heraldcoupe Posted October 2, 2013 Share Posted October 2, 2013 Hi i just got a new piston for a 1200 and the gudgeon pin can be pushed in and out by hand, I wouldn't worry about it, if it had circlips to hold the gudgeon in place but it doesn't. So how tight should gudgeons be in tolerance fit pistons? Also my old man recons some pistons are tight on the conrod and the gudgeon spins in the piston? is this correct it seems crazy to me but you never know with the English :P Last thing I want is a gudgeon pin putting a groove down the side of my bore. Quote Link to comment Share on other sites More sharing options...
dar Posted October 2, 2013 Share Posted October 2, 2013 never seen a pistone with out a circlip,and the conrod spins on the pin thats why it got a brass bush in conrod, do not place in engine with out a circlip to hold gudgeon pin in place Quote Link to comment Share on other sites More sharing options...
JohnD Posted October 2, 2013 Share Posted October 2, 2013 If the gudgeon will slide in and out by hand when its cool, then it will slop about like a mop in a bucket when it's hot. Aluminium's coefficient of thermal expansion is twice that of steel.If you don't want to use circlips to retain a fully floating gudgeon pin, then I have heard of using nylon buttons (not off your coat, turned from rod stock)in each end, but I've never used them.Agree with dar, if it ain't got a circlip groove then it ain't a Triumph piston! You could get one machined in but it'll cost you!JOhn Quote Link to comment Share on other sites More sharing options...
herald948 Posted October 2, 2013 Share Posted October 2, 2013 JohnD wrote:If you don't want to use circlips to retain a fully floating gudgeon pin, then I have heard of using nylon buttons (not off your coat, turned from rod stock)in each end, but I've never used them.I've a "race" 1147cc Spitfire engine, built originally in the late 1960s or early 1970s, that has those buttons. I'd never seen such until I had to open up the engine to replace some broken rings. Those buttons certainly seemed to do their job well! Quote Link to comment Share on other sites More sharing options...
heraldcoupe Posted October 3, 2013 Author Share Posted October 3, 2013 JohnD wrote:If the gudgeon will slide in and out by hand when its cool, then it will slop about like a mop in a bucket when it's hot. Aluminium's coefficient of thermal expansion is twice that of steel.If you don't want to use circlips to retain a fully floating gudgeon pin, then I have heard of using nylon buttons (not off your coat, turned from rod stock)in each end, but I've never used them.Agree with dar, if it ain't got a circlip groove then it ain't a Triumph piston! You could get one machined in but it'll cost you!JOhnMore likely aftermarket with circlips, Triumph made pistons that have circlips and also ones that have a interference fit gudgeon (Workshop manual mentions them both), Im just not sure how tight the gudgeon pin is meant to be in them. I could machine groves and put circlips in but I don't think its needed, Ill knock up some Teflon buttons and just 620 Loctite the pin in. Doubt very much that ill ever have a problem with it.Pic is a standard triumph piston with no circlips Quote Link to comment Share on other sites More sharing options...
JohnD Posted October 3, 2013 Share Posted October 3, 2013 Would that be a "press fit" piston"See: http://www.canleyclassics.com/searchforapart/?ptno=142659News to me! Thanks for telling!John Quote Link to comment Share on other sites More sharing options...
DanM Posted October 3, 2013 Share Posted October 3, 2013 Some of the 1147 engines used press fit pistons( no circlips and have to be pressed onto conrod), they also had different conrods. My spit mk11 engine has them. I would suggest you get the correct type for your engine. Mine is in bits and as the press fit ones are unavailable I have obtained a set of the full floating type con rods for if I ever get around to replacing the current 1500 engine Quote Link to comment Share on other sites More sharing options...
Slimboyfat Posted October 3, 2013 Share Posted October 3, 2013 7915 wrote:Some of the 1147 engines used press fit pistons and as the press fit ones are unavailable http://www.canleyclassics.com/searchforapart/?desc=&ptno=142659Other Triumph specialists may have stock, etc, etc.............(modified, sorry John didn't see your link before I did this) Quote Link to comment Share on other sites More sharing options...
Slimboyfat Posted October 3, 2013 Share Posted October 3, 2013 and they appear on internet auction sites regularly, usually described vaguely so as to 'disguise' the press fit bit. Quote Link to comment Share on other sites More sharing options...
heraldcoupe Posted October 3, 2013 Author Share Posted October 3, 2013 7915 wrote:Some of the 1147 engines used press fit pistons( no circlips and have to be pressed onto conrod), they also had different conrods. My spit mk11 engine has them. I would suggest you get the correct type for your engine. Mine is in bits and as the press fit ones are unavailable I have obtained a set of the full floating type con rods for if I ever get around to replacing the current 1500 engineI have a 1963 1200 so 1147, whats the difference in the conrod? gudgeon pin is the same size as a circlipped piston and in the same position. How do you know if you have the correct conrod for the piston? I can only find one part no. in my parts catalog Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted October 7, 2013 Share Posted October 7, 2013 The press fit rods have a smaller little end hole and no bronze bush.Nick Quote Link to comment Share on other sites More sharing options...
heraldcoupe Posted October 13, 2013 Author Share Posted October 13, 2013 Nick_Jones wrote:The press fit rods have a smaller little end hole and no bronze bush.NickCheers, wasn't sure if they would be sleeved or completely different. and as a note for anyone else with these pistons I ended up machining the gudgeon pin shorter and machined circlip grooves in the piston. For 30mins machining I, thought that was the best option.I also looked up the Teflon buttons and they only seem good for race cars that have motor rebuilds after each race, the Teflon rubs the oil off your bore and causes problems. Quote Link to comment Share on other sites More sharing options...
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