78 620, L20B foreign matter in combustion chamber.

[Atikin9000]

Also another fun question, #1 or #2 for cam sprocket position.

[wayno]

You should never lay an L head on it's face like that, you stand them on the end or on its side, laying like that can bend a valve.

My machine shop always adjusts my L head valves before sending it out the door.

L16 cam hole 1, L20b cam hole 2, don't know about the L18.

[datzenmike]

L18... I believe they run the L20B cam so #2. HOWEVER the hole position is less important that the V to etch mark alignment. This governs cam timing.

 

V in back of the cam sprocket should be below and just slightly to the right of the etch mark in the cam thrust plate behind it, regardless of the hole used.

 

[Atikin9000]

This will be the first engine I’ve taken apart and put together, first datsun too.

 

Any suggestions or things to look for besides fluids, timing? I’ve read about the torquing sequence, I plan on draining the coolant and oil prior too aswell.

[Atikin9000]

p.s. imageshack is the devil. Lol

[wayno]

No, Photolame is the devil, imageshack is just a pain.

[datzenmike]

p.s. imageshack is the devil. Lol

Try imgur .... https://help.imgur.com/hc/en-us/articles/210076663-Upload-Images

 

Not saying it's the best, there are others.

[Stoffregen Motorsports]

Two things I noticed.

 

One - the dowels go in the block and align the head gasket. If it was in the head, that just means it got stuck there upon disassembly. Not sure you were aware of that.

 

Second - BOTH the machine shop and the rest of you guys are right. Valves should be adjusted after the head has been torqued, but they should also do it after they assembled it on the bench. If for no other reason than to check the wipe pattern on the rockers.

[Atikin9000]

Two things I noticed.

 

One - the dowels go in the block and align the head gasket. If it was in the head, that just means it got stuck there upon disassembly. Not sure you were aware of that.

 

Second - BOTH the machine shop and the rest of you guys are right. Valves should be adjusted after the head has been torqued, but they should also do it after they assembled it on the bench. If for no other reason than to check the wipe pattern on the rockers.

 

As I mentioned this was my first time round with this, I didn’t think to mention any of this until I read it here. There was mention of shims as well, I was planing on calling the machine shop today to see if everything is still in spec.

 

I’ve heard a couple of things regarding valve lash and that I needs to be adjusted both hot and cold.

[wayno]

L18... I believe they run the L20B cam so #2. HOWEVER the hole position is less important that the V to etch mark alignment. This governs cam timing.

 

V in back of the cam sprocket should be below and just slightly to the right of the etch mark in the cam thrust plate behind it, regardless of the hole used.

 

Are you sure about this photo above, I cannot even get the lobes close to 10am/2pm with the cam timed this way, to get them at 10am/2pm the crank is at 30 something degrees.

[Atikin9000]

Are you sure about this photo above, I cannot even get the lobes close to 10am/2pm with the cam timed this way, to get them at 10am/2pm the crank is at 30 something degrees.

I second that, in the previous photo I posted head was to the right of the notch and the bottom end was no where near tdc.

[wayno]

So the engine I am putting together with the cam timed the way in the photo, my cam lobs are around 11am and 3pm, this is not how I have set up engines in the past, the chain is not lose, I barely could get the timing components on the chain is so tight.

So I looked at the work trucks LZ23 engine and it was way off, I have been driving it this way for years without issues, I tried it the way in the photo(2 links off), with it timed at 2 degrees BTDC it knocked so bad that I had to go back to the way it was to be able to drive it, the lobes are at 10am and 2pm and the timing groove is way left of center.

It's a little harder to see where the cam is timed on the work truck as it has no groove in the retaining plate, but using s screw driver as reference I can get a good idea where it is supposed to be, it's basically at the highest point in the retaining plate and the notch is way left of it.

[datzenmike]

Lobes at 10 and 2 is an approximation. It's more to tell you you are on the correct compression stroke than anything else. What ever they are at TDC is good enough.. 

 

 

Set engine to ZERO TDC on the timing scale or if you have a more accurate method. V notch and etch mark should be like the picture I posted. All my FSMs show this relationship for correct cam timing setting or for after chain stretch adjustment.

[wayno]

Well it appears I put it back to the way it was before even though I tried to go only one link back out of the 2 links I moved it, I may have only went half way back, it was so far off after I set it up the way it was in the photo that half way back looked way better/closer to what I am used to looking at.

