Datsun Roadster Forum-311s.org

Well, I've hurt the Datsun.
I think it happened yesterday. I won't know until I get into it, but a leak down test today confirmed a leaking exhaust valve in #3. Got on it hard yesterday and it was feeling great. Was blasting up a hill, working the auto tune into some of the higher cells, then had to back out of it quickly when I came on traffic, decelerating from high rpm. When I stepped into it again it felt flat and had a bit of shudder, and I was thinking my balance had gone out a little again. However when I checked today nothing was loose, so I did a compression check. All but #3 were 205-210... number 3 was 175-180. Spun the motor until #3 was sealed up and put air to it... you can hear it coming out the exhaust. Checked all the others and they were sealed. Crap. The problem is that these are custom valves, and I no longer have access to my cylinder head guy due to a falling out. I have way too much development time and money in this head to go back to stock, so I'm just gonna have to find someone who can make/repair/replace the valve (38mm). I had plans to pull the motor and fix the leaking rear main and address some transmission issues before spring... guess I'll be doing a bit more disassembly than I expected. I'm really bummed though, and I don't know how I hurt it if I did it yesterday. Before the valves were hitting the block (wider valve, high lift cam) but I thought I'd clearanced all that, and I didn't over rev the engine, just decelerated quickly. Ugh, no sense guessing until I can look at it, but unless it's burned or damaged from detonation that had happened before, I've got a clearance problem.
<sigh> Who here said I was never done? Ya well, I want to be done with the breaking the motor part... guess that's what I get when you push the envelope! And it was feeling sooooo Good! Grrrrrrrr

Sorry to hear Greg. You were making headway with the new injection too. Bummer Dude
Dan

Sorry to hear that Greg.

Shannon

Breaking new ground is always fraught with setbacks, but I know this won’t deter you Greg. Hope it’s something minor and just a freak occurrence.

You’ll bounce back after the tear down, plus you will have a better sealed engine!
But this is what happens to pioneers, they/we/you occasionally take some arrows and bullets living out on the bleeding edge.
Comes comes with the territory…

You almost certainly floated the exhaust valve. If it was a clearance problem, it likely would have happened when you first ran it.

Or just burnt it, #3 is the hottest cyl....btw
205 cold ? is too high compression originally it ran on 98 octane , now 91-93 . 20 -50 w oil is like 90 W when cool possible culprit

The cause is most certainly unknown at this point. I did some more testing today after warming the engine. 1 and 4 are both 205-210, 2 is 190-195, and 3 is 180. I again put air to it, and only #3 has anything coming out the exhaust. I plan to get a leak down tester tomorrow to get some general health on all 4, but clearly 3 is not happy. Interesting observation offered about it being the hottest cylinder. Nevertheless, it still runs fine in the garage, and had I not felt something and wasn't spiritually connected to the car (!) I would not be testing. A drive may show otherwise, but it's raining now.

Yes, we know the compression is too high for street gas. I know it detonated on the dyno before we adjusted timing so I could have hurt it then or any other time before. When I ran it last it had Boostane in it (96 estimate) and air temps were in the 40s, and of course timing had been adjusted. It revs more easily than before, and my data logs are showing as high as 6850 rpms at times, but it should handle that. I am wondering about the hard deceleration just before I felt it as I didn't clutch it and was near redline I think.
We'll see!

Nearly 7k? that's definitely pushing the limits depending. 6K is a better soft rev limiter point for a street engine. I think you said you are using an Isky or RB cam? Many of those cam profiles were never intended for street and the ramp profiles are very aggressive. The more aggressive, the more likely the spring loses control at some point due too excessive valvetrain acceleration or deceleration. Many of the isky cams were always intended for very high spring pressures which is foolish for a street engine (simply results in premature wear/fails), but necessary with those cams. If the spring pressure is too light, you float the valves.

Of course if you went lean at 6850 all bets are off.

