Guest norm[T12SDSUD] Posted April 11, 2003 Share Posted April 11, 2003 Well, it took 4 years this time around, but I finally broke my diesel crank just as I did the two 280 cranks that came before.As always, the break line was right in front of the #7 Rear Main bearing. The crank saw a ton of drag races and every day street abuse, as well as two loose flywheels AND a massive clutch explosion 3 1/2 years ago. I never once power shifted this crank as I did the 280 cranks, so that is no doubt why it lasted almost 4 years. I am thinking that maybe a lightweight flywheel might be the way to go to keep these long cranks from breaking, but I'm not sure.I would imagine a lighter flywheel should put less stress on the back of the crank. Also, I noticed tonight that the Crank damper pulley rubber had seperated from the main metal around 270 degrees of the pulley, so that may have played a factor in the crank breakage. Anyway, the main bearings look good still, so I may just drop another diesel crank in and go about my merry way or I may build that short stroke big bore motor I've talked about doing in the past. Anyway, I wonder if I now hold the world record for Datsun crankshaft breakage now? later,norm Quote Link to comment Share on other sites More sharing options...
yo2001 Posted April 11, 2003 Share Posted April 11, 2003 you are the man on breaking the crakshaft I guess ghirled (spell?)wouldn't help the #7 main cap. Well, may be you can get the next crank nitrided Quote Link to comment Share on other sites More sharing options...
denny411 Posted April 11, 2003 Share Posted April 11, 2003 Are you having the rotating assembly balanced? that could play a part. I would also suggest geting a new or possibly an aftermarket balancer/damper. does fluid damper or some other manufacturer make a fluid type damper for the L6? Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 11, 2003 Share Posted April 11, 2003 The pistons and rods were balanced to within .1 gram. The cranks are normally so well balanced from the factory that furthr balancing is unnecessary. The centerforce clutches are balanced from the factory and the flywheels get a good balancing as well at the factory. Basically if you've ever seen me run at the dragstrip then you'd know exactly why it broke. It's not uncommon for me to do 30 runs in one test and tune night. In fact, one night I made 44 passes! I feel like if there was a fluid damper available for the L series that it may go a long way in preventing crank breakage, but then again an inline 6 motor ihas such long crank and when you drop the revs repeatedly from 5-6K especially when using slicks that it is just a heck of allot of stress on the crank. From what I understand IT L series motors have a habit of breaking cranks as well ,but they are screaming at high revs for quite some time when coming down the straights. later Quote Link to comment Share on other sites More sharing options...
Mike C Posted April 11, 2003 Share Posted April 11, 2003 I think you need to work from both ends of the crank. It seems that the BHJ custom damper that Jeffp was working on is MANDATORY for your motor at this stage. The lightened flywheel will contribute as well. While it is not a 6 cylinder, dyno research on SBC show that reducing the flywheel weight increases acceleration, while INCREASING the balancer weight/diameter ALSO increase acceleration. Probably because it is better able to contend with crankshaft harmonics putting more power to the ground. That power is used to push the car instead of self-destructing the crankshaft. Another diesel crank, the BHJ damper and the lightweight flywheel and you go even faster. Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 11, 2003 Share Posted April 11, 2003 What sort of RPM do you turn your engine to? And, what exactly were you doing when the engine let go? Launching? Top end of the track(or rev range). I just want to know, so I don't break my crank . I plan on alot of boost and lots of drag racing. Quote Link to comment Share on other sites More sharing options...
slownrusty Posted April 11, 2003 Share Posted April 11, 2003 44 passes in one night! Holy moly! I would say the diesel crank held up well for 4years based on these conditions! Yasin Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 12, 2003 Share Posted April 12, 2003 Yeah, I saw that new damper and it looks sweet but I wonder how much it costs? Very interesting about a heavy damper helping acceleration. I did'nt know that. As far as what I was doing when the crank broke here's the scoop. I had went racing two days earlier at Wilkesboro and the motor was running good but seemed a little weak that night but since the clutch had started slipping two weeks earlier it was tough to say whether the crank was already having trouble at that time. Anyway, I was getting on the interstate when it broke. One thing I did do differently that I had never done before, was that I had the motor turning at an even 5000 rpm in 1st gear when I nailed the throttle and shifted hard into 2nd gear and then into third. More than likely the crack was already there but the violent torque coming on instantly at 5000 rpm's just snapped the crank. All seemed OK until a mile up the road when I slowed down. The motor vibrated badly when passing thru 3000 rpm and I immediately knew it was either a loses flywheel or broken crank. Turned out it was the broken crank. Although this time at least it was only cracked thru about 3/4 of the way and not totally in two pieces as happened the other times with the 280 crank. Anyway I still haven't decided what I am going to build as of right now.The easiest fix would be just to drop another crank in as I can do that without removing the head and exhaust and such. I am tempted to go with an 87 mm bore and 240 crank but I don't know if I want to spend the money for the machine work ,rods and pistons. According to Desktop Dyno the short stroke motor would make about 20 more peak HP, but the loss of low end torque would not be welcome. Hopefully I'll decide this weekend what I want to do so that I can be back racing again soon! later Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 12, 2003 Share Posted April 12, 2003 Interesting. Did you have the cranks checked (magnefuxed) prior to there short lived second lives? I wonder if some fractures had occured prior to your getting them. Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted April 12, 2003 Share Posted April 12, 2003 You have to be insane to break 3 crankshafts (in a good way that is). You must really do drive it like you hate it! I like the idea of the short stroke wide bore motor myself. A well balanced L24 crank would probably make the whole rotating assembly more durable anyways, because you would be slowing down the piston speed, improving the rod ratio, and there would be less stress on the crankshaft itself with the shorter arms. Needless to say, I think it would be a lot harder to break an L24 crank than an LD28. If the short crank hurts low end torque, maybe you could get a little smaller cam (as long as your high compression can take it...10.6:1 right?) With your big cam, your motor's almost completely biased towards high RPMs anyways, so why are you worried about the low end torque? The short stroke will pretty much just further adapt the motor to the high RPMs anyways. Why not just launch at a higher RPM with the shorter stroke crank? Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 12, 2003 Share Posted April 12, 2003 Interesting. Did you have the cranks checked (magnefuxed) prior to there short lived second lives? I wonder if some fractures had occured prior to your getting them. Well a crank that lasts thru 4 years of hardcore driving really isn't too bad actually. Yeah I had the crank magnafluxed when I installed it back in 99 and it was fine. The 280 cranks that broke before only lasted a year each.The 280 cranks broke thru power shifting. This diesel crank probably just broke from the fatigue of hard launches and the occasional 7500 - 8000 rpm hits during a missed shift. later Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted April 12, 2003 Share Posted April 12, 2003 I would have had the crank shaft balanced, and the flywheel and pressure plate. When I had my engine built, the machine shop balanced everything from the dampner to the pressure plate. I would think with your record that you would need everything balanced to the Nth degree. My engine is very smooth, and I know they had to take material off the crank to make it right. I also have a colored dowel on the flywheel and an indicated dowel hole on the pressure plate, and welded material on the pressure plate. I know from reading something that even a small imbalance is a huge weight issue as the rpms increase. Just something to think about. Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted April 12, 2003 Share Posted April 12, 2003 Heres another idea...try using the L28 crank, big bore KA24 pistons (89mm), and L24 rods. It will basically be a big bore L28 with longer rods. You will keep a decent stroke for more torque, a good rod ratio and bore/stroke ratio, not to mention 2.95 liters displacement! Whatever you decide to do, good luck! Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted April 13, 2003 Share Posted April 13, 2003 Thats what I built although I have 87mm forged pistons, and mine spins to 7k with no complaint with a stock turbo cam and lot o' boost. When it runs that it. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 15, 2003 Share Posted April 15, 2003 My first 3.0 liter had the flywheel bolts try to back out, The problem stopped when I went to a 16lbs cut down stock flywheel and a NISMO comp dampner.I later put port nitrous on this motor and ran about 80(yes 80) bottles of N20 through it in the course of a year.I didn`t have a flywheel backing out problem and I checked the torque on the front dampner bolt once every 90 days or so.On my latest 3.0 I went to a Tilton aluminium 11lbs flywheel and a new Nismo dampner, so far so good and I am launching at 5500 rpm on slicks with a 200 shot of nitrous on my turbo motor with no bolts backing out( I`ve checked).I do however have to praise the dual stage rev limitor of my MSD digital 6 for saving my motor more than once.I probably have 70-80 really hard drag launches on this motor , like almost 500rwh hard. Quote Link to comment Share on other sites More sharing options...
Moridin Posted April 15, 2003 Share Posted April 15, 2003 After reading something (I believe it was an article in Car Craft) they stated exclusively not to use a fluid filled dampner. They said one of the best solutions was to go to ATI and have them build a custom one based on the harmonics they record from their specialized equipment. There is also another person working on a universal dampner that is supposed to work well across the board for just about any motor. I'll look for those for the articles tonight or tomorrow. Quote Link to comment Share on other sites More sharing options...
johnc Posted April 15, 2003 Share Posted April 15, 2003 ATI Super Damper. Jim Thompson at Sunbelt has the part number for the L6 application. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 16, 2003 Share Posted April 16, 2003 ATI Super Damper. Jim Thompson at Sunbelt has the part number for the L6 application. http://www.wisespeedshop.com/ATI.htm Look at this website. It has an interesting chart. Notice the HUGE difference in vibration control between an ATI and a Fluid damper after 7000 RPM. later Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 28, 2003 Share Posted April 28, 2003 Just thought I'd post an update. I've decided to go ahead and put in another diesel crank instead of doing the short storke motor. I haven't decided yet if I'll do a lighter flywheel, although I have located a 21 lb. unit from a friend and have also located a machine shop that says they can safely lighten it 3-4 lbs. If I'd ever run slicks again though the stock 24 lb flywheel would be better for launch, but with street tires a lighter flywheel might even be preferable. I'm gonna have the replacement crank cleaned up and balanced for $55 bucks and I'll have the flywheel balanced as well for $20. I'm going to install a Euro Damper this time as new 240 dampers are no longer available. I found a dealer in Lynchburg, Va. that had the Euro dampers in stock and only charges around $90. Riley Curtis is the parts guy at the Nissan store and is very knowledgable on early Datsun Z parts and a pleasure to talk with as well. If anyone here needs parts I suggest you give Riley a call at 1-800-443-2117. Anyway, hopefully I will be up and running again soon and my hoped for addition this summer will be an MSD unit for a better idle and the rev limiter most of all! later,norm Quote Link to comment Share on other sites More sharing options...
turbobluestreak Posted April 28, 2003 Share Posted April 28, 2003 Hey norm I was wondering why you didn't replace it in the first place I'm going to see if I can use an RB20DET dampener. Then I wont be breaking cranks. tbs Quote Link to comment Share on other sites More sharing options...
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