Cam timing article in Low Flying

[I.Mupferit]

Just read this excellent article in LF and thought great, that's just the type of thing I enjoy reading and very relevant to me at the moment as I am in the throes of rebuilding my engine with a heavily re-worked DVA head and new Piper cams, but a thought then occurred to me.

 

If, like me, you are still using hydraulic valve lifters wouldn't you need to ensure these are pumped up before attempting to time the cams in using the 'Lift @ TDC' method?

 

Correct me if I am wrong here but wouldn't this method risk timing the cams far too advanced unless the lifters are fully pumped up?

 

I accept this is probably the best and potentially easiest method to time the cams, and if engine guru Dave Andrews recommends it then who am I to argue but I would have thought you need to time the cams by the traditional rotational method, start the engine to pump up the valve lifters and only then check using the 'Lift @ TDC' method.

 

Any comments from the knowledgable out there or am I, perhaps, missing something here?

 

Brent

7 in bits, LOTS of bits ☹️

[Lawrence_Z]

If, like me, you are still using hydraulic valve lifters wouldn't you need to ensure these are pumped up before attempting to time the cams in using the 'Lift @ TDC' method?

 

The valve is separated from the bucket by the pressurised oil. Therefore pumping up the oil pressure will only affect the amount the valve is open, it will not alter the values of cam lift at TDC.

 

Lawrence

[I.Mupferit]

But Lawrence that is exactly my point, the article states that you measure and set the valve lift at TDC to the manufacturers recommended setting. So it follows, therefore, that you can't do this unless the followers are pumped up and lifting the valve sufficiently.

Lets say, for example, that the follower is not pumped and some 3mm lower than it would be in normal running condition, then it surely must mean that in order to obtain the correct valve lift measurement @TDC, the camshaft would need to be rotated, or advanced, by a considerable margin thus leaving you with an incorrectly timed cam?

 

 

Edited by - brent chiswick on 9 Feb 2003 14:11:15

[Tony C]

Brent's got a point you know Lawrence.

 

I too believe what Dave Andrews says in the article, but I have to agree that what Brent is saying seems logical. I don't know how much clearance the hydraulic followers provide when pumped-up. Oily, maybe you can enlighten us.

 

Why didn't the article in LF just appear under Dave's name, by the way? - he wrote it after all 😬

 

 

Still waiting for my BRG SV kit. 😬

[Lawrence_Z]

When you try it you'll see how simple it is

 

You actually measure off the back of the cam follower (bucket) as these are on top of the valves.The valve is open remember, and under spring tension.

 

Yes the valve won't be at the correct setting when the measurement is made, but it will be as soon as you start up.

 

Lawrence

 

Edited by - lawrence_z on 9 Feb 2003 18:16:56

[Tony C]

Nah - still don't like it Lawrence

 

I think I understand what you're saying - you are measuring the cam 'lift' not the valve lift, and that when the hydraulic follower is pumped-up, the valve will then be at the correct 'amount' of openness. But, if that's the case, surely the valve will start to open earlier than it would do without the hydraulic lifter pumped-up.

 

Or am I still missing something here?

 

Is perhaps the difference in lift between pumped and not pumped allowed for in the cam manufacturers figures. I seem to remember Dave's advice that hydraulic lifter cams were different than solid lifter ones - I know that the significant difference is the ramp angle and tech. stuff like that, but perhaps the hydraulic cams have different set-up figures too. 😬

 

Still waiting for my BRG SV kit. 😬

[oilyhands]

Lawrence is right..

 

It's simple.. you are missing the point of measuring lift at TDC.

 

The whole point of measuring the lift at TDC is to ensure the cam timing is correct, you are therefore measuring the amount of lift *imparted to the follower at TDC* to make sure it agrees with the cams specification, whether this is exactly reflected in the valves lift when the engine is stationary is irrelevant, as soon as the followers are filled with oil the lift at the valve and the lift at the follower will be the same as will the time when the valve opens and closes. The only time they wont be the same is when the followers are empty or part empty.

