qwin456 Posted October 15, 2014 Report Share Posted October 15, 2014 (edited) Hello all! First time on the forum so i thought i'd say hello and see if i can get a little advise. I have been riding Jap sports bikes for ages and a few weeks ago i had a go on a mates trials bike and have got the bug! since then i have done a few rides with borrowed bikes any loved it so i got myself a 2001 Montesa 315-r. it was cheap but in a real bad state: filthy, suspenion needed refurb, fudged air filter, carb full of spooge..ect ect. I took the head off and some oily carbon but didnt look to bad, decided to take the cylinder off and found that the piston was badly scracthed and the bottom piston ring had beed destroyed, the cylinder had some light scoring so i have sent it off to langcourt to get it sorted. What is the likely cause of this ? I checked the crank and there is no free play, main bearings seem to be ok but i only know that there is no movement on the flywheel and they feel smooth. cleaned out clutch slave, clutch looks good and fitted a new water pump seal kit. When i emptyed the oil is was a sludgy grey mess? i have only ever seen milky white oil from getting water in it. having never owned/worked on a 2 stroke the engine is a bit of a mystery to me. I have done a lot of googling and reaserch so know some of the basic but i would really appreicate any tips or advise is setting up and maintaing the bike. Many regards Chris Edited October 15, 2014 by qwin456 Quote Link to comment Share on other sites More sharing options...
slickgolf_0 Posted October 15, 2014 Report Share Posted October 15, 2014 Hi More than likely been on its side and had full revs causing it to sieze . Very common , you are doing the right thing in having it repaired with a new piston . Fit a lanyard if you dont want to take any chances . Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 15, 2014 Report Share Posted October 15, 2014 Would I be right in thinking the damage is at the near the centre of the top of the exhaust port and that part of the piston that passes over it? If so the cause is almost certainly overheating or possibly a lack of oil, or both. Continual high speed running or mx type use can cause this in addition to the previously mentioned bike on its side with throttle stuck open. Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 16, 2014 Report Share Posted October 16, 2014 That piston has had a rough life. That is not a one time occurance . That is another piece off aluminum on the piston. High revs could have nothing to do with it, but heat and a crappy mixture sure could. The bike has had some dirt through it! Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 16, 2014 Report Share Posted October 16, 2014 The hottest parts of a 2 stroke engine are the plug earth electrode, centre electrode, top edge of exhaust port and top edge of piston adjacent to exhaust port. When the engine overheats the aluminium above the exhaust port and the piston in that area expand more than they should do, the first sign of this is a slight drop off in power as the barrel and piston distort, experienced road racers can feel this point and pull the clutch in just before the engine nips up. The oil film fails and the swollen areas of piston and barrel rub hard together and start to melt and weld to each other (look up friction welding on youtube). At this point the aluminium smears about, the engine slows dramatically and may even seize solid. If you look at most older water cooled trials engines the water inlet is at the intake side of the barrel (not a good idea), whereas on more modern engines the cooling water enters directly above the exhaust port in an attempt to combat this localised overheating. If you want to run an engine hard: Make sure cooling system is in good order. Set carb to give slightly rich mixture Put plenty of best quality oil in your fuel. 1 Quote Link to comment Share on other sites More sharing options...
thats_a_five Posted October 17, 2014 Report Share Posted October 17, 2014 It sounds like you have good motorcycle maintenance skills and I applaud you for saving this bike from forced retirement. Good on you. Others have correctly stated the piston has been seized in the bore. The cylinder bore has been damaged as well so it will need to be bored oversize and a matching piston and rings will need to be installed. Seizing can happen many ways, mostly related to excess heat, lubrication failure, or a combination of them. Things to keep in mind to prevent future failures Let the motor warm up gently. This allows the metal to heat expand in a controlled way. Use good 2 stroke oil with an appropriate fuel:oil ratio. You bike should run 80:1 for trials. Riding a trials bike is lots of slow running with some short bursts of full power. If you are riding like a Motocrosser or full throttle for extended times, increase the oil in your mixture to the 50:1 range. You can also turn on your “choke” when running full throttle for extended times.This is why most carbs on trials bikes use and enrichment circuit rather than a traditional choke.They add fuel with richens the mix but do not reduce the passage of air.Richer mixture will cool the combustion chamber and carry more oil to the vital parts. Fix that water pump seal and check your trans / clutch oil often for water getting in. That happens from failed water pump seals and in deep water crossings. Water is a lousy lubricant. Water in oil mixes to look like a foamy milkshake. Check for loss of coolant often. Other things to maintain regularly: Clean the air filter and spark plug Avoid ethanol in your fuel if possible. Ethanol causes damage to rubber parts and binds with water in the fuel that can clog the tiny passages in carbs. Check, clean and re-grease the dogbone bearings at least twice a year. More if you ride in a lot of water or mud. Most importantly, have fun! 1 Quote Link to comment Share on other sites More sharing options...
