pushrod seals and lots of smoke

[avant-garde]

I've done a bit of research whilst waiting for the minors to be rescued and I've found this info:

Smoke was coming out the crankcase...I think that the exhaust was getting into the crankcase (though the blown gasket or more likely, as piston blowby), picking up crankcase oil vapors and venting though the breather that is connected to the air filter box - hence the oily white smoke. http://www.scooterforumonline.com/index ... pic=1511.0" onclick="window.open(this.href);return false;

Re: oil in air box/filter
by ghost123uk » 03 Aug 2010, 08:20
Usually blocked crankcase breather...
Also could be worn piston rings and / or bores causing excessive crankcase pressure (more serious but not as serious as if it was watercooled !!) - A compression test would tell you if it was this.

Some folks do a temporary "fix" by feeding the pipe that goes from the crankcase to the air filter into a pop bottle instead of to the air filter housing (to catch the oil but still let the crankcase "breath")
The crank breather on the 2.0 is to the right of the distributor as you look in the back of the vehicle. Its unlikely to be a blocked breather but more the result of excessive crankcase pressure.

So it would seem that there is excessive crankcase pressure due to the lots of white smoke. I'm not very happy about this temporary 'fix' solution because that would mean that the garage is trying to ditch their responsibilities as they havn't told me it was a temp fix. Basically trying to brush me off. I will be caling the garage later

[avant-garde]

Okay, I rang the main man today and things are looking up. Basically he said that "if I'm not happy then he isn't happy", that's really good to hear and it puts my mind at rest. I'm taking it over on Friday for him to look at.

It was the barrels that were roughed up, not the piston rings and the reason why the crankcase oil breather pipe was not put back on the air filter box is that it would have messed up the carb settings while the pistons 'bed-in' resulting in a stalling engine...so he said that the breather pipe attached to the fan housing is a temporary measure...just wish he had told me all that when I picked it up.
(when would he have told me? in a weeks time? In a months time? ...mmmm!)

Anyway...
He is worried about the leaking pushrod seals onto both heat exchanger box's which is why he has asked me to take it back over there.

I hope that this is the beginning of the end.
Fingers crossed.

[BOXY]

Hi, good luck with the garage it sounds like it could be a happy ending. If you don't mind I'll give you a little bit of "engines for idiots" so you're ready for any garage techno babble.

The pistons in your engine slide up & down inside the barrels or cylinders. The piston travels up the barrel twice and down the barrel twice on each 4-stroke cycle hence "4-stroke" engine. The cycle is suck - squeeze - bang - blow. The cylinder head has two valves one inlet and one exhaust. The valves open in a sequence controlled by your tappets. Suck - inlet valve open - piston moving down - petrol & air from the carbs is drawn into the barrel. Squeeze - both valves closed - piston moving up - petrol/air mix compressed. At the "top" of this stroke the mixture is ignited by the spark plug and the cylinder forced down - Bang - both valves closed - piston moving down. This is what makes your wheels go round. Blow - exhaust valve open - piston moving up - burnt petrol pushed out the exhaust.

For this cycle to work properly the piston has to be a tight fit inside the barrel. This is done with piston rings. The rings are sprung so they maintain a good contact area with the walls of the barrel as the piston moves up & down. Now on the BANG stroke the pressure in the barrel increases dramatically because its almost a contained explosion. Any excessive wear in the barrels or rings will let the hot burning mixture past the piston and into the crankcase. This pressure & heat in the crankcase can cause white smoke to vent out of the breather. This wear can also let oil from the crankcase get drawn into the barrel. When this mixes with the petrol/air and gets ignited by the spark it forms the blue/white smoke that gets pushed out the exhaust pipe.

There are other possibilities but In your case this seems to be the most likely cause of your problem. When you speak to the garage ask them if the barrels were re-bored and new pistons and rings were fitted? If it was all new then there's a problem that the garage need to sort out. It could be a cracked piston, scored barrel or missing / broken piston ring(s). If they re-used your barrels & pistons then it looks like they might be out of acceptable tolerances.

