"Dialing" Valve Timing

[Carby131]

Afternoon all

Was watching a few engine rebuild videos and came across "dialing". After they timed the engine up they then added dial test indicators (DTI's) to the valve head to measure the lift, this may be a common thing but its the first i had heard of it and a few more people in here have been mentionaing it in vague detail.
What actualy is it? where can i learn how to do this properly without learning by hit and miss :P

Thanks
Carby

[blitzracing]

When you get a performance cam it will have a figure with it to say just how much lift the cam will give at a specific point in the engine rotation in degrees. You cant rely on the cut out on the cam sprocket being acurate enough to set this point if you are trying to get the best from the cam, hence the need to measure it acurately. You need a protractor on the crank shaft to measure the degrees rotation, and a dial test indicator measuring the valve lift from the cam lobe to get the read the two figures. The cam drive sprocket then needs some sort of adjustment system to allow you to alter the cam rotation against the crankshaft say +/- 10 to 15' so you can line it up as per its spec'.

[Carby131]

Ahh right thank you seems quite simple i'l have to look into it more, sounds like a common thing now.

[blitzracing]

I did a bit here on the RV8, towards the bottom of the page.

http://www.g33.co.uk/tuning.htm

[Carby131]

I take it it's fairly simple once you get the general feel and knowledge of it? or is it complex every time?

[blitzracing]

Carby131 said:

I take it it's fairly simple once you get the general feel and knowledge of it? or is it complex every time?

Its fine once you get you head around the the relationship between the cam doing one revolution when the crank does 2 so you need to make sure you are correct part of the cycle when the number inlet valve is opening ( this is the normal point of reference against the crank). Its fiddly getting the timing spot on, as you have to make sure there is no backlash in the cam timing gear, so you set it, do a couple of revollutions to make sure eveing is settled and then re measure the values. Invariably it wont be spot on so you will have to repeat the setting proccess untill you are as close as you can be.

[Carby131]

Thank you for this, hope i can get practicing it soon

[Steve_D]

An important start point is to ensure the TDC marking is correct before setting anything else.
If the head is off bolt or clamp a bar across number one cylinder and stand a nut on the top of the piston under the bar. With your timing wheel and pointer fitted rotate the crankshaft until the piston stops against the nut trapped under the bar. Note the reading on the wheel. Rotate the crankshaft in the opposite directions until the piston stops again. Note the reading from the wheel. Remove the stop bar. Rotate the crankshaft in the same direction until the pointer is half way between the degrees noted at your stop points. The engine is now at TDC so you can check the manufacturers pointers for accuracy and also reset your timing wheel so it reads TDC.

If the head is on then you can make a stop out of an old spark plug with a bolt through the middle. I've also heard you can poke the head of a large cable tie down the plug hole but I would not be confident it would be trapped in the same position on each rotation.

Steve

[Pupp]

You also need to be aware that the dial indicator will read slightly differently depending on which way the engine is being turned as bearing clearances etc are taken up. There is always an element of 'feel' around judging when you are absolutely on it. Sorting a nice solid pointer on the degree wheel is essential too

[spend]

Pupp said:

You also need to be aware that the dial indicator will read slightly differently depending on which way the engine is being turned as bearing clearances etc are taken up. There is always an element of 'feel' around judging when you are absolutely on it. Sorting a nice solid pointer on the degree wheel is essential too

I for one am very confused by what you are trying to say.

I can't understand why you would contemplate turning backwards at DTI time?

[Pupp]

spend said:

I for one am very confused by what you are trying to say.

I can't understand why you would contemplate turning backwards at DTI time?

Ideally you wouldn't and if you're looking for particular lift at some point prior to peak deflection then you shouldn't need to. If you have to time on the centreline of the relevant lobe however (as seems common), then there is a small period of 'dwell' (something like 2deg but maybe more depending on profile) and to ascertain the true mid point in the real world you will end up rocking back and forward.... obviously the definitive reference needs to be taken when the slack in the camchain or whatever has been taken up in the correct direction of rotation.

Confusion relieved?

[Carby131]

I come from a engineering background that has always taught me when measuring anything that rotates once you commit your self to one direction you never go against it, if you miss it by a degree you mark it and do a complete 360 (or in this case 720) so dont worry about that

thank you all for takeing interest im always willing to hear new tips and tricks from you all