Have recently set my silvertop's No. 1 cylinder to TDC, using the old-established screwdriver down the sparkplug hole. Then it occurred to me - how do you know this is true TDC? It could also be the non-firing, valves open position. How can you check it?

Does this mean that I'll have to whip the cam cover off, and check No.1 valves? Not as straightforward as the Xflow.

[Edited on 20/2/16 by Dick Axtell]

It doesn't matter, because if the valves were open, 360 degrees later the crank will be in exactly the same position, but the valves closed.

On your x flow it did because you had the rotor position to take into account.

[Edited on 20/2/16 by r1_pete]

Wasted spark, it fires on both the compression and exhaust strokes.

I have a whistle that screws into the plug hole , rotate the engine until you hear the whistle and it's on the compression stroke . My thumb isn't long enough to put over a zetec plug hole to feel the increase in compression on a Zetec

Remove all the plugs except no1 and feel for TDC cylinder on #1 compression stroke.
Modern engines are generally wasted spark so for ignition it doesn't matter if the pairs of companion cylinders 1&4 and 2&3 are transposed.
If the injection is fully sequential (ie it fire each cylinder's injerctor individually) it gets additional information from a Camshaft phase sensor.

To find true TDC you need to use a dial indicator gauge and extenstion tube for deep well plugs. even then you have to allow for the lost linear motion over TDC.


[Edited on 20/2/16 by britishtrident]

Your engine has 2 tdc position, power and exhaust. True tdc is best found with a dial gauge and suitable extension rod. With a suitable piece of rod, check that the piston is coming up the bore, install the dial guage, slowly crank the engine until the needle stops moving and note the position. Continue turning the engine until the needle starts moving again, (this will be the piston going down) and make a note of the reading again. If you then split the differance and mark it then wind engine backwards until piston start going down again, then forward to the split position and this is a true tdc. Always wind backwards to get rid of any slack in the belt/chain etc.....It might sound complicated but only takes a couple of minutes. You can use this method in conjunction with a crank timing gauge on the end of the crank and a pointer. The gap between the points when the needle stops and restarts is called the dwell angle and it is this you are splitting...................

[Edited on 20/2/16 by redturner]

The lost motion in the rock over TDC is one of the reasons the valve timing on Rover engines is set at half stroke, the half stroke position can be found much more accurately, of course Rover mucked it up by screwing up the cam dowel and crank pulley.

I drilled a old sparkplug down the centre 8.2mm, then got a piece of bar 8mm. Placed clock gauge on top of bar. To get a true TDC you need a dial gauge on the crank pulley.

I would assume that you meant a timing disc on the end of the crank. This will make it easier if you dont have a clock gauge with two adjustable pointers as opposed to one with just one needle. I also use a drilled out spark plug as a guide, but any-one making one of these should be warned to make sure the rod is long enough to ensure it cant drop through before the piston gets to the bottom.............

If you haven't got a dial gauge it's possible to remove the ceramic from a spark plug and weld a bolt so it end touches the piston when screwed into the plug hole , rotate engine forward until it is stopped by the bolt, mark the crank pulley by the TDC mark or temporary pointer, rotate engine backwards until it stops , make a second mark on the pulley . TDC will be halfway between the 2 marks

Ford's keyless pulleys are not one of their best ideas, and the D flat used by GM and MG-Rover isn't exactly precise.
Because of the increasing number of engines with variable valve timing and the return to using chain driven camshafts cam - crank timing drifting off is increasingly becoming a major issue in the tintop world. When the timing chain or variable valve ting unit wear beyond a set limit the engine managment computer detects a change in timing between the crank and cam angle sensors and triggers fault codes

Thank you LCB-ers, for your replies. All had interesting info, but rusty_nuts was definitely the winner, with his "whistling spark plug" idea!

[Edited on 21/2/16 by Dick Axtell]

Hijacking the thread from proven hands on methods there are some interesting advanced diagnostic electronics methods have been developed for checking ignition and valve timing and much more using a pressure sensor screwed into the spark plug hole.

http://www.atsnm.com/pressure-transducer-screen-shots-page-1.html

http://farm4.static.flickr.com/3488/3737361544_0b4eaa05ab_b.jpg

http://www.getlinkyoutube.com/watch?v=Kwy72aaAFvo

After another search, I found this relevant thread :-

http://www.locostbuilders.co.uk/viewthread.php?tid=199611

This seems to provide some interesting solutions, this one from dusty in particular -

Quote - "There is a special tool (actually just a bolt) that inserts low on the nearside of the block after removing the bolt that usually lives there. It screws in and its length is such that a web of the crank stops on it at tdc as you gently turn the engine with a spanner on the crank-pulley bolt.

If you are using megajolt and wasted spark you don't have to worry about (180 ?cam) 360 degrees out as both cylinders at tdc are fired. Ditto batch injection. And you would be running a cam sensor presumably if you were running phased injection." - unquote.


TDCbolt


[Edited on 22/2/16 by Dick Axtell]

[Edited on 22/2/16 by Dick Axtell]

My information is that these crank locking bolts are ideal for locking the crank so that a new cam belt can be fitted pretty accurately. However, if being used to swing a set of after market cams they are not quite near enough. I have never used one so cant confirm, as I suppose that I am old school and do it with a timing disc and a pointer on the crank and a mag stand and dial guage on the top end. I also prefer to use the standard Zetec cam wheels instead of verniers and just spend a bit more time getting it spot on, then drill and peg the wheels.

Mark the flywheel in a position you can see through the starter mounting when you establish true tdc that way you can line up the marks quickly and accurately.

quote:

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Originally posted by redturner
I would assume that you meant a timing disc on the end of the crank. This will make it easier if you dont have a clock gauge with two adjustable pointers as opposed to one with just one needle. I also use a drilled out spark plug as a guide, but any-one making one of these should be warned to make sure the rod is long enough to ensure it cant drop through before the piston gets to the bottom.............

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