Сonnecting rod bearing damage.

oneman

Member
Hi guys, I found a problem, on 2 different engine, we got severe bearing damage. And they are the same.
damage in the upper of the connecting rod, I think this is the most loaded place, but why did it start to crumble?

The engine were used by different people, with different components. But why did it come about?
 

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flattop1

Dawg 89
although oil type and viscosity is a concern . with the current oils , my opinion is that is not as much of a concern as it was say in 1970 .

Ignition timing over advanced with a high load .
contributing factor out of round with poor surface finish .
tight clearance and debris can not be ruled out .
 

oneman

Member
We are using Castrol racing 4T 10w30 we change the oil every 1.5-2 moto hours.
This is the wear that has occurred during a run of 6-7 motor hours.
Bearing clearance is acceptable, as indicated in the ARC connecting rod manual. I specifically measured it before installation.
Engine speed 8000-8500.
I have an ignition advance of 28-30, on one engine it is a key with an offset of up to 30. And on the second there is a PVL flywheel.
We use a standard 54mm clone crankshaft.
 

oneman

Member
29.965 -29.950mm

crankshaft journal size is normal, within acceptable limits no scratches or damage.
 

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oneman

Member
Thanks everyone for the comments, I appreciate that. And I will definitely check everything when I assemble a new engine.

I also wanted to ask, I noticed that some will enlarge the oil drain hole in the crankcase. Why is this done? so that at high revs the oil goes into the crankcase better, or for other purposes?

QHCXBLPiasc.jpg
 
Yes It helps oil drain back and allow the crank bearing to get oiled better.
If that is the crank the bearing came off of. It needs a lot work. or replaced.
 

oneman

Member
No, this photo is for example only. These engine have already been scrapped.
 

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R Bahnsen

Member
Hi guys, I found a problem, on 2 different engine, we got severe bearing damage. And they are the same.
damage in the upper of the connecting rod, I think this is the most loaded place, but why did it start to crumble?

The engine were used by different people, with different components. But why did it come about?
What piston to cylinder head clearance do you have? Anything less than .025 @ 8500 RPM can cause bearing failure.
 

oneman

Member
How many OZ of oil are you using? What type of racing are you doing? how long are you at max RPM? trying to help, just need more info.
My engine config: 70mm piston, 54mm crank, 18cc head, 27.5mm inlet 25.5 outlet valve. The camshaft is standard but its base is reduced to increase the lift, now the lift is + 1mm (0.270) to the standard camshaft. Springs 36lb, HD champions rockers. ARC connecting rod, flywheel aluminum PVL. PZ30 carb. And it is used in karting.

We use non-race grade conventional oils. These are mainly Mobil1 Castrol Shell 5w30, 10w30, racing oils in Russia are expensive for us.
24-25 OZ

Our race lasts one hour, during this period we periodically reach the maximum speed.

I have pinned data from telemetry. Here is a lap from our track, lap times 1:12 - 1:16 on average.
 

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