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NAPS Z24 camshaft issues


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#1 Spades

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Posted 04 July 2011 - 02:51 PM

So, I knew this motor had a large camshaft before purchasing it, the previous owner said it was a custom grind from OCG, and was as large of duration and lift as he could get without the valves touching each other.

Since I installed the motor, I could never get the timing dialed in. When tuned with a vacuum gauge and by ear, the timing was way advanced according to timing lights(the lights said 22 degrees advanced when it ran the best). When I lowered timing closer to the stock spec, it bogged so bad it had no acceleration at all until after 4k+ RPM...and if you set the timing at 8 degrees of advance, you could kill the motor by stabbing the throttle. When I run the timing close to stock spec, it has much less power and kills my gas mileage...if I run the timing high enough to get the best performance and gas mileage, the motor kicks back when I try to start it when it is warm, and it diesels(runs on) after you turn the key off.

This weekend I pulled the head, re-aligned the timing chain, and moved the cam gear from the #2 position to the #3 position as per the advice from people I talked to, hoping to advance the cam to make up for the oversized camshaft. The motor seems to rev up a bit faster than it did before, but has the same lack of low end power unless I run a huge amount of initial advance, and now if I run a large amount of initial advance, the motor has a steady misfire at 3k-4k RPM's. No predetonation(pinging), but I can not get it to run right.

I had the head off, set the chain marks where they were supposed to be, and had the crank and cam and crank pulley all lined up at top dead center. I even paid a fully ASE certified master technician from where I work to help me during the assembly to make sure I installed everything properly. I checked my marks today, and my distributor drive is on the mark.

I am running out of ideas, the only thing I can think of is that either I was supposed to move the camshaft to the #1 mark instead of the #3 mark to advance it, or this camshaft is just too big for this motor. I doubt the distributor is bad, because I would think I would have other problems besides needing to run extra advance.I know the motor is bored over and it has a few other modifications(shaved and ported head, ported intake manifold and exhaust, and a few other modifications), but I am starting to think this camshaft has way too much lift for this engine.

Before you reply to this post, read this!

*Yes, the shiny links on the chain were lined up properly on the crankshaft and camshaft
*Yes, the engine was at top dead center
*Yes, the crank pulley was in the right spot
*Yes, the distributor drive is in the right spot(according to Mike's pictures and all of my repair books)
*Yes, the vacuum advance is hooked to ported vacuum and is fully functional


The vacuum advance works, I used a vacuum gauge on the base of my 32/36, and it is giving ported vacuum, and I used a vacuum pump to activate the distributor vacuum advance, and it works. The mechanical advance and vacuum advance both work, and I can watch them kick in with a timing light.

EDIT: Keep in mind, I can watch what the motor is doing with a labscope, timing light, vacuum gauges, and have old school techs that are good at tuning by ear. I have asked more people than I can count about this, and the spark plugs are not showing signs of anything being wrong with fuel or ignition. During the assembly process, my dad(went to AIT and worked years on cars, and 27 years as a diesel mechanic and working on hotrods) and a technician where I work who has more knowledge than any other mechanic I have met(bachelors degree from a automotive tech school and 15 years of experience) both looked over my shoulder and made sure the head and plugs looked good and made sure I didn't mess up on the installation.

#2 Wide14u

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Posted 04 July 2011 - 03:01 PM

maybe not enough carb for it but that is just a guess
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i like the short bus and i can't do a long post :rofl:

#3 datzenmike

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Posted 04 July 2011 - 04:23 PM

Hmmm.... 22 degrees on the crank is only 11 degrees on the dizzy. Doesn't change anything just might explain the high number.

As for cam timing you are in uncharted waters with this mystery grind so you could probably throw out anything known about the stock L or Z series. I would try all three cam positions and record the results including the timing it ran best at. Then I would move the sprocket one tooth forward and do all three positions again and record the results. Last I would move the sprocket back two teeth so you have tried a tooth ahead of and one tooth behind where you are now. This could prove interesting. Each number adjusts the cam about 4 degrees, one tooth moves the cam 9 degrees so it's possible to advance 9 degrees and back up 4 for an overall 5 degrees advance. Even 9 plus 4 for 13 degrees. I know it's a bit of work but this may be necessary to dial it in.

