Who is the best person to rebuild your engine? You...
type4newbie Posts: 70 Joined: Fri Nov 02, 2001 3:01 am
What can I do to help prevent my motor from spinning rod bearings from over revving the engine? I just built a 2276 w/ 5.5 Scat I-beam rods, welded stroker crank, 30mm high volume oil pump, web 86b cam, etc. I built the motor and got it running great then after about 45 min break in run time I decided to see how fast my buggy would go and it quickly spun a rod bearing and is knocking very bad now. I now need to tear it back down have the crank ground and probably new rods. How much better will it be if I use H-beam rods? How much higher can I rev the engine safely w/ h-beam rods? How much of a difference would it have made if I had allowed the engine a longer break in period before hot rodding it?
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If you love over revving new engines, I am afraid you are in for
Mugsy Posts: 1162 Joined: Thu Nov 29, 2001 3:01 am
I don't know how to answer your question, but I have a related question...should you use red loctite on the rod nuts? Jake Raby says he never has used loctite and hes never had any problems. THanks, Andy
I used red loctite. Can't hurt. But spinning a rod bearing 45 minutes after a rebuild, that hurts. An engine needs time to polish the wear surfaces. With brand new bearings and a ground crank, there is friction that is dying to spin those puppies. The roughest you should get on a new engine is a modest acceleration to seat the rings maybe 2-4,000 then coast down X 10, then let it cool. Take it easy for a couple of hundred miles, lots of variation in load and speed, but no banzai. Colin
I suspect that those new Scat I beams are the problem, as they need some work to "work" correctly out of the box. My 1914 is using Scat I beams, and a stock CCW crank. It was ran on the dyno within the first 40-60 miles of it's life. Next time, make double sure that the rods spin freely on the crank, this may require that the tang on the bearing be filed down or the slot for the tang on the rod made larger.
tips check and measure actual clearance between rod bearing and rod journals. make sure the journals are round, make sure when rod is torqued, the bearing is round. Oil pressure. do you have it? are you sure? did you clean out your crank oiling ports before you installed? clean out the oil galleys in the case? and the list goes on. open up and see what exactly happened. then make some sort of diagnosis.
MASSIVE TYPE IV Posts: 20132 Joined: Fri Jul 07, 2000 2:01 am
What journals are on the crank?? I have recently been plagued with bad rod bearings for the 2" chevy journals... Rod bearings are not all the same, their metal composition has everything to do with their strength. Some bearings are a Bi metal which is not made to rev high. I have seen these spin the first time they touch 5,000 RPM.... Right now I'm testing a very small 40mm bearing from an Asian car with special rods and crank to see how it likes high RPM. The bearings for this are a tri metal from the factory and take 8K revs stock. The small journal will let us use a smaller rod and also trim weight off the crankshaft... and entire rotating mass. Do you have pics of what your beaings looked like or the chunks that came off them??
TECH Fanatic Thread Starter Join Date: Nov 2007 Location: NJ Posts: 1,193 Likes: 0 Received 0 Likes on 0 Posts
What would make a Rod bearing spin ? what would make a main bearing spin? Looking for all reason but i ran low on oil.
TECH Senior Member Join Date: May 2004 Location: Back in the Burg Posts: 6,492 Likes: 0 Received 5 Likes on 4 Posts
Excess wear on the bearings can cause the rods to have play and beat themself every time it goes up and down. If the low oil caused things to heat up and cause a out of round situation which beat it self up too.
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Stretched main or rod bolts.
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clearance issues and vibration (not balanced) correctly. The bearing should not ever touch the crank journals, they should run on a film of oil.
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Think about the abuse rod bearings take compared to the mains. On every power stroke a single rod bearing absorbs the shock which is then shared by all the mains. Friction due to lack of lubrication causes heat resulting in expansion. The result is not good. Oil is cheap. A tear down is not.
Staging Lane Join Date: Sep 2008 Posts: 97 Likes: 0 Received 0 Likes on 0 Posts
High RPMs on a cold engine greatly increase your chances of spinning a bearing, because the engine has not warmed and therefore expanded to the proper clearances prior to being run at the limits of normal operation.
