steve91tt

If it were me and the leak down test is good I would put the L28 back together, get it in the car and running. You can then decide what, if anything you need to rebuild. As you said, these engines can take a bunch of abuse/neglect before they need to be rebuilt. Once you get it running you can figure out what needs attention. Earlier this year, I bought a car with a half seized L24 that hadn't run since 1989. I replaced the gaskets/rubber bits and ran it with triples in my track car for half a dozen track days. It ran strong (for a bone stock L24) much better than I thought. I then pulled the engine and put it straight into my daily driver 240Z. It burns a tiny bit of oil but I think the oil loss is coming from the valve seals. I don't see any reason to rebuild it. These cars are so easy to work on, you could just get what you have running and if you need to rebuild it, pull the motor and rebuild it. But then again, rebuilding an engine can be a fun project and if it gives you piece of mind then go for it! Keep us posted with lots of photos.

Did you try running with the choke on (Doradox's idea above)? If the stumble is caused by being slightly lean at 4500rpm then adding choke should help. Just another data point.

I had a great time playing with the cars today. It's not very often that you get to see a couple of 901 silver Z's sitting with their hoods up next to each other in the driveway. Your's is the nicest looking and sounding 240Z I've ever seen in person. Now I've gotta go shopping for an Ansa exhaust! I agree with your assessment, even when we switched out your distributor, Pertronix and coil the car still stumbled at 4500rpm. It's interesting that the car pulls hard past 4500rpm and also works great at less than 4500rpm. It just has trouble in the middle of the rev band during medium acceleration. As we discussed, I don't see how it could be related to fuel supply to the carbs as there seems to be plenty of fuel once the engine gets past the 4500rpm bad spot. I also don't think it's a mechanical issue as the car runs great 98% of the time. I'm not an SU expert but I agree with you that this seems like some sort of transition/acceleration issue in the carbs.

Very impressive. Nice work!

Great looking project and great car fixing weather here in texas. I think I have a brand new never installed engine bay harness for your car if you need one.

I started with a 90's 300zx myself. You are going to love working with the simplicity of the straight six after dealing with the over engineered, computer controlled powertrain that was shoehorned into the 90's Z's. Looks like you have yourself a great project. Can't wait to see your progress. What are your plans? Straight-up restoration or something else?

Here's another twist for you...I have a balancer that has TDC marked about 8 degrees off of actual TDC. I suspect that the rubber in between the two parts of the balancer has given way and allowed the outer ring to slip slightly relative to the inner. In other words, have you checked that zero degrees of timing is actually at TDC? Mine was not.

I ended up taking the spray bar off and blocking the holes with the MSA block off plates. There seems to be lots of consistent oil pressure and if I carefully take off the oil cap at idle I can see a bunch of oil flying around in there. I put the engine back in the car and it runs fine. I've put a couple of hundred miles on it and rechecked the valve lash. No change or any visible issues with lack of oil. I will say that the valve train is louder than on other Datsun engines I've heard as you can see in this video. The cam is a mild track unit from Rebello. I lashed it at 0.010 cold, measured at the lash pad as per Dave Rebello's instructions. This equates to about 0.007 at the cam lobe. I assume the louder than normal valve train noise is due to the increased lift from the higher performance cam. Has anyone had experience with this sort of cam?

A couple of data points for you... As you are I am currently running Z therapy SU's with SM needles on my bone stock L24 without issues. I have also run them on a L30 stroker with no adjustment moving them between motors. They pulled stronger on the L30 than the L24 but other than that they seem to be equally at home on both motors. Incredible carbs. I am running about 30° of total timing with no vacuum advance on my track car with no issues. I keep the timing retarded to keep the detonation at bay when I'm not using race gas. The car happily pulls hard to redline and beyond even with 30° timing. Just my $0.02. Good luck tracking down your gremlin.

quick update...I tried removing the spray bar and blocking off the holes with fender washers (block off plates are on the way). The flow out of the cam oilers improved significantly. I also noticed that the oil system seems to drain fairly quickly in that it takes quite a bit of pumping to get the oil back up into the head even after the system was primed. Is this normal?

