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Post by niz76 on May 24, 2016 10:56:03 GMT -5
Yes you nailed it Florida Antique! I considered doing the reed valve conversion but it is quite expensive- like $400. My rotary pad is actually still in really good shape- better than it looks in the pic. There's no turning back after the reed valve conversion on a P200 engine- lots of grinding involved opening up the cases- plus I don't think there's too much performance to be gained for my 8500 RPM scoot. I would also need a new crank that's appropriate for a reed valve setup, maybe something full circle... |
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Post by stepthrutuner on May 24, 2016 14:29:40 GMT -5
Ya Reggie unfortunately this one suffered from my tuning deficiencies. I need to be much more careful with this thing. Still surprised it happened at only 325F but I need to take 190mech's advice and run the needle real rich. I think the new proper head will help a lot also as it has some extra cooling fins underneath and not to mention I modified the original head myself and have a feeling I didn't make the combustion chamber big enough. Luckily Brent has well documented the procedure for figuring out the correct ratios. Now I just need to apply the knowledge and do a lot less "winging it!" Despite attempting to follow established principles of fluid dynamics, materials science and combustion phenomenon two stroke tuning remains full of unforseen pitfalls for everyday and even expert tuners. Trial-and-error remains a big player to achieve a state of tune that realizes desired power with needed reliability. Everyone who has taken on the challenge of achieving high-state performance with livability has experienced frustration and setbacks. The risk/reward payoff is highly subject to intake and exhaust leaks as well as consistent fuel quality. Pretty much, if you haven't experienced serious failure with your highly tuned 2t, you haven't been doing it long enough. Three tools very helpful to monitor mixture and internal conditions are the head temp gage, exhaust temp gage and boroscope. For about seven years while I was not so gamefully employed as now and had the time I played around with porting, intakes, reeds, spacers, pipe effective lengths, headpipes, stingers, piston filing, base spacing, squish clearance, head configutation and volume, carb pilot and main jets, various needle tapers, etc. and still consider myself marginally knowledgable of two stroke tuning. Sometimes you get lucky and sometimes you build bombs. So,niz,don't get down on yourself. Keep at it as long as it holds your interest. Personally, I'm enjoying my maxi 4t scooters in basically stock configurations since they satisfy my needs and require little twiddling to keep running satisfactorily. Arthritis in my knees, hips and shoulders twarts working on scooters much anymore. |
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Post by niz76 on May 29, 2016 11:27:31 GMT -5
Ya Reggie I agree, if you haven't broken anything you're not trying hard enough! haha.
I'm really bummed that my S.I.P. order showed up on Friday while I was at work, but nobody was home to sign for it so unfortunately I'll have to wait until Tues now (Mon is Memorial Day) to receive it!
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Post by niz76 on May 31, 2016 21:02:31 GMT -5
Parts R Here!  |
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Post by acvw74 on May 31, 2016 21:15:00 GMT -5
Seeing all the parts makes me miss my old P200E
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Post by niz76 on May 31, 2016 21:50:00 GMT -5
Another part that came a few days ago is the ball hone. I honed the cylinder and it looks fantastic. I also decided to take the advice from S.I.P. and give painting the cylinder black a go.  Unfortunately I didn't have flat black high heat on hand so I went with the semi (it's still wet in the pic)... I wasn't too sure about doing this, especially since Mauibird just stripped the black off his cylinder but apparently there's some scientific mumbo jumbo to back this practice up. So I did it! I know most of the heat is in the head but I just could not bring myself to paint this beautiful new Polini head. I also didn't want to risk filling in the sand-blasted texture it already has and end up reducing the surface area. Just can't do eeet! fordsix.com/viewtopic.php?f=4&t=7838 |
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Post by oldgeek on May 31, 2016 22:33:56 GMT -5
Parts R Here! Wow! $$$ |
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Post by Fat_Panda on Jun 2, 2016 16:33:33 GMT -5
it keeps getting better cant wait to see the end result
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Post by vlatx on Jun 2, 2016 16:45:32 GMT -5
Be careful with that meteor piston,they have bad reputation of seazing during the brake-in.
