MGB maximum safe valve lash on MGB ??

[dansawyer]

All,

I am trying to pass OR emissions with a '77 MGB. The car has a mild performance including compression and cam. The result is a chunky idle with a miss. I believe reducing some valve overlap will reduce the idle miss. What is a safe maximum valve overlap? I am thinking 20 on the intakes and 24 on the exhausts. Has anyone done this? Are those clearances on the lands or are they on the lobs?

Thanks, Dan

 

[Bret]

While I’ve never tried this myself – I have actually read a lot on the subject. The thought is that if you open up the rocker valve clearance to about 0.024" it should help compensate for the profile of the hotter cam. But I wouldn't leave it there after the test and would put it back to the normal 0.013" (warm) after you complete the emissions test.

Here is a great link on the subject.

Emissions Research info

Scroll down to the Valve/Cam timing. It has a lot of information on the valve lash procedure and how it affects your emissions readings. There are also some great links and other things to consider if your having trouble passing emissions testing.

Good luck!

 

[DrEntropy]

You'll know not to leave the lash at .024" -- gonna sound like a marimba band!

Interesting site, Bret. Thanks!

 

[dansawyer]

Thanks. The plan is to try to run it through tomorrow. I have a load of gas to burn through and then to find blended regular gas. I will let you all know how it goes.

 

[Bret]

I probably don’t need to mention this but I will anyway for those that are new to this. But I would do a complete tune-up first before adjusting the valve lash. Once I adjust the valves clearance to the stock .013” settings I then go over everything – replacing the air filter, plugs (adjusted) rotor and complete all adjustments (timing idle etc.) only then would I adjust the valve lash.

Who unless you have a really “hot” came the stock settings might work. That is assuming that you still have all the original emissions equipment still in good working order. i.g. EGR valve, Cat and smog pump. Also do you know if Oregon checks the timing and idle speed? If they don’t you might be able to play with those settings a little.

Only real problem most folks with the Zenith Stromberg have is getting the air/fuel mixture set right. I am lucky in that I have a CO% Gas Analyzer to help me dial it in. If you don’t – its going to be a little harder. The Moss MGB cataloge has a pretty good procedure that should get you close. Once set I’d dial it back to lean it out before testing

Again good luck and do let know how it goes?