Jump to content
oldmates260z

Cam Timing - Is That My Issue?

Recommended Posts

I have the following spec of engine (work done by previous owner):

 

- L28

- P54 Block

- N42 head

- Reground crank

- All new timing gear

- Lightened and balance flywheel

- Flat top pistons

- Electronic ignition

- SU carbies

- New valves with heavy duty springs

- Oversize lash pads (whatever that is?)

- 72 degree cam

- Head machined true 

- Extractors

- Electric fuel pump

 

Sounds impressive I thought, my son's standard L26 eats it! Plus am told it was fitted with triples and did not perform any better.

 

I am now wondering if there is a basic set up issue with the engine as it was not done by a Datsun specialist.

 

From my searching on the forum I have found (thanks to 600Z):

 

“Another thing you could consider which some people don't seem to do too much with is check your cam timing. Slightly advanced will give you better top end power while slightly retarded will give you better low down torque. This is done by checking the lift of your intake and exhaust valves on the role of the cam.”

 

I was given the below cam sprocket which is adjustable and was think about fitting it I would like some advice:

  • How do I know if this sprocket is suitable?
  • Does anyone have a scale template for the timing chain wedge tool?
  • What is the trick for setting the valve timing (600Z did give a good insight) just wondering if there is a link I missed that has more detail?

post-100261-0-24895600-1441105364_thumb.jpg

post-100261-0-07863500-1441105373_thumb.jpg

post-100261-0-76587300-1441105388_thumb.jpg

post-100261-0-70261100-1441105402_thumb.jpg

Edited by oldmates260z

Share this post


Link to post
Share on other sites

I wouldn't be fitting cam sprockets until you figure out why your engine is under performing. Have you checked that your cam timing right now is correct? If they are retarded by one tooth it makes them super slow and not rev out. Does your son have the same car? 260Z 2+2? what ratio diffs are you both running. That will make a huge difference. Also while you are in there checking the factory sprocket has three positions and you can set it to the most advanced hole if you want to get a little extra.Haynes manual explains which is retard and which hole is advanced. Can't remember off the top of my head sorry.

 

I doubt with a stock L28 like that you will notice any difference going to a vernier sprocket and that one looks a little agricultural in my opinion. 

Edited by d3c0y

Share this post


Link to post
Share on other sites

Firstly i would hesitate to change the cam timing until you have eliminated other potential problems.

Maybe check

Ignition timing- should be around 34-36 degrees at 4000 rpm

Compression check- check each cylinder with compression guage

Mixture- do a hard run in 4th gear then switch of ignition without backing off throttle, pull over and check plug colour. Shouldnt be too dark or white.

 

Then start looking at cam timing- Retarding timing will move the power up the rpm range due to the later intake valve closing point.

A stretched timing chain or planed block/cylinder head will retard the timing somewhat.

I am unsure what a heavily retarded motor would do. Im sure it would not produce good power due to the fact the other valve timing events have changed. Intake opening point will be later (detrimental), Exhaust opening point (detrimental)

An engine is very sensitive to the intake closing point. The other opening and closing points do matter but no where near as much as the intake closing

Edited by lampy

Share this post


Link to post
Share on other sites

Thanks for input gents.

 

Both cars are 2+2's and running standard factory diff's I think. Mine I know has its original diff as the guy took it out and put in a lower ratio and it was revving too high on the highway.

 

It does use a heap of fuel so I am guessing it is running rich and after a bit of a run it will run one once I switch it off. Also once its hot it is harder to start.

 

Add to that the cam seems as lumpy as hell, shakes the whole car at idle.

 

Likely best to take it to a specialist tuner in Brisbane, anyone know one?

Share this post


Link to post
Share on other sites

Quite a few of the more performance orientated guts seem to use Jim Milliner at Smart Automotive, in Stafford.

Old school guy, but it may need a rekit of the carbs, which you could do prior?

 

It is diffcult to dial in a cam, properly, with engine in car, as you need to fit a decent size degree wheel on the crank, to discover current cam timing, and then to be able to either advance or retard to get it running better.

 

The L series cam and its timing is not a black art, pretty straight forward, but you need to know what it is you have fitted to the car now.

Most grinds are well knwn, either Phill DugganSureCam, or Clive/Clive Cams will be able to shed light on base timing specs based on the grind number you have.

Grind number is sually found engraved at the very back f the cam. Use a mirror and torch to check the letters/numbers.

Share this post


Link to post
Share on other sites

Had a bit of a play with it on the weekend and attempted to use the above advise with limited success (mostly due to lack of ability some lack of gear).

 

  • Checked plugs but struggled with getting from flat out to get plugs out (may have been some idling in that). Plugs looked a bit black and varied in colour (photo below)
  • Compressor test 195-200 psi across the lot
  • Also struggled checking timing at 4000RPM (by myself). When I revved it up the highest it would go was about 25 degrees, maybe 30.
  • The fuel mixture was also troublesome. I have Colortune devise that I have used with some success on my SR311 but struggled with it on the Zed.

