cornishflyer Posted January 6, 2017 Report Share Posted January 6, 2017 Hi all, First post here, hello! I know there are a number of threads already on the forum about top end noise, but I figure another can't hurt as it might help someone in the future. Before I strip the top end of my 2007 ST250 I would like to get the right parts ordered. What does this sounds like to you? I'm hearing the occasional pinging type rattle (not pinking). To me it's either little end on the way out or piston slap but I haven't discounted primary gear. The noise is unaffected by clutch movement, and it's pretty much the same as the engine warms up. Thanks, Dylan Quote Link to comment Share on other sites More sharing options...
sectionone Posted January 6, 2017 Report Share Posted January 6, 2017 I would pull the cylinder then decide what parts to order. You may need to have the cylinder replated. My enduro bike was making a similar noise and I pulled the cylinder off and found that I had up and down play on the connecting rod. Now I have to split the cases, replate the cylinder and order lots of parts for lots of labor. Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted January 6, 2017 Author Report Share Posted January 6, 2017 Thanks Section one. Just pulled the top end apart, and sure enough there is quite a bit of wear (see pictures). From the state of the nuts when I tore it apart it feels like this is the first time it was disassembled so it's not unexpected that there would be some wear I guess. There is some scoring on the exhaust port side but most of it is below the port where the rings don't reach. I have smoothed the worst with some emery paper. There isn't really a ridge at the top of the cylinder. There is play in the little end so I will replace that, also I can feel a slight ridge on the gudgen pin. There is also quite a lot of play in the piston/cylinder clearance, way more than the 0.03 recommended in the specs that I found on the net. This is the A piston, I wonder if I could get away with just ordering another A piston or would I have to get a re-plate the bore and go for the B piston? I measured the piston and it's oval, I wonder if that is from wear or if they come like that. The big end feels pretty loose side ways, and it does twist a little bit but I can't really feel any up and down movement so I'll leave that I think. Given that this is an oldish bike I need to decide how much to spend on it, I'm hoping a new piston, rings, little end and gudgen pin is going to sort it out..... or am I chucking money away without re-plating that cylinder? Cheers Quote Link to comment Share on other sites More sharing options...
smalley250 Posted January 6, 2017 Report Share Posted January 6, 2017 Looks rough so cant see a new piston lasting long. I had same issues but not as bad scoring and replaced piston n little end, it lasted 6 months so i cant see you fixing this with just a piston. Big end does move side wards and when its going sounds like loose spanner in your engine. Quote Link to comment Share on other sites More sharing options...
trapezeartist Posted January 6, 2017 Report Share Posted January 6, 2017 Obviously the piston has nipped-up at some time. It's worth cleaning up the scoring on the piston with fine emery and see what it's like then. As for the bore, you can still see the honing marks at the bottom below the ports so I would guess the bore is generally good, especially as you can't detect a ridge above the top ring. I would clean up the bore with a soft, fine abrasive and see how it looks then. Not sure exactly what to use as I've never done it on a nikasil bore. Quote Link to comment Share on other sites More sharing options...
steve1979 Posted January 6, 2017 Report Share Posted January 6, 2017 You could try a ball hone on the barrel, won't damage the plating like a stone hone would, it only removes a tiny amount of the cross hatching giving the piston rings more surface area to grip if you like. Might be worth a shot to see how good or bad the cylinder looks after! Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted January 7, 2017 Author Report Share Posted January 7, 2017 (edited) Thanks everyone so far for the comments. I thought I read that ball hones are not ideal for nikasil because the coating is porous and the grit can remain in there. At this stage though I can't see how I could really make it much worse. I'm thinking of getting a D piston in there which is 72.78mm at it's largest diameter, I'm not having the best time measuring the cylinder but I figure there has to be enough clearance.If not (once I measure it with feeler gauges) I'll then have to to the re-plate. Hopefully having a larger new piston will stop the slap till I can afford the full re-plate. Cheers Edited January 7, 2017 by cornishflyer Quote Link to comment Share on other sites More sharing options...
