southwester Posted September 30, 2013 Report Share Posted September 30, 2013 Quote Link to comment Share on other sites More sharing options...
southwester Posted September 30, 2013 Author Report Share Posted September 30, 2013 Here are some pictures of my 2007 rev 3 250's top end, I have had it off to clear out water ways in cylinder and head and thought I would post some pictures of piston ect. Having no experience of engines I don't really know what I'm looking for damage wise, there are some light scratches on inside of cylinder but arnt deep enough to feel with your nail so from other posts I have seen on the site I think this is ok. The piston has the same sort of light scratches but again can't be felt with my finger nail. There doesn't seem to be any up and down play in con rod or fly wheel so mains seem to be ok. Are there any checks I should do like measure tolerances of piston rings and cylinder bore and what's the usual good practice when rebuilding top end obviously new Gudgen pin circlips but would it be advisable to replace small end bearing and Gudgen pin also. Unfortunately I didn't check for any play in small end bearing when I took the barrel off. I have taken rings off piston now aswell so is good practice to replace Quote Link to comment Share on other sites More sharing options...
stork955 Posted September 30, 2013 Report Share Posted September 30, 2013 G'day, you need to measure your piston and bore and calculate the clearance. More than about 3-5 thou and you are looking at a new piston at least. The barrel needs to be de glazed (the brown stains need removal) at least prior to this to get an accurate idea of what is happening. Remove the carbon from the head and barrel. Use something soft to not scratch anything when you do this. Check the small end and big end for wear while you can. It looks like you have had some rubbish get through the air cleaner, it will pay to check this also before restarting the bike. Definately replace your rings but check the side clearance in the ring grooves before this -you may need a piston anyway. You should not be able to rock the ring in the groove more than about 20 degrees when slipped in "backwards" - with the ring off the piston slip it into the groove from the "outside" and check in a few spots around the piston. (I hope that makes sense!) Thats about it I think. See how you go. Quick tip -you can use a kitchen scotch pad to clean your gasket surfaces. make sure there is absolutely no gasket left anywhere. Dont let this rubbish fall into the crankcase. Also wash your barrel in hot soapy water after honing until a white rag comes out clean. Oil it immediately to stop rust. Cheers, Stork Quote Link to comment Share on other sites More sharing options...
zerorev3rev4 Posted September 30, 2013 Report Share Posted September 30, 2013 (edited) looks like theres a lot of blow by and piston has been rattling in the bore due to excessive wear going by the pics it looks like it needs cylinder re plating and a new piston kit get a engine re conditioner or good bike shop to look at it Edited September 30, 2013 by zerorev3rev4 Quote Link to comment Share on other sites More sharing options...
0007 Posted October 3, 2013 Report Share Posted October 3, 2013 Wow that thing is coked up bad, there are products that will decarbon a top end I use Ring Free for marine engines, works very well Have your piston miked and measure your ring end gap, I think a new piston may be in order there Quote Link to comment Share on other sites More sharing options...
neil king Posted October 5, 2013 Report Share Posted October 5, 2013 Is your fan thermostat bypassed? Quote Link to comment Share on other sites More sharing options...
southwester Posted October 5, 2013 Author Report Share Posted October 5, 2013 Thanks for the pointers. Neil I linked out stat when it packed up the first time the bike over heated because the fan came on after 30 seconds of engine starting and thought fan may as well be on full time. But it turns out the fan was coming on quick because the waterways throughout the system are partially blocked with emulsified oil getting in from the water impeller seal where the dreaded electrolysis has taken place. Oddly enough there was no sign of water in the gear box oil. Why do you ask mate? Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 5, 2013 Report Share Posted October 5, 2013 (edited) http://www.poetonaptec.co.uk/ Consider the above for replating. A word of warning, replaters use very strong chemicals to dissolve the old plating and this will dissolve the steel pipe connection on a 2007 beta barrel, so if you cant remove it you will need a new steel one pressed in or alloy one welded on afterwards. think your barrel will need replating and agree with previous poster that suggests dirt has been getting past the air filter.The brown staining is made worse by bore wear but it can also be a sign of insufficient oil in the fuel and or overheating. There are signs of what may be detonation / pre ignition or metal particles in the combustion chamber. Typical sources of these are parts of bearing races or balls that have cracked or main bearing cage rivets. If you want to know more about engine diagnostics etc I recommend two stroke tuning" by Graham Bell. Edited October 5, 2013 by dadof2 Quote Link to comment Share on other sites More sharing options...
