Jeff G 78

No and yes Steve. We took the bolt all the way out to inspect it, but we did not remove the damper or try to turn it without the bolt.

Charles, I checked the valve clearances during the prep for the race. The engine had about 16 track hours on it since I last adjusted them and 9 of the 12 were right on and the other 3 were only 0.001" loose. I adjusted them back to spec. The AFR is brand new and worked perfectly throughout the race. The plug readings also looked perfectly light tan, so I'd guess the AFR is accurate.

Hey Steve, I was awaiting your reply. I brought the borescope home from work, so I will at least be able to look down the front cover and in the plug holes. I'll also do a leakdown. With those two tests I should know if it will be a big repair bill or not.

Yeah. Even worse is that we didn't know it was the bolt that was loose. I had a teammate crawl under the car with the 27mm socket and a breaker bar to turn the engine over while I watched the valvetrain. He started turning the bolt and nothing was moving up top. I was sure that the crank had snapped or that something was very broken. I asked him to remove the socket and try turning the bolt by hand. Sure enough, it was backed way out, but once tightened, all looked fine. I have built about a dozen L series engines over the past 35 years and I've never had a crank bolt loosen.

Nice looking muffler!

Great points Zed. As an easy way of telling if the damper is good or bad, I painted a white line across each surface at the timing notch before installing it. If the rubber bond fails, I can easily see if the 2nd row pulley has rotated compared to the first row pulley and center hub. It did not fail as all paint marks are still aligned and they match the timing scale when the keyway is at 12:00. Also agreed on the compression check. I did use the same gauge as always, so the actual readings could be slightly off but they did drop compared to the last time I checked it. I believe my gear set does have the notch, but I am running a very different setup, so I'm not positive if it still applies. I modified the cam gear using eccentric bushings like the "How to Modify..." book describes. My head is shaved 0.050", so to get the timing right, I drilled the cam gear hole and installed offset bushings. I used a degree wheel and dialed in the timing exactly to my cam specs by choosing the correct offset bushing. I did check the bushing and it is still intact and properly positioned. The slack side chain guide as slightly modified to take up the additional slack due to the shorter crank to cam distance. Until I remove the front cover, I won't know for sure, but all looks good at the top of the slack side guide. It is possible the bottom guide bolt loosened allowing the guide to slide in the slot and the chain to go slack. Again, very possible that the spark isn't strong enough since the timing light wouldn't fire through the inductive pickup. I will check the wiring and power to the coil and distributor.

Mark, the initial high RPM misfire was about 5 hours into the race just before a fuel stop. The car progressively got worse (missing at lower and lower RPM) until it finally quit running just after the 6 hour mark. The last 15 minutes were far worse. Prior to that, it still did OK, just had a misfire according to the driver. I was in the car earlier and it ran fine, so I have no direct knowledge of the symptoms. The driver kept reporting that water temp, oil pressure, amps and AFR were normal throughout. We thought it might be vapor lock, so that is why we left him out. In the past, when that happened the symptoms were similar, but there wasn't a quick fix. This time, it was clearly something else since we let it completely cool and it still wouldn't run. The compression check was only done after we checked the easy stuff like fuel, spark, and valvetrain. The puffing was subtle. It almost could have been confused as attempted firing, but it just sounded like the intake charge was being partially expelled. Very tough to call since we were right next to an active race track with lots of background noise.

Pete, that was my #1 theory and it still could be true. I backed-off when I checked the distributor timing and found it to be where it belongs. I will certainly double check it though. Captain, it is certainly possible, though unlikely that both carbs clogged. The fuel flow to the carbs was great. I figured that the starter fluid would rule out a fuel problem, but again, I will revisit everything. Keep the ideas coming. Just because I checked stuff at the track, doesn't mean I won't check again. At this point, I think it's a fun exercise for those of us who have been doing this forever to diagnose the problem. I expected each of you to chime in quickly and there are a few others on the forum that I know will join the fun. It's a frustrating problem, but one that I WILL find the answer to once I fully inspect everything. Hopefully, it's not a catastrophic problem and I only have to replace a woodruff key or a faulty tensioner. Fingers crossed...

