Crank welding really necessary?

[RNBRAD]

I've yet to get some tangible evidence for welding cranks and quite the contrary. I try to do a reasonable amount of research to the extent of what's at my disposal. Maybe some members can enlighten me either way but would like some kind of measure or a educated opinion.

 

What I have found comes from the history of sponsored Rd350's and TZ350 race bike teams. These bikes run anywhere from 75 to 90 bhp and when specifically talking about these bikes cranks they do not recommend welding them . Truing is a different story. These bike engines I thought may be a good place to look for answers on this debated topic since they experience rpm and horsepower extremes.

 

From what I have found that applying heat to the crank throws it out of balance which decreases performance and longevity. I have also had company's that do this modification not recommend it stating that when your crank is going to seperate that a weld is not going to stop it. I know you have to take in a lot of variables because I'm sure not all trued and welded cranks are equal. Also these race bike engines and riding conditions may not exactly match that of what a Banshee owners machine may experience and a Banshee crank may be far inferior to those of these race bikes (I'm unsure). It could be just a quality control issue of crank balance from the factory or poor owner maintenance practice and this may have been thought as a quick fix without any real world controlled comparison testing. Either way I'm open to input. Heres some links about the rd350 and tz350's as well as others.

http://www.stannakajak.com/skalmanmc/rd350/mech/crank/

http://www.tz350.net/tztips.htm

[mat]

Interesting information. Hopefully the pro-engine builders that occasionally visit this site will see this post and respond.

[SDD]

I have discussed this with a few builders. A few of them say it's not needed on a race machine. The key word is race machine since they typically get torn down and checked after each race or race weekend. They use custom made cranks with much better quality parts and are trued to closer specs than what the factory slaps together. The race pilot also knows how to ride better than most of us and they don't make mistakes like pinning the throttle while landing a jump. Even if they did that crank wouldn't be used for the length of time that us recreational riders do. The best things you can do for your crank is feed it good premix and fresh clean gas. Keep the air filter clean and make sure your jetting is a little richer than spot on. Use a fuel filter to keep other crap out of the fuel. If your really picky you can replace the outer crank bearings and when ever you do a topend never reuse wrist pin bearings. The more engine work you do the more often you have to replace parts.

[Quick350]

Ok, here is the long and the short of this deal. The engines that you are reffering to are used in road race conditions. These engines make gradual acceleration and deceleration changes. Most banshees that are build for drag race applications are outfitted with big paddles and on asphalt tires. They are starting from a dead stop with machines that weigh 150 lbs more than the bikes. Well that ole 8lb flywheel can play hell on the left side of the engine when the clutch is dumped at 10000rpm. I have tested this in a sand drag application and a 75 hp engine on gas will separated a stock crank in less that 20 one hundred yard passes. Sure some are lucky, and others only think they are 75 hp or more. I have dont this more than 5 times in a row and now I weld and true every single one. I actually broke a 10mil in half on the asphalt a week ago on the starting line. So my advise is to send it to Phil at crankworks and have him true it up. Its cheap insurance.

[Nightrider]

I agree with quick350,Atv engines see far more abuse than any road race engine.Dumping the clutch at 6-7,000 rpm will wreak havoc on a crankshaft.As Quick stated road engines make very linear and gradual acceleration/deceleration changes.When you dump the clutch at 7,000+rpm,the engine is forced to combine with the speed of the drivetrain(0 mph) before it initiates forward movement.That force has to be transferred somewhere.The only place it can give is the clutch or tires.If both of them fail to slip/spin,that force is directly applied to the crank halves.

 

He also pointed out that the bike weighs alot less than a banshee,therefore it lessens the amount of force the engine needs to get the wheels in motion.

 

Remember the Banshee's engine was not originally designed for a quad bike.

[Oilsmoke]

Asset.

 

Personally I would Not run a 2,000.00+ engine with a nonwelded crank.

If you are only ported & piped and don't thrash your Shee like a hill shootin drag racing craised speed demon than you could go for a few years on a new crank. But who ride the shee like that?

Welded & trueing are Cheap, Don't hurt your motor, Stop the small amount of movement that can cause a crank to fail then blow up your motor.

 

Cases, topend parts cost alot why risk it?

Edited October 30, 2004 by Oilsmoke

[boonman]

Welding the crank WILL NOT throw it out of balance, unless you use filler material. WHich there should not be any filler material used. Welding the crank is necessary for longevity. I have seen cranks seperate. It is a fact, that it DOES happen. Not somehting that may happen. My crank is welded, and it hasn't seperated...... Think of this, would you drive your car if your wheels were "pressed" onto the hubs? Or would you want lug nuts holding the tire/wheel in place? Same thing with a crank. Merely using a press fit to hold the crank trued, and in proper spec, just isn't enough. The welding on the crank pins, holds the crank in tolerance......

[Leadfoot350]

I had my crank welded and the weld broke! Lucky we saw it and rewelded it. This time there is a nice weld 3\4 around the pin. The guy asked if I was revving the hell out of it and I told him I was just trying to keep up.

[Nightrider]

The guy asked if I was revving the hell out of it and I told him I was just trying to keep up.

 

 

ROTFLMFAO

 

 

That was a good one.

[sweetshee4312]

the 2 kids i know with banshhes all had there cranks go....so i got mine done for what 50 bucks...i would get it done

[joshv5.0]

got mine done. anything that keeps me from having to tear the damn thing down again soon is a good investment to me