Mn_Z_Man

When I had my head rebuilt, I made sure he measured the installed valve height, and then ground (tipped off) the valves to get them to the original height after the valve job. I was not able to find thinner pads either, only thicker for high perf cam builds. Good luck finding a shop that actually understands the L series head head geometry. I had 2 shops try to tell me the installed valve height didn't matter, thats what the lash adjustment is for, which is wrong. Depending on the amount they are off, its a toss up between shims and grinding the valve tips- maybe some of the more experienced members can chime in. The problem with grinding is I could not find an actual value for the stock installed height, and if you had shims in there it sounds like this is not the first rebuild. FYI, the L-series engine forum at hybridZ.org has a few good threads along this line. Eric

yep, and throttle wired open

OK, so I did a valve job to fix a bent valve, and am seeing something weird- lower, but more even compression across all the cylinders. Before I was seeing 175 +/- 5 psi, now I am seeing 155-160. 2 ideas- valve timing is slightly advanced (2 deg on the cam), maybe due to new timing chain guide which is giving a slight inward curve to the tight side of the chain. My other thought was could the carbon buildup on the head and pistons have raised the comp by 15psi? It didn't look that bad, but I don't have much experience to judge by. Obviously its all cleaned up now after. Head was milled 0.003". Valve lash are all properly adjusted, wipe pattern double checked and OK, cam OK, new Felpro gasket. Engine runs OK, maybe not quite as punchy as before. I've put on about 100 mi since the build. Some one on another forum suggested maybe the Felpro gasket having a larger cutout for the L28 engine, as they claimed to have had the same experience, but I can't remember how close the fit was. I was hoping the compression would go UP with a shave and valve job. Any ideas appreciated, thanks Eric

I did the tokico "upgrade", and am not happy with the ride, way too stiff and jittery for a daily driver, although ti does handle great, and looks great. It almost feels like the car is shaking itself apart on bumpy roads. I am going to put the stock springs back in and see how much that helps. Some mods are best left for the track or show cars. my 2 cents

Ditto, I did the suspension "upgrade" and am not happy with the ride. I am going to put my stock springs back in and see how much that helps. I hope I don't have to replace the struts as well, but I will if I have to.

your cam lobes for #1 will not be pointing up at TDC compression, they will be at about 10:00 and 2:00, both valves closed. That is the position to check your valve timing behind the cam sprocket. To set lash, you just rotate the cam with a vice grips (between the lobes!) to get them pointing straight up, or you can bump the engine. If you need more info on how to do it, and why, you should look into getting a manual, I recomend "how to rebuild your Datsun/Nissan engine", you will pick up all kinds of good ideas on how to do anything to these engines. Good luck. Eric

Mine looks like it has been brazed at some time in the past. The original looks like it is pressed together, and seems to work loose over time.

Ok, more info. Popped the head, and indeed the valve was bent about 1/2 open. Very small nick in the piston, otherwise seems OK. took rockers and cam out, measured valve wiggle at the top, slightly open, with dial micrometer, parallel to rocker travel. Intakes seem pretty tight, at around 0.001"-0.002" deflection, seats look good. Exhaust is another story, with about 0.004" deflection, a noticable "wiggle" at the valve head and some pitting. Need to get a more accurate mic to measure valves, but assuming they are OK- here's hat I'm planning. New exhaust guides, new seals, grind all seats and valves. Should I have them grind the tips of the valves to restore them to the original installed height, or just bite the bullet and adjust wipe pattern with new lash pads? Will a standard regrind change the installed valve hight enough to matter? Anything else I should do while in there? Does this sound like an OK plan? Cylinder bores look great for 120K, no scoring and can still see the factory honing marks. Warm compression was 170-180 PSI in the good cylinders.

Lacquer thinner works great for getting the yellowish varnish off, just watch the sparks and prop the door open. Also a much better degraser than gas or mineral spirit and evaporates with no residue, ready to paint

Ya, I hear you both- but what does a complete job mean on an OK engine- new seats, guides, grind whats there and but it back together? Especially the seats, I understand the '73 had bronze seats, should I plan on them too or just a grind? Also, If I grind the seats, will I need to get new different thickness lash pads so i don't wear out the cam and rockers? Grrr.... thanks

Hey gang, this is my first post in this forum, (long time member of the other Zcar site). My car is a '73 240Z, mostly original, overhauled suspension, pertronix ignition, 3-screw SU's, nothing exotic. Anyway, doesn't seem I can do any major project without one good "learning experience" involved. This winter I did the timing chain set, water pump, intake gasket, clean polish, paint etc. Was considering the on-head valve seal job, using compressed air to hold up the valve. I was playing around with adapters to get the air into the cylinder, and it turned over, and and stopped with a thunk. Unfortunately, I had the timing chain off, so that thunk was the #3 piston hitting the intake valve. I backed it up, got it timed, started it up, and it ran like crap. Long story short, #3 intake is stuck open enough so I get zero compression, backfiring, low vacuum, etc. So I know the head needs to come off, no big deal, good excuse to get the valve seals. My question is far do I go with the valve job? The engine has about 120K, great compression (170 psi +/- 5), and oil pressure. I don't want to pay for a complete head job if I don't need it, but I am willing to pay for what makes sense at this point in the engine life. Job could be anything from just replace the bent valve and seals, to popping them all and grinding, replacing the guides, new hard seats etc. With my decent compression numbers, I don't see the need for total rebuild any time soon with the low miles I put on it, and anyway would like to save that money for an L28 upgrade, or stroke the L24. It seems these cams and rockers are sensitive to change, and I really don't want to get into a complete top end rebuild I don't need it. Moral of the story- don't turn over the engine without the timing chain, even by hand! Thanks gang Eric