Engine seizure

[pjelec]

Hi Everyone I have just joined this Forum as I recently purchased a Vespa after 15 years without one.

I could do with some help Please. I have a MK1 Vespa T5 1987. It has the p200 engine fitted and I mix the oil in the fuel tank myself.

I was using a mix of 150ml for every 5 litres of fuel.
On a long staight road doing approx 70mph my engine seized. When I got it home it must have cooled down and it would turn over but not start. The piston was scored and 1 of the rings were damaged.
I replaced the piston and rings and was advised this happened as ny oil mix was too much. Even though there is no smoke at all coming from the exhaust.
I changed my piston and used a mix of 100ml for every 5 litres. I done about 15 miles and my back wheel locked until I pulled in the clutch. After 10 minutes it started and 1 mile down the road it locked again. Left it for half hour and drove 8 miles home not exceeding 30mph and it was ok. I dont think I am using enough oil but have been told I am. Can someone help me out here. Thanks

[kru251]

Sorry to hear of your woes!

Engine:
Type: single cylinder, two stroke
Bore x stroke: 66.5x57 (200)
Displacement: 198cc (200)
Compression Ratio: 9.3 (200)
Transmission: manual, 4 speed
Lubrication: 2% oil-petrol mixture

Two percent is basically 50 : 1 .
Think that's 100ml oil per 5 ltrs fuel.
Too much oil can make the fuel mixture weak leading to your problems. The same seizure problem can be had obviously with too little two-stroke in the mixture too!!!!!

So, you seem to now be using the correct mixture, but I'll bet there is barrel damage now causing your issues with 'high points' due to the previous issues.

[pjelec]

Thanks for your reply.
Once it happened the first time I was told it was too much oil. When I put the new piston in I drained the tank and filled with 5 ltres of fuel and 100ml of oil (2%). So in effect it ran with the correct mixture in with the new piston but only lasted about 15 miles. I have had the Vespa for about 5 months and done about 400 miles with the wrong mixture.
Are you saying that the barrel was damaged after the first time. I did check it and it looked fine. I have seen a lot worse and are still running.

[kru251]

When a piston has nipped/seized up the fact is that the metal surfaces have actually been bonded together if even for a micro second. That means that material from the rings/piston end up being removed and then deposited on the bore. As you said, the piston was scored. Where did the microscopic pieces of aluminium go? Well they can fuse to the bore. You'd never see it with your naked eye nor sometimes even feel them; but they do exist. These then cause the high points ie. the bore is slightly narrower here and certainly not circular. That can also cause the problems you've had. A rebore with new piston & rings to suit plus careful running in on the correct ratio fuel/oil may well be the only way you're going to cure the "clutch hand hover" syndrome you are having now.
Actually, my left hand does that out of habit as had a Lammie Li125 last year just lock the rear wheel as it seized up. I quickly grabbed in the clutch, coasted a short way, let the clutch out gently expecting it to lock up again but no and it all fired up again OK. A tad more oil now used! I got lucky!!!!!!!

[sbwnik]

Get the cylinder honed. It's not expensive but worth the hassle.

It's possible that a seal is on it's way out, that can cause seizures and is a fairly common problem.

[pjelec]

Thanks for the comments. What seal could be on its way out.
I took the plug out today and it is black. Is this a tell tale sign of anything

[colin4255]

Putting more than 2% oil in the fuel can indeed lead to a seizure. Oil burns about 50% hotter than fuel so adding more oil than is needed, far from lubricating, as most people think, will cause the mixture to burn hotter and actually increase the chances of a seizure! Vespas should generally run at a 2% mix, or 100ml for every 5 ltrs of fuel. Unless the maker of your barrell/piston etc suggests more, then don't do it. Like others have said either the crankcase seal or engine main bearing seal leaking or 'on its way out' could cause similar issues, but never put more oil in the fuel than the maker of the barrell/piston/ kit reccommends - it won't help at all. It will in fact, make matters worse s the engine will run hotter and likely cause more damage.

[sbwnik]

I've copied this from another forum I use, and i stick by it:

There's a lot of b*ll*cks talked by people who 'know the answer'.

Some say adding extra oil makes an engine run lean by thinning the petrol out, so overheating the engine. Some say it acts as a coolant. Some say it'll cause your plug to foul. Some say it'll be spat out of the exhaust and help your pipe last longer.

All I know is..... we call him The Stig.

Oops, sorry, got distracted by the obvious joke there.

At the end of the day, even with a fully ported and tuned engine, you're not looking at anything even close to the tight tolerances found in a racing engine, it's still a bit basic... And I think this is why there are such varied opinions, people have found that they ALL work!

My opinion? I'm not giving it in case you follow it and blow up your engine!

[bsr65]

You say your plug is black, is it sooty or oily black. check how many turns the carb air mixture screw goes in then return screw to original position then turn 1/4 to1/2 turn out, repeat procedure to your plug is tan/ brown colour. my p200e is set at 2, 1/2 turns out. Dont know if this would cause your bike to sieze but worth checking.