25 replies to this topic

[Stu.]

Could I ask for some guidance with my standard 850 please ?

The car was running fine before I started work to renew the timing chain, and have not moved the dizzy at all.

I'm in the process of replacing the rattly simplex timing chain with a new standard duplex kit.

I've set the engine to tdc and have removed the timing cover etc. I quickly noticed that the crankshaft woodruf keyway is at the 12 o clock position but the camshaft woodruf keyway is at around 8 o clock and the timing dot on the camshaft sprocket is not lined up with the crankshaft and is180 degrees out on the opposite side.

I know you think I might have tdc 180 out but I've checked this and confirm that the rockers are loose on number 1 cylinder (closest to the rad) and the pully marks lined up before I removed the pully and cover.

I assume the engine is correctly set at tdc as the dizzy arm is pointing at number 1 ht lead (closest to the rad). If this is not right I'm stupid and clearly have it 180 out but I could do with some help as I don't want to go any further until I can get some advice from you guys.

Obviously if I remove the old chain and sprockets as they are I won't be able to line up the new ones using the dots as the camshaft keyway is 180 degrees out.

Thank you very much in advance.

[Jordie]

Id say your TDC is 180 out

 

You could turn the engine over by hand, watching the rockers to see the inlet and exhaust opening to work out which stroke your on etc and find the correct TDC.

[Stu.]

Thanks Jordan. I'm sure I've got correct tdc, and in that position the rotor arm points at 3 o clock for the lead that goes to the far right plug next to the radiator.

As I said in this position the camshaft woodruf keyway is not at 2 o clock but at 8 o clock.

Are you saying that the camshaft is not timed properly with the crankshaft making it 180 degrees out, and the dizzy has been set in the wrong place to suit the firing order ? I'm not sure because at tdc the far right rockers are loose which I thought was right for confirming tdc.

When I align the dots and get the cam and crankshaft keyways correct, the rockers on the far left are loose.

If that was so wouldn't the rotor arm be pointing at 9 o clock at tdc ?

Sorry if I'm being dumb but I'm trying to understand why this is and how I can correct it withought screwing up the timing.

[Jordie]

If i remember right,
 
Crankshaft key is at 12 o clock. Camshaft around 2 o clock position.
Timing gears should fit in that position and line up dot to dot. I use a straight steel rule across the centre of the crank hole and the camshaft.
 
Id be tempted to remove everything and start from scratch to ensure its done correctly. Once you have identified true top dead centre on intake stroke, then fit timing chain etc, then refit dizzy drive ensuring its in the correct way (the connection to dizzy is offset, so it can be 180deg out.). Refit dizzy and set ignition timing.

[Stu.]

Ok thanks. Can you just confirm about tdc on the firing stroke that if the rockers are both loose over the valves of number 1 cylinder (closest to radiator) when 1 and 4 pistons are at the top of the stroke, is that tdc / firing stroke on number 1 cylinder (closest to rad) ?

I understand the dizzy offset and thanks for the reminder !

[Dan]

You understand that what you are suggesting here is that the cam is either made wrong or is out of time with itself somehow? Cam position is what defines the engine timing, nothing else. The cam needs to be timed with cylinder 1 on the intake stroke, not the firing stroke. Cylinder 1 on intake is the nominal start of the engine cycle, firing comes later! You can do it as you are if you want, with the cam dot on the far side of the wheel, providing the dots and shaft centres all line up on a straight edge still. This is the firing position for 1 though, not the cam timing position. You are confusing cam timing and ignition timing a little is all. Don't go changing anything to accommodate this apparent problem though, the cam can't be out of time with itself.

[Stu.]

Thanks Dan. I guess my inexperience is clouding rational thought somewhat. I am still learning and engine timing / ignition timing is all a new learning curve for me!

I'm perhaps worrying too much about trying to fit the new chain and sprockets dot to dot as the Haynes Manual informs. I guess as the engine was running fine before I should just fit the new ones the same way the old ones come off, making sure as you say that the dots and shafts line up.

I hate to be a pest, but can you give me info on what the rockers closest to the radiator should be doing at tdc on ignition timing then. I've seen other posts that say at tdc the rockers should be loose when you wiggle them. (for want of a better word).

[Dan]

There is more than 1 TDC remember. TDC firing stroke is when both valves are closed, the cylinder is charged and compressed and ready to fire. That is where you want to set ignition timing. TDC on the inlet stroke is when the valves are moving, it's just got to the top having expelled the exhaust and that valve is closing. It's just about to accelerate down the cylinder and draw in fresh charge so the inlet is just beginning to open. Both valves are doing something, so both rockers will be loaded. In this position cylinder 4 will be about to fire, so the valves over there will be loose.

You're not being a pest, questions are what this place is for. Everyone has to do something for the first time once.

[Stu.]

Haynes says that tdc locating for the purpose of engine timing should be set at the end of piston 1 compression stroke. It also says that this can be verified by observing that the rockers on number 4 cylinder are rocking (inlet valve just opening and exhaust valve just closing). From your advice it seems that the rockers on number 4 should be loose, this is why I am confused. Can you help to clarify what's right.

[Dan]

Haynes also says to do cam timing with the dots together and the key way on the cam at 2 o'clock!

No confusion, both are the same. Haynes there is talking about ignition timing. It is saying to do ignition timing when the rockers on 1 are loose and the rockers on 4 are loaded (or on the rock). This is also what I have said above and is the position you are in. Cam timing should be done with these two reversed, cylinder 1 rockers loaded (rocking) and cylinder 4 rockers loose. A rocker is described as rocking when it is doing it's job and operating the valve, not when it's slack. This is easily confused though.

[Stu.]

Ok that's great Dan thank you.

So I'm dealing with ignition timing then. That would confirm that I have correctly set tdc for changing the timing chain.
I'll fit the new sprockets and chain in the same position the old ones come off as you suggested.

Out of interest, do you know why the cam shaft keyway would be in the position mine is in, ie at 8 o clock and not 2 o clock ?

Appreciate your help, thanks!

[Dan]

Because your engine is set to TDC firing stroke on cylinder 1, not TDC inlet stroke. The crank will be in the same position for both, the cam will not.

[Stu.]

So is the info in Haynes regarding dot to dot and keyway positions not to be taken literally if your engine camshaft keyway is at the opposite side ? I'd have thought that if they knew this they might have made reference to it in the manual.

[Dan]

I don't think you fully understand this. Cam timing happens in a different engine position from ignition timing. Both positions have the crank at TDC, but have the cam at different positions 180 degrees apart. When we talk about the position of an engine being TDC this refers only to the crank, unless you define which stroke you are referring to it could be either. There is nothing unusual about your camshaft.

[dklawson]

To confuse this even more.... when the cam in installed and aligned dot-to-dot, yes... piston #1 is at TDC but NOT on it's firing stroke.  When the sprockets are aligned dot-to-dot, it is piston #4 that is at TDC on its firing stroke.  This confused me the first time I fit a new timing chain and it confuses almost everyone the first time they do this procedure and then start looking at ignition timing.

 

As Dan said, ignition timing is different than cam timing.  When you are looking for TDC to set your timing, you want the points to just open at the specified static timing mark when piston #1 is slightly before TDC on its firing stroke.  The rocker arms above piston #1 will be "loose" at that point.  The rocker arms for piston #4 will be "rocking" but tight as the valve springs will be compressed.