Weak areas on 650 motor?

TwoJugs

TwoJugs

Excess XS
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Has anyone discovered the weak links on this motor the hard way? I am building up a vintage drag bike and am looking to see what the max RPM is on the stock motor before things let go, and what goes first second and third.

I am guessing the crank spinning, weld it. Rods, valves smacking pistons, rods snapping, valve spring float. Seems the trannys are strong enough. I have some exotic parts laying around from the past. Trying to decide how to proceed. And yes I do have a small budget.
 
Hey 2jugs, plenty of shit can go south with a bit of hard work! Yep crank shoule be welded to stop it spreading out. Small ends can fail with stock rods. Standard head gear is ok if its new, you never know how much hard reving has been done on a 35 yo engine. might be an idea to address the gbox dogs, though the box is a sturdy unit. Racerdave drags his to mid 10's, quite impresive for a XS, good luck:thumbsup:

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Valve hats - I break them...
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Never once had a problem with a welded crank. I have had issues with non-welded cranks though.
 
The weak point is the loose nut that connects the handle bars to the seat. :thumbsup: :bike:
Leo
 
dwyatt said:
I have exactly the same problem with mine...... :wtf:
Click to expand...
is common.
Hugh, htf did that happen? ive seen lots of junked race motors(albeit v8's) and never seen a busted keeper.
dont forget to wash up for dinner. she made your favorite!!
 
I agree with brother I've split one in half well abve red line The stock valve springs are not designed to handle RPM above red line when new and most are not new. So a good set of springs is a good idea. And the loose nut as xs leo put it. :D
 
Brother said:
I'm guessing it has something to do with 11,500 rpm :D most likely caused from valve float.
Click to expand...

Still manages to blow my mind. I'd love to hear the engine at that RPM.

I'm sure that the stock firing order would not be able to do that very long, so something to be said for the rephase.
 
Twojugs
I have addressed the same issues because i am doing a turbo motor with a big carb and so far the thing that scares the hell out of me is the trans and clutch basket. You can weld up the basket and undercut the trans but when you start going into the 12,000 range i don't think its going to hold up. I have had baskets on other bikes explode and its not fun while you are going down the track. I was really impressed with the one guy on here running in the 10's with a 2 cyl motor and got a picture of his bike and so far it has stayed together from what he is saying but when you change valves and springs and put bigger cams in you alway have some week point and i think HUGH just showed you one. I just want a off the wall old school bracket bike that runs mid 10's to beat up on all the new bikes. Anyone who drag races test the bike breakage everytime they go down the track. I just don't have the reflexes like i did when i was 25 so i want to go a little slower HAHA . I have done my share of pleaseing the croud on my nickle of blowing up or crashing so now i want training wheels. If i can help you email me i have 35 years Drag Racing all over the US and next year i will have a ZX14 out of ATL. running and a BUSA out of Philly running the Grudge circut. NOT ME RIDING HAHA!!!!
 
There will always be a weak link. When you pursue performance this is one of the things you should keep in mind. One thing I learned is that no matter how good the build, when pushed, something WILL eventually fail. Your goal in a successful performance build is to engineer the machine to a degree that places the weak link where you want it to be: The safest and least catastrophic place. For those on a budget, an inexpensive a place as possible as well.

As far as speed goes, I'm not a fan of it personally. I love to watch others go fast, but it isn't for me. I'm the type who almost always builds to the point where the machines capabilities far exceed my own. So I shy away from speed in an attempt at self preservation. :D
 
The 4th gear is a bit a bit of a weak part, but you can't do much about it, as the dogs snap off, and suddenly you have a neutral where 4th was
 
Brother
You hit the nail on the head.........
When you build any performance motor you got to be prepared for it to break and cost you money. When i street raced i use to think it was insane for people to put all this money in something and then be afreaid to race it. I lost more money street racing guys like me who had the moto GO OR BLOW than the guy who came with his shiney car with $10,000 in the motor and a piece of paper that said what the car could do.If you were ever in the philly area in the late 60's and early 70's then you seen me race because i was a crazy person and raced every weekend but i had the money to fix my cars and bikes. If i blew it up on friday nite i was back out the next weekend with better stuff.
My point is if you are going to build and race then just race don't think of how much you got into it. Make it the best you can to get as many runs as possible. I raced a GS1100 for almost a complete season with no problems. Then i raced a KZ1000 and blew it up the third pass. Was one better than the other NO just lucky with one. Both were big motors that ran. In any motor builds stock or race motor things can jump out and bite you in the ass all you can do is double check all you have done and hope for the best.
 
The above carnage was with a stock profile cam, with HP springs, and rephased...

They gave plenty of warning before letting go, I just didn't know it at the time... The one that is still together but has a crack, was "clicking" and it sounded like my valves were out of spec. I kept adjusting the valves, but the noise never went away. I was running VERY hard when that let go... :shrug: It was fun, and I'd do it again :laugh:
 
my retainers on the turbo bike was probaly were giving notice but like Punkskalar didn't know it at the time.the turbo bike also has stock cam.
 
Cowboy
Did you have to weld up the clutch basket and how much compression are you running with the pistons on the turbo. I have two turbos to play with one that is on EBAY for like $300.00 and i have a RAY JAY from my turbo KAW that i use to run. The RAY JAY is a 28lb boost turbo but i know i can't put that threw the XS so i am going to play with the little exhaust turbo first thats only 11lb . I called WISCO and they said they would make me a 8 to one set of pistons so i would be able to rev a little higher on the turbo. A good turbo but had to find are on older DATSUNS i had one of them on a GPZ750 and was able to pull 22lbs of boost and it looked stock.
Very impressed with you bike and times got to post a video .
 
As jay760 mentioned the false neutral, I recall there being a miss shift, somewhere around third or fourth, in the gears on mine. It only happened a couple of times over the history of the bike's life though, and wasn't a consistent. It would shift fine most of the time, then just go into neutral. Like I said, I only remember it doing that a very few times very early on, and it has 29,000 hard miles on it.

-R
 

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