finding top dead center, 8 times

[joe'stoy]

I have a 351w and need to find TDC for piston #1. Is it a sure process if I rotate the crank with a wrench until the distributor rotor points to the #1 terminal on the distributor cap then fine tune it by moving the crankshaft balancer back or forward to 0 degrees?
Next question, after I have TDC for #1, is there a simple process to find TDC for the next piston in the firing order, such as 2 or 4 complete revolutions of the crank and stop at 0 degrees? AND will this work for the next 6 pistons?
Thanks, I am getting ready to do a leakdown test.
Joe

[redmt]

Pull all the plugs and use the "finger compression test" running through the firing order as you do your leakdown. As soon as you have "finger pressure" you can run your test without having to run the engine around more than twice. Be sure to hold the crank when you put the air to it or it could send that cylinder to BDC.

[Jerry Clayton]

If you don't know how to find top dead center, you are going to hurt yourself bad doing a leak down test

[Tom Cimino]

The easiest way to find TDC on #1 is to rotate the engine with the sparkplugs removed and your thumb over the plug hole until you feel compression leaking out. Then turn the engine until your timing pointer is at "0" degrees. Assuming your timing pointer is accurate, this will be TDC on #1 cylinder. You can "bump" the starter, but I prefer to turn the engine by hand. Just be sure to turn the crankshaft the direction it normally turns while running.

A four stroke engine revolves twice to complete it's four cycles.(Intake, compression, power, and exhaust.) All eight cylinders will complete their four cycles in those two rotations, so after finding #1 TDC it is easy to find TDC on the other cylinders by rotating the crank 1/4 turn for each cylinder, in the order of the firing order. This TDC will be on the top of the compression stroke for all eight cylinders.

I hope this makes sense.

[Caprimaniac]

Yes. Ff your pointer is correct.

But if you didn't chck that last time you had you rheads off or otherwise with thumb or TDC finder tool, then these are the options.

Then it's a matter of degrees if you find TDC on no. 1- although I do not have ( or bother to find out now) the degrees for the rest.

Anyway, what I should say was: I ordere myself a TDC finder for the plughole. All steel.

Did anyone use such a thing without getting piston top scratched? It's the stupidestr construction I have ever seen. They could, at least, put on a hard nylon/ PTFE or other tip on the tool to not destroy pistons... The Profom piece I will not tell you to get.

(And after trying 2 times, it was still 2 degrees off as I found out after taking the head off.)

RS

[Jerry Clayton]

And this is an example of what I meant about if you didn't know how to find tdc.

[Michael C Henry]

Piston stop bolt a tool offered by Moroso, Comp Cams, and the like. The stop bolts come in spark plug thread sizes. Mine #4792 is from Comp Cams and has a solid brass body 18mm x 1.5 and an adjustable brass bolt , my FE has those threads. The body screws in place of the spark plug and the adjustable brass bolt that will contact the piston. Remove all the plugs for ease of rotating crank by hand. Screw the stop bolttools body into the desired spark plug hole (#1) rotate crank gently in one direction, all the time feelling for resistance when piston touches the stop bolt. Mark or record that point, then rotate crank in other direction, again by hand feeling for that contact. When that stops markor record that point on the timing -balancer marker. Actual top dead center is exactually in the middle between those two marked points. If you have the stop bolt adjusted high or short the gap between the two marked (or recorded )will be smaller. But too high and the piston will not make contact with the stop bolt. They make degree wheels that can be attached to the harmonic balancer to make this as acurate and easy as posible. This process is often used when degreeing in a cam shaft. I used it when figuring out where my actual TDC was with my older original harmonic balancer (they can slip) making the original timing marks not acurate. I bought one stop bolt . I Know I put it some place really special, I haven't found it so I had to buy a second stop bolt.

[Mike_I]

Watch the Rocker arms in the firing order sequence after you find #1. After the Intake valve closes for the appropriate cylinder it should be coming up on the compression stroke.

Each cylinder will go through the following in Order Intake:Compression:Power:Exhaust hence why you can take note of the intake rocker arm on the desired cylinder,as it closes the piston is coming up on the compression stroke for that cylinder.

[Jerry Clayton]

If you try a cylinder leakage test without the piston at the tdc(not just on the way up) the air pressure will blow the piston down to the bottom and will cause any wrench /socket you have on the crank bolt to be turned violently at high speed. Not this can cause several things ----one of which is to cause the crank bolt to be loosened ---

[patrickt]

Originally Posted by Jerry Clayton

And this is an example of what I meant about if you didn't know how to find tdc.

