Gaskets, Ignition, Compression etc...

[modpx]

Hello everybody, today i finally put my PX 225 Pinasco back on the road after the seizure i treated in the post "seizing on the 1st day of the year". Just a little ride around the block, cause it's too cold and icy to go anywhere these days (though the new IRC snow freshly arrived from SIP are really great!).
The main jet is now 140, the cylinder has been cleaned and polished and the piston is brand new. I ordered a new part for the carburator (not arrived yet) www.sip-scootershop.com/en/products/float+chamber+cover+dellorto_128295t7 this shoud solve the problem of gas flowing at full throttle, i have the feeling that a SI 24 with that much of hp and torque might not be enough..(?). IF anyone had ever tested it let me know. I also spaced 1mm under the cylinder base, that's cause i noticed that there was still 1mm space left between the piston at its BDC and the transfer ports, i thought: if there's space why not to fill it? ;D Now: for what i know spacing the base gives more torque and spacing the head gives more revs... (correct?) Should i adjust the ignition or i can leave it where it is?

[pxguru]

I think you are getting the hang of this now From the measurements you sent me the transfer port open time with this 1mm gasket is much nearer ideal for the torque you want from this kit.

As a general rule packing the base gives more torque until you go 0.1mm too far then you start to lose power. Packing the base lowers compression which also loses torque.

Do you want to try to measure the squish clearance (space between piston edge and head) again?

[modpx]

Jan 21, 2013 19:22:14 GMT pxguru said:

I think you are getting the hang of this now From the measurements you sent me the transfer port open time with this 1mm gasket is much nearer ideal for the torque you want from this kit.

As a general rule packing the base gives more torque until you go 0.1mm too far then you start to lose power. Packing the base lowers compression which also loses torque.

Do you want to try to measure the squish clearance (space between piston edge and head) again?

I think you meant packing the head (not the base) lowers compression which also loses torque? I havent measure the squish yet or..let's say no squish has come out from my measurements yet! Do you think the squish is now bigger due to the base-packing? Tomorrow i will try if i can get a 3 or 4 mm stober strand and try again. What squish would be perfect on this set up? Another question about the exhaust pipe. JL is super torquey, i think is perfect for this kit, but it limits the top end a little to early. Ok the short fourth gear doesnt help to have a massive top end either especially not on a torquey cylinder like Pinasco BUT if i use a high rev pipe good on a Malossi kit, will i get abetter top end even though i lose a bit of power at the lower range? Which pipe do you have on your Polini? I know Polini is pretty torquey too. (btw videos are always welcomed)

[kru251]

Do you think the squish is now bigger due to the base-packing?

If you've packed the cylinder up by 1mm which has the same head attached, then the clearance will be whatever it was before plus 1mm!!!

[modpx]

the squish is the distance between the piston at the TDC and the head. but the head is attached to the cylinder so if you pack the cylinder the distance between the piston (that stays where it is) and the head (that moved 1mm upper) cant be the same! Or i'm missing something?!

[modpx]

Jan 21, 2013 21:43:28 GMT kru251 said:

Do you think the squish is now bigger due to the base-packing?

If you've packed the cylinder up by 1mm which has the same head attached, then the clearance will be whatever it was before plus 1mm!!!

I think we're saying the same thing. i misunderstood your comment

[kru251]

Yep. Same result either way you state it.
The squish figure that was, is now the same squish figure PLUS that 1mm ;D

[joey]

Packing the base increases revs, top end peak hp slightly but you end up with a narrower power band and less torque.
Packing the head raises compression (extra volume between top of exhaust port and head "corrected compression ratio") and increases torque with a slight loss on top end

[pxguru]

Everybody is correct! ;D Packing the base or head both lose compression.
No two engines are exactly the same (ie. why are the casings matched pairs?) And no two kits are exactly the same.The ports must be set to the right height first no amount of increasing the compression is going to get more torque out of the engine than the ports are set to allow.

modpx, you now have the barrel set at a good starting point. Next, how much is your squish now (gap between piston edge at TDC and head)?

[pxguru]

Jan 22, 2013 9:07:44 GMT joey said:

Packing the base increases revs, top end peak hp slightly but you end up with a narrower power band and less torque.
Packing the head raises compression (extra volume between top of exhaust port and head "corrected compression ratio") and increases torque with a slight loss on top end

Joey I think you are touching on something a bit too advanced for this class...lol
I am really tring to keep it simple and not confuse anyone.

[modpx]

ISorry guys, m a bit confused :

me: for what i know spacing the base gives more torque and spacing the head gives more revs... (correct?)

guru: As a general rule packing the base gives more torque until you go 0.1mm too far then you start to lose power. Packing the base lowers compression which also loses torque.

joey: Packing the base increases revs, top end peak hp slightly but you end up with a narrower power band and less torque.
Packing the head raises compression (extra volume between top of exhaust port and head "corrected compression ratio") and increases torque with a slight loss on top end

Let's just keep it on the torque and revs level for now. What gives what?

[pxguru]

It is not so simple as that.

Just concentrate on measuring the squish.

