How to be sure about a crank ?!

If your crank has been welded, and it is working well, then leave it be. If your partially welded crank has a problem, then sometimes it can survive being cut apart and re-built, or at least that was what I was told buy one shop that specializes in building cranks.

I doubt very much that a KZ crank that has been fully welded is re-buildable, though. Best to start over fresh.....

It is a 750 Z2 crank. It was checked and welded by V/H in 87. It had low miles in 98 when the bike was parked. I didn't know about the shorter stroke back then. The bike ran great and still does but I learned and proved it is in fact a Z2 58mm stroke crank thus detuning the engine. My 903 crank was destroyed in a fire that took my shop in 10. I have my eye on a 903 and would like to change it out and sell the 750 crank on eBay. It was only tack welded and it looks like the welds could be ground off so it could be rebuilt. It could provide enough to do all the things I'd like to do like a 1075 kit, etc.
Without having to go through all of it again, here's my thread on it. I was called a "poser" by one of our members.
Steve
kzrider.com/forum/2-engine/597654-poser?limitstart=0

swest wrote: It is a 750 Z2 crank. It was checked and welded by V/H in 87. It had low miles in 98 when the bike was parked. I didn't know about the shorter stroke back then. The bike ran great and still does but I learned and proved it is in fact a Z2 58mm stroke crank thus detuning the engine. My 903 crank was destroyed in a fire that took my shop in 10. I have my eye on a 903 and would like to change it out and sell the 750 crank on eBay. It was only tack welded and it looks like the welds could be ground off so it could be rebuilt. It could provide enough to do all the things I'd like to do like a 1075 kit, etc.
Without having to go through all of it again, here's my thread on it. I was called a "poser" by one of our members.
Steve
kzrider.com/forum/2-engine/597654-poser?limitstart=0

I think everyone should know "I ain't no expert" when it comes to the older big Z's and the smaller bikes - my personal comfort level really starts with the '81 and up 1000 / 1100's, but I still thought I knew more about the Z1 / Z900 / KZ1000's than that! I have never heard of a Z2 before.....

Anyway, if V&H did weld your crank, it is a pretty safe bet they did a good job. You don't win that many Pro Stock championships if your work is sloppy!

It would seem that V&H built your crank so that it could be ground and pressed apart at least one more time for repairs. That is a good thing to do for anyone who is building a crank for average hobby level street and track use, IMHO. It is a lot of money to invest in a "bic lighter" crank assembly otherwise....

You should get the earlier "porkchop" crank as a core if you want to build a fast bike Steve.....there should be plenty available out there. As far as I know, the really hard to get 900/ 1000 cranks are the 16 tooth chain sprocket 79 - 80 version.

The 903 and Z2 750 cranks are 15 tooth. I thought the 750 would be lighter. Being 58mm stroke as opposed to 66mm, it's a safe bet it would be. I was hoping the crank itself would be lighter. Time will tell when I weigh both of them. I had a friend that had a 750 Honda bored out to 1015, choppered out, the works. Honda Davidson. :lol: It did seem to help against him.
The two engines were identical otherwise.
Steve

Mk2Rookie wrote: Hi,

I do not have a 17mm rod but with piston pins in the con rods I tried fitting a 12mm rod through the pins (fit nice and snug in the pins) but con rod number 4 does not seem to align perfectly with the rest.
Simon

There's no almost, close enough, etc.etc.etc. Either it's straight or it's not. Get another crank. The reason you have the tight spot is because the index is out. It's not far out but it's out and that's all that matters. Only a farmer can start with shit and end up with something good...

swest wrote: What about if the crank has been welded? Does that mean my 750 crank is toast?
Steve

Steve, I did not mean to imply your crank is toast.....unless it was welded up wrong to begin with.
What I have come to understand is that once any welding is done to a crank, it cannot then be reworked......I am not a welder but I am heeding professional advice which I am passing on here.....only my 0.02

I guess the Op's crank is toast. Mine seems fine. I'd better switch it out before something happens to it. I'd get more HP too. :woohoo:
Steve

swest wrote: I guess the Op's crank is toast. Mine seems fine. I'd better switch it out before something happens to it. I'd get more HP too. :woohoo:
Steve

Actually, that depends!

When we started to buy up some obsolete pro racing engines, we were often surprised with what directions some of the teams had gone in as far as making power from the rule standard displacement limits. We saw long and short strokes, different chamber shapes and sizes, different pistons and piston heights, rod lengths, way different porting, cam, and valve combinations, etc., yet most were making about the same 1500 HP.

One really different engine used an extremely short stroke crank with huge pistons to make 503 c.i. that revved out to the moon. The heads on that engine actually out-flowed our flow bench - it was making over 500 cfm at only 3/8" valve lift. By 0.5" lift, the cfm number went off the scale on our bench. The ports were huge - I joked about watching out for a train headlight while looking into those intakes. We had some difficulty de-tuning that one down to 1000 HP to re-sell it for street use, as it didn't want to run under 2000 rpm even with a milder cam and lowered compression.....no intake vacuum.....

I'd think being it's #4 on the crank it might be possible to take it apart and fix it if the welding isn't too deep. They had problems in that area did they not?
Steve

bluezbike wrote:

swest wrote: What about if the crank has been welded? Does that mean my 750 crank is toast?
Steve

Steve, I did not mean to imply your crank is toast.....unless it was welded up wrong to begin with.
What I have come to understand is that once any welding is done to a crank, it cannot then be reworked......I am not a welder but I am heeding professional advice which I am passing on here.....only my 0.02

My crank started out stock then during 1rst teardown I had it welded locally in Detroit area to prevent twisting from power adders used
( Carbs , Cams , Pipe, Big block )
Then I went Turbo crazy and sent it to Falicon for the Super Crank treatment.
They never complained on my core I sent them being already welded and completed the work which is still holding up today.
Im sure in a ideal situation Falicon or Pearson would love a untouched crank to work on but its not the only way to build a good hot rod
Dave

I checked 2 MKII cranks in two days. Both stock. Both have issues. One is out of index and the other is this...

Street Fighter LTD wrote:

bluezbike wrote:

swest wrote: What about if the crank has been welded? Does that mean my 750 crank is toast?
Steve

Steve, I did not mean to imply your crank is toast.....unless it was welded up wrong to begin with.
What I have come to understand is that once any welding is done to a crank, it cannot then be reworked......I am not a welder but I am heeding professional advice which I am passing on here.....only my 0.02

My crank started out stock then during 1rst teardown I had it welded locally in Detroit area to prevent twisting from power adders used
( Carbs , Cams , Pipe, Big block )
Then I went Turbo crazy and sent it to Falicon for the Super Crank treatment.
They never complained on my core I sent them being already welded and completed the work which is still holding up today.
Im sure in a ideal situation Falicon or Pearson would love a untouched crank to work on but its not the only way to build a good hot rod
Dave

30 years ago Falicon told me they can rebuild cranks that are already welded. That was the old Falicon. Don't know what the new Faliicon has to say on the matter.