Blow-by on rebuilded engine?

Road-race engines and ancillaries - general discussion
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Honza
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Blow-by on rebuilded engine?

Post by Honza » September 30th, 2011, 7:04 pm

Hello,
I have one question regarding to blowby on engine.
I have Fiat Stilo 1.8 16v (same as Punto HGT, Barchetta, Lancia Lybra etc- engine type 192A4.000..). In recent days I tried to solve excesive oil consumption wich was almost 1l/800km.
I was decided to change all parts wich could affect oil consumption and repair/refubrish remaining parts.

- Head was checked and slightly modified (three angle valve seats, modified valves, cleaned ports and removed mismatch). Valve guides were measured and their measures are within the factory tolerances. Valve stems were sealed with new sealing rings. After carefull check of hydraulic lifter 8 were scraped because of erosion on contact surface and new ones take their place.

-pistons and bores were checked, bores were subsequently deglazed with flexhone (my first experience with this wery nice and usefull tool!) .
What is amazing on this engine is the fact, that it has only 1.2mm; 1.2mm and 2mm thick piston rings and nicely designed , wery light pistons.
Old piston rings had a gap 0,8 (first sealing ring)- 1mm (second ring), new rings has 0,3-0,38 mm. So it was probably the main reason for this oil consumption...

Today i started the engine-and what is interesting - when I remove the oil cap the engine has quite simmilar blowby (if i can name this effect this way) to engine before this repair.

First of all - rings are not bedded in yet- I will bed the engine tommorow.
Secondly - could the "blow by" through removed oil cap be caused by the design of crancase ventilation?
its only ventilated through the valve cover. There is no hose directly conected from crankcase to intake manifold.

I´ve attached scan from Fiat repair manual regarding this system (I hope that it isn´t break site protocols, in other case i will remove the picture)

REMOVED BY GC DON'T YOU HAVE ANY IDEA WHAT COPYRIGHT IS?

all comments or ideas are welcome
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fingers99
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Re: Blow-by on rebuilded engine?

Post by fingers99 » October 1st, 2011, 5:24 am

I'd wait for the engine to bed in before worrying overmuch. Then try replacing the PCV valve.

Guy might like to comment, but these engines do seem to have a high oil consumption relative to other modern (non Fiat/Alfa) engines. The factory manual, IIRC, does state a figure somewhere.
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Honza
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Re: Blow-by on rebuilded engine?

Post by Honza » October 1st, 2011, 6:52 am

factory manual states oil consumption 0,4l/1000km
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fingers99
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Re: Blow-by on rebuilded engine?

Post by fingers99 » October 1st, 2011, 8:58 am

Honza wrote:factory manual states oil consumption 0,4l/1000km
Interesting. I think that's a lower figure than stated for the Seicento 1108! Mind you, in the later case, we're talking of an "attention needed if this figure is exceeded" figure.

Still, bed it in, see what the figures are/how the blow-by is.
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Honza
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Re: Blow-by on rebuilded engine?

Post by Honza » October 29th, 2011, 11:22 am

after some 700km done I have bad news - engine runs quietly, It feels also to be more powerful, but it consumes oil in the same way...

I don´t know what I did wrong.. bedding in according to my experiences - let It rev freely without to much throttle on lower gears, without useless underrving...for the firts 200km trip (wich was done without problems..).

Only one sympthom is blue smoke from the exhaust after first start after long standing (hlaf a day, 1 day etc..) sometimes it smoke, sometimes not...in the last week it smokes more often.

My ideas are:
- bad/badly fitted valve stem seal (the man who built my head is one of 3 people/specialists who I am
trust because of their experiences with road/compettition engines, so mistake here is not probable..)

- badly working PCV valve (its already cleaned) - when I remove it from the hose to the TB (the hose remain connected to TB), the blowby through filler cap disappear, however the suction force is so high, that its difficult to remove filler cap, so my idea is that non ventilated increase of pressure could force oil to the combustion chamber...

- something wrong in engine block...
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fingers99
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Re: Blow-by on rebuilded engine?

Post by fingers99 » November 7th, 2011, 3:09 am

Compression test?
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robert kenney
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Re: Blow-by on rebuilded engine?

Post by robert kenney » November 7th, 2011, 6:20 pm

Hi Honza,
Seems like a PCV valve issue although it also seems like you have a missing vent hose.

The PCV removes the crankcase air and another vent hose allows air (filtered) air back into the crankcase. This hose usually goes back to the airfilter box down stream of the filter element. The fact that when you removed the PCV from the suction line and reconnected it you had a large pressure differential tells me that you have no return vent hose or a limited volume of it.

The PCV valve at idle manifold suctions, should almost shut down to prevent excessive alternate air flow back into the manifold and odd running due to it. Upon application of the throttle and the subcequet increase in manifold pressure the PCV valve should open fully and ventilate the pressure from building. I'd simply replace it and verify your ventlation hoses. That should solve your issue.
Robert Kenney # 111

timinator
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Re: Blow-by on rebuilded engine?

Post by timinator » November 7th, 2011, 8:03 pm

Honza,

Did you clean the ring grooves in the piston? The oil scraper ring groove can get a lot of build up that will reduce the scraper's effectiveness. Same with the second ring.

Were you able to measure the bore for taper?

Tim

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