|
Title: Rotating piston rings? Post by: Berger on September 07, 2008, 14:37:12 pm Have been struggling with my Ghia engine lately. It`s a mild 1950 (87x82), where the stock length pistons have been modified to stroker length. I have been testing 2x44 Empi HPMX carburetors on the engine, but could not get it to run good. Trìed different jettings, tuning and tuning, but it would not run good at cylinder 4.
At the last run it started to burn oil, leaving thick blue smoke down the street, and I thought that this is it, I must have broken some piston rings or melted the piston due to bad jetting or something. So I pulled the engine out, and replaced it with a stock 1500 so I could bring the car to SCC. So today I opened the engine, and found nothing wrong except from that the first and second piston rings at #4 was lined up! I`m pretty carefully when I assemble my engines, and sure that this is not how I set them! SO here`s the questions: Is it normally for the piston rings to rotate different? If not, could this be caused by the modified pistons? Could this really make this heavy oil burning? I have never seen this before... This is how they were set when i opened it: Title: Re: Rotating piston rings? Post by: richie on September 07, 2008, 15:20:42 pm Have been struggling with my Ghia engine lately. It`s a mild 1950 (87x82), where the stock length pistons have been modified to stroker length. I have been testing 2x44 Empi HPMX carburetors on the engine, but could not get it to run good. Tryed different jettings, tuning and tuning, but it`t would not run good at cylinder 4. Hi At the last run it started to burn oil, leaving thick blue smoke down the street, and I thought that this is it, I must have broken some piston rings or melted the piston due to bad jetting or something. So I pulled the engine out, and replaced it with a stock 1500 so I could bring the car to SCC. So today I opened the engine, and found nothing wrong except from that the first and second piston rings at #4 was lined up! I`m pretty carefully when I assemble my engines, and sure that this is not how I set them! SO here`s the questions: Is it normally for the piston rings to rotate different? If not, could this be caused by the modified pistons? Could this really make this heavy oil burning? I have never seen this before... This is how they were set when i opened it: It seems to happen quite alot,not really sure why,but if the oil scraper rings were doing there job then what you have shouldnt make any difference to oil consumption/burning,just possibly allow more crankcase pressure so I dont think that is your problem,possibly them being lined up meant that cylinder had poor compression?more likely those sh** carbs have been causing bore wash due to to much fuel cheers richie Title: Re: Rotating piston rings? Post by: Berger on September 07, 2008, 17:17:58 pm I know the carbs are shit...now...but I`m the "I-don`t-belive-it-before-I-see-it-my-self" kind of guy.... :-\
Was about to give them up when the oil-buring thing happend, and thougt it might be something else. So, your saying to much fuel could bring the oil to the combustion? Or is it likely that there is a problem with the oil scraper rings to? I haven`t measured yet, but it looks like there is little or no wear at all. Title: Re: Rotating piston rings? Post by: Sarge on September 07, 2008, 18:21:01 pm Did you check the expander on the bottom ring to see if it was "over-lapped"..., the ends need to butt into each other rather then overlap (an easy to make mistake)?
Title: Re: Rotating piston rings? Post by: Berger on September 07, 2008, 18:41:19 pm Did you check the expander on the bottom ring to see if it was "over-lapped"..., the ends need to butt into each other rather then overlap (an easy to make mistake)? Yes, I had a look at it and it was in correct position :) Mine are color coded, so it`s easy to see if it`s wrong. Title: Re: Rotating piston rings? Post by: Wünderwolff on September 07, 2008, 20:00:30 pm What richie meant was that due to bad carbs/jetting/tuning too much fuel goes into the engine, running overly rich. This excess fuel cleans the oil of your cilinder walls, causing bad friction with the pistons and quickly worn cylinders. Leading to oil consumption.
Title: Re: Rotating piston rings? Post by: Rasser on September 07, 2008, 20:17:27 pm Did you check your heads ? - maybe a loose valveguide ?