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#4 HRH

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Posted 04 July 2011 - 04:28 PM

Farther up the numbers advances the cam, you went right. Have you tried adding a number 4 hole? Depending on how it's ground, that may help quite a bit. http://www.mattalber...net/camgear.htm

What kind of carburetor are you running, and did you port match the intake to the head? (This is very important)

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#5 Wide14u

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Posted 04 July 2011 - 04:50 PM

i was hoping that i didn't sound to stupid saying the carb
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i like the short bus and i can't do a long post :rofl:

#6 Spades

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Posted 04 July 2011 - 04:54 PM

Farther up the numbers advances the cam, you went right. Have you tried adding a number 4 hole? Depending on how it's ground, that may help quite a bit. http://www.mattalber...net/camgear.htm

What kind of carburetor are you running, and did you port match the intake to the head? (This is very important)


yes on the manifold, and it is a Weber 32/36. I am wondering if this mystery grind is the problem, or if maybe I have an underlying distributor or coil issue...I think tomorrow I will triple check my timing chain marks, and check to make sure I have a really good spark on all cylinders(I would think if I had weak spark the plugs would look different or it would show up on the labscope other than a bobble around 3k rpms if I run the distributor advance too high).

P.S. The reason I wonder about the distributor as well as the camshaft is because when I turn the distributor, the engine idle picks up for a bit, then it seems to stop picking up speed and then almost slow down. If I put the distributor where it idles the best, I have no low end. When I advance it, I have a slight bobble when the mechanical advance kicks in, but more low end...then I have the dreaded dieseling. It actually has LESS power after I moved the cam gear forward...which makes no sense, because the head is decked and it has a big camshaft...

#7 HRH

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Posted 04 July 2011 - 06:01 PM

Is this on a Z24? A 32/36 is pretty undercarbureted for a Z24. You may well be hitting a gigantic lean spot.

On the Z24 head, it would make sense of no power with cam advanced. Unlike an L, that head is designed for low-flow, period. Unless you've ported it out substantially, a big cam in it is going to operate like a domestic V8. Lots down low, no top end. And 4500 is about the max for the stock head as far as breathability goes.

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#8 datzenmike

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Posted 04 July 2011 - 07:02 PM

P.S. The reason I wonder about the distributor as well as the camshaft is because when I turn the distributor, the engine idle picks up for a bit, then it seems to stop picking up speed and then almost slow down. If I put the distributor where it idles the best, I have no low end. When I advance it, I have a slight bobble when the mechanical advance kicks in, but more low end...then I have the dreaded dieseling. It actually has LESS power after I moved the cam gear forward...which makes no sense, because the head is decked and it has a big camshaft...


When idling the carb is shut tight and only enough air and gas gets in to keep the motor spinning. Imagine the the cylinder is almost 600cc of volume but only maybe 20ccs of gas/air mix gets in. This leaves a lot of space between all the molecules even when compressed at TDC. When the spark plug fires it it takes a longer time for the flame to jump from molecule to molecule so at idle a lot of advance is needed. When at WOT (wide open throttle) the cylinder is filled to the brim and all the molecules are tightly packed and the flame travel much faster and less advance is needed. This is why we have a vacuum advance that add advance in direct proportion to manifold vacuum. (this is over simplified)

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#9 Twoinone

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Posted 04 July 2011 - 07:04 PM

I recently came into a sort of weird ratsun motorhome. It's a 21 footer and I did extensive work to bring it to like new condition. The title says its a 1984 Datsun pickup but it's registered as a 1985 Nissan GranVille motorhome...it wears Nissan logos. I'm told the pickup was manufactured in 1984 as a Datsun then shipped to Elkhart IN where it was converted to a 1985 motorhome. In any case, after all the body and structure work I decided to bring it to a mechanic because of a dieseling problem. He told me he retarded timing 10 deg. Now it starts to buck in the high range of any of its 5 gears, especially uphill. I set the timing to its original mark (up 10) and the bucking diminished but still there some. I've been reading the above which is way beyond my expertise, but is my problem timing/camshaft as well. All wires and plugs are new and the previous owner had the original carb replaced with a Weber 2bbl. Should I advance the timing further or is the bucking/loss of power inherent in ths engine? Thanks in advance for your advice.

#10 Sealik

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Posted 04 July 2011 - 07:04 PM

I just had similar issues....was the dizzy

#11 Spades

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Posted 04 July 2011 - 07:29 PM

Is this on a Z24? A 32/36 is pretty undercarbureted for a Z24. You may well be hitting a gigantic lean spot.

