Modern Vespa

I was wondering if I could still use this piston. I cleaned it up with some sandpaper but I could also bead blast it to smooth out some of the deeper score marks.

Just sand a bit on the scuffs and it will be fine since they are mostly on the skirt.

They have been sanded with 220 grit. Can something more aggressive be used. Iron cylinder should clean up with some muriatic acid and a light hone.

No need to do anything more than that to the piston. Get the smeared alu off the cylinder walls and slap it together.

So you guys are good with that piston as far as cleanup? I have a piston and cylinder that are a bit better than that, I was hesitating to use. I set them aside for a better set, but it's good to know they might have life in them yet.

Yeah. Lower performance things can take some scuffs and still run just reasonably well. Of course it's not as good as pristine components but I doubt you will not even feel the difference.

I'd probably dress it back with some 400 and WD40 or some such to get it a little smoother, but the ring lands look reasonably clean. you've got a few really good scores, but I've run worse. it's not gonna be a world beater but it'll go. hone it and check the ring gap. if needed, snap in a new set of rings and roll.

Thanks, I've also got a used oversized 200 piston piston in good condition. I've never had a cylinder bored, but that's another option.

if you can find somebody local to do it, you're in great shape.

I'm in a position where anybody local is 75+ (and a good drive) so when you add in a piston kit, a bore, and driving to and from twice, a new $200 top end starts to look much more enticing.

just some food for thought.

Ah yes ... the point where you have so much crap you need to stop and rethink how you are going organize everything. Also known as "chaos".

what comes after "chaos"? insanity?

I TOLD YOU I HAVE A SYSTEM!!

Sure you do, it's called entropy, I know it well .

10-4 on that. Many assache variables to compute…and doesn't change the fact that must finish Stella engine rebuild. No more dicking around with random parts from other engines…just get. it. done.

Yeah, yeah, I'll believe it when I see the vid of it.

That's me goading you to make it happen!

I need some goading, so bring it on. Done with that engine yet? Waddaya building the space shuttle?

So moving forward a little, mocked up the piston and cylinder with no gaskets. I'm getting 1.42mm for the height of the piston above the cylinder deck at TDC. The depth of the cylinder head from the base is about 1mm. I'm not sure what I should be aiming for in terms of squish. I am running a 60. mm crank.

If you put in a 1.4 - 1.5mm base gasket, that should put your squish at ~1.0 mm which would be a good start.

What Christopher said

Thanks. Will do and the will check squish.

Okay.

With the 1.5 mm spacer I have, I am getting a squish of 1.46 mm after correcting a bit for last night's sloppy measuring. I guess the solder test is the most accurate measurement. There is some error in measuring with a crappy caliper. Getting there though.

For some reason my kick starter only engages the splines at an odd angle. What have I missed?

I was looking at instructions for the Polini kit couldn't find any info about recommended squish.

Thanks

Turn it the other way…

Well this was a priceless one

The best thing is that it does not require you to split the cases again to fix

I had an audible snort chuckle.

good work so far!

This made my day Thanks for that

At least I know there is someone else out there and I'm not the only Homer.... Dooohhhh

dude i got busted on that on here before, was just put on quick during a build to turn the engine over but got crap for posting it

Reminder. Always put the bolt on the kick starter and tighten it, before trying to use it. Otherwise you break your kick start lever! Yes, I've made this mistake.

Shit! Don't tell anyone. I'll get fired from my job as the propulsion specialist at NASA.

Lolz, that made my day too. WTF, this scooter sucks!! Goddamn scooter!!

stripping a K/S lever because you didn't tighten it is a right of passage. it's not #1 but it's right up there with running out of gas.

And 'fairly tight' is good enough for the flywheel nut only to see if at least it will fire w/ a squirt of gas to the intake port after you finally got motor all back together and it's only in the test stand anyway. WCGW?

It kind of looks like it's face palming itself.

So at this point, I think the 1.5 mm spacer is giving me maybe 2 mm to f squish. I only have a 1.5 mm spacer and some much thinner base and head gaskets.

What is the squish value I should aim for?

Should I mix and match head and base gaskets to get closer or sand the spacer on a surface plate to get it closer?

I know shimming head and base changes the exhaust port timing a bit, but not sure if it's really significant for this kind of build.

Thanks!

what barrel are you running on this again?

2ish mm squish should be fine for most applications

It's a Polini 177 with a 60 mm crank. Not looking to get fancy on this build.

If you're at 2.0mm with a 1.5mm, you could put in one of the thinner ones you have a 0.5mm base gasket or shim that should get you to 1mm.

You never know what you got for space until you do an actual squish test! Get some solder and go after it. Once you get a baseline, then you can make a game plan for a base gasket or a head gasket thickness.

Not to slow you down in all this, but did you measure for port timings?

Also, since you invited us to push you on getting this thing across the line, I think I've done three or four full engine rebuilds and a bare metal teardown in the time you've been dicking with this thing. Just sayin'

He's doing ok on time really, it was only a bit over a month ago he posted the seize pics. But then again, he does live in a seasonal scootering area, so the timer is ticking...

Honestly better to take the time and get it right rather than be back in there to fix what you missed, keep up the good work.

Yeah, I'm in the middle of moving houses and moving my kid to college tomorrow, registering younger son at new school, full time single parent, sole breadwinner, the bus alternator rebuild…this engine gets built 15 minutes at a time. If I ride at all this season, great, but either way.

I haven't considered port timings or learned how to measure them. I know I probably should. I have to do some reading up and that's all the figuring I have left and I can finish it up. All the rest is familiar except for jetting.

I couldn't get the solder trick to work. Solder I had was too thick or thin. It would either not squish or block the piston.