221 Polossi soon to be 221 Malossi

[pxguru]

Well it had to happen. I took the barrel off to tweek the packer size. While inspecting the heavily worn, battle scarred, legend of a barrel, that has given at least 10,000 miles of smiles, there is now sadly a crack, very small but very significant and not where we like to see one.

I have re-assembled (to test the packer) as it won't fail just yet but it will fail soon enough, so thats it. The crack is just in the skirt and could be repaired but I have been waiting for it to fail and there are no more re-bores in it.

The final tweek will stay in the plan and I will re-work my standby old Malossi 210 barrel from the shelf in my garage, to have the exact same porting dimensions as the iron Polossi had.

The plan is the same as ever; not an all out racer but a road rideable fully panelled scooter with about 30bhp, which pulls 4th like a train and will cruise in the centre lane.

[pxguru]

I haven't been lazing about. The malossi is now running Welcome to the 21st century!

Ported the Malossi to a reasonable level. I don't think I did quite enough but will have another go at tweeking the porting once it is run in.

Before


After


While at it I got all the other outstanding jobs done.

New clutch plates and springs (same type as before)
Newly sprayed un-dented mudguard
New sprayed old style horn cover
Millenium centre mat
New brake fluid
Matched the Malossi base ports to the Polossi cases
New base packer


I kept the jetting the same as the Polossi. Just dropped one needle clip so far but keeping it rich. The 60 pilot is too big though. Will change that for a 56 and see how that goes.

All in all, 50 miles into a short running in period (200 miles) and it feels like it has potential. Liking the ally barrel though, warms up quick and is a good bit cooler running but we will see how that it stands once its at WOT. Seems much quieter but that will be the rounder exhaust port (might change that later).

[sime66]

I wanted to say something intelligent when you first posted, but resisted, so forgive me if I say anything dumb here:
You’re pleased with 10,000 miles from a barrel on a 30bhp engine; what would you hope for from your tourer (or mine)?
I’m a little muddled which is/was 210/221, and what the photos are; a Malossi 221? Is it just the stroke that makes the difference? I think I just answered that myself 57mm=210, 60mm=221? Same head? I see this HTSR head; is that it?
Either way, it has a very thin skirt; looks delicate, is that why the Palossi cracked there too. That’s ally though; easier to work I imagine, but more or less likely to go in the same place do you think.
The difference in the transfer windows you’ve left in the skirt must be deliberate, so is that to do with the wonky 200 casings?
I think I can see the rest of the work in the transfers and exhaust; looks tidy, but then you have done a few before.
Anyway, interesting stuff; I’ll follow the rest quietly now.

[pxguru]

As I see it the difference between a 221 barrel and a 210 barrel is where the ports are. With the extra 3mm on the stroke it is nesasary to raise the barrel to stop the top ring coming out. How much it is raised depends on what port timing your expected riding requires and how much metal you want to be grinding out. At the bottom of the ports there is way less choice, they all need to be moved down by half the stroke increase plus thickness of the chosen base packer plus or minus any factory porting error (so BDC is flush with the ports). So a 221 barrel has the ports moved down.

In Europe they run Vespas 50,000 Km on the same piston. I would think anything over 25,000 miles is pretty good going.

The old Malossi 210 barrel is great but the ASSO piston is the issue. I believe it was changed later in the design by Malossi. Maybe the original was some other piston. As it is the frame side transfer lines up great but the out side transfer is 3mm out. The reason for this is that the barrel has mirrored transfers (exactly the same but mirror opposite). The ASSO piston however has the same recess each side (no mirror) as the gudgeon pin is in the way and doesn't line up (so the error is ground off the piston for the frame side).

Been riding her around plenty. Should be about run in by tomorrow. Goes so well. Standard 200 gearbox (with original 35 tooth 4th) and the 3rd to 4th change pulls just as hard as 2nd to 3rd does. I doubt as fast as the Polossi but my records show that was rev 13 by the time it cracked

[mijapxman]

🙉

[pxguru]

Well that didn't take long to run in

It jetted in so well. To ride around town you would think it was a standard engine on an SI carb.

