Brian & Stef Posted November 13, 2008 Share Posted November 13, 2008 Hi everybody, hope somebody can help. My sons SR125 recently decided to mash the exhaust valve and guide - thanks to his innability to look at the oil level! One replacement cylinder head later it has developed a habit of snapping the top of the inlet valve - obviously at the weakest part where the groove gets clamped into by the collets. Can anybody suggest what could be causing this strange problem? The oil supply is fine, all springs are OK, the gaps are set according to good old Mr Haynes' manual, but most of all, the valve has complete and unrestrcted access for the full extent of travel. So far as I can tell the cam chain is fine and tensioned correctly, and the cam sprockets seem in very good condition. I am reluctant to just throw another valve in because I don't know if the same thing will happen. After the last change it ran perfectly well for a few weeks, then suddenly, after about 10 minutes of running around at about 30mph (middle of the city, so not thrashed), the damn thing went again. If just getting another new valve (the last one was stripped from another motor) is the answer, can anybody suggest where to get one? Thanks in advance Brian (and Stef the SR killer) Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 13, 2008 Moderator Share Posted November 13, 2008 What year is it Brian? (and dont say 2008 ) Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 What year is it Brian? (and dont say 2008 ) '98 on an 'S' plate Link to comment Share on other sites More sharing options...
JimR Posted November 13, 2008 Share Posted November 13, 2008 Hi everybody, hope somebody can help. My sons SR125 recently decided to mash the exhaust valve and guide - thanks to his innability to look at the oil level! One replacement cylinder head later it has developed a habit of snapping the top of the inlet valve - obviously at the weakest part where the groove gets clamped into by the collets. Can anybody suggest what could be causing this strange problem? The oil supply is fine, all springs are OK, the gaps are set according to good old Mr Haynes' manual, but most of all, the valve has complete and unrestrcted access for the full extent of travel. So far as I can tell the cam chain is fine and tensioned correctly, and the cam sprockets seem in very good condition. I am reluctant to just throw another valve in because I don't know if the same thing will happen. After the last change it ran perfectly well for a few weeks, then suddenly, after about 10 minutes of running around at about 30mph (middle of the city, so not thrashed), the damn thing went again. If just getting another new valve (the last one was stripped from another motor) is the answer, can anybody suggest where to get one? Thanks in advance Brian (and Stef the SR killer) Hi Brian, I guess the new valve guides where fitted correctly (a guide off at an angle, no matter how small, could cause the top end of the valve to break these where bad to fit I had to find an oven in order to have the head at the correct temp and the guides cold so they 'fell in'). If the guide is off set when everything 'warms up' - in traffic, the guide may stress the valve, but I guess this is ok as it's a different head. but if your new head has been 'adjusted' the guides may be incorrect. Other things to check are if the valve guide seals retained there correct position of did they move ? With regard to Valve timing did you recheck it after the chain was tensioned, if the chain is worn the valve timing will alter after tension, again stressing the valve. Regards Jim Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 Hi Brian, I guess the new valve guides where fitted correctly (a guide off at an angle, no matter how small, could cause the top end of the valve to break these where bad to fit I had to find an oven in order to have the head at the correct temp and the guides cold so they 'fell in'). If the guide is off set when everything 'warms up' - in traffic, the guide may stress the valve, but I guess this is ok as it's a different head. but if your new head has been 'adjusted' the guides may be incorrect. Other things to check are if the valve guide seals retained there correct position of did they move ? With regard to Valve timing did you recheck it after the chain was tensioned, if the chain is worn the valve timing will alter after tension, again stressing the valve. Regards Jim Jim, many thanks for such a detailed reply - I have to admit to one thing which may, by looking at your response, be the problem. I simply removed the old valve and plonked another one back in from the original head. I didn't change anything else, just fitted it, gapped it, and hey presto - it worked (for a bit). Other than my failure to grind the replacement in I thought that that was all there was to it. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 13, 2008 Moderator Share Posted November 13, 2008 Jim, many thanks for such a detailed reply - I have to admit to one thing which may, by looking at your response, be the problem. I simply removed the old valve and plonked another one back in from the original head. I didn't change anything else, just fitted it, gapped it, and hey presto - it worked (for a bit). Other than my failure to grind the replacement in I thought that that was all there was to it. Brian, your first post said the valve and guide were mashed, Jim has assumed that you replaced both of them, now you say you just replaced the valve! Can you clarify this for us, did you put another valve in a "mashed" guide? Edit, sorry, re read and you robbed a valve from the original head and put it in a replacement head, you said it has developed a habit of snapping this valve, so has it snapped more than one? Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 Brian, your first post said the valve and guide were mashed, Jim has assumed that you replaced both of them, now you say you just replaced the valve! Can you clarify this for us, did you put another valve in a "mashed" guide? Edit, sorry, re read and you robbed a valve from the original head and put it in a replacement head, you said it has developed a habit of snapping this valve, so has it snapped more than one? Sorry - I'll start again...... First head - oil deprivation - mashed exhaust valve and guide - inlet valve was OK Second head - origonal valves - no oil deprivation - straight swap for origonal - snapped inlet valve after a couple of weeks. So - removed broken inlet valve and swapped for good valve from first head. Also used opportunity to replace piston, rings, all top end gasgets (bought them after the oil deprivation as I thought it may have blown a piston). Then - a week or so later, same thing happens to inlet valve. Snaps right where the collets clamp into the groove a the top of the valve. Have never changed anything else on the head except for the valves. To be honest I just thought that the guides were built into the head and didn't realise they were changeable until I read about the 'oven' trick. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 13, 2008 Moderator Share Posted November 13, 2008 so its happened twice but on a head that you never did anything to the valve guides, i wouldnt put a new valve in there no, thats just too much of a coincidence, maybe JimR can advise further. Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 so its happened twice but on a head that you never did anything to the valve guides, i wouldnt put a new valve in there no, thats just too much of a coincidence, maybe JimR can advise further. LOL - I have edited the last post as I forgot to mention that bit, but yes, it snapped that one too! Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 13, 2008 Moderator Share Posted November 13, 2008 LOL - I have edited the last post as I forgot to mention that bit, but yes, it snapped that one too! One thing i will say though, back in the day i had a honda CB175, i replaced all kinds of gaskets in the head, not long after that the head was trashed...the reason was one of the gaskets had a hole punched for an oil passageway to lubricate the camshaft, only the punched out gasket had not been cleared and was still there in the hole if you get my drift, so the camshaft journals didnt get lubed!...I dont suppose... Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 ...an interesting thought, but the first thing I checked was the oil flow since that is what caused the froblem in the first place. If I remember rightly there are only four holes on the SR head gasget and they are the ones where the head bolts go (not including the big hole where the piston goes....I'm not that daft!!!!) Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 13, 2008 Moderator Share Posted November 13, 2008 there are only four holes on the SR head gasget and they are the ones where the head bolts go (not including the little hole where the piston goes....I'm not that daft!!!!) Edited for accuracy I'm stumped now , see what Jim says and keep your eyes open for yet another head, then call the bike medusa!! Link to comment Share on other sites More sharing options...
Brian & Stef Posted November 13, 2008 Author Share Posted November 13, 2008 yeah...unfortunately that's the conclusion I'm being drawn to...another head required I can only be thankful that this hasn't happened on my GSXR Thanks for all the help anyway Link to comment Share on other sites More sharing options...
JimR Posted November 14, 2008 Share Posted November 14, 2008 Sorry - I'll start again...... First head - oil deprivation - mashed exhaust valve and guide - inlet valve was OK Second head - origonal valves - no oil deprivation - straight swap for origonal - snapped inlet valve after a couple of weeks. So - removed broken inlet valve and swapped for good valve from first head. Also used opportunity to replace piston, rings, all top end gasgets (bought them after the oil deprivation as I thought it may have blown a piston). Then - a week or so later, same thing happens to inlet valve. Snaps right where the collets clamp into the groove a the top of the valve. Have never changed anything else on the head except for the valves. To be honest I just thought that the guides were built into the head and didn't realise they were changeable until I read about the 'oven' trick. So I guess the history of head #2 is unknown ? perhaps the guide is no good there ? But why did head #1 run short of oil ? was that sorted out . simple check (with old SR125's) undo the screw on the oil filter cover & run the motor (oil should pee out of the hole, later bikes didn't have the bolt). Some modals had another 'test bolt' located on the head on the rear right handside of the head (the cylinder bolt that supplies oil to the top end) undo this one (if you have it ) and check for oil flow , which may sort the oil problem to the top end. The valve is (is breaking) at a non lubed part but if the rest of the motor is loosing lube it may get well to hot giving random failures. Just one more point did the collets seat well into the cap or did they sit 'proud' a bit ? if they did when you refit make sure they are well in the groove and level with the cap. with the oil loss to the top end I'm supprised that you didnt take a cam & followers out also, have you checked that the cam & followers are ok ? On a differnt point if the motor is not lacking in lube the intake valve getting hot points to other problems and perhaps thats phase 2.... any photo's of the distroyed bits/old head will make things easier for me. Regards Jim Link to comment Share on other sites More sharing options...
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