Cam gear position for L and naps engines?

[Spades]

So, I know that on the L and naps motors there is more than one way to put a cam gear on, and that the Japanese and Nissan cam gears use numbers to determine which way to instal the cam gear. I was told the numbers are so that when you shave the head or when the motor develops wear you can simply move the gear to adjust for it.

 

The motor is a bored over Naps-Z24 that I bought un-used from my boss(it was overhauled hopped up, then pre assembled by a local machine shop), and unfortunately, I do not know the specs on the camshaft. The cam was a custom grind and all I know is that it is close to the maximum allowable lift and duration for the restrictive naps z head. The head was shaved, but I don't know how much. What I do know is that the timing cover has a leak and that the engine runs as though the cam gear is retarded. I contacted the machine shop and what I did find out about the motor is that they relied on the advice from Jock at Bill's Datsun to assemble the motor(that little bastard screwed up another one of my motors without even touching it, impressive, isn't it?). Jock told them to use two head gaskets instead of one, and told them which setting to put the cam gear on.

 

So, I need to pull the whole front of the motor apart and take the head off to put one single Felpro headgasket on, and then make sure the cam gear is in the right spot.

 

In case anyone is wondering by what I mean when I say I suspect the cam gear is slightly retarded, I am going based off of how the motor acts. If I tune the car by ear and by what gives the best throttle response, I have to advance the timing to an insane degree...18+ degrees of initial advance on a 8 plug motor known to take 4-8 degrees of initial advance. Before you ask, yes, the vacuum and mechanical advance on the brand new distributor are functional and working great, and I can watch the advance with a timing light when I rev the motor up, and I do not get any pre-detonation even with insane amounts of advance, but I get the dieseling and other idle symptoms that are undesirable. When I set the base timing to the factory spec, I loose tons of power and my gas mileage tanks, and I am unable to go lower than 10 degrees initial timing...the motor runs best at 20 degrees initial, but then I have dieseling problems. To me that sounds like the cam gear is retarded a bit.

 

Any help is greatly appreciated!

[datzenmike]

Cam timing and ignition timing are not really related. One out does not affect the other.

 

Are you sure the timing notch on the pulley is correct?

Are you sure the timing scale on the timing cover is correct?

[DISLEXICDIME]

Is the distributor stock? Or idid some one recurv it.

 

Mike will a over advanced cam cause detonation?

[banzai510(hainz)]

Mike will a over advanced cam cause detonation?

 

usually it will run out of power sooner. But this is uausual a tooth or 2 off during reassembly Not by having it to a higher number. 2 teeth off will be noticable.

 

dial up to zero on crank and ck cam timming v notch and the dash on timming plate

[datzenmike]

dial up to zero on crank and ck cam timming v notch and the dash on timming plate

 

 

 

 

Word.

[Spades]

i already rolled it to top dead center and checked my timing marks on the pully and then on the timing plate...been there, done that. The distributor is stock, and is set in the right position. I caveman tested it, as in rolled the motor to top dead center and checked everything. I also have been using vacuum gauges to monitor my ported and manifold vacuum, and I get the best mileage, power, and if I time it by vacuum curve, the motor wants a huge amount of advance.

 

Everything I have ever read tells me that the cam gear is slightly retarded for these symptoms(when you can be positive that the timing is spot on)...so I am wondering if perhaps they used the most retarded position for the cam gear notch, and it is even more noticeable due to the modifications to the motor.

[datzenmike]

Well if you think the cam is retarded then pull the valve cover while it's at TDC and check it. The Vee or U notch on the back of the sprocket should be just below or very slightly to the right of the horizontal etched mark in the cam thrust plat directly behind it.

 

 

Should look like this: Disregard the number 1 you's is likely #2 but the proper notch to horizontal line governs.

[Spades]

Well if you think the cam is retarded then pull the valve cover while it's at TDC and check it. The Vee or U notch on the back of the sprocket should be just below or very slightly to the right of the horizontal etched mark in the cam thrust plat directly behind it.

 

 

Should look like this: Disregard the number 1 you's is likely #2 but the proper notch to horizontal line governs.

 

 

That is what my question boiled down to...what the numbers mean...I know there is a mark on the naps Z cam tower, and I understand a cam gear or the chain can be off a tooth...what I was wondering is which numbers they use from the factory on a naps z for the cam pully and exactly what the numbers mean in relation to each engine in regards to cam timing.

 

There is a possibility that the cam gear is on properly and they just have a very large cam in it(that explains the slightly low vacuum on a freshly rebuilt motor and the poor low end performance and needing a ton of base timing but having plenty of power from 4k+ RPM), but that would surprise me since I have heard the naps Z heads can only have so much duration and lift before the valves touch each other.