As it stands: 52 Pilot, B56 pilot atomiser, DQ261 main atomiser, 152MJ, 55 slide, K93 needle (clip 3 from top)

Runs at about 275F generally and just 300F at WOT. As I sort of expected, it isn't so fast. Runs great pulls really good, goes up hils at 60 mph in 4th and doesn't slow down but wide open just about manages 74mph (gps). Seems to struggle to rev and will just get to 8000rpm (64mph) in 3rd, this is just not enough. Needs more power. Will have a think about how to find some, without losing too much of anything else.

[mijapxman]

😉

[sime66]

That’ll need a tweak then – other than the pulling so well in 4th, it’s only a bit better than The Beast at its best last June (& hopefully this June again), which was 101kph (63mph) in 3rd, 116kph (72mph) in 4th, and also getting to 150°C (302°F) at WOT then. That is enough for me though, but it’s only a tweaked DR177, not a Malossi 221; there must be a lot more there with a bit of your magic; hopefully before rev13 - I realise getting the extra power at those higher revs/speeds is the hard bit though; I wonder how much you'll show when you do.

(Didn’t touch mine this weekend BTW.)  

[pxguru]

Took her for a run to Brighton yesterday to get some sea air and me to have some chips on the pier. Didn't go anywhere near the cliffs even though the temperature at motorway cruise was gently climbing all the time. I stopped a few times to tweek the jetting and it ended up obviously rich, even with this it was still getting slightly hotter than I would like after cruising for several miles. At cruise rpm ignition timing is not an issue, so this only leaves cooling or compression. Cooling is better than fine on a PX made for Italian weather. Came home through the villages without incident.

So it had to be compression. This MRP head is still new to me and is supposed to be about 12:1. I had a 0.8mm head gasket handy so quickly fitted that and returned the jetting to how it was. A quick test ride later and its all good. Was doing 67mph in 3rd and touched 77mph on the bypass and still only averaging 280F, which means I can drop the needle another half clip to bring the temperature up to where the power is. At least it is now quicker than your 180; still slower than the Polossi at it's best but its early days

[sime66]

Mayday, Bank Holiday, Brighton Pier, chips.... - good effort!   

It would take me ages to find it, but I recall now that you said the Polossi was a little off-optimum jetting to help control the temperature.
Also interested that heat/power balance is again seeming to be the limiting issue, and that you looked to compression to deal with it.
I don't think Italian old ladies were riding 30bhp shopping bikes when the fan was designed; I wonder if there's any ideas to improve airflow cooling over head - I made a little cone over the cowl round the spark plug to stop air-loss there to make it pass over the head, but not sure if it's helping. I also wondered about cutting slots in the fins like a T5 (or holes), but thought less aluminium or cast iron might actually make things worse.
I see you've left me at the lights now too; I knew it was temporary.

Interesting thread; following closely, but I'll try to interrupt as little as possible.

[pxguru]

Still getting hotter than it should when ridden hard. Much better with lower compression but still hotter and not as fast as the old iron barrel was. I think you are onto something with the head cowl. It is necessary to cut lumps of to get the MRP head on. And it's centre squish so has a huge hole in it for that. I think I'll patch up the gaps and rework it in general. Pop riveted aluminium palates? or any other suggestions?

Missing power: I think one issue is that it has a two degrees less blowdown duration than the Polossi and another issue is the Malossi 210 exhaust port has that rounded shape, which means even less blowdown width. These might even be not helping the temperature if too much exhaust gas gets left in each stroke. When I next get time I will fix these two issues first. The Polossi exhaust port was so huge it wouldn't have looked out of place on a Lambretta forum. Now I have tried it and don't like it, I don't mind so much.

[sime66]

Having bits missing off the cowling isn't a good plan; got to have as much air as poss passing over the cooling fins. The reason I made my cone was because I'd cut several slots out when I was playing with locating CHT sensor without bending the wire. My cone is just flooring vinyl and epoxy:



...but riveted aluminium sheet might be a good idea for more complex patching. I was wondering whether a metal cowl or a plastic one would be better actually; which holds the heat in, or cools quicker; just thinking aloud.
(Truth is, I quite like the look of the stainless cowl, but don't want to make things worse). Possibly fewer slots in the flywheel cover might help too; I'd thought about giving the intake a tweak as well.
I follow what you're saying about exhaust timing/blowdown and size/shape and how much hot exhaust gas remains in each stroke, but I'll chew on that a bit better, later as well. If you're thinking about temps inside the cylinder, I have to bear in ind I'm using warmer air for combustion under the cowl too, not cold from under the seat; some of that air has already cooled the head.