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well another problem is the factory design of the engine. if im not mistaken the oiling priority is cam first crank second which is why bearings get turned. stock cranks have one oiling point for each rotation and most aftermarket cranks have 2 oiling points per revolution. so a little is design but like these folks have said. engine temperature and oil condition is number 1 problem
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Originally Posted by 02 BLK WS6 Stretched main or rod bolts. DING DING DING! Over revving stretches the rod bolts that lets the bearing start to spin, once it starts your done, to answer your question. But as others have said, cold oil can do it ( oil dosent properly lubricate till is hot ) worn oil that has broken down can definately do it.Main cause, again, dufus's that think they can spin a bottom end to the moon, you cant. Look into "tensile load" its the load that is against the rod and bolts when it tries to yank the piston back down, at high rpm it can get really extreme, and its not only the weight, its changing the direction of travel of the piston effectively increases the weight, the vacuum the piston is pulling etc. will stretch a rod bolt and loose the "crush fit" so to speak of the rod cap on the bearing.
Staging Lane Join Date: Jan 2007 Posts: 82 Likes: 0 Received 0 Likes on 0 Posts
coolant in the oil and fuel in the oil can also cause it.
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Excessive boost pressure can "crush or squish" the bearing(s). I ran 150hp NX for 3 years with no problem on a stock bottom end. 200hp squished #6. King Alecular bearings claim 5 times the crush strength, (which I now use), in conjuntion with XPR Royal Purple, also claiming incredible crush strength, should give insurance from failure. I guess I'll find out the next time I take the motor apart. I'll try to find the bearing at my shop and put it on here for everyone to see what I mean about squish. There was only a knock, no rod or bolt failure. The rest of the answers above are also correct in regards to each individual situation.
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Originally Posted by 00pooterSS DING DING DING! Over revving stretches the rod bolts that lets the bearing start to spin, once it starts your done, to answer your question. The engine loses the "wedge" of oil between crank and bearing, and the two come into direct contact. The resulting heat welds the bearing shell to the crank, which then starts the bearing spinning inside its saddle.
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Originally Posted by crainholio Can you post any links to credible tech supporting this, or is it just a theory? The idea that "letting the bearing start to spin" causes spun bearing failures doesn't hold up. There has to be a great deal of force acting on the bearing to compel it to spin, which your theory doesn't account for. Every spun bearing we've seen at our shop traced back to oil film failure. Whether it's assembly error (bearing clearance insufficient) or oiling system failure (pump died or low oil level in pan or solvent contamination of the oil) or systemic pressure loss (bearing clearances opened up due to wear) the failure mode is the same. The engine loses the "wedge" of oil between crank and bearing, and the two come into direct contact. The resulting heat welds the bearing shell to the crank, which then starts the bearing spinning inside its saddle. Are you serious, ok put in a set of bearings a tad small for the rod end, they will get spun, thats what happens when the bolts stretch, there is tons of info out there on bolt stretch resulting in spun bearings and failure, have done it myself to an engine, sorry I dont have any research saved that I can post up, and im not gonna go search it out, its a well known fact, if you dont believe me contact an engine builder. Furthermore if you really dont think it is an issue why do you think people go and chage rod bolts ONLY, numerous threads on this very board about that, and the point of that is to prevent bolt stretch and bearing failure. My theory dosent account for the bearing starting to spin?.... If the bolts stretch, how tight do you think that bearing is in there at that point? You really think it takes "a great deal of force" to spin a bearing in a hole larger than its self? Bearings are crush fit to keep them from spinning, thats what you are reffering to, but if the bolts stretch the caps lift and where is your crush fit now?edit: this isnt a theory either, its researched info, and by the way how did you trace bearing failure back to oil film failure? That would mean metal to metal contact is what you found, that could be from multiple things, and egg shaping a rod end by stretching it will cause metal to metal contact also, when the cap gets loose and you start banging on the top and bottom of the bearing it can bring the sides inward and touch, then it spins then you are done. Again an experienced engine builder/racer should know this also. I didnt come up with this stuff, its stuff I have been told by builders, racer/fabricators of professional race shops and other old timers too, and have read about it too. Last edited by 00pooterSS; 10-20-2008 at 10:26 PM.
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Originally Posted by crainholio Can you post any links to credible tech supporting this, or is it just a theory? The idea that "letting the bearing start to spin" causes spun bearing failures doesn't hold up. There has to be a great deal of force acting on the bearing to compel it to spin, which your theory doesn't account for. Every spun bearing we've seen at our shop traced back to oil film failure. Whether it's assembly error (bearing clearance insufficient) or oiling system failure (pump died or low oil level in pan or solvent contamination of the oil) or systemic pressure loss (bearing clearances opened up due to wear) the failure mode is the same. The engine loses the "wedge" of oil between crank and bearing, and the two come into direct contact. The resulting heat welds the bearing shell to the crank, which then starts the bearing spinning inside its saddle. wait wait just noticed this part lol, what do you think happens when the bolts stretch from over rev? this is a much shorter summary of all the crap I was trying to type
FormerVendor Join Date: Nov 2001 Location: Houston, Tx. Posts: 3,065 Likes: 0 Received 2 Likes on 2 Posts
Insufficient rod bearing clearance and aerated oil at high rpm as well. Both let bearings touch or grab the crank and then all hell breaks loose!