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Post by niz76 on Jun 2, 2016 21:04:26 GMT -5
Be careful with that meteor piston,they have bad reputation of seazing during the brake-in. Really? This is supposed to be the bomb diggity with this cylinder. I kept reading over and over again that the stock Polini piston was the weak point in this kit. Either way it's been really touchy and I've learned my lesson that I need to be uber careful with this thing. |
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Post by niz76 on Jun 4, 2016 17:45:58 GMT -5
FROSTY! Crank dropped right in with no drama and I really like this different clutch side crank seal I got this time. This one is all rubber and I was able to just install it with my fingers. That first one I had in there was a fancy pants one with a metal ring and had to be drifted in...  Well I'm a little bummed. After getting the case sealed up and piston and top end re-installed I took some measurements of durations and squish etc. Unfortunately it seems the numbers have changed- the wrong way- with the new piston and the best measurements I should've taken for a good useful comparison, I didn't. I should've compared the Grand Sport piston side-by-side with the Polini 208 piston but I didn't even think of it. Now the durations are lower and I believe it's because the piston rings are located slightly lower on this GS piston. Well, in fact I know they are because of this description on grand-sport.de: " The position of the steel piston rings has been lowered by 1,8mm. This eleminates ring problems at the top edge of the cylinder when using a long stroke crank shaft.
Although the GRAND-SPORT piston is "stronger" than the original POLINI piston, the weight of this new piston is almost the same.
The transfer port design offers an optimized gas transfer with more "out of the box" power in the whole RPM range.
CNC manufactured boostport windows are enlarged and reinforced." Here's the compared with the stock Polini 208 piston this is all with a .5mm Polini base packer (thicker than the supplied base gasket that comes with the kit): Exhaust Duration: OLD 175. New 167 Transfer Duration: OLD 127(ish). NEW 120. Blowdown: OLD 24. NEW 23.5. Here's the squish #'s with my old modified stock Piaggio head vs. the new Polini head: OLD 1.60mm. NEW 1.85mm I'm not too sure how I feel about the numbers changing the way they have but I guess I'll have to see how it runs!  I did get a little lazy and didn't cc the heads. It looks like I got the stock one pretty close but the Polini head looks like the combustion chamber is just a tad larger. Should equal less holes in pistons!  Oh, almost forgot to mention- This Grand Sport (Meteor??) piston came with some instructions regarding ring gap...   As you can see I did some math and came up with a ring end gap of 0.244mm for this bore. The rings gapped out nearly perfectly right out of the box (the .229mm gauge slid right through and the .254mm gauge was a tight fit so it seems just about perfect). No modifying needed! Keep in mind that I have used a ball hone on this cylinder so if you're installing this piston into a fresh Polini 208 cylinder you'll def want to check your ring gaps!  Here's a shot of the piston sitting nicely just even/below the ports at BDC. Which is weird, because that's exactly where the original 208 piston landed but now my durations are totally different?? I checked them thrice...  |
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Post by SandStorm on Jun 4, 2016 18:54:10 GMT -5
I drooled over this! Gotta love it
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Post by 'O'Verse on Jun 5, 2016 12:24:45 GMT -5
With the bigger squish it might run a tad cooler. I'm running 2mm right now on the 100cc because I haven't decked the head yet. Max temp 270. 59 mph top speed though. Might be worth leaving it. Looking at your fan design in the fan thread. It might not be cooling the cylinder down fast enough to prevent seizing. Might be worth adding something to the cooling process to keep that purty cylinder and piston alive.
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Post by niz76 on Jun 5, 2016 12:43:34 GMT -5
With the bigger squish it might run a tad cooler. I'm running 2mm right now on the 100cc because I haven't decked the head yet. Max temp 270. 59 mph top speed though. Might be worth leaving it. Looking at your fan design in the fan thread. It might not be cooling the cylinder down fast enough to prevent seizing. Might be worth adding something to the cooling process to keep that purty cylinder and piston alive. Ya it really is a battle keeping this thing cool without any timing curve like our more modern scoots have. This Polini kit has earned the nickname "Seizeini" in the Vespa world due to it's tendancy to seize REALLY easily with the stock (Polini) piston. Hopefully I've got the bugs all ironed out this time. Third time's a charm! I'm really looking forward to getting a Kytronik smart booster for this so I can have some timing curves to choose from. That should bring back the lower end punch I'll lose by taming it down like I have and also keep it cooler at WOT with some retard... |
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Post by 190mech on Jun 5, 2016 13:42:50 GMT -5
Your port timing change has me scratching my head!More deck clearance should mean a dome below the ports at BDC(shorter pin to piston crown height,but NO!Shorter crown height is like stacking base gaskets=more duration..But we have less duration???STRANGE!!
Having a lot of squish clearance invites detonation as the flame front can easily move from the combustion chamber to the piston edges,,not what we want...
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