Uhhhh, if you just start the engine up with the piston stop fully seated in the #1 plug hole, won't the engine slam to a halt pretty close to TDC?

[redmt]

Originally Posted by patrickt

Uhhhh, if you just start the engine up with the piston stop fully seated in the #1 plug hole, won't the engine slam to a halt pretty close to TDC?

Plus it will make a really cool noise but only once!

[Jerry Clayton]

But Patrick---Pretty close to tdc is not the result we're looking for---When we degree an engine, whether its to check cam or set the timing pointer, we usually will use a positive stop piston stop that will contact the piston aprox 3/8 to 1/2 inch before tdc----mark the degree wheel--rotate the cranshaft in the reverse direction til the piston contacts the stop, mark the degree wheel---tdc will be EXACTLY 1/2 the number of degrees between these two marks---remove the positive piston stop and turn the crank until the newly arrived at tdc is lined up at the degree wheel pointer--at this point we'll do all the camshaft spec checking and adjust timing as necessary.and we'll then leave the crank/piston at tdc per our set up degree wheel, install the front cover and harmonic balancer, checking the degree marks are lined up and if not correcting them.

If the engine is assembled, and it is necessary to verify tdc, we will install a positive stop as has been described by others(not a thumb) and rotate the engine til it contacts the piston, mark the dampner, rotate crank the other way until contact, mark the dampner, splict the differance for tdc, and then will place marks at 90,180,270 for adjusting the valves, doing leak down checks, etc.

If doing a leakdown check, turn to tdc 0*, insert leakdown ---if it is 100 % your on wrong cylinder by one crank revolution and can either go to that cylinder of the firing order or preferably turn one rev til on #1 and start again, then turn to 090 and do 2nd cyl, 180 3rd cyl,270 4th cyl etc thru 2 complete revolutions of the crank/ I will also check the adjustment of the valve clearances as I work thru the order plus check spring pressures if at a race.

At the end of the firing order of checks/adjustments we will be coming up on the timing marks for the ignition and we'll check for anything gone array or change timing at this time. Valve covers back on, spark plugs indexed and now its time to make jetting changes if spark plug check/ air/weather data shows a need for rich or leaner jets.

Fill fuel cell, oil level, pack parachutes, adjust tire pressure---add/remove weight, gear ratio change then pretty much ready for interviews and signing autographs

The

[patrickt]

Originally Posted by Jerry Clayton

But Patrick---Pretty close to tdc is not the result we're looking for...

OK, then what if we try inserting our pinky finger in to the #1 spark plug hole while we use a remote starter to crank the engine? When we feel the the top of the piston smack against our finger we stop cranking real fast.

[Jerry Clayton]

well I mentioned not a thumb but if you want to use your righthand pinky, on a ford with #1 being on the same side as the starter, you won't need a remote switch---just use your lefthand ring finger and make contact between the terminals on the starter solenoid

[patrickt]

Originally Posted by Jerry Clayton

well I mentioned not a thumb but if you want to use your righthand pinky, on a ford with #1 being on the same side as the starter, you won't need a remote switch---just use your lefthand ring finger and make contact between the terminals on the starter solenoid

And, worst case scenario, I leave a piece of my finger in the cylinder. You think the piston could chew it up and spit it out the exhaust valve or am I gonna have to use my good hand to pull the head off?

[Jerry Clayton]

It'll spit it out without chewing it up---just remember that if the starter rotates the crank 300rpm(maybe faster with the plugs out) it will hit you 5 time a second until you get outta there. spin to left(counterclockwise) sometimes will help getting loose!
Of course that is if your ring isn't fused to the starter terminal restricting bodily rotation

[patrickt]

OK, maybe I'll just take it to Jiffy Lube.

[Jerry Clayton]

With that----Good nite

[Z-linkCobra]

Please oh please post a pic of your ring finger after you use it to bump the motor over...lol.

I would send you a pic of my wrist when my watch accidently shorted the starter relay one time, but I didnt have a camera handy. I suppose I could send a pic of the scar it left behind...lol.

[patrickt]

Originally Posted by Z-linkCobra

Please oh please post a pic of your ring finger after you use it to bump the motor over...lol.

Well, ok.