Agreed JT. The valves are lighter than stock but the cam certainly is aggressive. It has the same duration as a B but a lot more lift, making the ramps pretty steep. I had experienced some lobe and rocker wear previously on a couple. Several thousand miles ago I had Delta cam clean up the cam and effected rockers, I broke it in again and so far everything looks beautiful. I think the springs are stock but in good shape, though they may not have been tested in a while. Data logs show a safe 13 to 1 fuel ratio and believe me I'm watching the wide band any time I'm on it, and ignition timing was safe so I don't think it was detonating (so cool that I can go to the exact moment and see all engine parameters. It was right at the end of the log so I can easily find it). I wish I had a before and after leak down to know for future reference. I either burned the valve earlier and didn't know it, or bent it on start up after the last rebuild (honestly seems unlikely, I was even more careful checking things over and over since I had already experienced the valves hitting the block), or it was already bent and my test (filling the ports with carb cleaner and watching for any leaks for several hours, cam out valves seated... no leaks) didn't detect it. Or maybe it was slightly bent, sealed fine but rotated some the other day (can a valve do that?) into a less sealed position. Or I floated the valve and there was enough force and slop from decelerating that I tapped the valve. I have most of the slop shimmed out of the tensioner, but I have watched on the engine stand what happens to cam timing when its not shimmed, and maybe just a little is too much here given this engine. I think I have the rev limiter set at 7300 but I'll have to check and if so lower it to be safer.

I won't know what corrective action to take until I open it up. I know I'm pushing it and experimenting, but that's part of what makes it fun and thrilling when it performs. I really like this cam and I've tried several (B, variations of the B, Racer Brown, previous Isky grind, etc), it works everywhere for drivability (except maybe at 7000rpms huh!). Seeking that balance between max performance and reliability... closer, but haven't found it yet.

I'm telling myself I had to pull the motor anyway for the rear seal and trans fixes... just a problem to solve, not beyond me, I just need to get it done before Spring!
Stay tuned... ya, I'm never done...

If you whacked a valve, couldn't you look through the spark plug hole and see a mark on the piston. As far as the rpm, many years ago I spoke with Isky about the Z-196 grind I use and was told the stock springs will go to 8k. That is where I gradually worked up my limiter. Had it set at 7k and it pulled hard than blam, the limiter. Than "it" happened. I miss shifted at the limiter from 2nd gear back to first. Don't know how fast it went but I no longer feared 8k!

Somewhat irrelevant, the head is coming off anyway. Isky makes good race cams, but guys there know nothing about Datsun roadster heads or valve springs.

Since Greg is self tuning EFI and we don’t have any idea what kind of valves (manufacturer or material) they are, I’d say it’s about equal probability of float vs. burned.

No one at isky would know this either, but there also was more than one version of “stock” 2L springs, the early style had a much higher spring rate and probably would handle around 8k with the trade off of worse wear. Pretty sure Nissan backed off on the spring rates to help improve the one-piece rocker arm disaster. Regardless, 8k is asking for a bent valve with stock springs.

The one-piece rocker arms are a train wreck as soon as the chrome is gone. Certain cam death. Excessive spring pressures just compound any rocker wear/lubrication issues.

I appreciate all the input my friends. Regarding the springs, my (former) head builder knows his stuff, was very familiar with this head and what cam was in it and he didn't recommend a spring change. The valves were sourced and modified by him, and Steve didn't do anything that didn't meet his standards, so I'm confident of the quality. It's much more likely a Greg issue.

Well, more data today... some sobering truths and some mystery, comments encouraged .

I made my own leak down tester today (see Internet, works great, had done this before but forgot some details) and got the following sad/somewhat confusing numbers. First, I did another round of compression tests and got very consistent numbers (cold) #1 220 (!), #2 195, #3 185, #4 210. Leak down tells the story, or some of it... #1 13% rings (?), #2 25% ex valve, #3 50% ex valve, #4 3% no leaks. I repeated all tests multiple times. Ouch. She's hurt. The exhaust valves are obvious, 2 and 3 are either bent or burned. But what I don't understand is the 13% leak down in #1 PAST THE RINGS (damn it!) while it has 220lbs of compression, more that the only healthy cylinder #4. I even moved the pistons position some to see if maybe a ring was being exposed due to the deeper reliefs cut into the block (remember that fiasco?) but it made no difference. I'm disappointed and a bit concerned about the 13% leak down, as I can hear nothing getting past the valves. These are Total Seal rings, and it should be like #4. I really really really don't want to tear down the bottom end, but what is the groups thought on #1? Clearly, low compression is not its issue! Should I worry about 13%?
Thanks all...

Oh, and I know... the "really" wise thing to do would be to machine or replace my pistons to lower the compression, but I'm not there yet unless I commit to a complete rebuild again... just did that not long ago... I believe I can run this motor now with the timing map and fuel control I have.

I'd think you'd kear it at the intake.or dipstick. You could squirt some heavy oil in the cylinder to see if compression comes up.
Are you confident of your tester?
Dan