When I drove it timed the way the photo showed the intake made a lot of noise also along with the knocking/pinging, it was a very loud steady howl, it's never been that loud before, I also checked my valve lash and they appeared to be good(not tight), this notch and groove thing is likely going to be an issue for me, maybe it is why I can burn pump gas(regular) and not have it knocking/pinging with a 8.9 to 1 compression ratio.

As I said, my cam retaining plate doesn't have the groove, I suppose I could install the one I have from another head that has the groove, but that will likely make me crazy again seeing how far off it is, while right now I am just guessing how far off it is.

[Stoffregen Motorsports]

A more appropriate depiction of TDC is the rear (#4 cyl) cam lobes. They should be on what's called "split overlap" where the valves are open about the same amount. If the timing is off one way or the other, one valve will be open a lot more than the other.

[datzenmike]

 

Is it on backwards or upside down wayno?

.

[wayno]

 

Is it on backwards or upside down wayno?

.

 

I suppose it could have been put on backwards, but it wasn't me as I have never in my life put that part on a head, my machine shop does all that stuff, and then I just install the head on my block with the cam lobes at 10am and 2pm, I have never done it any other way and the engines have run fine so far, but my LZ23 in the work truck is definitely timed wrong, or at least was timed wrong, I will remove the cam gear again today since it is not raining and remove that retaining plate and look at it, I also removed another one from a scrap head(210 casting) that has the notch that I can install.

It sure seems weird that I could have went all these years hauling the weights I have hauled with that truck and had the cam that far off and not have any issues, I keep up with traffic except on hills with a heavy load.

[datzenmike]

If the cam is advanced retarded (valves open and close sooner later, usually worn chain or V to the left) it favors higher RPM power, if later closing, it favors lower speed torque. But not much and not much on a stock engine. I'd be very curious what you find wayno, not so much the mark but how well it runs. 

 

Each dowel pin moved is 4 degrees, about the width of the etch line on the thrust plate. Moving the cam a tooth is 9 degrees so lots of combinations.

[Stoffregen Motorsports]

A stretched chain results in retarded cam timing, not advanced.

[datzenmike]

A longer chain would make the valves open/close farther ahead of the crank position.

[Stoffregen Motorsports]

Um, no.

 

Do the visual.

[datzenmike]

I did.... and got it wrong.  Yes cam events trail their proper position.

[wayno]

OK, so the first thing I did today was  remove the cam gear and then remove the retaining plate and when I looked on the back the groove was there, so I mounted it the correct direction and installed the cam gear and cringed, then looked at it with a light, it was not so bad, the notch is slightly to the right of center on the groove in the retaining plate in your photo, mine is slightly to the left of the groove in the retaining plate about the same amount, I am calling it good enough, it runs good and doesn't knock to much, but I have not driven it much this way yet, I will know more on a longer drive.

My timing is set at 2 degrees before TDC, I will drive it some more before messing with it, I expect it will slightly knock/ping like it did on the last drive, I may have to have it at 0 degrees/TDC, I am just waiting to see if it runs better or if I cannot get it to stop knocking, if it continues to knock/ping I may have to put it back where it was before, it ran fine all those years. 

[Stoffregen Motorsports]

Wayno, try disconnecting the vacuum advance and set the timing at 30-32 degrees all in. I bet he t just needs a distributor recurve.

 

Do you know what CR it has? If it's above 10:1, you may benefit drastically from a cam change. More cam = more cylinder pressure used which means less pinging...and more power.

[wayno]

Wayno, try disconnecting the vacuum advance and set the timing at 30-32 degrees all in. I bet he t just needs a distributor recurve.

 

Do you know what CR it has? If it's above 10:1, you may benefit drastically from a cam change. More cam = more cylinder pressure used which means less pinging...and more power.

 

Yea more horse power, but I need torque in the work truck, I sometimes weigh over 5400lbs(truck weighs 3400lbs) and I am pulling a trailer that weighs close to a ton total(maybe more), I drove over the dump scales once at 7200lbs(just the truck).

I tried a cam to the dismay of my machinist once, he was right, I had no grunt, that head/cam is on my LZ20 build, that one is going to have a high compression ratio(peanut head/flat top pistons/long rod engine), my LZ23 that is in my work truck that I have been talking about, it is around 8.9 to 1 CR I was told(Z24 dished pistons/peanut head).

It wasn't pinging to much on the last drive to the yard debris recyclers, but I was only on the hiway for 2/3 miles, I need more time as the intake makes way more noise now and I need to get used to it, I was at least one link off on the timing gear for the last 5/6 years.