trapezeartist Posted January 7, 2017 Report Share Posted January 7, 2017 I'm not sure what a ball hone is. Is it one of those things that looks like a bottle brush with a little knobble of abrasive on the end of each "bristle"? If so I wouldn't use it on a 2 stroke cylinder as the balls will go into the ports and possibly round off the edges. Quote Link to comment Share on other sites More sharing options...
worldtrialchamp Posted January 7, 2017 Report Share Posted January 7, 2017 Quote Link to comment Share on other sites More sharing options...
steve1979 Posted January 7, 2017 Report Share Posted January 7, 2017 16 hours ago, cornishflyer said: Thanks everyone so far for the comments. I thought I read that ball hones are not ideal for nikasil because the coating is porous and the grit can remain in there. At this stage though I can't see how I could really make it much worse. I'm thinking of getting a D piston in there which is 72.78mm at it's largest diameter, I'm not having the best time measuring the cylinder but I figure there has to be enough clearance.If not (once I measure it with feeler gauges) I'll then have to to the re-plate. Hopefully having a larger new piston will stop the slap till I can afford the full re-plate. Cheers Ah, from what I have looked up since this post is ball hones aren't ideal for this job, I myself have not used a ball hone but was advised it would be ok as it wouldn't damage the plating, my apologies for the incorrect information. Appears to be either a rub with a scotch bride pad to clean or a re-plate are the best options depending how bad the cylinder is. Good luck with getting her up and running again Quote Link to comment Share on other sites More sharing options...
trapezeartist Posted January 7, 2017 Report Share Posted January 7, 2017 3 hours ago, worldtrialchamp said: Although I've done some pretty awful things to iron liners in the past, using emery cloth, I wouldn't do it to nikasil. And I'm not sure green scotchbrite is much better. There is a white scotchbrite which is described as "non-abrasive" but I think that must mean "less abrasive". I've never used it, but I might be tempted to try it on the marks left from a piston seizure. Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted January 8, 2017 Author Report Share Posted January 8, 2017 (edited) I'm trying to find which piston I need to order. Does anyone know where Sherco measure their pistons? On the piston crown it has 72.75 stamped, yet when I measure just below the gudgen pin holes, where I think I'm supposed to measure, I get a reading of 72.57. Even at the skirt of the piston it's not close to 72.75, perhaps that is the most worn part? I've discovered that the skirt is the widest part of the piston, they are oval and tapered to account for expansion at different rates. I've tried using feeler gauges (not the best way I know) to simulate a new piston + the recommended clearance of 0.02 and it's a very tight fit in the cylinder. If I am measuring in the correct location then that's a lot of wear, I might be good just going for an A or B piston. Edited January 8, 2017 by cornishflyer added detail Quote Link to comment Share on other sites More sharing options...
huski Posted January 8, 2017 Report Share Posted January 8, 2017 New piston in a worn bore isn't the answer.Either clean up what you've got and tolerate the rattle,or do it properly and spend the money on replating the cylinder and a new piston and small end 2 Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted January 11, 2017 Author Report Share Posted January 11, 2017 Just to update, I cleaned up the piston and very lightly cleaned the score mark in the cylinder with emery and put it back together with new little end. As predicted the slap is still slapping. I did order a B size piston though and tested it in the bore, the wear is pretty inconsistent down the bore, pretty much perfect near the bottom but out by almost 0.1mm near the middle. I'm now looking for affordable (to me) nikasil platers here in Australia and then I'll do the full replacement. I did notice that when I refilled the radiator I used quite a bit more coolant than came out of it, a bit of a concern because it was only just recently topped up, but that's for another thread. Cheers. Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted January 13, 2017 Author Report Share Posted January 13, 2017 5 hours ago, oni nou said: There is a 250 barrel/head and piston in excellent used condition on Ebuy right now[£215.00 complete be quick] off a 03/04 Sherco,Iam not familiar with any changes to cylinder port timing and crankcase to cylinder fit on a Sherco through the years, but if you contact Chris/Tim at Splatshop then you should find an answer. Thanks oni nou, I saw that one but I have already purchased a new B piston. Just waiting to be able to afford the re-plate on the cylinder. Cheers, Quote Link to comment Share on other sites More sharing options...
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