 

At no time do you measure the lift at the valve, it is safe to assume that this will be the same or less than the lift at the follower.

 

The lift imparted to the follower will *always* be correct whether the follower is full or empty since the follower is *kept in contact with the cam lobe* at all times by its internal spring, the only reason the follower might not impart the same lift to the valve would be because there may be compressible air inside. When the followers are latent (valve closed) they are the same height whether full of oil or not.

 

Oily

 

 

Edited by - oilyhands on 9 Feb 2003 19:00:01

[Tony C]

OK, got it now - thanks Dave. The cam is being co-ordinated with the crank and it's cam lift that is being measured, as per the manufacturers figures.

[sjwb]

I have an issue with the article.

The method of ascertaining TDC is flawed. Firstly it relies on the crank pulley mark, which in turn relies on the index of the keyway, which in turn relies on the crank keyway angular accuracy. No, this is not nit-picking its a stack up of unknown tolerances.

I believe an accurate (and only needs to be done once process) is to set a DTI in line with the cylinder axis, through the plug hole 1 or 4 and a dgree disc on the front pulley. Turn the motor clockwise towards TDC and note when the clock stops. Mark the degree disc position (relative to a pointer) and continue to rotate the crank very slowly. You will be surprised to see the crank rotate but the clock remain stationary. When the clock starts to move again (piston going down) mark the position. True TDC is half the angular distance between the two recorded points.

Try it.

 

Steve B

[Tony C]

Ineffective crank angle 😬

 

Quote/

"..... in fact most engines have a mark that is very close to TDC on the crank pulley, a quick check with a dti can be used to establish correct TDC and from then on the checking is straightforward."

Endquote/

 

Edited by - Tony C on 9 Feb 2003 21:11:05

[I.Mupferit]

Doh!!

Yes, like Tony I can see where my thinking was flawed now . I had it in my mind that we were measuring valve lift but of course the dial indicator will be resting on the top of the follower, not the valve. 😬

 

Thanks again Dave for clearing that one up

 

Brent

7 in bits, LOTS of bits ☹️

[philwaters]

It is easy to find TDC with a DTI and a long rod by passing it down the spark plug hole onto the top of piston no.1 and then rotating the crank and finding mid dwell with a protractor.

I used this method to mark my pulley as it had no mark.

 

Phil Waters

You mean you can drive these?

I thought it was just there to polish 😬

[Robster]

Thanks for a great article. Please can someone explain to me:

 

What is involved with converting hydraulic lifters to solid...what happens to the oil that would have gone into the lifter?

 

How much do you skim a standard K head to up compression ratio to 10.75:1...or to up it to a 'good' amount for 220 bhp ish??

 

Robster

[oilyhands]

Lifter conversion details are on the K site

 

http://members.aol.com/DVAndrews/kengine.htm

 

Basically the hydraulic valve is replaced with a specially designed shim which is ground to the correct thickness

 

The follower shouldnt fill up since the oil supply holes to the followers are blanked, the oil feed on the follower is soldered up and the locating shield is drilled to allow any oil to drain out.

 

In a normal situation the hydraulic lifters reach a state of equilibrium where the oil ejected from the follower on each lift cycle is minimal and the draw from the oilways is only slight. When the oil feeds to the followers are blocked less oil is vented to the valve gear and a minimal increase in oil pressure is sustained (within the authority of the pressure release valve).

 

On the CR side it depends on

 

i) your pistons, if you are using forged pistons the CR will be 11.5:1 with a stock head.

ii) how much material has been removed from the chamber, since the head will necessarily be modified to acheive 220BHP

 

On a stock head with stock pistons on a 1.8K, 10 thou will just about do it.

 

The 'right' CR for an engine of that spec would be 11.5:1->11.75:1

 

Oily

 

Edited by - oilyhands on 10 Feb 2003 09:52:56