L20B valve noise

[minitruckguru]

I've got an L20B with a fresh rebuild, bored .030 over, std height dished pistons, stock cam, brand new (rebuilt) U67 cylinder head, SBI valves, New water pump, alternator, oil pump, timing set, plugs, Rotor, cap, wires, points, weber 32/36 swap, stock manifolds, 17* timing at idle, cam timing done according to datzen Mike, electric fuel pump, all the goodies. I've now lashed my valves about 4 times to .008 and .010. However I have one valve that won't shut up. Can the stock lash pads make noise when worn? How about stock rocker arms? There is plenty of oiling on every lobe. I cut an old valve cover to make an oil spray catcher so I could listen with the cover off. Forgive me if I'm using this website wrong, I'm new to forums. Thanks in advance folks!

[datzenmike]

3 hours ago, minitruckguru said:

 17* timing at idle,

 

 

Timing for the L20B is 12 degrees BTDC.

 

 

3 hours ago, minitruckguru said:

I've now lashed my valves about 4 times to .008 and .010. However I have one valve that won't shut up. Can the stock lash pads make noise when worn? How about stock rocker arms? There is plenty of oiling on every lobe.

 

 

 

0.008" and 0.010" are a cold setting and assumes that when the engine warms up the lash will expand to the correct 0.010" intake and 0.012" exhaust. I guess you could try setting them hot.

 

If it's valve noise this is the rocker arm moving through the lash setting and hitting the top of the lash pad. If the lash is too wide the noise will be louder. Too tight is not good either as the valve is cooled by contact with the valve seat.

 

 

 

I guess new valve seats were installed?

 

Can you locate the noisy valve?

 

Does the noise get louder under load?

[DHale_510]

Lash pads need to be sized to the valve seated height. "Stock" lash pads are usually too thin after a "rebuild". Also "rebuilding" a Datsun head with a pair of stones like a Chevy will make them all different and wrong.

The cam needs to run on center of the rocker wear pad. The adjustment screws are long for rocker removal, about twice the range for centering the wear zone. Again, not a Chevy.

Worst case the Stellite wear pad is off the edge and is turning into a little lathe tool and cutting into the cam. I suppose that would seem noisy...

A good Datsun rebuild of a cylinder head is done with a cutting tool [Neway branded] on a mill table all set up true and parallel and equal depth. It takes tooling and time and costs more.

Dennis

[banzai510(hainz)]

not wise or at least to me of pulling the cam off with the rocker arms installed. I suggest you take the rockers off and turn down the pivot ball all the way down put the cam back in to I think 13pounds ( think)and see if cam spins of after torqed. then install rockers one at time then set to TDC. Hopefullyou have have crank at TDC and pout the chain on.

why those cam tower bolts are ez to strip out as they dont need alot of torq. 10-13 pounds I think. when putting it back on with rockers youll be pushing the spring tension on there and pull the alum threads out.!!!!

 

 

maybe the noise was just a lash pad fell out?  I would have just tighten it up untill the noise got better. whci cyl you think it is

 

hope you have you have the timing chain wedge in there.

 

i think you should have got on here and waited first asking more ?s  before pulling all this apart. This might never run again now

 

 

PS what kind of valve cover is that ?its a cut away? the top half removed

Edited June 15, 2023 by banzai510(hainz)

[Stoffregen Motorsports]

L series valve noise is not uncommon. Some cams are noisier than others, and the valve lash is usually specific to that cam. I can't tell from the pics, but it looks like your cam may not be stock. If your cam is not stock, did you install appropriately sized valve springs?

 

As Dennis mentioned, lash pad thickness affects rocker geometry. This is crucial. You can check the geometry by marking each rocker with a felt tip pen or blueing agent, and then turning the engine over once or twice. The contact patch needs to be in the center of the pad on the rocker. If it runs off either end, it will make noise.

 

Lastly, I assume you are adjusting the valves at the tip of the valve, not at the cam. This makes a big difference.

