compression ratio and quench distance. | If the engine is a short block on the stand, you can determine TDC with a simple homemade piston stop made from a strap of metal bolted across two head bolt holes, with the strap drilled and tapped for an adjustable bolt/nut assembly. A dial indicator can also be used on a fixture that bridges the bore or on a magnetic base. This would be an ideal time to note the piston-to-deck clearance for use in computing the static compression ratio and quench distance. | ||
| − | If the engine | + | If the engine has the heads on, use a spark plug-type piston stop tool. If there is a timing tab present, use it to mark the position with. If no tab, use a length of stiff wire that's attached to the engine to use to show the positions. This may be made easier by using a degree wheel or a timing tape on the outer ring of the damper. |
| + | #Set the plug hole-mounted piston stop to contact the piston close to TDC | ||
| + | #Rotate engine until the stop just contacts the piston- mark the location | ||
| + | #Then rotate in the opposite direction until the piston is stopped | ||
| + | #Half way between the two marks is approximately TDC | ||
| + | |||
[[File:TDC1.jpg |thumb|left|Strap-type and spark plug-type piston stop tools]] | [[File:TDC1.jpg |thumb|left|Strap-type and spark plug-type piston stop tools]] | ||
<br style="clear: both" /> | <br style="clear: both" /> | ||
| Line 76: | Line 79: | ||
==Getting started== | ==Getting started== | ||
| − | |||
Attach the degree wheel or refer to '''[[How To Make A Timing Tape]]''' or buy a timing tape that matches the diameter of the damper. Also buy or make a piston stop tool. Using a tool that has a hole drilled through the center of the probe will allow pressure or vacuum to escape through the hole from the piston moving up and down in the bore with the rocker arms disabled (valves on their seats). This makes turning the engine over w/the piston stop installed easier. | Attach the degree wheel or refer to '''[[How To Make A Timing Tape]]''' or buy a timing tape that matches the diameter of the damper. Also buy or make a piston stop tool. Using a tool that has a hole drilled through the center of the probe will allow pressure or vacuum to escape through the hole from the piston moving up and down in the bore with the rocker arms disabled (valves on their seats). This makes turning the engine over w/the piston stop installed easier. | ||
| Line 84: | Line 86: | ||
===Water pump suppliers=== | ===Water pump suppliers=== | ||
| − | |||
*[http://www.flowkooler.com/ FlowKooler] | *[http://www.flowkooler.com/ FlowKooler] | ||
*[http://www.stewartcomponents.com/ Stewart Components] | *[http://www.stewartcomponents.com/ Stewart Components] | ||
| Line 90: | Line 91: | ||
==The procedure== | ==The procedure== | ||
| − | |||
Thoroughly clean the harmonic damper and timing pointer. | Thoroughly clean the harmonic damper and timing pointer. | ||
===Procedure done with valves closed=== | ===Procedure done with valves closed=== | ||
| − | |||
Remove the valve cover for #1 cylinder and back off the rocker arms for both valves for that cylinder. COUNTING THE NUMBER OF TURNS YOU LOOSEN THE ROCKER NUTS WILL MAKE IT A SNAP TO GET NEAR TO THE CORRECT LASH WHEN YOU TIGHTEN THEM BACK AFTER THIS OPERATION. | Remove the valve cover for #1 cylinder and back off the rocker arms for both valves for that cylinder. COUNTING THE NUMBER OF TURNS YOU LOOSEN THE ROCKER NUTS WILL MAKE IT A SNAP TO GET NEAR TO THE CORRECT LASH WHEN YOU TIGHTEN THEM BACK AFTER THIS OPERATION. | ||
| Line 106: | Line 105: | ||
===Procedure without removing valve cover=== | ===Procedure without removing valve cover=== | ||
| − | |||
If checking an assembled/long block engine, you will install a piston stop tool into #1 spark plug hole ([http://www.offroaders.com/tech/V8-engine-firing-order.htm domestic V8 firing orders]). Screw the top dead center housing into the spark plug hole and snug it down. Insert the probe of the tool into the tool housing and screw it in until you feel resistance of the tool probe against the piston crown. Snug it down slightly against the piston crown and start from there. | If checking an assembled/long block engine, you will install a piston stop tool into #1 spark plug hole ([http://www.offroaders.com/tech/V8-engine-firing-order.htm domestic V8 firing orders]). Screw the top dead center housing into the spark plug hole and snug it down. Insert the probe of the tool into the tool housing and screw it in until you feel resistance of the tool probe against the piston crown. Snug it down slightly against the piston crown and start from there. | ||
| Line 133: | Line 131: | ||
==Timing the engine== | ==Timing the engine== | ||
| − | |||
Hook up your timing light to #1 plug wire. | Hook up your timing light to #1 plug wire. | ||
| Line 140: | Line 137: | ||
If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Some distributors, like those sold by MSD, use different bushings to control the ''amount'' of mechanical advance. The '''rate''' of mechanical advance is tailored by changing the springs and/or centrifugal weights. Usually just spring changes are all that is needed. If working on a GM HEI, the original weights are almost always a better choice than the weights sold in the various advance curve kits available from Mr. Gasket, Crane, Summit, Moroso, etc. | If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Some distributors, like those sold by MSD, use different bushings to control the ''amount'' of mechanical advance. The '''rate''' of mechanical advance is tailored by changing the springs and/or centrifugal weights. Usually just spring changes are all that is needed. If working on a GM HEI, the original weights are almost always a better choice than the weights sold in the various advance curve kits available from Mr. Gasket, Crane, Summit, Moroso, etc. | ||
| − | If you are using a radical cam and/or a converter that allows the engine to come up past where you would normally limit centrifugal advance (about 2800 rpm), you may want to | + | If you are using a radical cam and/or a converter that allows the engine RPM to come up past where you would normally limit centrifugal advance (about 2800 rpm), you may want to modify the distributor so that centrifugal advance is locked out and put your total amount of ignition advance in at the crank. Of course, the engine will not want to crank against this much ignition lead, so you will want to install a momentary switch in the wire going to the "+" terminal of the coil to disable the coil while you crank the engine. Once the engine is spinning, release the switch and the engine will fire normally. |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
Your Privacy Choices