Modern Vespa

Rebuilt a Stella oil pump last night and trying to get it to pump but no dice. Help with a friend showed I had all the right parts inserted correctly.

Today I had it idling with the pump full open for about 10 minutes. My gravity fed rig produced a few bubbles at the top but no significant oil use.

Is there any correlation between how deep the white plastic check ball plug is versus output? Maybe I pushed it in too far? Any other guesses?

The only time I had a pump not 'priming' was with a Cosa motor that someone else firstly rebuilt and seized after 100Kms (owner was also adding a bit of oil into the fuel that's why it didn't seize sooner). The culprit was a non injection carb that was installed by the previous 'mechanic' and thankfully I figured it out, since the pump was pushing the oil towards the tank and overflowing from under the carb tub…

Thanks for the reply! I verified it pumps one direction (out the check valve) by hand, but now that the covers on, I have only my test rig to confirm flow.

Anyone know if a PX pump will work with a Stella (LML) pump housing?

OK, this is going to sound lame...

Assuming you've got the spring and ball bearing installed correct, and everything else installed correctly....

I hooked everything up and started the scooter, then literally blew into the oil hole for a good minute to get some pressure going to force the oil into the works.

I know, I know, blowing the oil hole, but hey, anything to prime the oil pump! Ha!

For the record - no pictures were taken to demonstrate this maneuver..

When you do it that way, it's call "fluffing" not "priming."

Seriously, though, I don't think an LML pump would work because the pump rotates in the opposite direction. The LML spindle is two pieces, with the lower piece driving the upper, whereas the Vespa version is a single spindle, right?

I just did this last night after pulling apart my Stella carb. Could not get the bubble to move in the oil line. Also no pics... but it worked. I put a paper towel over the fill hole.

I use a syringe of oil to prime the pump. Easier and more dignified than the oral method.

As the idle doesn't generate enough pull for oil flow… You gotta rev it out.

Drill test:

Pull the airbox (I know a PITA)

Pull cog from case
Insert cog back in airbox
Attach drill
Attach gravity feed oil line
Spin drill

Watch for flow.

I don't know. Seems like a lot of work just to have your engine not seize.

Ok good stuff. Thanks for all the tips. Won't mix and match parts but heard from the guys at Scooterwest, there was a problem with the Genuine oil pump gears. They were machined incorrectly and pumped at a 1% mixture. The other thing they said was the little nub on the inside of the pump cover can be removed allowing more oil in the end. Figured I'd give it a try as it won't hurt anything.

Tonight is double checking the pump piston alignment under the gear and rebuilding everything. Too late to fire up the scoot, but will find a good syringe to force oil into the pump via my dummy hose.

Dremeled off the nub and confirmed a clear oil pathway. Pushed the wheel to simulate it working and it pumps oil as intended. Slap it all together and big womp womp . Still nothing even with a 10 minute ride.

I'm wondering now if it's the pump top? Not pushing the wheel down enough for it to work? Any Stella folks have a picture of the stock oil pump cover?

I gotcha, fam. I'll post up some pics in a few minutes. I have a Stella airbox on the shelf for whatever pics or meaurements you need.

Here's top and bottom of a Stella air box.

Lemme know what else you need, but I doubt it'll happen before tomorrow.

I sent my front and back over via double secret transmitter from kajiit secure tech and order fulfillment line.

because I'm discreet and shy, and I try to keep it classy.

Thank you both. Definitely matches what I'm dealing with. I'm guessing there's something wrong with the big gear. Not enough slope on it or something machined goofy with the bottom D.

are you saying you want me to send pix of my D?

I mean... I guess. but you first!












give me a bit and I'll take that thing apart and shoot some pix and measure it up for ya

overall length is 33mm and the shaft is 26mm with the cut out starting at 14mm from the bottom of the gear and going 12mm to the bottom of the shaft. shaft is 5mm with the cut out measuring 4mm

hth

Sadly no amount of rebuilding solved this. SIP has a whole carb box with pump installed for $100. Cheaper than just buying pump parts. Going to just swap and keep my fingers crossed.

That's strange. Just noticed that your Stella carb box has the hole for the countersunk screw that holds down the carb box. Mine doesn't and both Stella reed blocks I have don't have a threaded hole either. It makes the box difficult to seal because it's only the carb studs that hold it down.

Yep. It's annoying AF that they did that for sure.

Sip parts are in. Opened up box #2 to measure and inspect the big gear. Slope on the top is 2-3* whereas OG is in the 4*. D shaped shaft that goes into the piston is .03mm larger than OG. Last difference is #2 pump top distance is a little deeper to the lever arm than OG.

What that all means? No idea! Started by re-doing the plastic plug and check spring on OG as I pushed it too far in. Going to start with this and see if that was the culprit. If no, will switch gears and last box.

Good luck... still following along on this one.

Ok so guess and check worked. Resetting the check valve did nothing. Any bubble I introduced never moved. Didn't go the wrong way either!

Swapped to the SIP (LML) gear and the bubble moved. Confirmed it a few times. Confirmed oil being pumped out the carb. Tossed the Genuine gear.

Having to guess, I'd say the gear shaft probably sealed better in the piston than the Genuine one.