Valve Adjustment, ...why did I have zero clearance? Options

[tomeric914]

I had adjusted the valves to .006" before the last track event I went to in April. It was about a 4 hour drive to the track and probably 40 or 50 degrees F. When I got there, the darn thing wouldn't idle (dual IDF 40's, 2.1L). No matter what adjustments I made, I couldn't get it to idle when hot (right off the track) but it would idle if it sat for a while. So I came home from the event, parked the car and started on the flare installation.

Now 3 months later with flares on and driving it on a regular basis, it still didn't idle. Again, checked the synchronization on the carbs, idle mixture, etc. Still didn't idle. Thinking logically, if it won't idle hot, a valve must be sticking open. So I let the car sit for a day and pulled the valve covers to find that all 4 exhaust valves had ZERO (more like negative) clearance! (IMG:style_emoticons/default/WTF.gif)

So what happened?

A. The valves all stretched the same length.

B. All the seats got mashed evenly

C. The valves weren't adjusted at TDC

D. It was about 20 deg F in the garage when I adjusted them last


A and/or B? I doubt it.

D seems the most logical but does the valve grow .006" over 60 degrees?

You would think that finding TDC doesn't matter, but I believe it does. Years ago I tried adjusting them with what is now referred to as the "rocking method" using the opposite side valve as a guide with the theory that a valve closed is a valve closed anywhere on the cam. I found when checking the clearance at TDC that the valve did not have the same clearance as measured when using the rocking method. It ended up being too tight at TDC!

On my 914, the flywheel is paint marked at the groove for TDC and 28 deg BTDC. If I used the 28 deg BTDC mark, I was on another part of the cam that resulted in a different clearance than at TDC. The result being a valve held open when the engine is hot and no idle.

After adjusting the valves at TDC and confirming all adjustment through one rotation, it idles perfectly.

[ME733]

I had adjusted the valves to .006" before the last track event I went to in April. It was about a 4 hour drive to the track and probably 40 or 50 degrees F. When I got there, the darn thing wouldn't idle (dual IDF 40's, 2.1L). No matter what adjustments I made, I couldn't get it to idle when hot (right off the track) but it would idle if it sat for a while. So I came home from the event, parked the car and started on the flare installation.

Now 3 months later with flares on and driving it on a regular basis, it still didn't idle. Again, checked the synchronization on the carbs, idle mixture, etc. Still didn't idle. Thinking logically, if it won't idle hot, a valve must be sticking open. So I let the car sit for a day and pulled the valve covers to find that all 4 exhaust valves had ZERO (more like negative) clearance! (IMG:style_emoticons/default/WTF.gif)

So what happened?

A. The valves all stretched the same length.

B. All the seats got mashed evenly

C. The valves weren't adjusted at TDC

D. It was about 20 deg F in the garage when I adjusted them last


A and/or B? I doubt it.

D seems the most logical but does the valve grow .006" over 60 degrees?

You would think that finding TDC doesn't matter, but I believe it does. Years ago I tried adjusting them with what is now referred to as the "rocking method" using the opposite side valve as a guide with the theory that a valve closed is a valve closed anywhere on the cam. I found when checking the clearance at TDC that the valve did not have the same clearance as measured when using the rocking method. It ended up being too tight at TDC!

On my 914, the flywheel is paint marked at the groove for TDC and 28 deg BTDC. If I used the 28 deg BTDC mark, I was on another part of the cam that resulted in a different clearance than at TDC. The result being a valve held open when the engine is hot and no idle.

After adjusting the valves at TDC and confirming all adjustment through one rotation, it idles perfectly.

.........................Well you have experienced , and summerized the problem with the "rocking method",of setting valve lash......The "rocking method" only works with VERY mild, or stock camshafts...for all the reasons You , and several others on this post have stated and have discovered for yourself the "rocking method"or "opposing lobe method" simply is not and will not and cannot be as accurate as using T.D.C. as the valve adjustment point....Their are old dogs on this forum that will argue the point with you until hell freezes over. They are simply wrong. I am glad you discovered your problem, before you burned a valve.

[tomeric914]

.........................Well you have experienced , and summerized the problem with the "rocking method",of setting valve lash......The "rocking method" only works with VERY mild, or stock camshafts...for all the reasons You , and several others on this post have stated and have discovered for yourself the "rocking method"or "opposing lobe method" simply is not and will not and cannot be as accurate as using T.D.C. as the valve adjustment point....Their are old dogs on this forum that will argue the point with you until hell freezes over. They are simply wrong. I am glad you discovered your problem, before you burned a valve.

Except in this case I wasn't attempting to use the "rocking" method. I somehow consistently used the wrong timing mark that I put on the flywheel. However, the point is just the same. Just because the valve is closed doesn't mean that the clearance is going to be the same at any closed position on the camshaft. This would make a huge assumption that in any closed position, the cam has ZERO runout.

To me, this was more backup to why the other method doesn't work and why the TDC method is the only method I use.