The V8 Owners Forum -

Hi, its me again.

I have just got the new engine running reasonably well. But I want some advice on setting TDC. I normally get no 1 coming up on a compression stroke and stick a welding rod into the bore so I can feel the piston coming up. I gently rotate the crank in the correct direction of rotation until I feel the piston stop. Then I fit the dissy with the the rotor arm in the middle of number one segment. Then I advance it a bit and start the engine to set the timing with a strobe. The damper I am using has no marks on it, so at this point I mark TDC with a felt tip and stick the marker tape on. I now assume I have TDC marked ok. But I can still rotate the crank a bit more before the piston starts to move down and this equates to maybe another 10 or so degrees.

My question is, Do I set TDC at the end of the upward piston travel as I have done, or should I try and find the mid point between piston stopping and piston starting to move down again.

Sorry if this a bit of a basic question, but this new 4.6 seems bit more sensitive to this type of adjustment than my old 3500 did.

the generally excepted way to find TDC is to use a piston stop down the plug hole and to approach it from both clockwise and anti-clockwise and mark where they hit the stop, then you take the stop out and split the difference to give you TDC. It is reliable and repeatable.
Mike

I should have used my cam timing disk to do that before I fitted the engine shouldnt I Mike.
Oh well. I have time to tweak that before I roll her out for shakedowns at the Pod on 13th Oct.

did mine with a scribe and a set of deviders, very acurate and no phaffing about if you just want TDC.
Mike

mind if I ask what a piston stop is? I'm paranoid that my engine wasn't built properly and TDC isn't correct, but this is a completely new ball game for me! I really dont wanna fit the engine etc. only to have to take it out again to set TDC. The engine is pretty much built.

chodjinn wrote:mind if I ask what a piston stop is? I'm paranoid that my engine wasn't built properly and TDC isn't correct, but this is a completely new ball game for me! I really dont wanna fit the engine etc. only to have to take it out again to set TDC. The engine is pretty much built.

A piston stop is just a stopper for the piston!

Basically you need to stop the piston reaching TDC by it hitting something solid. (Gently, maybe 2-4mm before actual TDC)

You could use an old spark plug, knock out all of the centre section and weld a rod of steel in its place. This will only work if the plug points in the general direction of the piston and the steel rod does not interfere with either of the valves.

If the heads are off then its dead easy to just bolt a strong piece of steel across the cylinder bore with a bolt poking out the bottom that hits the piston.

What ever method you use it needs to be solid and reliable, not just a screwdriver bunged down the plug hole .

All the other import measurements are referenced to TDC. (Cam and igintion timing).

Once you have found it make sure the damper mark for TDC and its pointer are spot on, adjust the pointer if required.

HTH,

Pete

Hello
I assume you have the heads on, on a rover get an old plug as sugested above and knock the innards out and either tap a thread down the center and put a short bolt in, or just weld one in as said. knock the corners off the bolt so you don't mark the pistons and away you go.
if you have ilned up the dots on the cam sprockets and been in the ball park when you did it then you won't be far out on a near standard engine, I assume you were not asking sooner then you are probably not far from standard.
Have you turned it over yet? do it first plugs out by hand this will tell if anything is not right before it gets bent!
I think isky cams have the procedure for finding TDC on their website somewhere. Don't fuss too much as yet obout their cam timing procedure it is worth a read but only really applies to bigger cams and higher tune engines.
Good luck
Mike

my megasquirt arrived this morning so I suppose I better start fitting it!

Firstly; setting TDC.

So you lot are basically saying use an old gutted plug with a rounded bolt shoved in, put it in cylinder 1, rotate gently either way and mark both. Then take the half way point.

Seems a bit caveman, but if it works, then it works.

ANyone got an old plug?!? I binned my old ones when i fitted some new ones, and they haven't been used yet!

chodjinn wrote:my megasquirt arrived this morning so I suppose I better start fitting it!

Firstly; setting TDC.

So you lot are basically saying use an old gutted plug with a rounded bolt shoved in, put it in cylinder 1, rotate gently either way and mark both. Then take the half way point.

Seems a bit caveman, but if it works, then it works.

ANyone got an old plug?!? I binned my old ones when i fitted some new ones, and they haven't been used yet!

Marking the damper would be very "caveman" as you put it and no good at all!

You need a degree disk on the end of the crank, you note the reading against a pointer when you turn the crank round either way, work out the angle between the two points, divide that angle by two, add it to one of the angles when it hit the stopper and that's TDC.

Use a bit of wire or something as a pointer and get it very close to the degree disk, 1-2mm away max.

You can then remove the stopper turn the engine to TDC, then carefully turn the degree disk WITHOUT moving the crank so that the zero lines up with the pointer.

You can then re-fit the piston stop, the crank should then stop at an equal angle either side of the zero on the degree disk. As you can see this can take quite some time but its vital that you know where TDC is if you are going to set the timing up from scratch or fitting a cam etc.

You can buy a quite large 360 degree protractor from Smiths or Woolies that you can use as a degree disk.

Once you have TDC you can mark the damper against the standard rover pointer for future reference.

