Valve Lash Clearance Oddities

[ZigzagZ]

I finally got the chance to take off the valve cover and check the valve lash clearances and I noticed a strange consistency with my measurements. I have measured every exhaust valve clearance to be exactly .009mm and every intake valve clearance was between .004-.006mm except for one. The one valve was too tight for the smallest feeler gauge which was .004. 

 

To measure, I used a feeler gauge to feel for the highest gauge where it could slide between the cam and the lash pad while the lobes were facing straight up. This was also done with a cold engine.

 

Now, I know the stock clearances are .008mm and .010mm when cold, but my engine has been modified. I am unaware of the exact specs, but my camshaft (E30 Japan) says "Americam 060 1" on the end of it and the PO stated it had been bored/ported at some point. Regardless of the modifications, the clearances should be much higher than .004mm-.006mm on the intake valves, correct? The only reason my awareness has been raised is the consistency of my measurements. Could there be a reason the PO or a previous tuner to have set the intake clearances that low? Or were they likely properly set at one point, but over time have all evenly deteriorated to their current state?

 

Edit: Car is a 1973 240z with an L24 and E88 head

Edited December 29, 2020 by ZigzagZ

[NewZed]

One "trick" to increase cam lift is to run tighter lash.  But it's dangerous, if a valve doesn't close completely it can burn/warp.

 

Another possibility is "sunken" valves.  Early gasoline had lead in it which lubricated the valve seats.  When the lead was removed valve seat wear increased dramatically.  It's not uncommon to find sunk valves on 240Z's, as I understand things.

 

So, could be intentional, could be valve seat wear.  

 

 

[ZigzagZ]

3 hours ago, NewZed said:

One "trick" to increase cam lift is to run tighter lash.  But it's dangerous, if a valve doesn't close completely it can burn/warp.

 

Another possibility is "sunken" valves.  Early gasoline had lead in it which lubricated the valve seats.  When the lead was removed valve seat wear increased dramatically.  It's not uncommon to find sunk valves on 240Z's, as I understand things.

 

So, could be intentional, could be valve seat wear.  

 

 

 

Now is there any relation to the ratio of exhaust/intake clearance? Say the PO wanted a tight intake lash but left exhaust near stock sizes. Does having a clearance difference for intake/exhaust of greater than .002mm have any side effects?

[jonbill]

I think you've mixed up measurement units. cold clearances should be 0.15 and 0.25mm I reckon. 

0.008 to 0.010 sounds reasonable for measurement in inches. 

So your exhaust is ok and your inlet is too tight. 

If your measurements are really in mm,  its all way too tight. 

[NewZed]

To jonbill's point, below.  And if you post a picture of a few cam lobes a guess could be made about whether it's been reground or not.

 

[ZigzagZ]

You guys are right about the units, I had them mixed up. My measurements were actually inches, not mm. The unit labeling on the gauges are a bit confusing but I see where I misread it. 

 

I added a few photos of the cam and lashes. All the contact patches on the lash pads are pretty even and seem to be a healthy distance from the edge. You can see a few of them if you look closely at the picture with the 'E30' side of the cam.

[NewZed]

jonbill knows more about performance engines but it looks like the camshaft might have been reground.  The base circles are close to the main shaft.  You can measure lift if you want to be sure but it doesn't really matter much.  Also you can see that the wipe pattern is close to the edge of the lobes, so the shaft has been out and back in and might be off a little bit.

 

If you take your calipers and measure the area of the lobe that has no rise, then measure the lobe height, the difference should be 7 mm if it's stock.

 

Big picture-wise though, you might as well just reset the lash to factory specs, and run it.  No obvious problems there and the engines are generally durable.

 

 

Edited December 29, 2020 by NewZed

[ZigzagZ]

Ah I see, it appears it has been reground. I took some crude measurements with an analog caliper yesterday and I measured the following:

The intake base circle and overall lobe were 30mm and 38mm respectively and the exhaust were 30.5mm and 39mm.

 

My measurements are probably a half mm off but with that the lobe lift would be about 8mm on intake and 8.5mm on exhaust.

 

With that, I think I'll set the lashes to about stock as you said and adjust if I notice anything odd.

 

[jonbill]

Yes, I think all the indications are that it has been reground. It also looks to me that there is evidence of the clearances being too tight - the engine is really dirty,  but the base circle of some of the lobes are still bright, which suggests they're in contact with the rockers. 

I'd also set it back to standard.