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v twin crank pin damage

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v twin crank pin damage

Postby motionper » Sat Sep 21, 2013 11:33 am

help any ideas, turbo 45 degree v twin 4.375 bore-5 inch stroke 20 lbs boost methanol fuel 11.5 static compression. wipes crank pin out on the BOTTOM of the pin 300-400 feet out-have tried less boost goes a little farther out before seizing. why is the problem on the bottom of the pin????? all i can think of is the setup is beyond the mechanical limit of the roller lower end??
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Re: v twin crank pin damage

Postby lorax » Sat Sep 21, 2013 11:50 am

caged bearings or is it individual pin full compliment bearing?
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Re: v twin crank pin damage

Postby motionper » Sat Sep 21, 2013 1:58 pm

have tried both clearance tried .001 -.002-.003
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Re: v twin crank pin damage

Postby lorax » Sat Sep 21, 2013 2:06 pm

Seen full compliment setups wear the opposite side of the load over time, like a roller lifter. Never seen it in caged bearings.
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Re: v twin crank pin damage

Postby motionper » Sat Sep 21, 2013 3:48 pm

it flattens the rollers and puts a .200 deep groove in the pin at the bottom
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Re: v twin crank pin damage

Postby Schurkey » Sat Sep 21, 2013 6:25 pm

Too much pull on the rod during overlap???
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Re: v twin crank pin damage

Postby motionper » Sat Sep 21, 2013 7:02 pm

you just went over my head what causes to much rod pull on overlap?????
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Re: v twin crank pin damage

Postby Keith Morganstein » Sat Sep 21, 2013 7:38 pm

motionper wrote:help any ideas, turbo 45 degree v twin 4.375 bore-5 inch stroke 20 lbs boost methanol fuel 11.5 static compression. wipes crank pin out on the BOTTOM of the pin 300-400 feet out-have tried less boost goes a little farther out before seizing. why is the problem on the bottom of the pin????? all i can think of is the setup is beyond the mechanical limit of the roller lower end??


Fuel lubricated? how is the oil introduced?

How is the inlet controlled ? piston, rotary, reed?
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Re: v twin crank pin damage

Postby motionper » Sat Sep 21, 2013 7:41 pm

i run upper end lube in the methanol, fuel thru intake valves camshaft controlled, belt drive oil pump i have tried oil pressure from 10 lbs to 45 lbs
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Re: v twin crank pin damage

Postby Schurkey » Sat Sep 21, 2013 7:51 pm

motionper wrote:you just went over my head what causes to much rod pull on overlap?????

Connecting rod is in tension, rather than compression, as the piston is decelerated at the top of the exhaust stroke, then pulled downward for the intake stroke. Puts the load on the bottom of the rod journal. The effect is greater on overlap because there's no compression above the piston to help slow it; in fact there's considerable "vacuum" due to exhaust scavenging in some engines.

Short story is that piston wants to hit cylinder head, rod and crank pin prevent that. Loads under-side of crank pin. Heavy piston/rod makes this worse, but RPM makes it MUCH worse. Double the weight, double the stress. Double the RPM, stress increases 4x. A minor reduction in RPM could make a significant difference in stress.



My understanding is that roller bearings don't need squat for oil pressure, but they need a huge amount of oil volume. Perhaps I'm wrong.
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Re: v twin crank pin damage

Postby Cedarmachine » Sat Sep 21, 2013 8:46 pm

In the later HDs I see the cranks and bearings set up tighter and tighter from the factory. They won't even slide sis to side because they are so tight.

I would try getting the crank pin DLC coated and set up the clearance to a "plug fit" or literally zero clearance. It's nothing new to preload or run zero clearance on a roller bearing. Look at every carrier bearing on rear differentials.

I think having actual contact of do the sides of the roller itself will perpetuate it to roll rather than "slide" across the pin and race.
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Re: v twin crank pin damage

Postby lorax » Sat Sep 21, 2013 10:21 pm

Cedarmachine wrote:In the later HDs I see the cranks and bearings set up tighter and tighter from the factory. They won't even slide sis to side because they are so tight.

I would try getting the crank pin DLC coated and set up the clearance to a "plug fit" or literally zero clearance. It's nothing new to preload or run zero clearance on a roller bearing. Look at every carrier bearing on rear differentials.

I think having actual contact of do the sides of the roller itself will perpetuate it to roll rather than "slide" across the pin and race.

Having tighter clearances can be a benefit.
I have had 2 sets of Jesel lifters that were run for very extended periods and both sets in time developed grooves from the needles on the TOP of the axle. There should never be any load on the top of the lifter axle, yet that's where the wear always occurred. My belief is that the full compliment bearings are being stacked to the top by the axles force on the the needles trying to drive itself between them, and they "bunch up" on the top of the axle. The adjoining surfaces between any 2 needles is traveling in opposite directions and as the force driving them into each other gets higher and higher, the friction can get high enough to stop them.

With the forces of a highly boosted, high HP deal, the same thing can happen on the bottom of the rod pin. A caged arrangement can help, but the caged arrangement has considerable lower load capabilities.
When Suzuki first came out with the GS sports bikes in the early 80s, the 750 had needle rod pins, but the 1100 had plain bearing rods because the needles could take the load at that size.

The idea that needles bearings need lots of lube volume but low pressure is not all the true. Look at 2 strokes. 10,000 RPM is common, and 100 to 1 fuel to oil ratios. And they live for thousands of miles. But there is a load limit based on their size. Its the buga boo in rollers lifters with high spring pressures. Pressurizing them is a band aid at best. Trying to "pressurize" a needle bearing is a joke.
My guess is the OP has exceeded the load capabilities of the bearing size. Also, pin flex could be playing a part in the failures as well. But that gets back to SIZE again.
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Re: v twin crank pin damage

Postby Cedarmachine » Sat Sep 21, 2013 10:36 pm

With roller lifters, they say "pressure fed". I don't see them advertised as "pressurized". It just means that it's force-fed oil from a pressure scource instead of relying on splash....

I like the idea of needle contact on the host bore and the axle all the time regardless if they are caged or not.
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Re: v twin crank pin damage

Postby lorax » Sat Sep 21, 2013 11:15 pm

Cedarmachine wrote:With roller lifters, they say "pressure fed". I don't see them advertised as "pressurized". It just means that it's force-fed oil from a pressure scource instead of relying on splash....

I like the idea of needle contact on the host bore and the axle all the time regardless if they are caged or not.

Yes they are "pressure fed". The point I was trying to make is that many think of it as pressurized, as if there is a hydro dynamic wedge taking place.

I agree, tighter clearances do seem to be beneficial. You cannot possibly create a wedge, so there is no point in clearance beyond a thumb press fit. In high HP high RPM 2 strokes I would set the bearings in both ends pretty snug.
But like everything else, there is a limit to the load any given needle bearing can handle.
Along with pin strength/flex, there is also the fact that the rod bore could be distorting from the load. Plain bearings cannot only handle this better than needled bearings, but can be designed to take this into account with a delta wall.
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Re: v twin crank pin damage

Postby Dan Timberlake » Sun Sep 22, 2013 5:51 am

the Hertzian stresses when curved surfaces are forced together (as in rolling element bearings or gear teeth) are highest just below the surface. I think This spells trouble for any plating or coating applied to a hard working roller bearing or gear, since the bond strength of the coating to the substrate will be severely tested, and is likely not more than a few thousand psi.
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