So, what are you guys welding when you weld the crank?

 

The pin for the big end of the rod.

 

Ahight. [img]i/expressions/face-icon-small-smile.gif[/img]

 

These are just like Harleys. Multi piece cranks have to be trued correctly, as well as the reciprocating mass balanced. Dynamic balancing is best, but more expensive. I dont know what effect the counterbalancer has on formulas on a Raptor, but if you add weight with a new rod, you have to add weight to the throws on the crank. As was stated before, the weight has no appreciable effect on horse power, but enough weight can add or subtract crankshaft inertia, commonly called flywheel affect. Weight should not be confused for strength however. I could cast you a cast iron rod that weighs 5 pounds but it would not be strong.

 

Did trinity "true" your crank ?? My 686 was a "turnkey" job, I dropped it off ,they did everything 100% and I picked it up from them , it always had a vibration issue after they worked on it,I do not recall them saying they "true" the crank to account for the piston and carrillo rod. I called Harry but he never heard of such a vibration issue either,either the crank need to be trued better or it was improperly put back together at trinity. It ran good ,just vibrated like crazy. I have since spent more $$$ to fix it (vibration) but now I just bought a 03 and going to to pipe,jet it for right now.

 

My final answer to the rod. If it broke install a carrillo and balance the whole thing. Noone seems to address what caused the failure. Was it a lack of oil?? Was the motor built from the ground up, meaning that it had been dissasembled?? There does not seem to be a pattern here. There are a lot of high HP machines running regular stock rods and some of the failures are stock bores with high comp pistons only. Extreme had a 11-1 and stage 1 cam. Are people just slapping the stock bore pistons in?? Not checking if they need to bore or hone a little bit?? Maybe the bore is to tight?? Is every one file fitting the rings?? I think there is a coomon reason for rod failures and it has not be established yet.

 

This is what I'm going to do, If it works or doesn't I will be the guiena pig. I'm going to have my parts Cryo'd. Don't know if it will help but what the hell, its cheap. I'm going to make sure the cylinder, rings, piston are perfect. Then run it. And not worry about it.

 

I think that is an interesting theory 14mins. I could see how things could be too tight around the piston and cause a rod failure. But if it were too tight, wouldn't the motor seize up after getting warmed up or hot or take a significant hit in HP?

 

ba01raptoraz, yes.

 

I also have noticed that it seems stock bore high comp. combos have had more rod failures than others. What 14mins said crossed my mind also. Different types of pistons need different clearances.Forged piston generally call for more clearance (JE) and cast usually less (STOCK). But a tight piston will usually give you some signs of a problem like hard or won't start hot.Bad harmonics is a long shot, but some things just don't go together well.