| Author | Message | ||
     Sportyeric |
Installing the new rings on new stock pistons, the top ring is tight at one point to the point that the ring won't rotate at all. The ring has to be "stuffed" a bit to get it into the groove. Is that a problem? (The service manual only gives outer wear limits.) | ||
| Pammy |
That is a huge problem. Either It sounds like something may be wrong with the ring land on your new piston. Putting a motor together should never involve the old "if it don't fit, force it" mantra. | ||
| Sportyeric |
Its the ring that has the tight spot. I didn't think that I twisted it putting it on but I suppose buying a new ring set is the recommended solution. (Message edited by Sportyeric on April 10, 2008) | ||
| Pammy |
Are you sure it's the ring? If you tweaked the ring, all you can do is replace it. | ||
| Sportyeric |
Yeah. Thanks Pammy. My crappy workmanship. I've put a bit of a spiral in it, now that I look at it again in the daylight. I'm off to the dealership for a replacement. Pleasantly surprised that I can buy just one cylinder's worth. Thought I'd have to spring $40 for a pair. Thanks for your input. | ||
| Pammy |
Good for you looking out and finding that problem before something bad happened. Make sure you have the proper ring end gap before installing the rings. | ||
| Strato9r |
Make darned sure you follow Pammy's advice on ring gaps; it is ABSOLUTELY critical to have the ring gap set for the exact pistons you are using! Different piston materials, designed for specific applications and construction techniques, will affect the amount of heat the piston radiates, and since the piston rings actually provide a major thermal conduit for cooling the pistons, having the gaps set at the optimal room temperature gap will ensure that the expansion of the ring at full load operating conditions will not cause the ends to butt together. If this happens, bad things start happening instantly; first, the pressure being exerted radially by the ring against the cylinder increases dramaticly, increasing friction, further increasing the ring temperature. At this point, the ring may actually provide enough resistance against piston motion to break the ring lands, especially in the case of hypereutectic alloy cast pistons, which are more brittle than their more malleable forged alloy counterparts. At any rate, the piston ring temperature will instantly rise to the point where they will be incapable of transferring heat away from the piston, and REALLY crappy things start happening at that point. First, the temperature on the piston faces will rise to the point where they will ignite the intake charge WAY before the spark plug is supposed to: detonation at a time when the engine is least capable of dealing with it. Piston cooling jets will have little effect by this time, as the underside of the piston crown will have reached a temperature where oncoming cooling oil will fry itself to the metal, building up a very effective heat insulating layer. By now, the piston crown temperature will have exceeded it's fatigue point, softening it, weakening it's ability to maintain it's dimensional stability. After that, it's all over but the cryin'. Hypereutectic alloy pistons have a very low expansion rate, allowing tighter skirt clearances for a quieter running engine with better ring sealing characteristics at lower engine temperatures. Partially because of the high percentage of silicon dispersed throughout the alloy to stiffen it, hypereutectic pistons run hotter, and therefore require a larger room temperature end gap to prevent butting. Some modern forged pistons actually use a smaller top ring gap than second ring gap, factory pistons use different specs from year to year and model to model, so follow the manufacturer's recommendations for the piston you have, and the conditions the engine will be subjected to. If there is ever any doubt, always lean toward the high end of a recommended ring gap. There is excellent research to support the fact that even intentionally excessive ring gaps have very little effect on such phenomenon as "blow by" or increased oil consumption; poor cylinder finish and out of round bores are the cause of these problems in the vast majority of cases. As a matter of fact, ring gaps, when properly set, will allow just enough pressure to come by the top ring gap to purge accumulated oil past the second ring gap, actually reducing oil consumption. All of this applies to nearly any type of engine, and I see the effects of ring gap problems on a daily basis. Late model diesel trucks, 5.9 liter Cummins powered Dodges for example, can run just fine for thousands of miles, but two or three times a week, one of the local dealerships sends over an engine that someone has pushed a little too far with electronic tweaking, and invariably, the engine damage can be pinpointed to operating conditions that heated the top rings past the point that they will butt together. Natural gas powered irrigation pump engines can also be affected, as they see higher combustion temperatures than gasoline engines, especially when compression ratios are too low to result in complete combustion. Any good shop can tell you that it's all in the details. Just follow the instructions, and keep things clean, and things invariably work out great! | ||
| Sportyeric |
Nice write-up, Rick. For myself, I'm just using standard Harley?Buell fare. Checked the gapping and all is good. A little closer to the outside of specs from the manual but within the range. Now back to the pinion gear battle! |