dan williams Posted October 7, 2013 Report Share Posted October 7, 2013 Those dimples on the piston skirt say something's been bouncing around in there. Quote Link to comment Share on other sites More sharing options...
neil king Posted October 7, 2013 Report Share Posted October 7, 2013 Thanks for the pointers. Neil I linked out stat when it packed up the first time the bike over heated because the fan came on after 30 seconds of engine starting and thought fan may as well be on full time. But it turns out the fan was coming on quick because the waterways throughout the system are partially blocked with emulsified oil getting in from the water impeller seal where the dreaded electrolysis has taken place. Oddly enough there was no sign of water in the gear box oil. Why do you ask mate? If a 2 stroke motor is run too cool for an extended period of time carbon builds up and causes piston an cylinder scoring. Also causes the rings to stick for excessive blowby. Quote Link to comment Share on other sites More sharing options...
southwester Posted October 7, 2013 Author Report Share Posted October 7, 2013 thanks for the further replies. My local trials bike shops mechanic has taken some measurements and done a visual and he said it needs a re plate and new piston ect. He reckons the marks on the piston are consistent with piston slap rather than anything breaking up so that's at least some good news. About Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 7, 2013 Report Share Posted October 7, 2013 Your comment on compression and "hard enough to kick over already". As I said previously there is evidence of what may be detonation which could be caused by too little squish clearance. Get this checked when your engine is rebuilt. Too cool running rarely causes coke in an engine. The usual cause of the dark stains on your piston skirt is blow by and overheating which are made worse by insufficient oil in the fuel. In the last few week I have stripped 3 engines. The 97 (stripped for inspection only) had been run at 30:1 fuel to oil and had virtually no carbon on the piston and the crank case was clean, the second was an 09 (gearbox broken) run at 75:1 and there was a lot of coke on the piston and crank cases. The third was a 2011 50cc 16 year old road legal scooter (piston ring location pin sheared) with separate oil tank and it had significant coke on piston skirt , top of piston and crankcase. Quote Link to comment Share on other sites More sharing options...
southwester Posted October 8, 2013 Author Report Share Posted October 8, 2013 Thanks for the advise dadof2, I will. Well I got in touch with the shop I bought the bike from and although the owner said he isn't accepting liability he has agreed to send me out a piston kit so at least it's something towards the cost of the replate ect. Quote Link to comment Share on other sites More sharing options...
0007 Posted October 8, 2013 Report Share Posted October 8, 2013 Agree with Dad, cool running engines don't build carbon, the engine components (piston) need to reach a temp where fuel burns onto the aluminum, that's what carbon is If the engine is cool it's clean as a whistle as it is eternally washed down by the fuel Pistons should have carbon dot in the centre and a clean area as it approaches the edge of the crown Carbon the the edge means lean condition (high combustion temps) Quote Link to comment Share on other sites More sharing options...
dadof2 Posted October 8, 2013 Report Share Posted October 8, 2013 Look at your engine parts (if you have not yet cleaned them) and you will see part of the head, top of piston and top of barrel have tiny grey fleks on them. On the head these are in a paler / less coked area. These grey fleks look very much lke where the shockwave from detonation has blsted away the carbon. Also I see there is pink build up in the water passages. This occurs where long lfe OAT antifreeze (usually VW / Audi type) is put in an engine that has been run on standard ethylene glycol for some time. If the coolant system is not chemically cleaned and flushed before changing to OAT this insulating layer builds up and causes overheating which can lead to detonation. The cost of mixing antifreezes can be high. A couple of years ago I know of a 125 Beta where the parts came to well over £300 and I have seen cars written off because of it. Although its going to cost you a bit now the upside is if you put in new main bearings and seals whilst you have engine out you should be trouble free for 5 years + Quote Link to comment Share on other sites More sharing options...
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