gira Posted April 6, 2009 Share Posted April 6, 2009 Good Day everyone, I have a general question about the stroker engines out there. We built one and it recently beat the middle crank bearings up pretty bad without much time on the engine. My belief is we turned it too many RPM's and I want to know from the list if there has been a general consensus of where NOT to go with the RPM's on these engines, or where the harmonics are. This was a professionally built engine with very good parts. Thanks a million, Greg Ira Revtec Race Engineering www.revtec1.com Quote Link to comment Share on other sites More sharing options...
1 fast z Posted April 6, 2009 Share Posted April 6, 2009 What do you mean "beat up"? I run my strokers to 8500 with no crank problems. I would suspect your builder did not set the bearings up right. Quote Link to comment Share on other sites More sharing options...
josh817 Posted April 6, 2009 Share Posted April 6, 2009 What do you mean "beat up"? I run my strokers to 8500 with no crank problems. I would suspect your builder did not set the bearings up right. That or your setup was out of balance... by a lot. Maybe a mixture of bearing, wrong clearance, and balancing... Quote Link to comment Share on other sites More sharing options...
blackwidow Posted April 7, 2009 Share Posted April 7, 2009 check crank trueness, I'm sure if it is an awesome shop they checked it, but its something that could cause that along with a lack of oil, viscosity, pressure, or otherwise. Back up on this? Quote Link to comment Share on other sites More sharing options...
Daeron Posted April 7, 2009 Share Posted April 7, 2009 Good Day everyone,I have a general question about the stroker engines out there. We built one and it recently beat the middle crank bearings up pretty bad without much time on the engine. My belief is we turned it too many RPM's and I want to know from the list if there has been a general consensus of where NOT to go with the RPM's on these engines, or where the harmonics are. This was a professionally built engine with very good parts. Thanks a million, Greg Ira Revtec Race Engineering www.revtec1.com Greg: sorry, I can't help you that much myself; my brother Tim Carey was with you at Sebring though. How high in RPMS did you take it? What kind of reciprocating mass are we talking about, and how finely balanced were the piston/rod combinations? What chance is there of a fuel, spark, oiling, or cooling issue particular to these two cylinder that might've been overlooked? These guys are data fiends here, because the numbers are what tell the story. your questions might generate more and better responses with more specific information; for those of you who do not know, RevTec is an established SCCA racing team that you should simply google if you don't know who they are. This isn't Joe Q. Zcarowner asking about some random stroker build here What sort of dampener were you running, and what history have you personally got with those dampeners? Like I said, I couldn't answer you any better than Tim could, but someone around here must have had this problem before, whatever "this" problem is. Quote Link to comment Share on other sites More sharing options...
gira Posted April 7, 2009 Author Share Posted April 7, 2009 Good questions from all. I'm going to dig for more specifics. Several observations though. I won't give away our secrets but this had one of the highest HP numbers I've seen on this list for one of these engines. The parts used are high quality parts. High RPMs in the L engines has always been a harmonics issue since day 1. We set this engine up similar to our championship EP engine, the most reliable race engine I've ever had. This wasn't a backyard build. 8500 in a stroker? Not necessary is all I can say. That has to be 2k off the peak hp if I had to guess. Even our EP engine with all the smaller recipricating mass doesn't like much over 8200, as the harmonics begin at 8 so we have to get through that point quickly. It wouldn't like Daytona where you inch up on that mark for 10-15 seconds. We used this trick new dash with all this electronic F1 crap on it. I have a sneaky suspicion that the RPM weren't calibrated correctly. This happened on an earlier generation of this same brand unit. We didn't set the rev limit on our Electramotive crank fire ignition either. Remember this is a race engine, and it'll sit up at redline in the danger area for a much greater percentage of the time compared to a street engine. I'll get back with more details. Greg Ira Quote Link to comment Share on other sites More sharing options...
gira Posted April 7, 2009 Author Share Posted April 7, 2009 1fastZ, I meant to ask you what balancer you run on your car. Thanks in advance. Greg Quote Link to comment Share on other sites More sharing options...
josh817 Posted April 7, 2009 Share Posted April 7, 2009 I didn't look at your user name until now... If you're who I think you are then I don't think any of your motors would be sketchy, therefore I have absolutely no idea what to think now. I didn't know they allowed crankfire ignitions in the class you're in. Quote Link to comment Share on other sites More sharing options...
Cobra_Tim Posted April 7, 2009 Share Posted April 7, 2009 I didn't look at your user name until now... If you're who I think you are then I don't think any of your motors would be sketchy, therefore I have absolutely no idea what to think now. I didn't know they allowed crankfire ignitions in the class you're in. If you recognized the name then I’m SURE you'd realize he classless Greg... Just run some Marvel Mystery oil next time... That'll fix it all up. On a serious note, It could be the same problem we had with the U20 in the BRE car. Clutch pressure can kill that center bearing. You dont have a picture of it do you? Quote Link to comment Share on other sites More sharing options...
gira Posted April 7, 2009 Author Share Posted April 7, 2009 Josh, Thanks, ignitions are open. Tim, no pictures but I know from a top notch engine builder what he described. What he described is not an oiling issue, I do know that. Usually the clutch pressure will hurt the thrust surface, not necessarily the bearing itself, right? This clutch is the same set up I've had for 9 years in the EP car. Marvel Mystery Oil, yeah we might try that. I might just put a Helicoil in it too. That's my friends answer for everything. All assemblies were balanced and all clearances checked during build as normal for this builder. We used one of our special cam grinds that we use on the EP car which is lower lift and more duration. Unfortunately this wants to make the power up higher. We're changing that out. I didn't like that idea to begin with. Connecting rod bearings look great. Center main looks worst and then gets better as you go out. Builder said he knew it was harmonics within the first minute after seeing this, since he's seen this before, mainly in the U20. Quote Link to comment Share on other sites More sharing options...