I am not ruling anything in or out, but to clarify, here is what I do know: Cliff, the valve springs are all intact and appear good. They are high performance Schneider springs. Phillip, I am with you. I think that the issue is very possibly in the chain guides or tensioner. The top end of the guides looks fine, but until I pull the front cover, I will not know for sure. Pete, I thought that too, but I swapped the entire distributor, so I'm leaning away from that being the issue. I checked the rotation and the lash in the rotor at several positions and all felt correct. Bart, interestingly, I did try to use a timing light to watch for ignition while cranking the engine and it did not work. I will revisit this with another timing light since my advance light gets flaky at times. I have never tried to use a light without the engine running, so I wasn't sure if not getting a light flash meant anything. Again, I swapped the coil, distributor, cap/rotor and wires individually and all together with no change. These are all GREAT suggestions and I would have said exactly the same things if it were me being asked. Keep the ideas coming. I'd love to figure out what happened without needing to tear it all down, but it will likely come to that. I promise I will update the thread as I learn more, though I will not be pulling the engine apart for several months if that's what it comes to. I'm moving the car in November to a new winter home where I have lots of space to work on it over winter. What does everybody think about the low compression and slight puffing? I have run engines (not L Series) a tooth off and they still run fine, just down on power. I would think that if it was off by more that a tooth or two, I would be dangerously close to having piston to valve contact. Oh, one more item that I forgot to mention. While diagnosing, we found that the crank damper bolt was loose by several turns. The engine has 20 race hours on it and the everything was torque checked before this race, so would anything specific cause the bolt to get *impacted* and lose tension? It could have happened when it jumped timing I guess (if the timing jumped).

I'm not necessarily asking for help here, but rather, I'm curious if the armchair Z experts can figure out what is wrong with my race engine. Here is the background... My engine is a F54 block with a shaved P79 head, Web Racing camshaft and a 3-2-1 header. I run SU carbs and a ZX distributor with the E12-80 module. I built the engine a few years ago and it now has two endurance races on it with a total of about 20 race hours. Last weekend we raced the car and the engine was running great with plenty of power. About 6 hours into a 9 hour race it started missing at high RPM just before a fuel stop. We thought it might be a fuel starvation issue, though the AFR never went lean. After the fuel stop, it began to run worse and worse, missing at lower RPM and losing power. The driver radioed in and said that it died and he was coasting into the pits. Oil pressure, water temp, and AFR were all right were they should have been while it was losing power. All of the fuel was bought together and the issues started close to 2 hours into a fuel run, so bad fuel can be ruled out. We began to try different diagnostics, but nothing seemed wrong at first. It had fuel and spark, but wouldn't fire. We thought maybe it had vapor locked, but even after it cooled, it still wouldn't fire. Starter fluid didn't work, so I pulled the plugs and valve cover. The plugs had a perfect light tan color and all of the valves were going up and down with no obvious problems. Next, we checked the ignition timing and valve timing. Both appeared to be correct. With the crank damper mark at #1 TDC, the #1 piston was confirmed to be at TDC and the #1 cam lobes were both up. The distributor rotor was pointing towards #1. I then looked at the cam gear pin with the crank showing TDC and the pin was up where it should be by the naked eye. Next up, the compression was checked. This is where the first problem was found. All 6 cylinders were near 140 PSI with all plugs out and the throttle open. The compression should have been closer to 180 with my engine setup. Again, the engine ran strong earlier in the race. 140 PSI isn't great, but the engine should run reasonably well with 140 PSI if that is the only issue. Next, we tried a different known good coil as well as a known good distributor and module, cap, rotor, and plug wires. We still got no fire. The engine never even tried to start after it initially died on track. Spark was checked at the coil as well as at the plugs and it showed good no matter what ignition parts were used. The fuel lines were removed at the carbs and the electric pump fed plenty of fuel into a pop bottle. We tried bump starting, starter fluid and new ignition parts with no luck. My thinking is that somehow it must be valve timing or valve related due to the low compression readings. It doesn't appear to have skipped timing and the valves appear to go up an down smoothly. The distributor rotor turns as it should and oil pressure was always good, so the crank worm gear and oil pump/distributor shaft do not appear to be stripped. The engine oil and water look fine with no signs of mixed fluids. It could have bent valves, though all six have equal compression and 140 isn't horrible. The engine does appear to puff a bit strangely when cranked, so it feeds the theory of valve timing or bent valves causing the intake charge to escape through the exhaust ports. We also tried to turn the distributor back and forth while cranking. It never sputtered, backfired, or coughed. The engine never made any bad noises while running or when turned over via starter or by hand with a breaker bar and socket on the crank bolt. The engine should not have been money-shifted, but with three drivers, anything is possible. There was only one downshift per lap from 4th to 3rd gear. So... I have not yet done any further diagnostics since getting home, but I will do a leak down and put a borescope in the plug holes within the next week. If I don't see anything, I will pull the engine over the winter and tear it down to check everything. Any theories? Winner gets nothing other than bragging rights and internet accolades. GO!

