flyhighprerunner Posted August 14, 2009 Report Posted August 14, 2009 How come that piston doesnt have any carbon build up at all or and oil on it of anykind looks like you just smashed it with a mallet! Quote
Wildcardracing Posted August 14, 2009 Report Posted August 14, 2009 Looks like the aftermath of too much piston clearance to me. I'm not a fan of the namura pistons, I've seen a lot of them fail. Is your crank a short rod or a long rod? Short rod cranks will put more of a side load on the pistons and can cause broken skirts, especially if the clearance is a little loose. Quote
stroking Posted August 14, 2009 Author Report Posted August 14, 2009 Looks like the aftermath of too much piston clearance to me. I'm not a fan of the namura pistons, I've seen a lot of them fail. Is your crank a short rod or a long rod? Short rod cranks will put more of a side load on the pistons and can cause broken skirts, especially if the clearance is a little loose. brandnew 5mm longrod 4mill HR cylinders where freshly bored to fit piston Quote
stroking Posted August 14, 2009 Author Report Posted August 14, 2009 How come that piston doesnt have any carbon build up at all or and oil on it of anykind looks like you just smashed it with a mallet! ive never seen a alcohol motor build up carbon on top of the piston...... Quote
BigRed350x Posted August 14, 2009 Report Posted August 14, 2009 Excessive piston/cylinder clearance can also let the piston rock back and forth in the cylinder on each revolution. If this happens too much it will crack and break skirts. I would slap whoever had you put a spacer plate on the top of the cylinder. The spacer plates go on the bottom, or you get a set of custom cut domes for the stroke you have and the deck height you end up with, with whatever gasket you are using. Most 4mil setups are not just a bolt and go setup with stock cylinders. There are a few critical measurements that you have to find and adjust before you ever fire the engine. Piston/cylinder wall clearance (which is something you do on any top end rebuild, not just strokers), deck height, gasket thickness, what porting you have, port durations in relation to the thickness gasket you have or that your builder recommends, squish clearance, squish angle, dome size... Anyone who builds these engines can tell you that you don't just bolt on a spacer plate and let her rip down the track. Quote
KEVSWS6 Posted August 14, 2009 Report Posted August 14, 2009 You can buy kits that run spacers on the bottom or head gasket spacers that run on top. The problem may have been not doing the homework on what you bought. Also not doing all the checks and measurements while assembling. That's an expensive lesson but fear not. It doesn't come close to the cost of just the last motor I toasted on my bike. Quote
blowit Posted August 14, 2009 Report Posted August 14, 2009 I would note that clearance for cast pistons is N O T the same as for forged. This is where cast pistons get their bad name!!!! People do not see a clearance on the box so they assume to use the Wiseco clearance, and they break!! Cast pistons run at about half the tolerance of forged. Port chamfering is also very important. Seems way too many motors that are killed just by rough port openings. If the specs are right on the engine, it will hold. If not, well, the pics above show it all.. I would not point at the pistons yet. I think there was a reason it let go. Yes, if piston contacts the head, it can break the pistons where it did due to violent skirt loading and shock through the piston. It will break at the weakest point and that is it. B Quote
flyhighprerunner Posted August 14, 2009 Report Posted August 14, 2009 ive never seen a alcohol motor build up carbon on top of the piston...... Didn't know that it was on alcohol...... Quote
stroking Posted August 15, 2009 Author Report Posted August 15, 2009 here is a better view of what happen PISTON Quote
blowit Posted August 15, 2009 Report Posted August 15, 2009 (edited) here is a better view of what happen Yep, you found your culprit. Bottoming that edge will load the hell out of the intake skirt. Pushed until it broke. Get things lined up better and check squish. Wisecos would have failed too. I am surprised you did not "hear" that B Edited August 15, 2009 by blowit Quote
stroking Posted August 15, 2009 Author Report Posted August 15, 2009 here is a better view of what happen Quote
stroking Posted August 15, 2009 Author Report Posted August 15, 2009 Yep, you found your culprit. Bottoming that edge will load the hell out of the intake skirt. Pushed until it broke. Get things lined up better and check squish. Wisecos would have failed too. I am surprised you did not "hear" that B Another head has been cut milled and its on and running.....this head is cut to run one head gasket with NO plates. Quote
SonOfSand Posted August 16, 2009 Report Posted August 16, 2009 Yep, you found your culprit. Bottoming that edge will load the hell out of the intake skirt. Pushed until it broke. Get things lined up better and check squish. Wisecos would have failed too. I am surprised you did not "hear" that B I don't understand, what do you mean by "bottoming that edge"? What was the culprit? Quote
sheeban Posted August 16, 2009 Report Posted August 16, 2009 I don't understand, what do you mean by "bottoming that edge"? What was the culprit? I bought that same kit from motosport and had the same thing happen both pistons broke like yours my was still running good before i took her apart what a supprise that was. Quote
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