Title: Re: Rotating piston rings? Post by: Berger on September 07, 2008, 20:43:25 pm What richie meant was that due to bad carbs/jetting/tuning too much fuel goes into the engine, running overly rich. This excess fuel cleans the oil of your cilinder walls, causing bad friction with the pistons and quickly worn cylinders. Leading to oil consumption. I see, but I have only been running these carbs for about 200 km, and there is almost no signs of wear. Title: Re: Rotating piston rings? Post by: Berger on September 07, 2008, 20:47:23 pm Did you check your heads ? - maybe a loose valveguide ? No not yet. Will do! :) Title: Re: Rotating piston rings? Post by: Bruce on September 08, 2008, 07:46:59 am ....the stock length pistons have been modified to stroker length. What exactly did you do to the pistons?Title: Re: Rotating piston rings? Post by: Berger on September 08, 2008, 08:16:43 am They are shortened at the bottom:
(http://www.vwnorge.no/index.php?action=dlattach;topic=320.0;attach=2071;image) Title: Re: Rotating piston rings? Post by: Bruce on September 08, 2008, 08:30:54 am There's your problem. You can't just do that.
Look at the piston on the left. Notice the center of the pin is exactly half way from the tip of the skirt to the crown. This is so the tip of the skirt and the edge of the crown both control piston rock. On the modified piston, the tips of the skirts are doing nothing because you cut them off. This allows the piston to rock a lot more than the left piston. If you set a true stroker piston beside your right piston, you will see that the center of the pin is a lot closer to the crown. That is why you're burning oil. The excessive piston rock prevents the rings from properly sealing. Title: Re: Rotating piston rings? Post by: Berger on September 08, 2008, 08:40:16 am There's your problem. You can't just do that. Look at the piston on the left. Notice the center of the pin is exactly half way from the tip of the skirt to the crown. This is so the tip of the skirt and the edge of the crown both control piston rock. On the modified piston, the tips of the skirts are doing nothing because you cut them off. This allows the piston to rock a lot more than the left piston. If you set a true stroker piston beside your right piston, you will see that the center of the pin is a lot closer to the crown. That is why you're burning oil. The excessive piston rock prevents the rings from properly sealing. This was the big question when I buildt this engine, and there seems to be more than one opinion about this. Look at a true race piston, there is almost nothing under the pin. And note that this is ONLY happening at #4 sylinder. The three others are clean. But it may be the case... :-\ (http://www.roadracemotorsports.com/store/images/piston.jpg) Title: Re: Rotating piston rings? Post by: Rasser on September 08, 2008, 10:19:52 am There's your problem. You can't just do that. Look at the piston on the left. Notice the center of the pin is exactly half way from the tip of the skirt to the crown. This is so the tip of the skirt and the edge of the crown both control piston rock. On the modified piston, the tips of the skirts are doing nothing because you cut them off. This allows the piston to rock a lot more than the left piston. If you set a true stroker piston beside your right piston, you will see that the center of the pin is a lot closer to the crown. That is why you're burning oil. The excessive piston rock prevents the rings from properly sealing. This was the big question when I buildt this engine, and there seems to be more than one opinion about this. Look at a true race piston, there is almost nothing under the pin. And note that this is ONLY happening at #4 sylinder. The three others are clean. But it may be the case... :-\ (http://www.roadracemotorsports.com/store/images/piston.jpg) You can´t compare two different pistons like that - the weight/balance can be completely different (end to end). I remember Johannes Persson talking about the pistons he uses, they have the wristpin moved so far up to the top of the piston as possible (very close to the rings), this makes a very light piston and a very narrow engine. Maybe he has some more advice on what to do, and what not to do ? Opinions differ - thats for sure ;-) Title: Re: Rotating piston rings? Post by: Bruce on September 08, 2008, 15:34:51 pm I remember Mark Herbert showing me a custom ultra short piston he had made where the edge of the wrist pin was into the oil ring. In other words, you had to assemble the piston on the rod before installing the oil ring.
|