Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Valve or tappet clearance

Hello there.

I have just changed the oil in Nero (1982 cross flow 4/4) and I thought I would have a look at the valve clearances. In the Morgan handbook the clearances are shown as 0.5mm exhaust and 0.2 but I have read on line that the GT (which this should be) needs 0.59 & 0.22. Not a massive difference I hear you say. I adjusted the valves which was interesting as there is no lock nut as in most cars, just a very tight 7/16 nut on top which works very well in adjusting the gaps.
The gaps were all too tight and now she starts far more easily and feels a little friskier to boot.

My question is, does anyone know what the actual clearances should be and what the actual firing order is, as this seams to vary between who is answering the question.

Many thanks

Matt

Hi
I have never understood why the engine seems to run worse on tight clearance.

If you look at it logic would say if it opens sooner, lifts higher, and closes latter, it should be more powerful.

If anyone has an answer i would like to hear it.

Jon the Chief

From memory ford cross flows firing order is 1243.

Valve clearance I'll have to look up but seem to recall they used to be set hot and of course it all depends on what cam you are running.

Bit of research since it's a long time since I ran a standard (GT) cam in a crossflow. 12 inlet and 22 thou exhaust (non GT is different but you should not have one). I don't do metric on that engine, it's got imperial bolts! Supposed to be set hot, but you try getting round a hot engine before it cools.

If I recall correctly what I was told by a mechanic friend years ago. The tappet clearances if too small can result in valves loosing their seal in the head milliseconds early and can result in loss of power. If tapet clearances should be set as specified and if it states when engine is hot then it should be. The reason being the valves expand as they get hot and the clearances will changes so if set when cold when the same clearance was specified for a hot engine then the gap will decrease as the engine heats up. I hope the makes sense.

One of the reasons altering the valve clearance can affect engines and cause rough running is if you alter the clearance you alter the timing, it's the same with contact breakers on points systems. If the clearance is too tight the valve (or CB Points) open sooner and close late, if the gap is too wide they open later and close earlier.....it's all to do with when the cam lobe ramp has an effect rather than a running clearance. The other and more significant one is as mentioned in extreme cases the valve is open when it should be closed and some of the gases are getting where they should not be. Valves have an 'overlap' where both are open, the outgoing exhaust gases actually help draw in the incoming charge, if the gap is too close this overlap is affected and too much of the incoming charge goes straight out of the exhaust. If you have a decent exhaust gas analyser run the car, warm, at correct clearances and measure the HC and CO and then close the gaps just 0.002" and see what happens to the exhaust gases!

Just a throw away, but the clearances on my JAP LTOW are supposed to be 2 thou! As a quick check, if you can rotate the pushrods but can't feel loseness, it is going to be about right.

The tight nuts are probably oval nuts designed to not slip.
You couldn't use nyloc in that heat environment so the oval can do the same job.

How is all this altered by Hydraulic lifters?

Hydraulic lifters are designed to be self adjusting, they still have a running clearance but drop the volume of retained oil when a certain pressure is released, pressure is affect by contact with the cam lobe so the concept is they build up pressure which takes up slack/wear and then bleed off to give a running clearance. That's why they sometimes 'clatter' on start up when the engine has been left standing for a while but soon, hopefully, correct and all is well. Some engines are more prone to this than others, some never have the problem.....as an aside some historically had issues of 'pump up' when sludge blocked the hydraulic follower drain holes and clearances reduced and valves burnt out, regular oil changes helped reduce this.