[minitruckguru]

Thanks everyone for the replies and help. I checked the wipe and it's perfect, all the valves were set to the same and correct height, courtesy of redline machine in lehi utah. Yes I am checking lash at the cam, not the valve tip, the cam is a u20 letter B stock cam, yes I lashed at TDC on 1 and 4 when hot, I used a timing chain wedge and my timing chain tensioner was installed correctly. I did loosen the rocker adjustment before installing the cam, and torqued it in a pattern very delicately to avoid bindage and whatnot. All the lash pads are present, that's the first thing I checked. Just for your information, I found a spec for valve height, and installed valve stem height and the machine shop was willing to oblige. I also had him check how straight the cam tower mounting was, and it was correct. Very little was removed from the deck because the head was not warped, Banzai510, thank you for your input, however I was delicate with my research and my rebuild procedure, I did not use a pair of stones to rebuild it XD. I puttied the pistons to check clearance, measured installed valve spring height, gapped the rings, no platigauge used anywhere, I am not new to rebuilding Motors, just datsuns. It turns out the issue was my feeler gauges. I bought a new set specifically for this valve lash because I had lost mine during the rebuild process, and they were cheap autozone ones, I borrowed a set from my coworker at the shop I work for and reset the lash after the drive home asap, had it done less than 5 minutes after I shut her down, and now she sounds awesome. I measured my feelers with dial indicators and they aren't even close. My .008 was .016 and my .010 was .18. Don't buy autozone feelers!

[banzai510(hainz)]

so you putting the cam and towers ON with the rockers already in the head??

 

 

 

I do .006 and .008 cold on Schneider cam.

 

 

so more or less you took apart a good running head cause of bad feeler gauges?

[datzenmike]

What about the 17* timing at idle? Datsuns like about 32-33 total advance under full throttle. This is 5 degrees or 37-38 degrees high.

[minitruckguru]

I corrected the timing. It was actually at 15 and I set it at 12. It seems to idle a little lower but that's not really surprising. Runs good. Banzai, I had an old head with 156k miles, now I have a head with new valves, seats, seals, that runs awesome. I fail to see the issue

[datzenmike]

At idle where there is no throttle and the cylinders filled just enough to power an idle the amount of air is so thin that the burn time is much longer. 12 degrees is for emission purposes but all engines would like more and will rev up if you advance the timing. The reverse is true when the timing reduced, it slows. The problem is that total advance, the initial (12) plus mechanical (around 20) should not exceed about 32 degrees or damage from detonation can ocure.  

[Stoffregen Motorsports]

14 hours ago, minitruckguru said:

Yes I am checking lash at the cam, not the valve tip,

They need to be set at the tip of the valve.

[Stoffregen Motorsports]

13 hours ago, datzenmike said:

What about the 17* timing at idle? Datsuns like about 32-33 total advance under full throttle. This is 5 degrees or 37-38 degrees high.

17 degrees is a bit much at idle, but if the total is limited to @ 32 degrees, then it's ok. 12-15 degrees at idle is common practice for an L motor.

[shlammed]

whats the reason to limit to 32 degrees on these engines?

 

 

i have seen a few EFI maps out there (albeit for boosted L's) that run nearly into 40 degree range in mid to high rpms in the areas where transitioning into boost.

[banzai510(hainz)]

I think the Lseries is a old design and just slop in the system Im  guessing.

[datzenmike]

Every engine is different at WOT. Compression, bore stroke, EFI vs, carb, rod length, cam profile, combustion chamber shape, knock sensor/ignition retard is a big one. It just happens to be about 32 degrees +- on the L series

[d.p]

I was told 38° at 3600-4000 RPMs is ideal on a built l20b.  Any truth to that? 

[datzenmike]

Good question. I hear about 32.

 

Cherry picking info the

 

'75-'76 federal automatic 710 is 24 mechanical @ 4,600 RPMs (plus the initial 12) for 36 degrees

'77 federal automatic 710 was 22 mechanical @ 3,900 RPMs (plus the 12 initial) for 34 degrees

[d.p]

Supposedly the Kameari l4 dizzy locks it to 38°. 

[Stoffregen Motorsports]

The most I've ever run on an L motor was 35 degrees. It has a lot to do with the cam, but the inherent design of the cylinder head (ports, combustion chamber and spark plug location) are what determine flame throw and ultimately ignition timing.

 

As Mike said, it's an L thing.