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Rb30 big end bearings pics inside

General Engine Building Discussion

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Hi guys i found a problem i need help diagnosing . I changed the oil and cut open the oil filter (with proper tool) and found what seemed to be bearing material. I have been keeping a eye on oil as it had been a metallic since it went in the car doing oil changes roughly every 2-300ks. Seemed to be getting worse So out the motor came again pulled the sump off nothing in the sump. Pulled the big end caps and found cylinder number 6 rod side bearing had some pitting. From what i can see the journal is still fine. Does it look like detanation could cause this damage. Moter only has 2500ks on it since full build cheers

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G'day Jesse. Any history on the motor before it was built? How did it fail previously? That bearing doesn't look happy though, something has been in there making a mess :-(.

Any bearing clearance measurements from when you built it available?

I had a shop down in Melbourne build the motor so they got the core to build. as for clearance i am unsure he seemed hesitant to let me know the clearance. He said to put acl/h bearings back in it. Just not sure if it is a clearance issue causing this

Ok so a couple of things to add to this. First of all when you're running in a fresh engine, you're likely to see a metallic shimmer to the oil during the first 200-500 km of use. This is a result of normal wear as the hone pattern on the bores and the rings bed against each other. What you're looking for in the oil filter is chunks of copper coloured material - What you've got in that filter looks like aluminium to me (which in itself is still a little worrying).

the damage you've got to the bearings is a little unusual. There is some minor wear showing in the form of light marks in the direction of rotation, but nothing that indicates metal to metal contact as this will quickly wipe through the surface layer of the bearing and show up as a polished copper colour. If I had to guess right now, I'd say that those marks on the bearing were potentially made prior to installation. I simply can't explain them with the lack of other obvious damage to the shell. If the clearance was too tight, you'd have much more damage visible to the bearing so I'd say with the evidence available, that the clearance is probably not the culprit. Detonation can damage the bearing but this is generally going to push the bearing shell through the oil film and cause metal to metal contact which almost immediately wipes the bearing surface, removing the thing surface layer and revealing the copper layer below, which isn't the case here.

I have never had any detanation on this cly. Well the plug never showed any signs anyway. i do know we had detanation on number 1 cyl when i last raced the car to point it nipped the tip from plug 1. But cly 1 has no sign on the bearing of it. So i cant really see it being detanation but i could be wrong. nothing looks like it has gotten hot either and i would thing if it was lack of lubrication it would be much worse? Could it be a faulty bearing maybe?. If u see attached photo tbis is cyl 5 bearing there is a funny spot on it. You can not feel it with your nail

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Here's a useful pdf that covers the common bearing issues you're likely to see. I find this quite useful for analysing a failure or problem.

The damage you're seeing is probably closest to Mahle's description of surface fatigue, however it's hard to be 100% with the photos you've taken. Personally I'd be very surprised if you were seeing a fatigue related issue in the time frame you've mentioned unless you're making some absurd power levels. Even then, with good quality oil, fatigue related failures are very rare.

Thank you for your help. Was using penrite hpr40 oil and motor would be in the 8-850hp reign at 32psi of boost and turn it to 8200rpm i will look in to the link you have sent me

What sort of oil clearance would u be sitting on big end and mains on a motor like this. Just used a abit of plasti gauge on the mains(deciding on a bore gauge still)and with the old bearings in the mains it came back at 0.0015" and the bearings look a little worse for wear thinking they sound a little tight. Number 1 journal especially to look at

It has manley h beam rods mahle pistons and standard crank. still have not pulled the crank out to look at the upper main shells

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At that power level I'd be personally aim for 0.002" on the big ends and 0.002-0.0025" on the mains. A couple of your pics show some polishing on the side of the bearings that is normally indicative of the crank flexing. A slightly looser clearance along with a better quality oil goes a long way to preventing this - Of course it does speak to the rigidity of the crank and block too.

Hi andre i did work out that the rods that were in the motor were poor quality rods and the caps had been pulled the big ends were out of round anywhere from 0.0004 to 0.0007.

I have since brought a new set of rods and i have been having a little look around at what ppl set the oil clearance to in the little end for a floting pin. I did bore gaige the old small ends but they have also been pulled all over the place unfortunately

It seems like not many ppl give the small end much thought. What would u normally aim for on something like mine? (see above)

I also.noticed that there is a slight bit of wear on cyl1 pin boss i bore gauged the piston boss and it has 0.0011 clearance on both side's the pin doesn't seem to be bent at all. They are mahle pistons that use a 21mm pin that is 5mm thick. I can not feel the wear at all with my finger tips or nail

Also the side clearance on the big ends with the old rods was set at 0.010 the new rods are 0.0028 thicker at the big end would u have the new rods set to 0.010 side clearance as per the old rods? I will be setting the thrust at 0.006 if that matters.

Look forward to your response cheers

i have photos of piston but it will not let me post

The reason there isn't much information about wrist pin clearances is because we can't really do much to influence it other than have the machinist re bush the rod and hone to achieve the correct clearance if required. I'd check with the rod manufacturer as they will be able to provide a recommendation, however for a 21 mm wrist pin you're likely to find the clearance somewhere in the range of perhaps 0.001"-0.0016" so you're likely just fine.

If you have insufficient side clearance on the rods then you can have the machinist remove material from the side face of the rods to achieve your desired clearance. This understandably may impact the balance of the rods.

Sorry i should have been more clear the pin to piston oild clearance is 0.0011 but the pin to small end oil clearance is only 0.0006. As for balance i haven't done any balancing yet so that is fine

It's typical for the clearance to be slightly looser in the piston than in the rod. Generally aspects such as the wrist pin to rod or piston boss clearance can be checked by feel (ie inserting the wrist pin and moving back and forth). You tend to develop a surprisingly accurate feel for what is normal and what is too loose - This doesn't help when you're still building up experience of course!

All feels well i will get in touch with the rod manufacturer. what would u likely be aiming for with big end side clearance? The manual for the motor only shows max side clearance. They recommend 0.0157

The side clearance isn't as critical as the actual bearing clearance. I usually aim for at least 0.010"

Hi andre just at the point of setting side clearances on rods. With your experience do u think 0.010" Big end side clearance is to tight on on something like my engine? I cant seem to find much on side clearance on a motor that doesnt use 2 rods per journal. work shop manual says 0.0157" is the limit of the rod side clearance. Have u personally seen the affects on oil pressure with opening up just side clearances of the big ends by any chance?