HTH,

Pete

I made one like this. I ground off the earth electrode, then wiggled the inner electrode and insulator with a screwdriver until I could get some long nose pliars on to snap it out. I cut the head off a bolt and ground the threads off until it fitted snugly inside. Then I brazed it in with the oxy propane kit. It worked a treat mate.

http://s205.photobucket.com/albums/bb27 ... DCtool.jpg

I have to admit, I marked the edge of the damper with a scriber on both sides of TDC. It was easy to mark the middle of the two marks with a needle file. I dont have enough room to fit my big degree disk when the engine is in.

I bought the disk to do just this, but I forgot to do it.

sidecar wrote:

chodjinn wrote:my megasquirt arrived this morning so I suppose I better start fitting it!

Firstly; setting TDC.

So you lot are basically saying use an old gutted plug with a rounded bolt shoved in, put it in cylinder 1, rotate gently either way and mark both. Then take the half way point.

Seems a bit caveman, but if it works, then it works.

ANyone got an old plug?!? I binned my old ones when i fitted some new ones, and they haven't been used yet!

Marking the damper would be very "caveman" as you put it and no good at all!

You need a degree disk on the end of the crank, you note the reading against a pointer when you turn the crank round either way, work out the angle between the two points, divide that angle by two, add it to one of the angles when it hit the stopper and that's TDC.

Use a bit of wire or something as a pointer and get it very close to the degree disk, 1-2mm away max.

You can then remove the stopper turn the engine to TDC, then carefully turn the degree disk WITHOUT moving the crank so that the zero lines up with the pointer.

You can then re-fit the piston stop, the crank should then stop at an equal angle either side of the zero on the degree disk. As you can see this can take quite some time but its vital that you know where TDC is if you are going to set the timing up from scratch or fitting a cam etc.

You can buy a quite large 360 degree protractor from Smiths or Woolies that you can use as a degree disk.

Once you have TDC you can mark the damper against the standard rover pointer for future reference.

HTH,

Pete

Seems like a bit of a po lava to go through everytime you want TDC!! I am with the accurately mark the damper and I don't understand why you reckon its no good at all to do it that way. Your describing exactly the same way to get 0 on a degree disk as everyone is for marking the damper so its just as accurate. Besides a degree disk is useless when you come to set ignition timing but an accurately marked damper is easy.

mgbv8 my tdc stop is pretty similar only I made the extension out of alloy, theory being it was less likely to ding the piston.

katanaman wrote:

sidecar wrote:

chodjinn wrote:my megasquirt arrived this morning so I suppose I better start fitting it!

Firstly; setting TDC.

So you lot are basically saying use an old gutted plug with a rounded bolt shoved in, put it in cylinder 1, rotate gently either way and mark both. Then take the half way point.

Seems a bit caveman, but if it works, then it works.

ANyone got an old plug?!? I binned my old ones when i fitted some new ones, and they haven't been used yet!

Marking the damper would be very "caveman" as you put it and no good at all!

You need a degree disk on the end of the crank, you note the reading against a pointer when you turn the crank round either way, work out the angle between the two points, divide that angle by two, add it to one of the angles when it hit the stopper and that's TDC.

Use a bit of wire or something as a pointer and get it very close to the degree disk, 1-2mm away max.

You can then remove the stopper turn the engine to TDC, then carefully turn the degree disk WITHOUT moving the crank so that the zero lines up with the pointer.

You can then re-fit the piston stop, the crank should then stop at an equal angle either side of the zero on the degree disk. As you can see this can take quite some time but its vital that you know where TDC is if you are going to set the timing up from scratch or fitting a cam etc.

You can buy a quite large 360 degree protractor from Smiths or Woolies that you can use as a degree disk.

Once you have TDC you can mark the damper against the standard rover pointer for future reference.

HTH,

Pete

Seems like a bit of a po lava to go through everytime you want TDC!! I am with the accurately mark the damper and I don't understand why you reckon its no good at all to do it that way. Your describing exactly the same way to get 0 on a degree disk as everyone is for marking the damper so its just as accurate. Besides a degree disk is useless when you come to set ignition timing but an accurately marked damper is easy.

mgbv8 my tdc stop is pretty similar only I made the extension out of alloy, theory being it was less likely to ding the piston.

I'm not saying do that everytime you want to find TDC!!!!


I'm saying do the degree disk thing once to find TDC then mark the damper!

In fact the damper already has a mark on it and the RV8 has a pointer, the problem is that they can be miles out.

Once the true TDC is found it is possible to "adjust" the rover pointer so that it lines up with the damper mark.

The reason that you need a degree disk is that if you just marked the stop points on the damper it would not be easy to split that angle in two and mark the centre, you only need to be a couple of degrees out to throw out all your other settings, after all TDC is the reference for all other settings but at the end of the day I guess its up to you how accurately you want to find TDC).

I agree that a lot of degree disks are too big to fit whilst the engine is in the car, the 360 protractors that you can get for peanuts are about the same size as the damper, you could even tape it to the damper!


Pete

thankyou very much guys!

once again legends all round; I gave myself a headache trying to understand all the megasquirt manuals last night, but its very interesting!

chodjinn wrote:thankyou very much guys!

once again legends all round; I gave myself a headache trying to understand all the megasquirt manuals last night, but its very interesting!

That's why I stuck with a weber 500!!!

I'm sure that you'll get it going and I suppose EFI is really the way to go.

Cheers,

Pete