Potential Valve Spring Problems

[aps]

I looked at a head at work today and there are no lifters on this motor. The cam works directly onto the rocker arm which works directly onto the valve, and I mean directly strait onto the valve, nothing in between. Correct me if im wrong.

The correct terminology for the part is hydraulic lash adjuster. - Apologies for the confusion.

Regards

Peter.

[Turbo6man]

I looked at a head at work today and there are no lifters on this motor. The cam works directly onto the rocker arm which works directly onto the valve, and I mean directly strait onto the valve, nothing in between. Correct me if im wrong.

That's exactly as I understand it too - sorry APS and others but I'm still not able to "see" where there is any hydraulic lash adjuster between the cam and the rocker arm or the rocker arm and the valve. The whole theory behind utilising an OHC design is to alleviate the need for constant valve lash adjustment due to far less moving/wearing parts in the mechanism - no cam followers, no push rods.

I'm not doubting that there is an engine with a damaged piston - just can't see that the explanation that has been given is possible.

Certainly weak valve springs may cause valve bounce, in extreme cases leading to piston crown contact - and a broken spring will have disastrous results if the valve is let "fall in the hole".

I also can't understand that the engine can "rattle" and misfire, and then after a period of idle suddenly come good - if it has valve bounce then it will stop as soon as revs are dropped - it doesn't need any period at idle to do this. And if the spring breaks then it breaks - end of story and one very sad motor in an INSTANT - there is NO "period of grace" if this happens.

[Turbo6man]

Yes there is a lifter type device between the overhead cam and each valve.

Thanks, it is new to me but I accept if you say it is so. How large (height-wise) is this device and what potential does it have to cause the problem mentioned do you think?

I mean, compared to a convential lifter which we know can vary in height by a considerable amount, just how much height/lift variation could occur with this "lash adjuster" if it malfunctioned?

[Guest ante]

Im sorry guys Im wrong. It is exactly as venom xr6 says, roller finger followers I just had a look. (closer look) Ill stay off that homemade whisky.

[aps]

Guys,

Thought this might clear it up for you. – As you can see the hydraulic lash adjusters sit opposite the valve / spring assembly, acting on the other side of the rocker arm (inlet and exhaust).

Now functioning as designed, the valve spring acts against the rocker arm and cam lobe and the lash adjuster ensures the roller in the rocker arm is always in contact with the lobe of the cam when the valve is closed (zero clearance).

Taking this one step further, if the valve spring does not properly close the valve, that is, if the spring is soft or undergoing valve bounce, all of a sudden there is clearance between the roller and cam lobe that the lash adjuster immediately takes up. The valve being partially open causes the engine to miss on this cylinder.

When the revs reduce, the valve spring effectively acts against the lash adjuster again, bleeding off the excess oil built up within. This doesn’t happen immediately and may take several minutes or may require shutdown and restarting of the engine. Of course if the valve springs are soft / below spec, the problem will take longer to rectify. – New springs is the only answer is this is a persistent problem.

Regards,

Peter.

[Cobra]

thanks Peter ... B)

[Turbo6man]

Yes, Thanks Peter - that is an excellent cutaway and explanation and it shows what none of us have been able to see by looking simply from the top of the head.

All is now clear.

[Guest Northerly]

I am still experiencing a loss of power (misfire) when the motor is under load (ie if in fourth gear and accelerate to overtake) but (unfortunately) this only happens now and then and it goes away as soon as I back the power off for a second and then power on. I don't think it is a valve spring becasue the problem goes away real quick.

[RAPHOON]

I am still experiencing a loss of power (misfire) when the motor is under load (ie if in fourth gear and accelerate to overtake) but (unfortunately) this only happens now and then and it goes away as soon as I back the power off for a second and then power on. I don't think it is a valve spring becasue the problem goes away real quick.

Sounds a little like pre-ignition.

Does the problem usually occur when trying to accelarate in a higher gear (ie. Higher load -> more boost)?

Do you use regular ULP or 98 RON?

[aps]

I am still experiencing a loss of power (misfire) when the motor is under load (ie if in fourth gear and accelerate to overtake) but (unfortunately) this only happens now and then and it goes away as soon as I back the power off for a second and then power on. I don't think it is a valve spring becasue the problem goes away real quick.

The engine miss you are describing sounds very much like the soft valve spring issue. - It would be worth having your local Ford dealer check the valve springs and lash adjusters. Better to be safe than sorry.

Regards,

Peter