utahpete Posted October 17, 2014 Report Share Posted October 17, 2014 I agree with all said, but lineaway has it right ... that engine has ingested some dirt. My TY 350was as quiet as a sewing machine (okay, I'm getting to be a bit deaf) when I first bought it, but I made the mistake of taking for a spin around a dusty area before I really took a close look at the air filter. The 28-year-old foam filter had become un-welded at a few points along the seam. And after just an hour or two of that, I now ride something that sounds like a barrel of nuts & bolts rolling down a hill. I put a new piston pin in last winter and saw some of the same scoring/transfer on the intake side. Bob @ BJ Racing is going to make a sleeve and fit it to the RT piston that I found on ebay. Next season should bring a bit more peace and quiet. Good luck with your rebuild. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 17, 2014 Report Share Posted October 17, 2014 Don't want to start an argument on mix ratios but be aware of the following. Motocrossers can manage at 50:1 but they have far bigger radiators and far more coolant capacity than trials bikes. I run my trials bikes at 30 cc oil per litre of petrol which is 33:1 and my crosser at 20:1. By doing so I probably avoided costly engine damage in May this year. I was on a trial when 1/2 way round last lap the engine felt a bit sluggish in 4th gear and stalled unexpectedly. Restarted, engine sounded and ran ok and completed last lap of trial. Following evening I noticed a bit of damp on floor under bike. Turned out to be coolant but no leak obvious. Eventually I found a pinhole in the underside of the hose near the water pump. Something like a thorn or wire barb must have done it. Upon stripping barrel I found the bike had very little coolant left in but barrel and piston were completely unmarked. Quote Link to comment Share on other sites More sharing options...
tail Posted October 17, 2014 Report Share Posted October 17, 2014 Welcome on board buddy, good choice of bike, the 315 are usually bullet proof if looked after, my guess would be the amount of crap that was in the air filter plus never being serviced or looked after. Couple of points for a healthy 315, i've had 3 and always run Castrol 747 oil. 80-1 mix and always run high octane fuel, (super unleaded) Make sure the air filter is cleaned every few uses, there's 4 holes in the back plastics above the air box, i attach wire mesh to the inside with silicon, this stops a lot of **** getting into the air box Also if you can, ditch the standard carb and put a Keihin pwk28 on, makes the bike run so much better Quote Link to comment Share on other sites More sharing options...
guys Posted October 18, 2014 Report Share Posted October 18, 2014 Don't want to start an argument on mix ratios but be aware of the following. Motocrossers can manage at 50:1 but they have far bigger radiators and far more coolant capacity than trials bikes. I run my trials bikes at 30 cc oil per litre of petrol which is 33:1 and my crosser at 20:1. By doing so I probably avoided costly engine damage in May this year. I was on a trial when 1/2 way round last lap the engine felt a bit sluggish in 4th gear and stalled unexpectedly. Restarted, engine sounded and ran ok and completed last lap of trial. Following evening I noticed a bit of damp on floor under bike. Turned out to be coolant but no leak obvious. Eventually I found a pinhole in the underside of the hose near the water pump. Something like a thorn or wire barb must have done it. Upon stripping barrel I found the bike had very little coolant left in but barrel and piston were completely unmarked With all due respect dadof2, but isn't that a bit over cautious? I'm sure you don't have the intention to scare people unnecessary. One could also ride in a car with the airbag already inflated because it might fail in an accident. I think it's more important to do regular checks of the fluids, decent maintenance and ride a trials bike the way it's designed for. 1 Quote Link to comment Share on other sites More sharing options...