Like Zed Head said, it might not be as bad as it looks. Rails can be replaced. Find a rear ended Z and have the whole front clip cut off and replaced. It's not an easy job, but it can be done. At least you end up with the same Z. Sorry to see a Z wrecked. Glad you are OK.

Yes, that's a single seam cover. It uses one piece of leather. The three-seam is three smaller, therefore cheaper, pieces of leather. It has a seam at 6 o:clock as well as seams at 2 and 10 o:clock. The cover was still a single color. EDIT: This is interesting. I went to the wheelskins website and clicked on one-color leather. As I went through the four sample colors, the gray, red and blue are single seam, but the black appears to be a three-seam cover. They say nothing about it in the description. http://wheelskins.com/original

Yeah, the first one I bought was a single seam and it was awesome. For my next Z, I went back to the same auto parts store (a year or so later) and went to the same rack and bought what I thought was the same thing. The price was about the same as before. When I went to put it on, I immediately noticed how much thinner it was and that there were three seams. It was thin enough that there were bulges at each seam when installed. I left it on and used it, but it was never as nice. The third time I needed one (for a Toyota 4x4), I tried a different store and found that some on the rack were singe and others were triple seam. The single seam ones were more expensive, but much thicker leather.

I had Wheelskins covers on several Z cars in the past. They make different quality covers, so if anybody gets one, make sure it is a one-seam leather rather than a three-seam leather wrap. The single-seam cover is much thicker and higher quality leather. I agree that the single-seam one fit perfect and was very high quality. The three-seam cover was just OK.

I got my new OE and RT diff mounts installed, put my new seat harness in, and got the brake ducts partially done. Back at it tomorrow. I need to tune the carbs with my new wide band O2, finish the brake ducts, and tidy up a few last things before my track day next week.

I got the new OE mount and RT mount installed today. Beautiful mount, but it sure wasn't easy to install. I think it would have been easier to pull the diff, but I managed to get it in by just removing the crossmember, lowering the swaybar, dropping the exhaust hanger, and flexing the RT mount just a bit. The RT mount makes tightening the OE mount bolts very difficult. Again, had I removed the diff, I could have installed the OE mount to the diff first, then put the RT mount in place. The diff would then go back in. I cut three sections off the snubber. I started with two, but it was preloaded with the mounts in place. I pulled it back apart and cut the third section. That left a gap of about 3/16". I'm very happy with the results.

My RT mount arrived today, so I will install it along with the OE mount tomorrow morning. I really want to thank Technoversions for a great looking product and very fast delivery. Their website said that they would not be shipping any orders for about a two week period, but I asked them in the order notes if they could ship it quickly upon their return. Rather than wait, they shipped it right away 2-day express mail. I got it in time to install it prior to my track day and race. I would recommend them to all S30 owners. I have torn OE mounts on every Z I have ever owned and this product should cure the Nissan design flaw once and for good. I will purchase another RT mount from Technoversions for my street Z. Great company! By the end of the weekend, I should be ready for the track.

That's a pretty sweet looking mount.

I repacked my front wheel bearings today and removed the dust shields in preparation for brake ducts.

I ended up ordering an OE mount and the regular RT mount. I got some feedback from another Z owner that the top-down mount that replaces the OE mount didn't fit right. I'd still love to hear any feedback on the top-down mount. I still have to install an RT on my street Z. Timing was bad though. TechnoVersions isn't shipping anything between 8/3 and 8/14. Of course right when I need it to ship.

I have 2500+ race miles on my 40+ year old studs.

My only worry is that the Dorman studs are probably crappy Chinese steel rather than the good, but now 40+ year old OE studs I have.

I just posted a new thread about RT mounts. Do you have the basic RT or does it also replace the stock mount with the top-down front mount?

Hey gang, I just found a broken front diff mount today on my race car, so rather than destroy another stock mount I thought I would install the RT mount by Techno Versions. I did a search, but couldn't find a definitive answer on whether or not to include the Energy Suspension mount or not. I saw a thread a while back about added vibrations due to a different driveshaft angle, but there was no follow-up stating if the mount was the issue. I have to get the car back together soon as I have a race coming up in a few weeks. Can the poly top-down mount be modified, or should I just order an OEM mount and the RT mount with the snubber? http://www.technoversions.com/DiffMountHome.html

That's funny, I too replaced the front and rear studs on my 260Z race car today with Dorman studs. I went with stock length though. I also found a broken front differential mount. I need to get a RT mount.