On the Z24 head, it would make sense of no power with cam advanced. Unlike an L, that head is designed for low-flow, period. Unless you've ported it out substantially, a big cam in it is going to operate like a domestic V8. Lots down low, no top end. And 4500 is about the max for the stock head as far as breathability goes.


yeah, a bored over Z24, ported and polished intake manifold, head, exhaust manifold...has a camshaft(and supposedly upgraded valvesprings,ect...not sure about that though) and a few other modifications. Maybe it is lean...kind of hard to calculate a carburetor size when you don't know the specs on the camshaft. I think it is a big cam because it has huge bog when you stab the throttle, and the motor is still pulling hard at 5500+ RPM...it doesn't peak at 4500rpm...it was still pulling hard when I have shifted at 5800 RPM.


I am starting to wonder if this is a distributor problem...because it is doing some really weird stuff, and advancing the cam should help low RPM throttle response, not hurt it...

#12 Sealik

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Posted 04 July 2011 - 07:33 PM

Try turning the dizzy rotor and see if it 'snaps back'/and or.......... into position

#13 Sealik

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Posted 04 July 2011 - 07:47 PM

Also...vacuum.... lb at idle?

#14 datzenmike

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Posted 04 July 2011 - 07:48 PM

I recently came into a sort of weird ratsun motorhome. It's a 21 footer and I did extensive work to bring it to like new condition. The title says its a 1984 Datsun pickup but it's registered as a 1985 Nissan GranVille motorhome...it wears Nissan logos. I'm told the pickup was manufactured in 1984 as a Datsun then shipped to Elkhart IN where it was converted to a 1985 motorhome. In any case, after all the body and structure work I decided to bring it to a mechanic because of a dieseling problem. He told me he retarded timing 10 deg. Now it starts to buck in the high range of any of its 5 gears, especially uphill. I set the timing to its original mark (up 10) and the bucking diminished but still there some. I've been reading the above which is way beyond my expertise, but is my problem timing/camshaft as well. All wires and plugs are new and the previous owner had the original carb replaced with a Weber 2bbl. Should I advance the timing further or is the bucking/loss of power inherent in ths engine? Thanks in advance for your advice.


Retarding timing 10 degrees is excessive but depends where it was previously set. Normally the Z24 is set at about 3 degrees. Running 13 degrees would almost certainly ping. The only way it will need that much advance is if the exhaust side plugs are not firing. Pull a wire off the exhaust side and put an old plug in the end and lay on a grounded surface and crank the motor over. You should be able to see it spark. If no spark check the first fuse on the left (door jam side) of the fuse box and replace it. With both sides firing have timing set to 3 degrees before TDC but first make sure your wiring, cap and rotor are in good shape. 'Bucking' could be miss firing from bad/worn out ignition parts. Also to eliminate the possibility of a tight valve check and set the valve lash. Setting the valve lash costs nothing to do yourself.

If you haven't done these things it's probably time it was done anyway.

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#15 Spades

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Posted 04 July 2011 - 10:19 PM

Try turning the dizzy rotor and see if it 'snaps back'/and or.......... into position

Also...vacuum.... lb at idle?



Vacuum is very good, manifold and ported working properly and within factory spec, the rotor moves well and seems to plop over like it should, so I can feel the magnets working. I am going to do some more tinkering with the vacuum advance tomorrow, check all my timing settings, and then hook up the sunscope so I can see what the air/fuel mixture is. The distributor was new when I put the Z24 motor in a couple thousand miles ago, and seems to be functioning well, but I will still do some further testing with the sunscope and measure spark output with my spark tester to see if it is weak.

#16 datsunaholic

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Posted 04 July 2011 - 10:51 PM

Honestly, it sounds like you have a cam designed to run at RPMs over 4K, and it's compromised everything below that. Basically the opposite of an RV cam. A race cam- or probably a turbo cam.

If everything else checks out- ignition, valve lash, etc, and it's not barking out the intake (carb backfire, that's one indication of over-lean condition) then really I'd step back to a stock cam and see what it does. The porting and polishing won't help low end either, but the big cam is probably gone to where you'll never get low end torque back without totally losing the top.
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#17 Twoinone

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Posted 05 July 2011 - 03:42 AM

Thanks for the advice. I'll recheck the ignition circuits and wiring. Other than the change to the Weber, everything's stock on the engine. Being a little used motorhome the vehicle has only 43,000 original miles on it. Again, I've only had the rig a few months and been working on cosmetics mostly. If memory serves me, it ran beautifully until the mechanic retarded my timing to stop the dieseling. It may be that I just haven't got it back to the original setting yet. Slightly fast at idle, but starts in a snap, good economy (15 mpg) and sounds great...just the darned bucking at upper rpm in any gear, particularly uphill inclines. Will keep y'all posted on my progress. Sure glad this site was recommended to me by the kid at Auto Zone who has a Z24 in his car.

