understanding puch polini seizing


so i've read a lot of the posts about the sensitivity of the 64cc polini. and i can testify that this is true (i seized twice, once broke the piston ring, and more recently slightly and only enough to stop the engine).

so i now have the cylinder with one "soft" seize history (sold my first polini kit after the first seize).

now i have a "B" cylinder with a "B" piston. i have a 21mm dellorto, malossi 4 petal intake with dual stage boyesen reeds, e12 filter, proma circuit pipe, hi comp head. 102 main, 60 idle jets. b9 spark plug. minimized the number of fins cut off the polini cylinder (kept all the fins on the head)

no air leaks, everything runs well. almost 100 miles with a new piston.

however, at around 40mph, when cruising, if i lay off the throttle, i feel the engine slowing me down. it sort of feels like a "pre-seize". like there is friction between the piston and the cylinder. i have 30:1 gas oil mix, think i have a pretty rich jet and the plug looks like a dark coffee color.

i am impressed with the acceleration (my front wheel lifts off sometimes) but past 35 mph, the bike engine just doesn't sound good, especially when laying off the throttle at a higher speed.

and it has always been this way. thanks for reading...if you have any ideas on how to improve this/tune it better, please share.

Re: understanding puch polini seizing

I was told that its due to overtightened the intake manifold, which makes sense, it would completely disfigure the cylinder bore.

Re: understanding puch polini seizing

wow. good point. i'm gonna try loosening the intake a bit

thanks for sharing. any other ideas?

Re: understanding puch polini seizing

lean at the needle?

Re: understanding puch polini seizing

i was going to check the needle next. i think i'm at the stock position of second from top. i was going to move one more in to second from bottom.

Re: understanding puch polini seizing

to much oil? doesn't more oil make u leaner?

Re: understanding puch polini seizing

i think everything is running fine, "pre seizing" = running really fucking fast cuz its a bit lean and then bam u seize. too lean with a phbg, sounds like its gasping for air and will generally happen when you give it throttle at certain positions.

polinis sound super dodgy when they are 1st installed u will get used to it.

Re: understanding puch polini seizing

ok...got a plan for tomorrow...slightly loosen intake, richer needle setting, maybe upjet a bit. thanks guys.

p.s. zeke, i'm pretty sure that too much oil makes you richer (more lubrication ratio in air/fuel/oil mixture that goes to cylinder).

Re: understanding puch polini seizing

why would you want to loosen the intake...? that sounds like a horrible plan,and quick way into air-leak town...

I doubt that's your problem...

play with your needle. make it a bit richer, and see what happens... don't loosen your parts for performance lol they'll do that enough on their own...

Re: understanding puch polini seizing

Nope, leaner. Oil doesnt really burn that well in the combustion process, thats why you leave a trail of smoke. So lets say in one intake cycle you breath in a unit of pre mix which is say: 40 parts fuel, 1 part oil, and a constant volume of air. When you switch to 30:1 thats 30 parts fuel, 1 part oil, and the some volume of air (a constant in this equation). So, you actually end up with a smaller volume of fuel in the whole combustion mix.... Run the 30:1, jet accordingly based on the plug and apologize to the folks behind you :)

Re: understanding puch polini seizing

Don't just willy nilly loosen the intake, but pull it off, inspect your gaskets, and torque it evenly and snug using a criss cross pattern.

Re: understanding puch polini seizing

well i don't know what to think now. i seized my polini the other day, 400 miles on it. i had heard the polini was kind of a bitch before i got it. disregarded! what the hell! now i have to replace pistons, rebrake it in. all the fun stuff. what is it that makes the polini succeptable to seizing? i have to know this. and by the way check out the soft seizing discussion on general discussion.

Re: understanding puch polini seizing

ok...good point about blindly loosening the screws...will try richer needle setting first.

michael, i think i understand what you're saying about the oil mixture ratio. yes, technically you're leaner with more oil in the mix, but i wouldn't think too much oil in the mix would cause a cylinder to seize, as the gas you take away is replaced with lubricating oil so i was thinking that that shouldn't be a reason why the piston felt resistance and closer to seizing.

i guess more fuel and oil makes sense which is why some guys run such big jets. i think i'm going to 107 now. ha.

Re: understanding puch polini seizing

maybe get a bigger pilot jet. and change your needle

thats for some where around 1/4-3/4 throttle and that sounds like where it happend at.

Re: understanding puch polini seizing

just a note about the intake... you should check when you take it off to see if it is perfectly flat... if it was already overtorqued and has been sitting like that it is probably slightly concave and therfore fucked no matter what the tightness is.

You can take a piece of glass or if you have a perfectly flat metal shop table and put some 320-400 or so wetordry sandpaper on there and mill it down evenly until it's flat.. then go to 600 grit for a second, then 1000, that should be good. It will be really really shiny and you should barely be able to see any scratching.

Might help?

Re: understanding puch polini seizing

) Cupermcnewbster ( /

Your needle is lean. I don't know about this intake stuff. If you don't have an airleak you should be totally fine.

30:1 is leaner and you MUST jet accordingly. I was running a 106 last time with a polini, malossi (stock reeds), proma circuit, e12, etc with 3 oz or oil to the gallon. This ran amazingly but was a bit lean in one or two spots on the needle (which was fully rich) so I gotta adjust accordingly with different needle/jets.

Re: understanding puch polini seizing

Nils has pointed out that those polini reed cages are not flat out of the factory. I would add some Permatex aviation grade sealant also

Re: understanding puch polini seizing

All I hear about is these things seizing and cracking off peices of the crown.............................so I'm not getting one...........