Twist together a few stands of solder wire to about 3mm thick and 150mm long. Take out your spark plug. Move the piston to 10mm from the top. push the twisted solder down the spark plug hole until you feel it touches the barrel wall. Turn the flywheel to squash the solder. Measure the squashed end. easy....lol ;D

[modpx]

Jan 22, 2013 12:48:01 GMT pxguru said:

It is not so simple as that.

Just concentrate on measuring the squish.

Twist together a few stands of solder wire to about 3mm thick and 150mm long. Take out your spark plug. Move the piston to 10mm from the top. push the twisted solder down the spark plug hole until you feel it touches the barrel wall. Turn the flywheel to squash the solder. Measure the squashed end. easy....lol ;D

Alrite then: 1) The squish is 2.92mm,
2) here are some pictures: imageshack.us/g/1/9977548/ in the first three you can see in which condition i found the cylinder/piston/head: drawned into oil That must have been when i firstly started the vespa, i saw a mixture of air and oil bubbling out from somewhere (carburator?) then it immediately stopped but the marks are still there. The other pix are about the transfer ports/piston BDC and the piston at the TDC. There's also a pic of the spark plug, do you think it goes too deep into the head?
3) The distances between transfer ports/head and exhaust port/ head are: are 37,15 and 48 approx

[kru251]

That spark plug picture.
Yes, I do think it is too deep because if the carbon builds up around it and carbon can be quite hard you can damage the threads in the aluminium head when trying to remove it.
Personally, if it is the correct one for heat range etc I'd add another spark plug washer to the underside to elleviate the protrusion issue!

[modpx]

Edit: the distances are: 49 and 38. The spacers i used to pack the base are 3 standard base gaskets one on top of the other so they are a bit less than 1mm approx 80mm. The oil spread all over the piston head/cylinder head could be caused by the fact that i didnt empty the carburator before i started to work on the cylinder. It's good rule switch off the gas tap and keep the motor on until the carburator is empty but i only switched off the gas.

@kru yes i asked cause Pinasco gives a washer with the kit, before the seizure i drove all the time without it, now i put it back.

[kru251]

Edit: the distances are: 49 and 38. The spacers i used to pack the base are 3 standard base gaskets one on top of the other so they are a bit less than 1mm approx 80mm.


That's an 0.8mm cylinder raise then overall.

[pxguru]

Yes, put the washer on the spark plug. You don't want to see any thread showing inside.

Are you sure that measurement is 49.0 mm from the transfer to the top of the barrel? I prefered it when it was 48.0 mm

The piston looks like its 0.5mm from the top of the barrel at TDC. Do you agree?

The head was really leaking. You are going to have to fix that!

[modpx]

Jan 22, 2013 21:47:43 GMT pxguru said:

Yes, put the washer on the spark plug. You don't want to see any thread showing inside.

Are you sure that measurement is 49.0 mm from the transfer to the top of the barrel? I prefered it when it was 48.0 mm

The piston looks like its 0.5mm from the top of the barrel at TDC. Do you agree?

The head was really leaking. You are going to have to fix that!

Spark plug is ok now, the measurement is approx 49 yes a bit less, maybe 48,80, it's hard to tell exaclty i couldnt use the micrometer for that. the piston is 0.5mm i agree, maybe slightly less 0,4. How to fix the head? Where is it leaking from exaclty? Are you making all the calculations with the squish and all the rest? Whats the response for the perfect set up? (cool video your polossi btw )

[pxguru]

That is always the big question. What is "the perfect set up". The perfect set up is like the perfect girlfriend! There isn't one! So pick a few factors that you insist on and compromise on the rest! ;D

For yours you need to achieve at least 7 to 7500 rpm in gear, pull like a train and not blow up, all with a 24mm carb. This is possible.

To get there as easily as possible with what you have, you need to raise the barrel by another 0.9 mm that will be 1.7 mm in total. The piston should then be 1.3mm from the top of the barrel at TDC.

You need to do something with your cylinder head. Can you measure the the gap indicated in the photo? Should be about 1.5 mm

Attachments:

[modpx]

Jan 23, 2013 9:55:20 GMT pxguru said:

That is always the big question. What is "the perfect set up". The perfect set up is like the perfect girlfriend! There isn't one! So pick a few factors that you insist on and compromise on the rest! ;D


If i keep seizing in the snow, spending tons of euros in spare parts and especially spending all my spare time in the garage i will soon not have a wife anymore! ;D I have like the feeling i was more mature when i was 15 riding my Piaggio Ciao!

For yours you need to achieve at least 7 to 7500 rpm in gear, pull like a train and not blow up, all with a 24mm carb. This is possible.

To get there as easily as possible with what you have, you need to raise the barrel by another 0.9 mm that will be 1.7 mm in total. The piston should then be 1.3mm from the top of the barrel at TDC.

but if i pack 1,7 mm the base then the transfer ports wont be anymore completely open cause now theyre only 0.5mm or so distant from the piston ring..is that ok?

You need to do something with your cylinder head. Can you measure the the gap indicated in the photo? Should be about 1.5 mm

yeah the measure is 1.5mm, im worryed cause today it happened again : detonations, air and oil on the piston and the cyloinder head and then it didn't start anymore.

