Box Stock

Сonnecting rod bearing damage.

oneman said:
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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You could've used the wrong crankshaft size and there was play in it, you dont want play in the crankshaft and piston rod, happened to me before, luckily we caught it when rebuilding the engine not on the track, predator 212cc parts aren't completely compatible with 196cc clones there are some different measurements for crankshafts, for piston heads, and for piston rods because of the difference in bore and stroke (x number of cylinders too) which gets you displacement in cc or cid, get specific stock or aftermarket parts for that engine, so if its a box stock project 196cc engine, only get oem BSP parts or aftermarket ARC bsp parts for it, sane with predator 212cc, you only want oem parts or aftermarket ARC parts, no interchanging
 
Shorttrackthing said:
You could've used the wrong crankshaft size and there was play in it, you dont want play in the crankshaft and piston rod, happened to me before, luckily we caught it when rebuilding the engine not on the track, predator 212cc parts aren't completely compatible with 196cc clones there are some different measurements for crankshafts, for piston heads, and for piston rods because of the difference in bore and stroke (x number of cylinders too) which gets you displacement in cc or cid, get specific stock or aftermarket parts for that engine, so if its a box stock project 196cc engine, only get oem BSP parts or aftermarket ARC bsp parts for it, sane with predator 212cc, you only want oem parts or aftermarket ARC parts, no interchanging
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We use clone crankshaft and 6270 ARC Rod for Honda. Before installation, be sure to measure the crankshaft journals
 
For a pokey motor seeing 8500rpm you need to be on a minimum of 10W40 oil viscosity, then let the engine idle for an absolute minimum of 10 minutes before leaning on it on track or dyno....the 2nd number is more important than the first one as this us the viscosity when over 80DegC or so, you need 40 weight oil, I have seen loads of ARC rod bearings fail on just 30 weight oil, its too thin, if your in a hot climate don't be afraid to use 10W50.

If your crank was more than 0.0012 out of roundness (half a thou) replace it, and polish the new one to a shine to start with.
 
Just a normal old school machinist here, but I've seen this type of damage before. It was not in an engine, but a prototype pump. The idea was using a cam driven off an electric motor to force a 5 inch diaphragm into a pressured system. Everything worked except we had excessive wear like in the pictures. It was caused from a massive amount of pressure on the cam lobe, and the metal would slightly compress and decompress. Over time the surface material became hard and brittle until it cratered. Since the motor was electric it completely destroyed the cam lobe over time. The entire system was submerged in oil. We hardened the cam and it seem to last a quite a bit longer, but we still had trouble with the cam lobe cratering, but smaller pits.

If you notice in your pictures the majority of the craters are on the rod side of the bearing, to me this indicates the pressure from the combustion is causing the same compression and decompression in that bearing, resulting in the damage. As some have stated before me it could be a timing issue, or the tolerances. I'm not a motor builder so I cant say exactly what to change to fix it.
 
oneman said:
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
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Is that an oil hole on the journal? If so, how is the oil being supplied? Maybe the hole should have been chamfered
 
271mac said:
Is that an oil hole on the journal? If so, how is the oil being supplied? Maybe the hole should have been chamfered
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The big through hole in the crank is just a void . No forced lubrication . Drip or splash .
Although the dipper has a pathway for oil to be forced up and in .
Drip threw the top hole in the rod .
 
We decided to install a new crankshaft and new connecting rod bearings. We will also slightly reduce the compression ratio, and we will check.
 
10W30 is too thin......I have seen loads of ARC rod bearing failures with 30 weight oil, just like your delamination issue, you should be using 10W40 fully synthetic and no thinner, use a reputable brand like Petronas, Lucas, Amsoil etc.
 
knighty said:
10W30 is too thin......I have seen loads of ARC rod bearing failures with 30 weight oil, just like your delamination issue, you should be using 10W40 fully synthetic and no thinner, use a reputable brand like Petronas, Lucas, Amsoil etc.
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Not true at all... we race all day on Gibbs KRT oil that is 20WT or thinner with absolutely NO engine failures on clones turning 7000rpm every lap.
 
1fasttiller said:
Not true at all... we race all day on Gibbs KRT oil that is 20WT or thinner with absolutely NO engine failures on clones turning 7000rpm every lap.
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We have run plain old 5W20 synthetic in all of our modified gas motors with zero oil problems. 7500-8000 rpm.
 
5w20 synthetic in all my plate clone engines.. they all look just fine at seasons end. Keep a good air filter on it and the dirt out and the oil changed after every race day and it’s good to go!
 
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