I haven't heard anywhere near as much about metras, gilas, malossis, athenas, airsals, etc, seizing. With as durable as the stock cylinder is, it is hard to believe that seizing needs to happen this much on any well built cylinder. Perhaps Polini should reengineer their piston/cylinder for greater durability, or whatever is making them break all the time......

I want a Polini, I just can't afford to do the kind of repairs and deal with the kind of disappointment that many I see are facing with these.

I want a 70cc unstock cylinder, made in Austria by Puch, with that famous anal Austrian engineering...I'm sure it would fly...and be hard to break.

Re: understanding puch polini seizing

not a bad point fubaman.

i have a 64cc malossi for my vespa grande and i run that thing very hard. wot on 95 degree days, no problems for 2500 miles.

i have to spend more time tuning the polini and understanding how to tune the dellorto phbg, but still, the kits shouldn't be breaking this much/so easily.

Re: understanding puch polini seizing

The polini cylinder seizes so often because it is a fucking fast-ass racing cylinder. It is not meant to run at WOT for extended periods of time. It's not meant to be run on a half-assed setup, it needs to be tuned correctly. And during and after break in, it needs to be checked fairly regularly to make sure it's staying tuned in.

Kits are for people who know what they're doing. When people who don't know what they're doing buy kits, a seizure is often the result. The polini is an especially seizure prone kit, and even people who DO know what they're doing seize them occasionally, simply because it's just a sensitive cylinder.

Puch went out of business years ago, my friend. They made no performance parts. Puch stock cylinders are reliable because they are designed conservatively, and as such, do not go very fast without modification.

Re: understanding puch polini seizing

yes, i think we all know that the polini is a very fast, sensitive kit. it has been said many times that it needs to be tuned correctly. however, i don't really believe that designing a cylinder to be both fast AND reliable should be mutually exclusive.

I also acknowledge that they were not designed to work with such big carbs (19, 21 mm phbg). but i hear that they seize occasionally with the smaller bings too.

Re: understanding puch polini seizing

💀Kim Jong illest💀 /

my buddy round has blown like 9 polinis now. totally rediculis. is there a puch parma? if so i bet its super high quality.

Re: understanding puch polini seizing

i like the puch polini, hard seized mine once, just from moving the needle one notch tho. it is very unforgiving. I have also soft seized 2 others on other ppls bikes as well but no real damage occured.

I have run it really hard at wot for miles on end, and its been the most reliable moped i have ever owned.

Its a 4 pedal 19 carb setup, and heavily ported, it revs out higher then most other ppls polinis.

Polini makes a great kit, and i have seen many ppl seize them, its like popping ur cherry in SF, u can't say shit till u seized a polini or 2 lol.

also about the 80 kits ppl seize those all the time as well (just as often as polini), but u just don't hear about it as much since they have only recently become very popular, and alot of ppl don't like to "brag" about how they seized there $350 kits to everyone on MA.

The most forgiving kits are the tccd kits, malossi kits, and metra 65's, and also the less powerful kits

athena reed kit is good, pretty forgiving to tuning mistakes and quite fast, but still not up to par with the power of polini.

Re: understanding puch polini seizing

once i do soft seize, i will lightly hone the cylinder, not taking any material off other than what is fused to it. is it ok to just buy the same piston and put it in. or do i have to hone it more and get a bigger piston. what about the ports with a bigger piston. and what is the difference between the C and D, size, ports?

Re: understanding puch polini seizing

Ok, I was a bit baked and I may have come off harder on the Polini than I should have. I understand a lot of people have them and that alone will make it seem like there's more problems with them than there is. They look like a sweet kit, and I'm sure they are tunable, and I have heard the 64 can be tuned to rival many 80 kits.

I guess what I'm saying is that I'm not feeling like a kit that sensitive is for me yet, even if I sacrifice some potential speed getting a different one. Who knows, I may find, when I finally am ready to get a kit, that though sensitive, it _actually is_ the one I want, due to it's output capabilities.

It sounds like one should care for a Polini like a racing professional would, and get one only when they are ready to provide a professional level of care.

I kinda want a mk 65 I think, they sound harder to noob-destruct :-)

There is a parma for the Puch...

Yup, I am aware Puch is gone, I was just dreaming of Austrian engineering and metallurgy in a big shiny (probably kind of heavy) indestructible kit.

Re: understanding puch polini seizing

i moved the needle to the second from bottom post and down jetted to 97 and it runs much better now. the one area that needs improvement now is 1/4 open throttle acceleration. but that is not critical...the cylinder feels safer, less "pre-seize"-ish. i got it faster than i've ever taken it and the cylinder didn't seem to be slowing me down when laying off the throttle at 40+.

i'm still settling in on a setup that works, but yes, it does look like the polini can be controlled, just takes more than normal amount of attention to get there.

Re: understanding puch polini seizing

the bike should slow down when you let go of the throttle. if it doesn't then you are running too lean.

Re: understanding puch polini seizing

Plug chops all around! Polini's may be over zealous on the seize train, but they can also take it. I've seized one of my own kits 4 times (one hard seize) and after a little muriatic/wet sand tender loving it was back to feeling like new.

Re: understanding puch polini seizing

i'm assuming you replaced the piston each time. did the acid eat away anything critical. dd it work well, you have seized 4 times some i'm kind of curious

Re: understanding puch polini seizing

Replaced the piston only after the hard seize. The acid doesn't eat away the metal as fast as you think, it's basically wet sanding out the scuffs for a couple of hours until the piston will drop through without any hangups. It still runs great pulls as hard, if not harder than, my friends bikes with newer kits.

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