Modern Vespa

They're another one of those tools that you don't think you need until you have them, and then it's like, "How did I ever live without this?"

$30 from Amazon and the ball hone makes short work of cleaning up 2 cylinders.

that's a total of 250 cc of power there, step back folks!

Damn it, frustrating day. Trying to button up and check sealing but the crank won't rotate without binding. The clutch isn't on, so the binding is crank to case, I think. Is there any option besides crank out of true??

Can you suck the crank further into the clutch side? Hmmmm....

BTW - cool shirt!

My try was to sit the race for the split bearing deeper and pull the crank back in but you can see that's not the ticket.

Shit the evidence is right in front of me. One - the crank now has witness marks from the rotary pad. Two - the hot spot discoloration says it was bad in whatever engine it came out of (not this one).

Urgh... that sucks man.

is it the same crank with the notchy big pin? the non-free spinning conrod?

108 - Yeah.

Anyone have a good reference for checking crank true? I'm happy to go to harbor freight and get a dial indicator. This is likely to go into my engine building routine now.

Yeah, unfortunately I couldn't find any decent tools, besides making your own stand.

Which I don't trust machine shops in my area to help out with and ended up buying one online for truing cranks… it's piece of mind

Interested if anyone has a decent solution too… it's a pita if cranks are out.

You can buy a stand on line or make one yourself. There are lots of how to videos. Even cobbling something up with a dial indicator will give you an idea. The nice stands are when you are going for dead nuts.

share up any links you have for truing stands

The one used on the video above has bearings to roll the crankshaft on. I don't like this because bearings always have their tolerances and play which adds unnecessary uncertainty to the measurement. V-shape wedge is better and if you are worried about leaving a slight marks on your crank bearing necks, you can add a strip of softer metal to the edge. This should not be necessary though, because you will not be spinning the crank on the stand (at least hopefully) for thousands of revolutions. Smooth surfaces on the V with dab of oil and you are golden.

1. Make it beefy enough - you don't want to guess if you have flex
2. No need to make it very tall unless you want to use if for some static balancing action
3. Adjustment for crank width is nice to have
4. Get two dial gauges with mounts to see both sides of the crank at same time

NOOO! say it ain't so! you were making good time just trucking along on the project!

thanks for the bat signal earlier. I'll check on a crank tomorrow once I'm freed from kajiit house of broken stud removal and exhaust gasket replacements.

Yeah it's a setback, I was hoping to install the engine next weekend when the rest of the family is away. Now I need gaskets, a crank, and probably a new split bearing.

Anyone know where I can find those v-blocks you are talking about?

https://www.mcmaster.com/v-blocks/

cool, thanks Swiss. it looks like they are short - do you have to fab something to get them off the table to use them?

btw after knocking my crank back out I got to wondering - shouldn't I be able to use the case splitter to push the crank out? I'm trying to eliminate all hammering from my build techniques. I think there are holes for the clutch side to do just that.

A table saw with an extension or some wood blocks of different thicknesses. Yes, you can use the case splitter to push the crank out of either side of the cases.

I'm assuming you're just trying to see if the crank is out rather than take a detour into crank truing…

Piece of plate-steel and an angle-grinder

Yeah I'm not going to save this crank but I'd love to figure out how to measure that it sucks so I can avoid this happening again.

I can make the stand in this video for $20 + shipping if anyone's interested.

Sign me up for one - and thanks for the great video link. PM me whatever I need to do.

That guy is awesome.

I'll fab-up a few on Tuesday and test them out with the two cranks I have on the shelf with a dial indicator.
Literally a mountain of that material here at my shop, going to waste.

BTW it's safe to tap a crank out from the clutch side with a soft blow hammer.

I went back and watched Sausage tap out a crank with...

a soft blow hammer. Which wasn't enough, so then he used a drift. On the second engine he got away with the soft blow hammer.

New crank ordered. This $200 worth of stuff was out of budget - we weren't supposed to be doing a crank. I'm curious about the repairing of cranks - let's say I knock this one back into true using the methods above - will it stay? Or will it be likely to twist again?

I'm thinking this as more a crank checker.

First practice try today. What do you guys think?


Stable rotation. But I don't think the positioning is ideal.

Thinking these landings are better(?)

I would try to land on the bearing surfaces and not the sealing ones, myself. So the second pic is good on the clutch side but would come in to the race on the fly side. Next question is having spots to mount your dial indicator. Also would be smart to make sure it works for large frame 150 or 200. Can a small frame crank also be accommodated? That would be the bonus.

I always forget I work at a place with everything I need.

Runout about 0.020" on the fly side

About 0.016" on the clutch side

And I was able to get access to a bearing puller and save the sleeve.

BTW Ray8 - still interested in the stand, it's nice to be able to check things at home.

Had some time to play today with a dial indicator. P125x crank in pic was dead-on on the flywheel taper (+-.0001) and .0006 on the clutch side. Two hammer blows with the crank in hand (following 2StrokeStuffing's video) worked.

So here's where I'm at:
At 65mm between landing points a largeframe crank can be mounted in either direction. If one side includes the race with the first iteration it'll be tilted if rotated, with inconsistent readings.

Also, if testing a crank without a race installed it wont work at all. 65mm out might save someone installing a new race on a shot crank.

The stand metal is mild steel vs the hardened crank. Took a look at the crank with a jeweler's scope afterwards. Nothing to worry about there.

Never seen a smallie crank. Can you measure to see how it would land at 65mm?

Thinking best option on the cheap would be a simple stand, to be used with a dial indicator with a magnetic base, and neodymium magnets under the stand. I'm going to build mine all together with a fixed dial indicator, so no magnets or stand for the indicator. That would be a lot more bulky to $hip.


Mock-up

Lucky for you, you Know A Guy who has a couple smallie cranks close at hand.

65mm is going to be pretty wide, and definitely can't be done with a bearing race/bearing in place.


New school (Mazzi full-circle)

Old school

Could a person bolt an adapter on one side to fit a small frame crankshaft?

I'm starting to think the v-blocks are the easiest answer .

I have a purchased 4 bearing jig and it works perfectly well enough for tuned scooters. The most amazing thing is half the new cranks I put on it are not entirely straight, requiring a smack on the bottom to bring them to life.

That runout isn't too bad actually.

I'm a little surprised it's binding.

I've had worse runout on my pinasco crank and the spins smooth still.

watch the flywheel end of the crank as it spins - you can visually see it. I have no reference for how much is too much but I don't think you should see it

No, rewatched it a bunch of times and still think it's ok…

It's strange it's binding so much

well the new crank arrives today - perhaps we'll measure before installing for science