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Originally Posted by racer7088 Insufficient rod bearing clearance and aerated oil at high rpm as well. Both let bearings touch or grab the crank and then all hell breaks loose! Thanks man, hadn't heard of the aerated oil but makes sense, I believe bolt stretch took out my last blown motor, not LSx motor, the bottom end was factory redline 6800, I was taking it to 8k daily since the factory redline in the ECU was 8K and the head was built to take it, and lastly because the bottom ends were a dime a dozen so **** it. lasted 2 years on short spurts to 8k, until I did a 5th gear pull racing a bike and took it to 8k in 5th ( top gear in that tranny )thats a long time above 6800, then I had razor thin bearings on 2 cylinders. It also seized I broke it loose coasting on the highway by letting out the clutch lol, got me home and to the shop the next day.then there were the bike motors, one spun bearings cause I got pissed off ( stupid ) and pounded on it with the motor cold, took out the bearings right away, next time was riding extended wheelies and lack of oil killed it, so yeah im good at killing bottom end bearings
TECH Addict Join Date: Aug 2003 Posts: 2,977 Likes: 0 Received 2 Likes on 2 Posts
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Originally Posted by 00pooterSS I didnt come up with this stuff, its stuff I have been told by builders, racer/fabricators of professional race shops and other old timers too, and have read about it too. I see now what I'm up against, and will avoid any further debate with you.
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Originally Posted by ajsfirehawk High RPMs on a cold engine greatly increase your chances of spinning a bearing, because the engine has not warmed and therefore expanded to the proper clearances prior to being run at the limits of normal operation. i learned that one the hard way.
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mine spun 2 shells after a track day when the oil was hot and i had been caning it. i had also upped my rev limit to 6500rpm from 6200rpm that day, coincidence or not. only mod to engine as such was arp rod bolts and a cam (220/220) with valvesprings and pushrods. oil pump was original but had relief spring mod done. car had already done 2 trackdays and about 200 miles on track but as i had used a 2nd hand ls1 it wasnt a major disaster.
TECH Addict Join Date: Aug 2003 Posts: 2,977 Likes: 0 Received 2 Likes on 2 Posts
Quote:
Originally Posted by chris-m mine spun 2 shells after a track day... ...only mod to engine as such was arp rod bolts... Those two facts are likely related, unless you measured clearances with the new bolts installed and torqued.
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Originally Posted by crainholio I see now what I'm up against, and will avoid any further debate with you. His "edit" was spot on. Darin Morgan, formerly of Reher Morrison, would hone the rod big ends out of round (larger at the parting line, similar to how a bearing is eccentic) to prevent the parting lines from pinching in at high inertia loads/RPM. This has been a well known trick among the stock/comp eliminator crowds for decades.
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Moderator
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Originally Posted by crainholio Those two facts are likely related, unless you measured clearances with the new bolts installed and torqued. I agree that these two may be related, not just with clearances, but bearing crush as well. I have seen stock rods with ARP's installed as much a .0007" over the high out of round. Thats a lot.
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Originally Posted by KCS His "edit" was spot on. Darin Morgan, formerly of Reher Morrison, would hone the rod big ends out of round (larger at the parting line, similar to how a bearing is eccentic) to prevent the parting lines from pinching in at high inertia loads/RPM. This has been a well known trick among the stock/comp eliminator crowds for decades. Thanks and thanks for the info I did not know that, just fortunate to have worked/associated with some highly intelligent "car" people and learned alot.
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hey i got a question what the heck is that squeaking noise they make whenever the bearings spin ahhhh what a horrible racket wtf is that squeaking all about
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Metal on metal. So...what size stroker are you going with?
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The sounds engines make when they fail are very subjective. Groan, moan, squeal, squeak, scream, knock,etc. The list never ends. None of them are good, but once a bearing spins it doesn't make a whole lot of difference what sound it is making. You still have work to do.
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Has anyone ever put locktite on back of bearing?😭
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Originally Posted by David- bee Has anyone ever put locktite on back of bearing?😭 No....
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Originally Posted by David- bee Has anyone ever put locktite on back of bearing?😭 That would be dumb.
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Originally Posted by David- bee Has anyone ever put locktite on back of bearing?😭 Rectal cranial inversion....
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How to prevent spun rod bearing
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