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MG MGB Technical - Adjusting valves

I need some instructions from you folks that know. My new engine is running an APT VR12 cam. New short lifters and long pushrods which are are different from the tall lifters and shorter rods the motor originally had.

Slacked off all lash adjusters to assure nothing was too tight. APT says set the lash at 0.018 to 0.020 hot. I would assume a 0.016 cold would be ok for the initial startup?

What is the best way to get the initial adjustment? I am assuming, you watch the pushrod until it is all the way up to indicate what valve should be down? I.e. #8 pushrod all the way up to start adjustment on #1?

It looks like the adjusters are going to be nearly at their limit. Is that normal or do I need a different set of adjusters for the different rods/lifters?
Bruce Cunha

Hi Bruce

usually the clearances tighten up 2 thou or so when hot in B engines. I tend to set a tight clearance for first start up so I would have a tight fit 20/22 for your APT VR12which seems to put that cam into the range of ex Crane cams kent favour with the larger cold clearances than most cam ranges. I use the 'rule of nine' then if tappety chase the clearances on all lobes from just opening to just about closed to get loose point. On billet cams this does not seem to be a problem.

Peter
Peter Burgess Tuning

I could never get a consistent gap using the rule of nine - I could set them one by one, then checking them some were bigger or smaller than I had set them. Then I realised that on some valves the gap was still changing at the strict rule of nine point, hence a small movement either way changed the gap. So I started adjusting at the point of biggest gap, which can be a few degrees retarded or advanced from the the strict rule of nine point depending on the valve, and now they are consistent. What's more they haven't needed any adjustment over several years. What that says about my cam I don't know, but I've found the same thing on a pal's engine.
Paul Hunt

I agree with Paul,
I get number one at or near the top of compression stroke (get the biggest gap) with rockers "rocking" Set the gap, then turn exactly 180deg set cyl 3, then TDC again, set cyl4 and finally another 180deg for cyl 2.
To make this properly accurate I mark 180 deg with a centre finder head on a combination square.
Allan Reeling

As always, most appreciate the feedback. I normally use the rule of 9 method, but I can see the reasoning for Pauls information. rocking the crank until the widest point is found and adjusting at that point may take a bit more fiddling but right now, with the radiator our, it is easy to fiddle.

I would think a degree wheel would make this easier. May just put it back on and give it a try.

I know that while valve adjustment is important, I also understand that 0,1 or 0.2 difference here is not as critical for a standard street engine.
Bruce Cunha

Bruce,

I suggest you call APT and ask if you should adjust where you find the most clearance, or if you should adjust when the cam follower is exactly opposite of the peak of the lobe. I didn't ask this question of APT when I put their cam in my Spridget, but I did ask Delta cam before putting their cam in my B.

Delta told me to set it when on the base circle opposite of the lobe peak. They further said finding more clearance elsewhere is an effect of ramping and should be ignored for setting the valves. I don't know enough to decide something like this myself, I'm just telling you what I was told.

There was a post here a few months ago about the hot/cold settings. The poster found that he had greater clearance when hot than when cold. No positive explanation was agreed upon, but the most likely was that metals used today might be different than what was used in the past. So, while valves and push tubes expanding with heat reduces the clearance, the rocker pedestals and head expanding increases the clearance. If I was doing it and only had hot specs, I would use the hot spec on the cold engine and then check it later.

Charley
C R Huff

With any Hi-performance cam I like to be sure that I am adjusting on the "back of the cam. With the plugs out turn the engine till a valve is fully open then turn the engine one full turn and adjust, you are exactly on the back of the cam. Mild cams I use the opposite end down. Denis
Denis4

This thread was discussed between 05/03/2015 and 07/03/2015

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