[pxguru]

Had time to think it over and I really think this head cowl is a big part of my temperature issue. The way that MRP head splits into top and bottom most of the air flow from the standard cowling is directed at the bottom fins and not so much for the top.

www.sip-scootershop.com/en/products/cylinder+head+mrp+px200+race+_22159419

This head is 11.2:1 on a 57mm crank but 12.2:1 on a 60mm crank. Quite high compression but not too much. The 0.8mm head gasket is reducing the compression too far now, so in the final version I think I will use a thinner one and be more like 11.9:1 and that drops the trapped compression back in the zone too.

Not going to get a chance to fix this for a while but I will report back when I do.

In the long term I would think about moving your air filter. The hotter under panel air is a slight issue but worse is the cooler air comes from the road level. If the filter works well it is little concern but if you are touring in the rain there could be a possibility of the filter getting wet.

Edit: I have done some big sums and determined that the compression is not so bad. Slightly too high but not so much. Next revision will be 12:1
The missing power: Is the exhaust port shape of the standard 210. The calculations concur. I thought it was worth a go as you can't put the metal back but it's sh**e. Keeping the blowdown duration near to as it is, I'll reshape the whole port and that will fix it. Almost certain ;-)

[pxguru]

Well.....I am surprised

I modified the head cowl and closed up the old plug hole now it's centre squish, with pop riveted ally sheet. And re ducted the air flow to be 10mm further forward with more ally sheet (no picture as its not pretty) due to the way the split MRP Race head works.
Re-shaped the old Malossi exhaust port to a 21st century design and widened it a bit more too.
Test ride was c**p. Revs a bit more freely but overall exactly the same, 152 main jet and temperature sky rockets still when thrashed. Got it up to 355 degrees F which is at least 50 more than safe but luckily no catastophe. Was really running hot and not a gauge issue, as it felt terrible cruising until it cooled down to about 330F.

After some pondering I decided it wasn't the cooling. 'the Germans' MRP know what they are doing with heads so isn't that. Jetting is slightly too rich, so not that either. Still at a loss to what is causing the over heating and as it was overheating even at 5000 rpm cruising, changing the timing would have solved it but the further loss of power would be an issue with the P200 gearbox.

I decided to fiddle with the porting to get the squish tighter while I was thinking about it. I just plonked the head on knowing the squish was 1.5mm but as the compression is still at least 11+:1 there would be no real issue....usually correct but in this case.....wrong!

Compromised the porting a little but closed the squish to 1.2mm. Goes great and gets to 290F max at full thrash. I like this. Straight home and closed the squish some more to 0.9mm (don't do this at home kids) and is just wonderful. Some average thrashing got to 67mph (GPS) in third gear and 75mph (GPS) in 4th and still humping along(backed off as too gusty/windy to keep it on the road today)temperature not over 270F. Next time out I now need to down jet to get the teperature back up!

Now who'd have thought that? When the squish clearance is 0.3 mm too big it overheats. I would have had money on the opposite. More pondering required.












PS. Put new clutch steels in it while I was at it, as the last ones were looking chewed in the centre when I changed the plates last month.

[sime66]

I had a quick read-round last night; Malossi have obviously paid a lot of attention to getting the cooling air right, so it is an issue, but you’d expect them to have dealt with it adequately. I hope to have more time next week, and I do have some questions about timing and jetting relative to temperature, optimum performance and economy, but I've not gathered my thoughts tidily yet. I also stumbled across an interesting thread on MV, which leads to a possibly interesting thread on GSF (which I haven’t looked for yet); here’s the MV thread (I’m not entirely sure which head you have, but Think it’s similar with fins above and below?):

modernvespa.com/forum/topic146417

Hopefully I’ll get back into it more next week; the compression squish result seems odd, can you think of any feasible explanation?

[pxguru]

Mine is the race head. There are two and they look identical. The race head doesn't have the built in 1.5 mm.
I like the 0.9mm clearance and might keep it. The compression is about 13:1 which is my new top limit but the exhaust port is fairly high so trapped compression is still about OK.

You might want to recheck the squish on the beast? Should be not more than 1.0 mm on your smaller bore.