tail Posted October 18, 2014 Report Share Posted October 18, 2014 Don't want to start an argument on mix ratios but be aware of the following. Motocrossers can manage at 50:1 but they have far bigger radiators and far more coolant capacity than trials bikes. I run my trials bikes at 30 cc oil per litre of petrol which is 33:1 and my crosser at 20:1. By doing so I probably avoided costly engine damage in May this year. I was on a trial when 1/2 way round last lap the engine felt a bit sluggish in 4th gear and stalled unexpectedly. Restarted, engine sounded and ran ok and completed last lap of trial. Following evening I noticed a bit of damp on floor under bike. Turned out to be coolant but no leak obvious. Eventually I found a pinhole in the underside of the hose near the water pump. Something like a thorn or wire barb must have done it. Upon stripping barrel I found the bike had very little coolant left in but barrel and piston were completely unmarked. Also remember that running a bike rich on oil actually makes the mixture week, more oil makes less air in the mix, by running it rich actually doesn't prevent damage is causing damage 1 Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 18, 2014 Report Share Posted October 18, 2014 I am well aware that putting more oil in weakens the mixture but this is fine so long as the carburation is not too weak, if it is just adjust jetting or needle position. I will tell you a interesting story about this. In the mid 1980s a person I knew used a honda cr250 motocrosser for checking round the sheep in his fields in winter when they were off the fells. He asked me to look at it because it kept "oiling up" plugs and stopping. I had a look, carb settings were fine but plug was wet and black, ie excess petrol. He was running it at 50:1 on Rock oil, honda recommend 20:1 and and therefore presumably supplied the bike jetted for 20:1. By putting less oil in he was actually richening the mixture causing the bike to run cool and blacken the plug, compounded by the slow stop start running in cold weather. I switched the mixture to 20:1 and blanked off some of the radiators. Bike ran fine for a couple of weeks then I got a call "bike is oiling up again". Upon checking the bike I found radiator blanking had been removed and the mixture put to 40:1. He had been to the local honda dealer and mentioned what I had done. Without even looking at the bike the dealer had been adamant that 20:1 was more likely to oil the bike up and blanking of the radiator would cause the bike to overheat and seize. 33:1 too cautious? Well it maybe. I have posted at length on mix ratio previously and am not going to redo that long post here. The facts are, more oil gives more power and less wear, and so long as the oil is of the correct quality and the carburation is set correctly the balance of advantage lies with richer oil mixtures. Many people state (wrongly) disadvantages of more oil such as exhaust clogging and carbon build up, but these problems are the result of poor carburation and or poor quality oils and fuel not rich oil ratios. With a typical top end rebuild costing about £300 + labour I think a bit extra spent on oil is a wise investment. I am not out to scare anyone but based on experience believe the following to be true. If you ratio is 70:1 and the bike revs because the throttle is stuck open it will probably seize as the fuel runs out. If the ratio is 24:1 there is a fair chance the bike will not seize as the fuel runs out. Similar arguments can be applied to 4 stroke lubrication. Most 4 stroke trials bikes will run perfectly well and reliably with semi synthetic 10w40 costing about £2 per litre, changed every 4 trials. On the other hand you can put in motul 300v (£13 per litre) and change it every outing as an insurance against the odd bit of hard riding and to reduce wear in general. Quote Link to comment Share on other sites More sharing options...
qwin456 Posted October 20, 2014 Author Report Share Posted October 20, 2014 (edited) Thank you for the replies, its been very useful, I think the damage on the piston/cylinder was just to the side of the inlet, the Air filter was shagged and the drain pipe was missing so the air box itself had a layer or mud and ***** inside! which I'm sure didn't help. I have been busy this week so not got much done on the 315. I have sent the shock off to Brooks Suspension to have it refurbished, so without the cylinder or shock i cant really start building the bike back up. It has given me time to look over the bike properly and start fixing a few things. Forks have been striped, cleaned and rebuilt, All new bearings for steering stem, linkage, swing arm and wheels ( they where all shagged!) and i gave the carb a good clean. I have got a load of questions about the Montesa so i thought i'd just list them and if anyone can help me out it would be greatly appreciated! but if you can't be a***d no problem : Cleaning the carb I have noticed that i don't seem to have standard jetting, i have 120 main, 44 slow? common jetting ? also it seems that i should have an air vent hose attached to either side of the carb but mine is missing, it looks like it connect to the air sub assembly but all the tubes are missing now =( As the bike has been so neglected i don't trust anything so would like to flush out the old oil completely, What is the best way to do this ? best gear box oil? i know the elf stuff is recommended but i cant get it locally and it costs a fortune, any decent alternatives? There are two wires with bullet connectors under the tank that don't seem to be used, Any ideas what they are for ? Thank you in advance! Chris Xx Edited March 15, 2015 by qwin456 Quote Link to comment Share on other sites More sharing options...
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