when to weld a crank?

liquid cooled T.I.G. tip

heat shield the bearings when you get near them.

direct the heat straight into the flywheel material.

the type rod is debatable because there are more than 1 type that will work just fine.

What exactly is welding a crank?

Modern 4 stroke engines are high pressure lubed, the crank is one piece with the rods and their bearing shells split around the big end.
Two strokes and early four stroke racing engines have ball or roller bearing cranks that are low oil pressure fed or in the case of two strokes, rely on oil mist. So with this type of bearing, the rod is one piece with the big end bearing being pressed together with the crank pins and the counterweight flywheels or porkchop shaped "cheeks" making up the crank assembly. An over reved and tire load up situation can twist this assembly askew. So you weld the crank pins to the counterweights in effect making the assembly more of a one piece unit that will hold together better in a high stress situation.
'Hope I didn't miss anything.
Stephen

So basically the connecting rod "caps" are pressed onto the crankshaft. And when its welded you are making the cap and Connecting-Rod one then?


If thats the case thats no problem for me. I have access to TIG machines. Would it need to be balanced afterwords? Due to the excess/imbalance of filler material applied to each weld?

I was thinking that the crank would need to be indexed and balanced first to make sure it's in true before welding. I don't know that saving two three hundred dollars is all that big of a deal. I would have falicon do the crank.
I don't think my welding skills are all that honed from doing cranks all the time that I would even try to do it myself. The machinery to do all that stuff is not something I would just have laying around and in the grand scheme of things you get what you pay for. It's just that sometimes you pay a little more than planned but still done right and out of mind is good to feel when you beat the snot out of your bike and know that nothing is going to break.
You're a teacher. You know the value of an educated person doing something right versus someone with no experience or little experience doing something the first time. I would leave that stuff to those who do the kz cranks all the time not just people who weld cranks for other bikes or cars and there are several guys that have worked for falicon that are on their own now. Have someone do it for you and get it done right. Or not and risk it. Either way.

Bullitt03737 wrote:

So basically the connecting rod "caps" are pressed onto the crankshaft. And when its welded you are making the cap and Connecting-Rod one then?

No, that's not what I'm saying.
The rods on plain bearing cranks are two piece, to bolt around the crankpin, which is one piece with the counterweights to make up the crankshaft.
The rods on a roller motor are one piece. The roller element bearing is pressed into it. The crankpin goes through that and the counterweights are pressed into the pin on both sides of the rod to support the pin. This is what's welded, each end of the pin to it's counterweight.
I agree, leave the indexing and welding to the pros.

ahhh. i see. Thanks for clarifying that. Yea something that spins that fast needs to be handled by a pro.

a long blank for a drill is all thats needed to check the crank for straightness before welding,nohing too complicated for a streetbike or mild dragbike motor.falicon did the crank for my 1385 with a nice purdy set of knife rods only because i dont want something exploding between my knees like grenade when i get goofy and throw it on a dyno with way too much boost and some juice running through it !:laugh: around $75 around these parts for a basic check for straightness and weld job around here.

Crank welding ain't exactly a science. Indexing a crank definintely ain't science. Straitening a crank IS science. Balancing is science. Don't know how many of you remember Shannon Clem, Old School Racing who used to be on this board fairly frequently. Anyway, when he would drag race his old KZ, he would take PILES of welded crank shafts to sell. He was living down in Houston at the time but has moved up to Indiana. You might want to contract him at:
www.old-school-racing.com/KZZ1Parts.htm

Ask him if he has a straight 903 crank that has been welded. I suspect it would be a better deal than sending a crank to Falicon. He is still selling parts as I saw him year before last at Mid-Ohio with his crew selling out of his race trailer.

To "index" a crank, you buy a 17mm drill blank and stick it through the holes the piston pins fit into. Put some grease on it as it fits snug. If you can't get the drill blank through one of the holes, the crank is BENT. If you get it through all four, the crank has done been indexed. I can't recall where you get the drill blanks but McMaster-Carr would be a good bet. If you have a bent crank, it would be cheaper to pick another up off eBay and toss the old one than to get the old one trued and then welded. If your old crank is bent you will want to weld the new one before even thinking about resuming your ways.

How can you be assured of the longevety of the welded eBay crank? My experience lie with plain bearing cranks where you Plastigauge them and do whats needed with grinding, oversize bearing shells, etc.
How well and how long do these rollercranks hold up? I've been using Mobil One synthetic on the GPZ since new and with 30 thousand miles, an oil/filter change every 2 thousand miles or once a year.
I know that on my '81 Ducati beveldrive, which have never had the reputation of being bulletproof like the roller Z's, you had to change the oil and non full flow filter every thousand miles. Also, you had to be picky about what type and brand of oil that you used. If everything was taken care of properly, then you were lucky to get 50/75 thousand miles before the big end needed attention.
Stephen

Schnitz racing sells the rod you are talking about. On the cheap, I have seen a few guys using PVC pipe. There must be a size that works as I've seen this used a few times....and this wasn't a backyard deal....this was a shop, so check that out and let us know if it works. If that rod doesn't fit through all the rod ends, it means that the crank is out of index. How much is acceptable is beyond me, but it doesn't mean crank is bad. They take them apart and put them back together so the rods are indexed and then weld them. Most Z1 cranks are good or close. Seems the newer you get, the better chance the crank is out of index and needs worked on. They raced these cranks for years without indexing them so unless it is way off, for a daily driver, it probably wouldn't hurt anything. Wouldn't be the best, but it should work. I would bet that most of the cranks you would find in streetbikes and even lots of dragbikes are slightly out of index as it costs to have a crank tore apart and put back together right and most guys probably aren't doing it. Lots of places can weld a crank but only a few can index them, so like Plummen says, unless you are going to really abuse this bike, it should be fine. Check it and if it's not too far off, weld it and go.

saxjonz wrote:
.
You're a teacher. You know the value of an educated person doing something right versus someone with no experience or little experience doing something the first time. I would leave that stuff to those who do the kz cranks all the time not just people who weld cranks for other bikes or cars and there are several guys that have worked for falicon that are on their own now. Have someone do it for you and get it done right. Or not and risk it. Either way.[/quote]

I guess the point is, to do it myself. If i don't dive in i'll never get the experience. I took some 34mm ninja carbs that i had and respaced them. A lot of people were like why go through the hassle buy some 34's off a police bike etc. well i did it anyway because i just wanted to be able to do it myself.

thanks i'm learning a lot from this board