I tried the engine stand oiling technique outlined in Madkaw's thread above. I cut the handle off of a 12" flat blade screw driver and installed through the distributor drive hole. I turned the screwdriver with a drill (counter clockwise) and oil streamed out all 12 of the cam oil holes. Oil also appeared at each hole in the spray bar but the oil flow through the spray bar was very low. Oil was also leaking between the spray bar and the cam towers (no gasket). I don't have a oil pressure gauge installed so I'm not sure that I'm building enough pressure with the drill as the drill was not able to turn the pump very quickly. I'm going to try experimenting with another drill and I will also try removing the spray bar and blocking the holes. I also confirmed that I have a high volume pump by taking it apart and measuring the rotor to be 40mm. I cut a new internal oil pump gasket out of gasket paper but I'm not sure that was the best way of sealing up the pump. I fear that the clearances in the pump are changed by the fact that the gasket paper is thicker than what was there previously. I tried bolting together the two halves of the pump without a gasket but in this configuration the pump was locked solid. Does anyone know if I should worry about the gasket paper or if a stock gasket is available anywhere? Neither MSA or the local autoparts story seem to have one.

I'm not finding useful information using that search strategy. Do you have a link to a thread?

After taking a closer look at the spray bar I don't think a gasket made from parts store gasket paper would work very well. The spray bar is only held on with one bolt per cam tower. If I put a semi rigid gasket material in the joint I'm afraid that it would compress at the bolt and not at the oil hole. It may even cause the oil bar to deform. If the oil hole had a bolt on either side then the gasket would likely work fine. I'm considering removing the spray bar and blocking off the holes. The cam that I'm using is internally oiled. I bought it from Rebello. Dave recommended that I run both spray bar and internal oil system at the same time. However, after reading about several spray bar failures, I may be better off to use the internal oil system only. I'd rather have all of the oil going through the cam rather than risk having some or all of it leak out of a broken spray bar.

I'm in the process of assembling an engine and I need to know whether or not to put some sort of gasket material on the spray bar to cam tower joint. I want to make sure that I minimize the oil leaking out of the joint. However, RTV makes me nervous as it may break off and plug the spray bar holes. I wasn't able to find any mention of a gasket in the FSM. Anyone have any experience with this?

I was in your shoes a couple of years ago after spending 10 years working on a 1991 twin turbo z. I ended up selling it and started working on a couple of 240s. The 240 is a very different car than the twin turbo with very different challenges and learning opportunities. I enjoy working on both but in different ways. You might consider selling your current project and move to something completely different.

I've never measured a cam profile so hopefully someone else can chime in. I'm very interested in what you find as I have a new Rebello head sitting in my garage right now. I was planning on installing it on a 3.0 liter short block over the holidays. Do you know what cam was installed? The cam number is engraved in the end opposite the timing gear.

Wow, no noticeable power increase with a Rebello head? That's quite an investment for no gain. What makes Dave believe that cam timing is to blame?

I don't think side draft carbs have chokes. My mikunis have a cold start circuit but it does not function as a choke would. As the previous posts state, I find a couple of pumps on the accelerator gets them to start very easily without the cold weather circuit hooked up.

I don't think it matters which line goes where. I'm currently running mine front to back.

Welcome Ted!

But unlike other forms of masturbation I enjoy watching other people do it. I always learn something from these sort of threads.

I'm not sure I would want to add seafoam to the oil system. If the material that plugged your spray bar is sand or similar then the oil additive might knock more of it loose. In theory, the oil filter should catch all of the solids from the pan so if there is anything that will get caught in the head cam oilers it has to come from the oil passages in the block or head. I'll bet you had residual junk in the spray bar that you did not catch with your carb cleaner.

The demands on both the fuel system and ignition go up as you load the engine up on the highway. It's not uncommon to have issues under load that don't show up while driving at lower speed.

depends which year. For the +1990 cars twinturbo.net is excellent.

When I had a similar issue I T-ed into the fuel line at the carbs and ran the new line up, out of the back of the hood and under the wiper blade. I put a fuel pressure gauge on the end of the line so that I could monitor my fuel pressure on the highway. If the fuel pressure stays steady then your fuel delivery system is not the issue. Are you sure it's fuel related? The ignition systems on these cars can give similar symptoms as you describe.