I hope this helps a bit. I've PM'd you as well. You got your last post in as I was writing this. I must type faster.

[sarran1955]

Hello,

I think a compression test, engine cold, engine hot, might be revealing.

Try and get this done before you see him, A compression tester is not dear or hard to use, or maybe someone to help.

Should be 8 to 10 bar, or up to 150 psi in old money,

Good luck, don't get technobabbled.

Cordialement,

[avant-garde]

Okay...took the van over to the 'man' today and there was burning oil everywhere. Mainly from the pushrod seals dripping down onto the heat exchangers and burning. I assume that must be due to the excessive crankcase pressure? At least the guy that fitted the 'new' engine has now seen it with his own eyes.

Anyway the bottom line is that he is going to replace the whole lot as there is obviously something that can't be seen with the naked eye - like a bent this or a bent that. He said to me "I'm not happy with this engine and I have ordered all new parts....etc etc.
I guess that is a result. I just hope that he doesn't turn round and expect payment for it all... Could he lawfully do that?

I will keep you guys updated on what happens.

Thanks again for all your helpful advice - very much appreciated.

Kevin.

[sarran1955]

Hello,

Well done,

I wonder whether he is aware of the unexpected publicity on the forum/ web.

Give him time to strip it down and diagnose, then go back to see him. Is there someone on the forum who could go along as 'an interested friend'

Cordialement,

[avant-garde]

Okay, just a quick update on the van and its smoky oil/excessive pressure/piston rings etc ...I've had the bus back now for a week and everything is back to normal again - perfect. The main man (Nigel Allen) put in new pistons and barrels, new pushrod oil seals, sorted out the excessive pressure in the crankcase, he replaced the carb metal pipe thing that runs from one side to the other etc and then even made up some pushrod aluminium guard plates to stop debris from the road getting up into the seals etc...and it hasn't cost me a single penny.

He showed me one of the pistons and it had friction marks on two places...the piston should have been a uniform grey colour instead there were two areas on the piston that were not grey but a worn metal colour, in other words friction. He showed me the piston rings that he fitted previously and they were fine, so I'm slightly confused as to what actually caused the problems in the first place.

I still have reservations about the engine letting go again, but I guess only time will tell?

While I'm here, I would like to take this opportunity to mention that Nigel bent over backwards to get my van sorted and so I only have praise for the man.
and yes I'd recommend him.

[kevtherev]

...and breath out..
glad it all over and worked out right.

[silverbullet]

put in new pistons and barrels, new pushrod oil seals, sorted out the excessive pressure in the crankcase

The reason for excess crankcase pressure was that it needed new pistons(& rings) and barrels in the first place...but now it's sorted.

made up some pushrod aluminium guard plates to stop debris from the road getting up into the seals

Not so sure about this but can't do any harm
All's well that ends well anyway.

[avant-garde]

put in new pistons and barrels, new pushrod oil seals, sorted out the excessive pressure in the crankcase

The reason for excess crankcase pressure was that it needed new pistons(& rings) and barrels in the first place...but now it's sorted.

made up some pushrod aluminium guard plates to stop debris from the road getting up into the seals

Not so sure about this but can't do any harm
All's well that ends well anyway.

The pistons and rings and everything else on the engine were new in the first place which is why he was having trouble trying to figure out why the engine failed. Nigel showed me the piston rings which were fitted last time and they were fine...even though there was blue smoke/oil dripping out of every pore! That's why I took it back to him for a third time...and the rest is history.
The bottom line is that I have had in effect TWO new engines now and we don't really know what caused the failure in the first one other than the fact that the piston (he only showed me one) had a couple of friction burns on it.

Time will indeed tell.

Cheers.

[BOXY]

Without actually seeing the bits that have been replaced it would be impossible to be sure what caused the previous problems.

Make sure you follow the running-in instructions until everything is bedded in. Keep an eye on the oil level and hopefully you'll have an engine that will last for years.

[riffboy]

Glad its all sorted for you mate. Made my palms all sweaty reading this!

This forum is amazing for this kinda stuff, nowhere else would people take so much time to try and help you!!