josh817 Posted April 7, 2009 Share Posted April 7, 2009 Here's a picture of the bearings on my customers U20... He complained of a knocking noise plus it ran like crap. From what I remember all the bearings were raped in his motor, even the jackshaft bearings so one must've gone out and debris into the oil maybe. However, piston #4 was starting to melt so it could have been several things I guess, I didn't build the motor before so what do I know. >_< Your bearings look like his? So I assume everything else is just fine in the motor or did you have problems in several other places too? Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 7, 2009 Share Posted April 7, 2009 Thats pretty interesting as I thought (can't remember where I read it) that the crankshaft oscillations due to harmonics would result in the twisting of the crankshaft along the main axis. I also thought I remembered that the twisting would be greatest at the front, as the rear (flywheel + drive) is what is resisting the torque, but perhaps in your race motor you are running a large dampener + dry sump thats adding a bit of load to the front and reducing this factor. So perhaps thats why the twist is greatest towards the middle of the crank, also, perhaps the twisting is deforming the crank so its less than perfectly round, which, depending on your clearances (race motor so I'm assuming they're larger than stock), could perhaps be causing interference to the bearings. Isn't it true that you can determine the engine harmonics on a dyno simply by looking at dips in the power curve? I heard rumours that V8SC engines in oz the crankshaft harmonics were almost a 20hp drop. Dave Quote Link to comment Share on other sites More sharing options...
johnc Posted April 7, 2009 Share Posted April 7, 2009 An ATI Super Damper solves a lot of harmonic problems. Quote Link to comment Share on other sites More sharing options...
Daeron Posted April 8, 2009 Share Posted April 8, 2009 What Josh pictured is very very similar to the bearings from our uncle's U20 motor (unless my memory is REALLY failing me.) However, oiling was not an issue in our situation either; oil pressure and supply were constant and the entire oiling system was well set up and plumbed. We didn't have the money to do our BRE car ALL the justice it deserved, but the accusump and oil cooler/filter setup was done very well. The motor trashed the crank bearings nonetheless. I should be around the shop sometime in the next few days; Tim or I will get some pictures of the spun U20 bearings in question, if they are still around. Quote Link to comment Share on other sites More sharing options...
woldson Posted April 8, 2009 Share Posted April 8, 2009 I'm just going to jump in here. Could something caused the rotating assembly to go out of balance? Also maybe the crappier oils today take a situation that was tolerable, and cause it to crap? Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted April 8, 2009 Share Posted April 8, 2009 This may sound crazy but I've heard and seen the L6 cranks shortened 4mm at the flywheel end. The starter is offset with a spacer and either the fork fulcrum is spaced out or a 240mm clutch with a 280 throwout bearing is used (I think I've got that straight) to set the fork angle correct. This is apparently a popular mod in Japan. It is suppose to make a dramatic reduction in harmonic issues at upper rpms. While I don't expect to see rpm's so high I've made the same mod to my V07 crank. No harm. No foul. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 8, 2009 Share Posted April 8, 2009 4mm out of the flywheel flange? Any ideas why that would help? Dave Quote Link to comment Share on other sites More sharing options...
1 fast z Posted April 8, 2009 Share Posted April 8, 2009 Less moment arm, I suspec is the reason. Quote Link to comment Share on other sites More sharing options...
blackwidow Posted April 8, 2009 Share Posted April 8, 2009 Well if I recall correctly torsional vibrations get worse as they move further away from the load, or flywheel end of the crank in this case. So I am guessing by removing 4mm off that end of the crank you just changed how bad the harmonics get at the blancer end of the crank. I can't really tell you how much that just helped or even if it changed the RPM at which the resonant harmonics happen(which i don't think it would because you havent changed one of the variables which matter to harmonics, cept maybe a little weight at the end), but I can tell you it was done for the right purpose. Hopefully? Either way a good damper is needed for sustained useage at those RPM's. Edit: just read the above posts again. What helix said. Also were the bearings like Josh's or pushed out on the sides? Quote Link to comment Share on other sites More sharing options...
gira Posted April 9, 2009 Author Share Posted April 9, 2009 Wow that's some radical stuff! The bearing didn't look like the above. His piston looks like detonation or too lean. His bearings look like they wore from junk in the oil, possibly particles coming off during the event. My bearings were through to the copper and got better as you go out. It's not the crank twisting necessarily as much at it's the crank whipping like a rope that you raise up and cause to oscillate. The U20 is real bad about this. Anyway, we have a new method in hand to try on the engine dyno where we're going to measure the oscillations with an oscilliscope and accelerometer. Really just where it vibrates the most. How's that sound? This hopefully will tell us where the event is happening so we can tune out OR avoid. Here's the deal. Many of these engines have these harmonics issues that you won't feel. The trick for the driver and unbeknownst to most of us is to be able to blast through that point. For instance my EP engine has an event a 8,000 rpm, not at 5000 rpm. As I am approaching my top gears to shift at 8200, it sits in that bad spot for a second or two. A 3.1 might have this spot at 5k where you blast right through it causing zero damage. We'll figure it out. Harmonic balancers are a must. It's the right one that is the guess, but maybe we'll be able to tell the difference. Thanks for all the great information. Greg Ira Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.