[pxguru]

1.7mm on the base calculates as correct for what you need. The piston ring may be 1mm past the port at BDC this is not important when the port is fully open.

Sounds like you may have a problem with a crank seal. Check your gear oil level and read the thread on "air leak test". You need to fix this problem before going any further. Your wife might not be so happy about this!

[modpx]

Jan 24, 2013 12:13:02 GMT pxguru said:

1.7mm on the base calculates as correct for what you need. The piston ring may be 1mm past the port at BDC this is not important when the port is fully open.

Sounds like you may have a problem with a crank seal. Check your gear oil level and read the thread on "air leak test". You need to fix this problem before going any further. Your wife might not be so happy about this!

Good to know, i'll fix the head and then i'll try the different set ups. Im thinking of putting back the original piaggio cylinder+head to make a long stroke 208 Piaggio packing 1.5mm the base for the long stroke also to verify if the problem is in the head or somewhere else. i'll keep you posted.

[pxguru]

The problem sounds like a crank seal. You shouldn't start it again until you have fixed it. If the cluch seal is spinning in the casing it could really damage your engine!!

[modpx]

Jan 25, 2013 18:27:38 GMT pxguru said:

The problem sounds like a crank seal. You shouldn't start it again until you have fixed it. If the cluch seal is spinning in the casing it could really damage your engine!!

This is what happens, at evry kickstart you see a "cloud" fuming out the cylinder head!! :

[modpx]

i thnk i know what it is, must be that the head is crooked and now it has to be grinded.. alternatively i could try to use some sealants to see if it works... or put the Piaggio cyinder back.

[joey]

Don't use any sealant kid............. lap it in properly on wet & dry sprayed with WD40 as was explained in the other thread.......... it'll take a while but it'll be worth it.
I did say on the other thread that a leaking head was your problem

[modpx]

Jan 25, 2013 20:42:48 GMT joey said:

Don't use any sealant kid............. lap it in properly on wet & dry sprayed with WD40 as was explained in the other thread.......... it'll take a while but it'll be worth it.
I did say on the other thread that a leaking head was your problem

Hi joey,i tryed that already i bought a sheet of glass appositely for that purpose but the result is even worse! Now it doesnt even start. How long should i lap it for and how? and should i lap the cylinder as awell? I dont know if the head crooked because i made some mistake while taking it on and off the cylinder (like leaving the head hanging from the studs from one side only) or cause the first time i lapped it with wd 40 to get rid of the blue sealant i didnt use a perfect flat surface..this might have caused some gaps in the head surface. I dont think the head was leaking before the seizure cause i had no major signals like accelerated idle and so on...

[joey]

Your original pictures show that the head was leaking, signs of blowby on the cylinder and head, and I did say that quite early on.

Lapping the head in can take quite some time, ages if the head is warped badly, but does work.

Start off with quite rough wet & dry (600 grit,) and colour the head sealing face with black marker pen, after a few seconds of lapping have a look at the sealing face and where the marker has been rubbed off is a high point and where it's still coloured is a low point.

Lap in a figure 8 motion to ensure it laps evenly.

Once all of the marker colour starts to disappear after only a few seconds you can move down a grade on the wet & dry finally ending up on a 1200. You don't really want to go any finer.

Once it's all nice and flat make sure you torque tighten the nuts using equal and opposite and do each one a bit at a time.
Once the head is correctly tightened let the motor warm up on a high tickover for 20 minutes or so and then retorque the nuts.

I generally torque head nuts to 20lb/ft, not sure what it is in newtons, so do each nut to say 16lb/ft (or metric equivalent,) then do each one to 17 etc.

Personally I think doing the head properly will cure all your problems.

[modpx]

Jan 26, 2013 16:50:57 GMT joey said:

Your original pictures show that the head was leaking, signs of blowby on the cylinder and head, and I did say that quite early on.

Lapping the head in can take quite some time, ages if the head is warped badly, but does work.

Start off with quite rough wet & dry (600 grit,) and colour the head sealing face with black marker pen, after a few seconds of lapping have a look at the sealing face and where the marker has been rubbed off is a high point and where it's still coloured is a low point.

Lap in a figure 8 motion to ensure it laps evenly.

Once all of the marker colour starts to disappear after only a few seconds you can move down a grade on the wet & dry finally ending up on a 1200. You don't really want to go any finer.

Once it's all nice and flat make sure you torque tighten the nuts using equal and opposite and do each one a bit at a time.
Once the head is correctly tightened let the motor warm up on a high tickover for 20 minutes or so and then retorque the nuts.

I generally torque head nuts to 20lb/ft, not sure what it is in newtons, so do each nut to say 16lb/ft (or metric equivalent,) then do each one to 17 etc.

Personally I think doing the head properly will cure all your problems.

Ok i'll try again but as you seem to know Pinasco, which head would you pick between MMW central plug and Pinasco VHR central plug for my cylinder? Do you have any experience or know anyone who has had those heads? And is there big difference between the central plug and the side plug? Cause now i have the side plug. This question is for everyone who has some knowledge about these heads and wants to help.

[modpx]

I bet one of you with all the Polini and Malossi out there must have an MMW..