#18 Spades

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Posted 05 July 2011 - 07:15 PM

Ok, so I think Datzenmike steered me in the right direction. I did further research, and while ported vacuum is a must when running EGR, ect...my bored over Z24 has no EGR system, so from what I deduced manifold vacuum is the way to go.

Sure enough, I plugged my vacuum advance into the manifold vacuum instead of ported, and much better idle and throttle response. I will need to play around with it some more, but I seem to be headed in the right direction. No pinging, idles better, and even with the timing very retarded it has the same get up and go as it did when I was running ported vacuum(with a very high initial advance).

This has all been a learning experience for me since I rarely work on cars this old, and this seems to be more like an oldschool V8 than the modern fuel injected 4 cylinders I am familiar with.

For those still wondering about timing, after reading and speaking with people more familiar on the subject, when the motor is running lean, you need to start the burn sooner like Mike said in order to make it run right...that is where older motors running manifold vacuum come in...at idle when the mixture is less, you run more advance and less fuel, and constant vacuum adds a few degrees of extra timing. When the mixture is rich (stabbing the throttle at low RPM), it takes less time to light it off, so you would want the timing backed off a bit. manifold vacuum is perfect for that scenario. As the engine speed picks up, you need more advance because as the engine rotates faster, you have less time to light the fuel mixture...mechanical advance provides a kick at middle RPM, and manifold vacuum will start to return as the RPM's get higher and you get past that initial bog of stabbing the throttle. I may be wrong on this, but it is what I have read and heard/seen thus far.

The goal is to have low enough timing on start up and shut off that you do not get kick back or run on, and timing that will drop a bit when you stab the throttle at low RPM, but enough initial timing to not bog, and enough timing at mid to high RPM so that the mixture has plenty of time to burn fully at the right time.

I miss being able to program a timing curve...this is all about trial and error and tuning by ear and unknown engine specifications...something I haven't had to do before, but it is nice to know how older distributor setups work. I think the reason this engine is running better at 15 degrees of initial advance with the distributor vacuum advance unhooked and about 36 degrees total advance(and the cam advanced to the #3 slot, which I have read is about 4 degrees advanced) is because the cam lift is large with low overlap(circle track camshaft!) and fuel mixture is so lean...according to what I measured, the motor is almost 2.5 liters after the boring over, and I am told a 32/36 may be a little under fueled for a stock 2.4l...This may explain why this engine wants more advance than stock.

p.s. No pinging/predetonation, and I was able to verify that the distributor is working properly and both coils are functional. The spark is great(the spark from the 30k volt coils was able to lob a spark over a 1" gap on my spark tester), the ignition pattern is fantastic on the labscope, and the 8 plugs are definitely helping(makes a huge difference if the exhaust side coil is disconnected and takes much more advance to make the motor idle properly). The slight misfire was from the #2 cylinder due to a slightly loose valve. So everything is working right, I think because of the camshaft and carburetor this motor just needs a little more cam and distributor timing. After it is all dialed in and has the power I want, I will see if I can step down to 89 octane or lower. Thanks to all that replied!

#19 banzai510(hainz)

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Posted 06 July 2011 - 07:31 AM

I would try another distributor. if no fix
then see if anybody has a spare 38/38weber that you could borrow see what that does.
Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#20 Spades

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Posted 22 July 2011 - 07:24 PM

so...update after moving the cam gear from #2 to #3...did not get what I was looking for...at all. I found that my NGK spark spark plug wires had some splits in the silicone, the rebuilt distributor was not working properly(and had to be replaced with a factory nissan one). After advancing the camshaft, I lost bottom end because I cannot even advance ignition timing to where it was before because it will diesel on shutoff and will not start by the time I get to where it has any low end performance at all...I was hoping advancing the cam would help compensate for the oversized camshaft and shaved head...but it did not.

I am guessing the camshaft is just a terrible setup for high RPM performance, and was not designed for torque or a 2k-5k RPM range.

Now I am left trying to decide what to do next. I guess I will most likely set the camgear back to the #2 position and increase base ignition timing, then hook it up to our exhaust gas analyzer and see if I am running lean, and rejet the carburetor if I am. If I am not running lean, then the only other thing I can think to do at this point is buy another damn camshaft that I can actually see the specifications on rather than this mystery grind.

Any advice?