Can't adjust valve lash

[trogdor1138]

I posted recently about a timing "incident;" you can read about that here: http://www.classiczcars.com/forums/thread46029.html

I've finally gotten the head back from the machine shop and everything back together. The shop replaced two intake valves and all six exhaust valves, as well as the valve guides for the exhaust. My problem now is that I can't get any gap at all between the cam and the exhaust rockers.

I was able to adjust the intakes successfully, so I know I'm not stupid. What's going on here? My father is visiting just to help me finish up and drive it, and now it's looking like a no-go. The valve adjustment was fine after I rebuilt the engine and before dropping off the head for repairs; did the shop goof up?

Timely help especially is appreciated. Thanks everyone

[black gold man]

[trogdor1138]

Thanks, but I'm not sure of the intent? I know how to check valve lash; as I mentioned all of the intakes were set successfully.

Maybe I wasn't clear enough in stating the problem. The exhaust rocker arm studs are bottomed out but still have no gap.

This means that the valve stems/lash caps are too high. I set the valves just after the initial rebuild no problem. The only thing I can figure is an overly aggressive valve seat grind at the shop this last time.

Anyway, returning to stock lash caps on the exhaust valves from the thicker .175 caps I had installed resolved the problem and allowed adjustment.

[Diseazd]

This whole thing sounds funny. If you are installing an Isky Stage II camshaft, the .175 lash pads should be correct, unless as you stated, the head shop sank the valves so far into the head (probably unlikely if they do this for a living) that they require thinner lash pads. The important thing is to make sure the wipe pattern is centered on each and every rocker arm, so when you fire it up, you don't destroy your new Isky camshaft. If you don't know how to geometry the rockers, read up on it in the book "How to Modify Your Nissan and Datsun OHC Engine". It's critical to get this stuff right.........you don't want to do this a third time. Good Luck

[dltalfa]

Another thought,..are you sure you have it timed right? Being out of time might prevent the valves being completely closed thus you could never adjust the lash.

[Zed Head]

Are there different valve lengths available for the L24 heads like there are for the L28 heads - N42/N47 vs P79/P90? Maybe they installed longer valves. Probably want to double check the two new intake valves for wipe pattern also.

And, isn't grinding the valve stems to the same length common for a well-done valve job? So the lash pads are all the same thickness. Maybe the shop didn't complete the job or used the wrong spec. Did they install the cam or did you? They should have checked the clearances.

I agree with Diseazd, there's something wrong with your situation and you could be one the verge of destroying your cam and rocker arms. Better get that book and spec. everything out.

[Diseazd]

240 Z valves are all the same length unlike the L28.....early long.....P90 and P79 short. Just a note....if you grind the top of the valve stems and use the early lash pads (cupped), they can bottom out on the keepers.....not good! A good head shop will check valve stem height......it's a Hell of a lot easier if you can use all .175 pads instead of a .150 here and a .190 there. Talk to your shop and always get this straight before the work begins. Now we tell you......right?

Edited May 20, 2012 by Diseazd

[trogdor1138]

Thanks guys. My first thought was valves from the wrong year or head type, but my research shows that all valves are the same length as noted above.

I can't see how timing would be off either. The chain in there has two dark links for the purpose; the cam and crank were timed with the shorter length between the sprockets on the tension side.

I also don't exactly figure how they could goof something up, but everything keeps pointing to something done during the latest machine work. I started her just briefly yesterday to test and everything sounds fine. No clacking, no metal on metal, etc.

I do plan to take it to the shop tomorrow to discuss the situation and possible causes.

[emptech]

This is probably not your problem but years ago I greatly overheated my engine. My head was warped like a banana. The machine shop had to surface both sides of the head in order to make it true. That brought the cam towers down a bit. I found that I had no clearance like you have. I ground the valves to make up, seemed like a good idea. Next problem, the valve lash pads would hit the keepers (can't remember what they are called) on the ends of the valves instead of the ends of the valves. Couldn't have that, so machined a tool to hold the pads in a lathe and used a tool post grinder to shorten each valve lash pad. Solved my problem. There were other problems, since the timing chain essentially got longer, I had to machine an extension for the chain tensioner piston. Down the road I eventually bought a new head at the time when I replaced my 2.4 with a rebuilt 2.6 block.

Jim H.