canada280i Posted April 6, 2011 Report Share Posted April 6, 2011 Hi all: I also have a question regarding possible piston slap that I hope someone here can help me with. I have a 98 Montesa 315r purchased late in 2010. The bike runs perfect and has plenty of power for me, however at tick-over there is a noticable slight rattle which of course dissapears when the revs increase. I have read elswhere in these forums that some people say this is normal and okay, and other say replace the piston etc. I have removed the front exhaust pipe and when i stick my finger on the piston through the port it feels like I can move (rotate)it slightly from side to side, almost like it has a little play on the bearing. Does anyone know if the top end bearings have a little play in them or woudl this be the cause of the rattle and therefore require the new piston/bearing etc. When i look through the port the piston appears in quite good condition, as do the rings and the cyliner bore. Any advice would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
dombush Posted April 7, 2011 Report Share Posted April 7, 2011 Hi as you say piston slap in itself whilst not ideal, isnt a huge problem. Like everything else, there are degrees of slap and if its low key & goes away as the revs rise its probably ok. However, small end wear is a different matter. When the con-rod bearings (big end or little end) start to wear the free play allows the bearing to "hammer". This means that wear accelerates rapidly. Little end wear tends to be audible at all revs, piston slap only at low revs... but diagnosis isnt really possible by sight/sound. There really isnt a way of avoiding taking the barrel off and checking. If you've got the measuring tools to identify piston/bore clearance..great. If not, you can check for little end play and eliminate the more serious fault. Its important to check only for vertical movement, anything discernable by hand is probably wear that needs dealing with... also little end bearings are cheap!! Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 7, 2011 Author Report Share Posted April 7, 2011 Hi Dombush, thanks for the response. When I bought the bike it came with a spare piston kit so I wonder if the previous owner was thinking of doing it but never got around to it. I would hate to strip it down and put the new piston in only to then find it still has the rattle at idle.I think I was just trying to avoid having to take the head and barrel off, but I may have to bite the bullet and do it while I have the spare kit. many thanks! Quote Link to comment Share on other sites More sharing options...
chewy Posted April 7, 2011 Report Share Posted April 7, 2011 Would you need to split the head off?...It's only going to cost you an hour and a base gasket plus the bits to find out.. good luck with it Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 7, 2011 Author Report Share Posted April 7, 2011 Hey Chewy, are you suggesting that I leave the head attached and just remove th barrel and head as one piece? I hadn't thought of that, will the head and barrel come offas one without removing the engine? Quote Link to comment Share on other sites More sharing options...
varadero Posted April 7, 2011 Report Share Posted April 7, 2011 Hey Chewy, are you suggesting that I leave the head attached and just remove th barrel and head as one piece? I hadn't thought of that, will the head and barrel come offas one without removing the engine? I looked at that aswell, I took the engine out ,there doesnt seem to be enough room Quote Link to comment Share on other sites More sharing options...
smalley250 Posted April 7, 2011 Report Share Posted April 7, 2011 (edited) About 10 years ago i removed cylinder head then barrel whilst the engine remained in place. Mine rattled all the time and i replaced A piston for an A piston as advised at the time, also replacing the little end whilst doing the piston. Is about an hour or so job and fairly easy i thought. This fixed my constant rattling. I believe the air filter is prone to allowing mud etc to pass through it unlike GasGas type air filters that fit directly onto the inlet manifold, thus the piston skirt wears causing said rattle. You will know for sure when the BIG END is going, its like a loose spanner in the engine type sound Edited April 7, 2011 by smalley250 Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 7, 2011 Author Report Share Posted April 7, 2011 My confidence is growing that I can do this! I have already briefed the wife that I will be "unavailable" this Sunday Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 8, 2011 Author Report Share Posted April 8, 2011 Okay,so I have started the big strip down to replace the piston, when I removed the exhaust front pipe there wsa what appeared to be a crush washer that was mangled a little in the port, when I pulled it out it came out like a spiral as if it was wound in place. It is now knackered but I cannot seem to see the part number on the parts list. So the question is, is it really necessary tohave this type of crush washer, or can I fashion a seal washer myself from gasket material? anyone got any advice! Quote Link to comment Share on other sites More sharing options...
sherco29 Posted April 8, 2011 Report Share Posted April 8, 2011 http://www.apexmotosports.com/montesa%20parts%20book/f-12.htm #2 Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 8, 2011 Author Report Share Posted April 8, 2011 Thanks Sherco29, before I order one do you know if one can be made or do I realy need the correct piece -the reason I ask is that to order one will take likely a week to get to me here in Canada and I was hoping to get it fixed and back together this weekend Quote Link to comment Share on other sites More sharing options...
outlaw dave Posted April 8, 2011 Report Share Posted April 8, 2011 Not sure where you are located, but have you checked with Don from Cascade MC in Mission BC? Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 8, 2011 Author Report Share Posted April 8, 2011 Thanks Outlaw Dave, I haven't checked with Don yet (even though I ordered some parts from him yesterday...damn!)as I only noticed it was damaged last night...I was looking for a quick fix so I could hopefully ride on Sunday to get her run in. If there is no other way around it I will contact Don on Monday and order the bit. Thanks to all for the replies, very helpful! Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 9, 2011 Author Report Share Posted April 9, 2011 Okay, so I could not wait until Sunday, I ripped into the new piston job today. All tolx it took about one and a half hours to get the barrel off, piston, bearing, rings etc. removed and new ones installed. Tope end bearing was definitely a little on the worn side and there was definite movement so I am glad I did the job. The actual piston was in pretty good condition overall, but i had the new one so in it went. With the head back on there does seem to be a noticable increase in resistance when moving the kickstarter and the piston moves very smoothly in the barrel so hopefully this will mean a sharper tighter engine. While I had evrything apart I also took the opportunity to re-tape all the loose wires and make sure everything was nice and tidy. I also gave the radiator a good wipe over and also ran some silicone sealer over the wires that go into the back of the fan motor to offer a little protection. Hopefully I manage to get evrything back together over the weekend and that it then starts and runs with no more rattle! Big thanks to all who offered advice on this, it is much appreciated. Big thanks also to my wife who got me some Harveys half way through gthe job tonight....kept me going! Quote Link to comment Share on other sites More sharing options...
canada280i Posted April 9, 2011 Author Report Share Posted April 9, 2011 Rushed home from work.....put it back together.....fired up first time......purring like a kitten! Quote Link to comment Share on other sites More sharing options...
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