Modern Vespa

Hi everyone
before a few days I instal Big Bore Cylinder Kit (80ccm) by Malossi and alsow I instal Power Cam from same producer to my Vespa S50 4V 4T. I did it slowly ... no hurrying, each part of this "puzzle" was check before instal. Everything goes slightly, piston rings "clic" nice, tightening of all component on correct Nm, applycation of new bearing to camshaft was smooth ... and in my mind I telling "that will be nice tune up". After asembly I tryed to start engine. Rear wheel slowly spining and I could hear only starter but nothing more.
Starter works well, after a few attempts I smel gasoline so fuel supply should be OK too, carb is ok and all hoses are connected, spark plug is OK but dry. (should had be wet from gasoline after a few attempts to start???) What about ignition ... could it be that problem ?
Thanks for all opinions and replies.

cam timing?

In my opinion I did it correctly ... set center mark to the middle, chain were take down, ... etc .... before assembly I checked mark 4T on flywheel, put back the chain and check if is cam correctly moving with a few spins by flywheel.
Is it OK ?

I'd say Cam timing, fuel issue then spark.

Cam you've addressed

Fuel issue- is the carb cleaned and is there fresh gas reaching the carb? Don't forget to upjet the main jet to compensate for the larger displacement.

Spark- you can test this by holding the bottom of the spark plug against a cylinder stud (ground) and cranking over the motor. It helps to have a friend kick over the motor so you can securely hold the spark plug/watch. Make sure to hold the rubber cap as you can get zapped

Appologies but sometimes mistakes are made by well meaning people. Cranshaft could have been at the bottom of the stroke when the flywheel marks lined up. But if you are confident the piston was at top dead centre then we will have to look elsewhere.

Sparkplug car not fully secured?
Fueling can be isolated by spraying some cold start fluid into the air intake whn cranking. If it fires on that then is is the fuel system.

Off the top of my head bedcause i'm not stood next to the bike

Did you remove thlearnacese ce engine from the bike? Did you reconnect the grounding connection to the frame? maybe the plug is trying to spark but has not ground to go to.

Did you reset the valve clearances? New cam has higher lift and valves are not fully closing.

Carb were cleaned before a few weeks and gasoline is fresh. Jets are replaced too.
I try the spark plug.

Yes I put whole engine out and work with it separately...it's better then geting hands into small holes where is no free space.

OK ... I understand what you mean.
I have to disassemble it again and check all parts and setings.
I am patient and I like to learn some news ... but I should to consultwhole process with someone "who knows where and what to touch".

unfortunately ... it happened

will it be re-usable ?

Sure. It looks like you dodged a bullet. Have a really good look. That one valve only just touched and wiped a bit of carbon off. It also look like it did might not even have made a mark in the piston?
You need a thicker base gasket or a thicker head gasket. What do the instruction say?

Edit sorry had a brain fart yesterday

In the piston are two small imprints "like from children teeth" ... nothing deep. As you wrote on one of exhaust valves is probably wiped a bit of carbon off. Isn't necessarily to clean head and valves?
There were packed three gaskets. I used two of them (green waxed paper and black I think this is metal sheet ). Green gasket has thickness 0.8 mm and I used as base gasket and black one has thickness 0.5 mm and that I use as gasket of head. In box was one more gasket (gray) it is widest it has 1.00 mm. But I'm not sure from which material is made.
May I have to use the gray gasket as replace for base (green) gasket ?
Instruction manual didn't talks about which gasket should be placed on base or between cylinder and head ... in fact there isn't mentioned anything about gasket at all. There is used word "assembling".
So what I should do now?

Difficult doing this at arms length. Is the kit one that can be used for both two valve and 4 valve engines? Maybe the 4 valve engine requires the use of all the gaskets so tow at the bottom.

Edit OK found this If your kit is Art. 3117771

http://storage.malossistore.com/files/montaggio/pdm/7317771.pdf




Arrow on piston is facing the exhaust/bottom of the engine. (sorry if this is an insult)

I can't find the instructions on line. (See edit above)

If you have the piston the correct way around and you still get interference then use both gaskets together at the bottom.

I'm running out of ideas.

I have this kit

https://www.sip-scootershop.com/en/products/racing+cylinder+malossi+79+cc+_m3113905

it's same kit only different product number.
Piston is instaled correctly. You can see arrow on the bottom at the first attachet picture.
OK I try to use at first only the thicker gasket and if it will looks still to low I add a second gasket and check how it looks.
What about carbon on head and valves .... should I have to clean it ?

Technically you don't need tp remove the carbon deposits but it wouldn't hurt while it is apart.

Give it a soak in WD40 and use a scotchbrite pad. Bit messy but it doesn't have to be perfect.

Do you have a new sparkplug? If not you'll have to give that a good clean after the soaking process.

Wash off the cleaned surface before reassembly.

NB I think your kit has superceded the older one but it is difficult to tell. Same instructions should still apply.

Marten,

Whats happened?

Hi waspmike ... sorry lot things to do in the job. At first I installed the thicker gasket. Next the head was cleaned and valves were set to the correct allow run-out 0.10 mm and when I assembled it I realized that on the first assembling I didn't correctly set a piston. I didn't think about it and set it into the top position (and that was wrong). Problem was on my side ... probably I was hurry. The correct position for asembling is 3mm before the top of cilinder and "4T" mark on the ventilator confirms it. So I put everything together and .... she lives !

Thanks for all replies in this thread !

Result.