swooshdave Posted January 20, 2019 Author Share Posted January 20, 2019 There were a bad batch of rods in 1974, I think. You also have to keep in mind that Commandos get ridden way more than Triumphs or BSAs so they are going to have more reported issues. Bikes don’t break if they don’t get ridden. I’d always been against an oil pressure gauge but due to the recent expensive lesson I’ve changed my mind... 2 Link to comment Share on other sites More sharing options...
Lucky Phil Posted January 21, 2019 Share Posted January 21, 2019 There were a bad batch of rods in 1974, I think. You also have to keep in mind that Commandos get ridden way more than Triumphs or BSAs so they are going to have more reported issues. Bikes don’t break if they don’t get ridden. I’d always been against an oil pressure gauge but due to the recent expensive lesson I’ve changed my mind... What caused to Oil pressure failure? Ally rods in my view have their place.....in drag cars. The metallurgical facts remain as valid now as ever. Aluminium will fail eventually due to cyclic load strain no matter how small the loads are it will eventually fail. Steel properties are totally different in this regard, steel will sustain cyclic loads below the yield point for an infinite number of cycles. A second hand alloy rod that looks and measures up perfect will always have a question mark over it where a steel rod under the same circumstances wont. Tell you what if I was living in the states where Carrillo rods come from I know what i'd be using. The Daytona engine I'm currently putting together uses Carrillo's as standard. I sent them back to the factory states side and they refurbished them for me and posted them back for $120/rod. Great service and company. Ciao 1 Link to comment Share on other sites More sharing options...
swooshdave Posted January 21, 2019 Author Share Posted January 21, 2019 The seal between the pump and timing cover fell off when I was refitting the cover. It fell into my oil pan and I never knew it. Until it was too late. Failure had nothing to do with the rods. Sent from my iPhone using Tapatalk 1 Link to comment Share on other sites More sharing options...
Lucky Phil Posted January 21, 2019 Share Posted January 21, 2019 The seal between the pump and timing cover fell off when I was refitting the cover. It fell into my oil pan and I never knew it. Until it was too late. Failure had nothing to do with the rods. Sent from my iPhone using Tapatalk Yes I understand that, just pointing out if you need new rods then steel is the superior way to go from an engineering perspective. Also the harsh reality is and not trying to be an ass about it is that you also can do without the oil pressure gauge if you eliminate the assembly errors. Ciao Link to comment Share on other sites More sharing options...
swooshdave Posted January 21, 2019 Author Share Posted January 21, 2019 I have heard stories of that same seal splitting even when installed correctly. I was on borrowed time without knowing the oil pressure. Sent from my iPhone using Tapatalk 1 Link to comment Share on other sites More sharing options...
Scud Posted January 21, 2019 Share Posted January 21, 2019 Sorry to hear about the Norton. It always hurts most when the damage is self-inflicted, huh? FWIW, an oil pressure gauge alerted me to a problem on my prior red LeMans that I would otherwise been ignorant of. I put it on because I thought it would be cool to have, along with a voltmeter. Didn't expect any useful information... just liked the idea of have some more gauges. But it surprised me with a low reading (not low enough to cause the low pressure light to come on though). Investigation eventually revealed two missing tabs on the sump gasket - installed that way by previous owner or mechanic. Anyways... back to your bike and best wishes with it. Link to comment Share on other sites More sharing options...
swooshdave Posted January 21, 2019 Author Share Posted January 21, 2019 I have a saying, education is expensive. I’m getting educated! Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
al_roethlisberger Posted January 21, 2019 Share Posted January 21, 2019 ..... yep, sorry to hear about that, but at least you know why. That's a much better place to be in than wondering. It'll be a cool bike once back together Link to comment Share on other sites More sharing options...
MartyNZ Posted January 21, 2019 Share Posted January 21, 2019 A friend here is building a '72 Norton engine to put into a flattrack racer he is making. He recommends Jim Schmidt at jsmotorsport.com for supply of improved Norton parts. He tells me that the 850 has relatively short con-rods, so the rods see undesirably high angularity. Jim sells pistons with the piston pin position slightly higher, and matching slightly longer Carillo rods, which are claimed to be more durable at higher rpm. Lucky Phil is right when he says that the original aluminium alloy rods have a limited life. Forging helps improve fatigue life, so does compressive stress peening, but no matter how it is made, alum rods will fail eventually. High rpm and high loads make that inevitable failure happen sooner. A bigger problem for that engine is the position of the oil pickup at the bottom of the crackcase. At sustained high rpm, the oil collects in an area further back from the pickup, the pump gulps air, and the big ends fail. That, along with the popped seal, may have added to the cause of your engine failure. My friend's fix is to apply the scoop shape to both sides of the crankcase, and reposition the pickup point to force more oil to the pump. A lot of work, but I think he enjoys the welding and machining involved. He is also making his own 270 degree crank for the engine. I think that this is so that it sounds more like a Guzzi. 2 Link to comment Share on other sites More sharing options...
Lucky Phil Posted January 21, 2019 Share Posted January 21, 2019 A friend here is building a '72 Norton engine to put into a flattrack racer he is making. He recommends Jim Schmidt at jsmotorsport.com for supply of improved Norton parts. He tells me that the 850 has relatively short con-rods, so the rods see undesirably high angularity. Jim sells pistons with the piston pin position slightly higher, and matching slightly longer Carillo rods, which are claimed to be more durable at higher rpm. Lucky Phil is right when he says that the original aluminium alloy rods have a limited life. Forging helps improve fatigue life, so does compressive stress peening, but no matter how it is made, alum rods will fail eventually. High rpm and high loads make that inevitable failure happen sooner. A bigger problem for that engine is the the position of the oil pickup at the bottom of the crackcase. At sustained high rpm, the oil collects in an area further back from the pickup, the pump gulps air, and the big ends fail. That, along with the popped seal, may have added to the cause of your engine failure. My friends fix is to apply the scoop shape to both sides of the crankcase, and reposition the pickup point to force more oil to the pump. A lot of work, but I think he enjoys the welding and machining involved. He is also making his own 270 degree crank for the engine. I think that this is so that it sounds more like a Guzzi. A one piece 270 degree crank would be fantastic. Its what all parallel twins need in reality. Ciao Link to comment Share on other sites More sharing options...
swooshdave Posted January 22, 2019 Author Share Posted January 22, 2019 It’s actually quite easy to change the pickup location on a 72. Grub screw in the front hole and some light grinding to the windage spur. Look at the notch at the bottom of the crankcase. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
swooshdave Posted February 1, 2019 Author Share Posted February 1, 2019 So with a parallel twin the pistons are typically symmetrical... Good indication there is a problem when they aren't level. Link to comment Share on other sites More sharing options...
gstallons Posted February 2, 2019 Share Posted February 2, 2019 You got that right ! Link to comment Share on other sites More sharing options...
swooshdave Posted February 3, 2019 Author Share Posted February 3, 2019 Link to comment Share on other sites More sharing options...
swooshdave Posted February 14, 2019 Author Share Posted February 14, 2019 https://youtu.be/a4P4js2trmA Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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