[datzenmike]

They come from the factory on the #2 but the V notch to mark relation is the most important.

 

Low vacuum can also be bad valve clearance.

[Spades]

They come from the factory on the #2 but the V notch to mark relation is the most important.

 

Low vacuum can also be bad valve clearance.

 

 

Thanks Mike. The vacuum was not bad, well within Nissan's perimeters for a healthy motor, but it was in the middle of the acceptable range of vacuum, rather than at the top, which was odd for a higher compression and completely rebuilt motor. Not a major issue, but definitely seemed a bit odd...I am suspecting that the cam gear is slightly retarded and that the cam is a bit bigger than I expected. Either way, I will be pulling the head soon so that I can see if there is anything else wrong.

[banzai510(hainz)]

I dont think changing the cam gear to another number is going to make a difference.

 

I got a bigger cam and I cant tell if the vaccume has chaned a bit. seem like a stock cam to me (.460 lift)

 

I had it a tooth off and still seemd OK.you hav the vaccum advance run off the carb and not the manifold. Its a long shot but have seen this about 3 times on here so far.

[Spades]

I dont think changing the cam gear to another number is going to make a difference.

 

I got a bigger cam and I cant tell if the vaccume has chaned a bit. seem like a stock cam to me (.460 lift)

 

I had it a tooth off and still seemd OK.you hav the vaccum advance run off the carb and not the manifold. Its a long shot but have seen this about 3 times on here so far.

 

 

Idle vacuum will be a little lower with a large camshaft due to increased intake duration. This causes some valve overlap at low RPM and will create that lope we all know, but will also allow part of the compression stroke to sneak into the intake manifold before the intake valve closes all the way. So your camshaft may have the same lift as mine does, but mine may have a longer intake duration which is what creates the "lopey" sound and can result in slightly lower vacuum at idle.

 

The bigger the cam, the more timing can affect it...More timing advance means better low end performance and increased gas mileage(to an extent), where as you often retard the cam or timing in order to gain more high end HP and avoid pre-detonation. I am guessing that the camshaft I am running has a large intake profile for extended duration, and that makes the gear being slightly retarded much more noticeable. Either way, when I tear into it, I will know for sure, and now I know where the factory puts the cam and will give me a better idea when I do tear into it...I will post some pic's and info when I get the time to work on it.

 

I am guessing in the last part of your post,you are asking if I am running the vacuum advance off the manifold rather than the ported vacuum at the base of the carb. The answer is, no, I am not running manifold vacuum to the distributor. I am sure it sounds like I am, but keep in mind, I used vacuum gauges, a labscope, and a timing light to watch my initial timing, ported and manifold vacuum, distributor vacuum advance, and mechanical advance. I can watch the timing curve with a timing light(and scope) and see the advance kick in from the vacuum advance and the mechanical advance. I am able to use a vacuum pump to activate the vacuum advance of the distributor. I also can watch the timing light or lab scope and see the ported vacuum activate the extra advance when I stab the throttle.

 

Right now, everything is functional, and the motor still has a ton of zip, but if I want an extra 5-10 mpg and for the car to run like a raped ape (rather than a slightly molestered squirrel monkey), I have to set the timing to 18 degrees of initial advance.

[banzai510(hainz)]

Idle vacuum will be a little lower with a large camshaft due to increased intake duration. This causes some valve overlap at low RPM and will create that lope we all know, but will also allow part of the compression stroke to sneak into the intake manifold before the intake valve closes all the way. So your camshaft may have the same lift as mine does, but mine may have a longer intake duration which is what creates the "lopey" sound and can result in slightly lower vacuum at idle.

 

The bigger the cam, the more timing can affect it...More timing advance means better low end performance and increased gas mileage(to an extent), where as you often retard the cam or timing in order to gain more high end HP and avoid pre-detonation. I am guessing that the camshaft I am running has a large intake profile for extended duration, and that makes the gear being slightly retarded much more noticeable. Either way, when I tear into it, I will know for sure, and now I know where the factory puts the cam and will give me a better idea when I do tear into it...I will post some pic's and info when I get the time to work on it.

 

 

I think your over analyizing this? I have a 270 duration cam and still sound stock to me. Nomatter what block I put this on. the over laping isnt going to be to much if anything to worry about.

 

If running a break booster I guess ck there but maybe swap anynother dizzy in there. You say the motor is spot on mechanical timming wise so I would look at the distributor/

as for carb vacuum you got a Weber down draft. I would think 4 cylinders going thru one barrel would be enough vacuum to suck the gas in.

 

I would move the sprocket up # number in a last ditch effort to find this proplem. after a dizzy swap