 

Few questions:

 

  • If I set the timing as per the book at 10DBTC shouldn’t that be correct at 4000 RPM? What is the importance at the higher RPM?
  • The adjustment of the mixture only has effect at idle for a SU?
  • The manual states to start at ½ to 1 turn out, mine was 3 turns. I though the more turns out that was more air and less fuel, is that correct? The Colortune indicated it was running rich at 3 turns out and leaned up as I closed it off
  • Also it did not make a significant difference no matter where I had it adjusted

 

I ended up putting a set of horns and it did seem to run much better and a little more torque. Is there an ideal length for horns on the SU’s? Also where do you buy the socks/filters for them

post-100261-0-97574600-1442830288_thumb.jpg

Share this post


Link to post
Share on other sites

Three of those plugs looks super rich to me (and the other three are still rich). I bet it's running mainly on one carb too. If you take the air cleaner off you should be able to lift the piston in one of the carbs and still have the motor run, but only just. That's how i set the mixtures on each carb and then sync them and repeat.

 

This will make life a lot easier:

http://www.ebay.com.au/itm/Carburetor-Syncroniser-Weber-SU-twin-carb-throttle-body-motorbike-sync-balancer-/161057523703?hash=item257fc6c7f7

 

Warm the car up pull the vacuum advance off and set the base time at around 10 - 12 degrees depending on the fuel you put in it.

 

If that's all too hard just drop it off to CnJ motorsport in Underwood.

Edited by d3c0y

Share this post


Link to post
Share on other sites

These are the only guys i would take my car to in Brisbane for carb tuning and we have taken many zeds there in the past. If you go there put in a fresh set of plugs before you drop it off.

Share this post


Link to post
Share on other sites

make sure your points gap is right first.

I run 17deg static, hopefull you have a carb sync or at least a rubber hose and balance the carbs at idle, then again at 1500rpm

Share this post


Link to post
Share on other sites

Ignition advance is critical for making good power. you need 34-36 degrees in by 4000 rpm for a good l series

10 degrees initial would be too low for a modified engine. Maybe try 15.

The reason why people get there dizzys regraphed is to modify the curve and get the right amount of mechanical advance in

 

Be careful with reading plug spark plug colour. The correct method needs to be used to read them.

Use new plugs if possible

Run the car hard and fast eg 3000rpm to redline a few times to clear them.

hold the car at the desired rpm and load point , quickly ignition off and coast to side of road. Pull plugs on side of road and check colour

 

A dyno is the best way to do this faultfinding.

Share this post


Link to post
Share on other sites

Still not right, lacks power over about 2500 RPM and prone to pinging under load.

 

Took if for the run at 4000 RPM after redlining it a few times and these are the plugs

 

Definitely not running rich, look maybe a little lean.

 

Still has a major "running on" issue when I switch it off.

 

Changed timing from 12 BTDC to 8 BTDC runs better and does not ping anymore.

 

Runs advance to around 30 BTDC at 4000 RPM.

 

Any thoughts would be appreciated

post-100261-0-24336000-1452410935_thumb.jpg

post-100261-0-75022700-1452410953_thumb.jpg

post-100261-0-90714800-1452410968_thumb.jpg

post-100261-0-60862200-1452410983_thumb.jpg

Edited by oldmates260z

Share this post


Link to post
Share on other sites

What's your static compression ratio?

Too much CR (anything over 9.1:1 with a performance cam while retaining the Hitachi's, will cause the problems you are describing.
Put simply, the Hitachi's can't supply enough air to feed the performance upgrades, hence the detonation.

Fit triple carbs Webers/Dellortos/Mukinis.

Edited by Lurch ™

Share this post


Link to post
Share on other sites

Thanks Lurch, how can I determine the static compression ratio?

 

Always felt it needed triples ..... but am concerned with getting good set and setting them up ....looks to be the next project

 

Previous owner could not get triples to work but that should not stop me getting them right I hope

Share this post


Link to post
Share on other sites

Before I give up on my SU's I would like to extract as much as I can with them and my set up. I do not think I have a great set of headers/extractors (see photo below). Have looked around the forum but have not found a good thread discussing header options. Am I missing it?

 

Any recommendations for my N42 L28 setup?

post-100261-0-87784100-1453031967_thumb.jpg

Share this post


Link to post
Share on other sites

If your car is not performing as expected I don't think fitting those extractors will help.

 

Who built your engine and why are you so sure of it's specs? It seems if it doesn't perform as expected the parts in it may not be as described? Just a thought.

Share this post


Link to post
Share on other sites

Thanks Gav, interesting clip. You can put a heap of indentations into headers for limited effect.

