Honda Spree and Elite 50 Forums

I going to install a corsa 72 kit on my dio,but when I bought the scoot ,the honda mech said the crank bearing was going out,it ran ok for awhile a started popping the top ring.I would install new rings and piston and run for awhile and sure enough pop the top ring.I found that there was alot of metal shavings in the case so I got those out and then I saw the bearings was lose if you wiggle the end of the crank up and down you have play.?Is there if any play there?Thats why I want to change them out before I install the kit.Thanks and is there any tool to take the case apart? thanks Bill sa50sr maybe sa72sr

to split case can use specific honda type puller or be very careful and use basic puller for flywheel then press crank out and gently hammer

just buy new crank/bearing/seal. cost around $200.

metal shaving , need to rebuild your dio motor!

I got a use low miles crank $100. 2800miles

Crank has to be pressed apart to change big rod bearing. $200 crank or $20 worth of bearings.

crank wiggle is not good , just tore down motor apart, add new bottom end parts!!!! worry free ridding!

new crankshaft complete is 150.00$

I have a 20 ton press, I will never buy a crank unless its out of spec.

new crank bearings are must for any bore kit unless the engine is new, check lateral slap on the con rod.

Kenny_McCormic wrote:I have a 20 ton press, I will never buy a crank unless its out of spec.

Kenny: Do you know how to split a crank to change the bottom rod end bearing? If so, care to share?

I can understand how it would come apart. What I've always wondered was how one presses it back together while keeping the crankshaft aligned and without over-compressing the halves onto the rod.

I have never actually done it but I know I could do it, I bet there is a key or something of that sort, cant believe it stays there on good luck. Over compression is easy, the pin is level with the crank wheels, big steel block outta keep it level.

Greetings:

There are detailed instructions on crank r&r in the service manuals. Unless you want all the glory for yourself, which I can understand completely, consider having just that part done by someone with the experience and all the special tools to get it right on the first try. Hello, Honda-san? Then all your other work won't be as likely to go kchkkkk. If it does you can blame them

Kenny_McCormic wrote:I have never actually done it but I know I could do it, I bet there is a key or something of that sort, cant believe it stays there on good luck. Over compression is easy, the pin is level with the crank wheels, big steel block outta keep it level.

motor fire up and running , then crank wobble and vabrator sit on a moped(scooter)

Kenny_McCormic wrote:I have never actually done it but I know I could do it, I bet there is a key or something of that sort, cant believe it stays there on good luck. Over compression is easy, the pin is level with the crank wheels, big steel block outta keep it level.

Kenny, it sounds like you understand how it can be taken apart; I think you're underestimating the complexity of putting it together right. Wheelman; I think the job you're referring to is the crank side bearings. That job is listed out in the service manuals. What I'm talking about is replacing the lower rod bearing.

If you look at the Honda Common Service manual (on this site), book page 199 (Honda page 14-2), it shows an "assembly type" crankshaft. The bottom-end crank pin is a press-out, unlike most 4-strokes, which are solid. To replace the rod bottom-end bearing you push out the bottom end crank pin, seperating the left and right hand sides of the crank.

Now the hard part is putting it back together. If you overpress it, you'll take up all the side clearance, and if the halves are crooked the radial runout will be off.

And no, Kenny, there is no key to index it. I hadn't thought of looking at the tops of the crank pin, but you wouldn't be able to see this while you've got it in the press, anyway. It would be a good tactile check when complete.

All of this complexity is why you need to be very careful not to drop the crank; you can easily knock it out of alignment or bend the crank pin.

I think that the answer is that you carefully gauge re-assembly to prevent overpressing, and you either jig the halves together so that they're straight, or you put the crank in the press sideways and twist it back to straight when done (this may damage the crank, I'm just not sure). I've never seen the actual procedure written out. I know it can be done; there are shops that can provide this service. And I would probably have this done by a shop; I always like to know how things are done though This is a key gap in my 2-stroke knowledge set.

Anyone with information on this procedure that can pass it on, I would appreciate it. It will get posted in Adv Tech Docs.

Thanks!

Greetings:

The Black Art of crankshaft disassembly is extensively described somewhere in the Sportster website: http://www.sportster.org

If I come across it again, I will remember to post it here.

You are right that the Honda Service Manuals don't cover crankshaft disassembly and truing. The crank and lower end bearing is to be replaced as an assembly. No tellin' now Honda-san does it, but it probably involves a very large dedicated assembly facility. And lots and lots of micrometers.

I read the service limit for the NB50 big end bearing is 0.04mm If you can feel ANY play it's too much. Sounds like an excellent opportunity to purchase a 50mm stroker kit to me!

Ah, I didn't realize Harleys had this type of crank as well. That significantly enlarges the audience, doesn't it?

Here are some instructions on crankshaft truing, which describes how to fix all the problems above. It's much more manual than I'd expected. Brass hammers, clamps and wood wedges, which, if used with the right measurement tools, are perfectly adequate.

http://www.roweusa.com/PDF/09-1179%20%2 ... ctions.pdf

And here's some tools for the jobs. These prices are a lot higher (like the $500+ truing stand that can be had for $70 elsewhere) than I've seen elsewhere, but it's a good assortment on one page. Kenny, your 20T press will do the job if you have a couple of press pins in the right sizes around:

http://www.cyclewareables.com/pages/too ... _tools.htm

I'm going to keep looking for something scooter-specific. Scooters would be pretty straightforward, with 1 cylinder. How about 3? This is probably out of an older 2-stroke KZ-750 or something:



I think the reason most don't mess with this is that it's very manual and requires a lot of tweaking. It's not something that you can do step 1,2,3 and have it come out right. In fact, you could just end up with paperweights if you're not careful.