Landracing Forum
Tech Information => Technical Discussion => Topic started by: Jonny Hotnuts on February 04, 2009, 08:29:34 PM
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I have a shiny spot on one of my crank bearings. It is perfectly smooth to the touch.
There is no mark on the journal. Should I replace the bearing?
(http://photos-c.ak.fbcdn.net/photos-ak-snc1/v2235/69/50/1114496579/n1114496579_30321474_4208.jpg)
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It bugs me that it's on the top side. Jonny, refresh my memory, what engine are we looking at? No other problems with the rest of the mains?
You got it apart, so yes. It could simply be an out-of-round bearing insert.
But I'd also check the crank for straightness, and maybe polish the crank journal, but I'm real picky on this kind of thing.
How are your clearances?
Are we looking at the front or back of the engine? Front - check harmonic balancer. You running any accessories (alternator, oil pump)? If it's on the rear, check flywheel/clutch assembly for balance and make sure your pilot bushing is centered.
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Its a busa motor.
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It is on the top side, outboard bearing on the cam chain side. The rest of the bearings looked as if they were off the shelf including the bottom side bearing mate of this one.
Could excessive cam chain tension cause this?
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Put a new insert pair in there and check it next year about this time...
No Cam chain tension won't cause it. I vote for just a faulty bearing half if the crank looks good.
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Noonan, Yacoucci, where are you? on this one.
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Should I replace the bearing?
(http://photos-c.ak.fbcdn.net/photos-ak-snc1/v2235/69/50/1114496579/n1114496579_30321474_4208.jpg)
Jonny please.... you see damage to a critical part of a high performance engine! you ask if you should replace an $18 bearing shell?... do yourself a favor... don't cheep out!...
Kent
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When I started out I would seek the advice of one of the best general mechanics/welders in town when I was in doubt on something. Answers were usually "You'll never be any closer" and/or "Why is it you never have time to do it right the first time but always have time to do it a second time?". They have served me well and continue to hold true for my experiences after nearly 50 years.
Ed Purinton
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I know ZERO about bike engines , But,..Wouldn`t chain tension tend to draw the crank and cam towards one another? Seems like if it were tight the crank would move up/over. J.B.
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If you have gone to that much work to get that picture, then change the bearing. You aren't planning to take it back apart any time soon, so get it all done now.
There is no positive outcome to leaving it alone.
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Dean,
I love your quote: "There is not positive outcome to leaving it alone." I'm going to use it!!
Jonny, I agree with everyone, you are there, polish the crank, check for straightness and replace the bearings. If you don't you will worry about them until you have the engine apart next year, that is if it doesn't come apart by it's self! and you are viewing the crank thru the new "viewing port" in the case.
Rex
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Jnuts, although this was not a "we didn't replace a bearing" deal, it is a Busa gone bad... rod failure on one of the made way too big motors. They don't fail often but when they do....
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I can assure you all that I ask if this is OK to leave this bearing in the motor not because I want to save money. I could see something like cam chain tension causing the crank to touch the bearing when the motor was not running and could polish the bearing during start up, like shown in the pic, before oil pressure comes up. I could see this happening without causing damage and being completely normal and would look like this 10 minutes after starting for the first time.
With that being said I understand that this in fact may not be the cause and will change the bearing, but I would like to know if I should change the entire set if the rest look perfect or is changing the one OK. Again this is not because I am trying to save money its merely due to not knowing if by normal use the bearings change stock tolerances or will they remain the same as a stock bearing.
ALSO....
Will be using the good rods.
(those look like stock rods in the pics stainless!)
:wink:
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JHN, :-D
I know very little about this particular engine, but I have a pretty reliable working knowledge of bearings and scary things that rotate in them. :-o
The pic shows an odd wear pattern that is opposite an oil hole. My guess is that the bearing is loaded more there but the oil wedge must not be up to the task of supporting the crank like it should. :roll: Perhaps one should take a look at the oil pump and make sure that the clearances there are correct. 8-)
Bearings are built with pretty good control of the diameters and thickness, but there are normal variations that are just part of manufacturing tolerance. The only way to assure that a new bearing has correct clearance is to MEASURE the parts involved. :?
Since cost is not the issue, simply try and re-fit a fresh bearing into service. If the clearances all turn out correctly, you won't have any problems with it. 8-)
Best of Luck with the project. :wink:
Regards,
HB2 :-)
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That set was Carrillo, three good ones left.... The next year we used Falicon, one of the soft plugs in the head popped that time, similar result, windowed the block in the middle. Look at your head and consider modifying it to screw in plugs.... water is a poor lube at 9000 RPM
We quit running 2 liter class...
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:-D NEVER replace only one insert bearing. Inserts come in sets for a reason...they are matched. If you replace only one insert and the remaining inserts have some time on them, then there will be a slightly closer fit and there is a real likelyhood that you could spin a bearing. Also, inserts have a "crush factor" so when installed and torqued properly, there is less possibility for the insert to spin in the journal. 8-)
Please, do yourself a favour and change all the inserts at the Same time and never re torque the same insert (even though the manufacturer may claim you can re torque the inserts up to three times). :wink:
Terry A. Hume :cheers:
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Another quick thought. Any marks on the back of the insert or the aluminum? Do they feel smooth?
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Hi Jonny....noticed the pic of the bearing. I've seen this kind of thing on cam-chain and cam-belt type engines (in cars, at least). Usually fired up and revved/run hard before the oil pressure comes up. Always on the "front" end of the crank. If you bought a used engine/bike...well, now you probably know a little bit of its history. Part of that condition can be promoted by oil choice (too thick....some cool guy using RACING stuff for the street) which makes the film build late on a cold engine that is treated badly.
This may mean the crank and block will prove to be straight, when you check it out. Regarding "front main bearing" clearance; in Toyota-world, we often "select fit" one step tight on that bearing, to prevent crank thump when the modern "fuel efficiency" oil is fully heated, and the engine idles for long periods. By the way, I don't mean "one step, as in .010"....it's more like .0005" difference. In those cases, all bearings are replaced, but the front is selected "one step tighter". We've been doing this since the early '90s and I've seen Lexus V6 run 300,000 miles with this fitting.
I don't know if the Hayabusa experiences that condition; I usually see it on "sequential throw" cranks, as opposed to "opposed throw" cranks (boy, that's a butchered up sentence!) Anyway...my bet's on a mean former owner.
In the decades I was a line tech, I had a good friend worked next to me for many years. He always said, "These cars want to run, people just won't let 'em!"
Regards, JimL
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As noted by JimL, I have seen this bearing condition several times back in the "old days" on
Tri. and BSA triple (3 Cyl.) engines due (as noted by Jim) to reving the engine up before proper oil pressure was achieved. The trick was to kick the engine over about a halve dozen times (yes, that was in the days of kick-starters) with the ign. off
to get oil into the system.
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I thought you had to kick them over a half dozen times (or more) just to start them! Well, at least in the 60's
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First you had to tickle the carb float bowls and get gas all over your hands, then you start kicking ... Joe