I am confident on specs but not sure who built the engine. I have experienced massive gains on my U20 engine with valve timing, jetting and pipes. With a good set of long pipes you can get 20% more power at mid range revs.

The pipes I have shown above which are like mine have very short primary's and this I am told is not great. Also with the different port sizes on the heads I assume that will also effect performance if the headers do not suit.

I know very little about headers but understand that they are just as important as the carbs. Just wondering where to find the tests that people have done on them and others experiences.

Share this post


Link to post
Share on other sites

*sigh*

You are over-thinking the situation Tim.
Your current extractors are not the issue. Understand that you have 20,000+ PSI of spent gas moving past the exhaust valve - it's going to be moving out of your pipes regardless of what you do.
Design & size play a role, yes. BUT IMHO that is not the issue in your case - the header design is limited by the twin Hitachi manifolding.

1. Do a comp test & I'll work out the static CR for you.
2. Put triple carbs on it, OR pull the cam & fit a 733a grind.

 

Share this post


Link to post
Share on other sites

Thanks yet again, I know. A little knowledge and not listening! Dam I am one of those blokes :(

The real issue is that I do not want to put triples on it at the moment as with my limited knowledge getting triples setup is beyond me until I have much more time and money for this car.

The Zed is getting caught short when I go for runs as the Sporty guys pull away from me in that mid range power band.

The Zed runs really well and is great fun to drive but I know it's missing something...so it's the triples ...so it is what it is and I will live with that.

The compression is 195-200 across the lot.

Share this post


Link to post
Share on other sites

 

It does use a heap of fuel so I am guessing it is running rich and after a bit of a run it will run one once I switch it off. Also once its hot it is harder to start.

 

Sounds like its running rich to me, possibly to the point of excessive carbon build up in combustion chamber / plugs which will cause the running on issue.

 

 

  • If I set the timing as per the book at 10DBTC shouldn’t that be correct at 4000 RPM? What is the importance at the higher RPM?

 

 

 

Depends whether everything else in your ignition system is good. eg is the vacuum advance working correctly ? Checking for full advance at higher revs will test this.

 

 

  • The adjustment of the mixture only has effect at idle for a SU?
  • The manual states to start at ½ to 1 turn out, mine was 3 turns. I though the more turns out that was more air and less fuel, is that correct? The Colortune indicated it was running rich at 3 turns out and leaned up as I closed it off

 

More turns out is richer - you are lowering the jet tube, therefore creating more area around the needle for fuel to flow through.

 

 

 

 

my son's standard L26 eats it!

 

 

 

If a standard L26 is quicker, then there is something basically not right with your setup. My diagnosis ? Get a decent tune up before spending lots of money on parts.

Edited by 1600dave

Share this post


Link to post
Share on other sites

Where is your power at the moment as in what revs?

 

Have you checked that your timing mark on your harmonic balancer is actually TDC #1 ? Most likely it's right but something to rule out.

 

Do you have a dial indicator or access to one to check your cam timing?

 

It seams you have and are now starting to go around in a circle and you have checked the compression (which you can't really work out your compression ratio from as there are far too many variables), ignition timing which seams not too bad, and any real changes would now really only give you small gains, air/fuel mixture, the grade of oil in the su's (what air filters and do they allow good flow, try it without them) do the Pistons fully open on the su's? I can't remember if they are over filled if they with hydraulic lock and not fully open or not.

 

I think cam timing is due to be checked now unless you already have by now. There isn't too much more apart from going over the same things that will only give small degrees of increases.

 

If you want to quickly check your cam timing:

 

1. Place a dial indicator on your inlet valve retainer on the cylinder that's going to be on the roll roughly 20 degrees before TDC but make sure the valve is closed. Zero the dial.

 

2. Turn the engine over until you get to TDC and record the amount the valve opens.

 

3. Place the dial indicator on the exhaust valve retainer and make sure you allow for the dial to read in the negative as it will be closing.

 

4. Turn the engine over until the valve is fully closed and record the amount it was open.

 

5. Compare the two figures, both the same is neutral, intake open more its advanced (better high rev performance), exhaust open more (better low down torque).

 

Slightly advanced I have found is better but each to their own.

 

That's just my two cents mate but check one and get it close to being correct as you can then move on and check the next until everything is checked then tweak.

Edited by 600Z

Share this post


Link to post
Share on other sites

Thanks very much 600Z, great info.

 

I am likely just working on the fringes due to my lack of abilities and equipment. The car runs very well but lacks mid range power (2000-3500 rpm). Over 3500 it pulls really well.

 

The tweaking is making marginal changes. Fitting 3" ram tubes (sadly only fitted with socks) and dropping timing back to 8 degrees have made good improvements. 

 

The cam timing I believe is most likely my cause of the issue but I do not have access to the gear (or ability to use it) to do the check. I will get this done next as I think I have someone now that can do it for me.

 

I will however check that TDC is correct.

 

Thanks again

Edited by oldmates260z

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×