Edit: Had a bit of a think about the squish clearance and getting hot. Best I can come up with so far is that when you close up the squish a greater proportion of the mixture is burnt towards the centre of the head and caught in the primary ignition, which then makes more power, saves fuel and is fairly well documented everywhere as doing so.
Conversely if you increase the squish clearance, more fuel is compressed at the edge of the head, which is still burnt but squish mixture is only burnt as a follow on from the primary ignition and possibly even not fully burnt to the edge until too far after TDC, as this squish mixture takes too long to burn it isn't creating more kinetic energy (power), therefore as it does burn and there is an energy conversion in progress it must go somewhere and that would have to be as even more heat (and much more than the increase in compression).

A consensus of all information tells us a 221 squish clearance should be between 1.0mm and 1.5mm. Always knowing that a big squish was costing power and that the 1.0mm limit was just caution (could really be 0.5mm if you are really careful) I always preferred nearer the smaller value myself (the Polossi was at about 0.7 mm for most of it's life). I have never really ran anything with this kind of power at anywhere near the 1.5mm let alone slightly over it, like I said I just plonked the race head on when I got it out the packing and thought I would tweak it later.

Note to self: The more power you have the tighter the squish needs to be to stop it overheating. The list of what makes a scooter overheat just got one item longer.

[sime66]

Ahh, I’ve only just seen your 13th June edit, though I’ve been pondering and reading about this for a few weeks myself, but still not found the time to get stuck in again, or get all my thoughts together into a comprehensible post on my own thread. Here's my numbers:
With the 0.2mm gasket my squish is 1.35mm and my compression is 10.35:1 (compression, cold engine, is 130psi).
Without the gasket my squish would be 1.15mm and my compression would be 10.54:1.
To go to 1mm would be a smaller (1.8mm or whatever combination to 1.85mm I can find) spacer and Dremelling (raising) transfer ports (and checking all others, and probably opening combustion bowl for compression – not a mid-Summer job for me).
It seems you are confident that removing the extra 0.2mm gasket would improve my (possible) temp problem, by improving where and when the mix burns (primary ignition, centre of head); I’m happier with that now there is a feasible explanation; previously I was dubious that one result on yours was sufficient to draw conclusions, but didn’t want to say so, which is why I asked if you could explain it.
Also removing the 0.2mm gasket will reduce my transfer timing, which will also tame the beast a bit.
In addition, retarding my ignition timing to 18° will help. (Is this contradicted by the earlier burning being better for temps theory though?)
These two jobs do seem to be what I should do next; granted with a very warm ambient this weekend, I was seeing 184°C (with dodgy CHT on plug) on short runs only up to 7800rpm in 3rd, 6000rpm in 4th, but still with a decent plug - remeber that 184 might-well be only 135°C. Even if my CHT temps are falsely high, it won’t do any harm to be careful if warm air isn’t cooling efficiently enough either.
I wasn’t sure which thread to post this on, but it’s mainly in reply to your 13th June edit, so I’ve put it here for now.
I don’t want to clog up your thread, but I’m not ready to pick mine up again yet; too many questions and jobs, and too much other stuff going on to find time to concentrate on thinking it through, or doing any jobs.

I’ve sent you a question via PM, if you’d have a quick look....

[pxguru]

Retarding the timing more than necessary does still make heat but without so much power. Not been something that has much interested me but the torque does apparently go up. Overall retarding the timing is when it is detonating or as a last resort.
With my 221 there is no detonating, piston is clean of scratch marks on the top and I can hear pinking from 100 yards, so clearly not a timing issue but killing the power by retarding does overall bring the temperature down but I guess that is mostly with making the primary ignition weaker, which is not in our interests.
I am often sure but from my last two tests this has really worked for my 221. Once I get the final jetting tweak done to know it is all ok, I will turn my Kytronic back on (3rd Khepher failed a long time ago).

For your 177 the squish should be smaller anyway. 1.2mm is what the books say is for a 250cc (a 50cc would be 0.5mm). Really should be aiming for 1.0mm but its all a compromise and taking that out of your transfer delay may notice a little too much.
Take out the 0.2mm packer for sure. Will reduce the rpm and won't notice too much. The compression will then only be 10.5:1, so no issue at all. My new 221 head is now about 13:1 and seems to like it. 12.5:1 is where I am comfortable though so might need some tweak later on.