yamaha sr125 inlet valve

[nightshaddow]

hi this is my problem

i have a 1991 yamaha sr 125 and i had some really bad rattleing l8ly, i reset the tappets and it ran smooth for about 250 miles, then it started again, so i looks at the tappet again and the bottom of it was compleatly crushed, i replaced the tappet thinking old bike needs replacing so did the inlet and the exhaust tapets, i have done about 500 mile since then and the inlet tappet has been crushed again, i have ajusted it twice (second this weekend) and a bit worried anyone have any ideas, could it be a dodgy valve or something more serious

cheers
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Ichy]

Do you have any photo's? It takes a hell of a lot to damage a healthy tappet, they tend to be at least surface hardened.

Did you adjust it correctly, ensuring there was a gap when the valve was closed?

[TUG]

My god, sounds like you set the gap at the wrong point maybe???
250-500 miles and it died again thats really bad, if its not you setting it wrong then there is something seriously wrong.
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Haz ER-5, innit!

[aero]

Those engines tend to suffer from a lack of lube at the top end. It maybe that the cam is wearing away at the cam follower.
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70's & 80's 4 stoke Yamaha Guru and professional workshop dweller.

[nightshaddow]

i will take photos of current tappet at the weekend when it's light, i sould explain i am no newbee wen it comes to mechanics i set it right everytime,

engine tdc bothe valves are closed
set inlet to bettween 0.05 - 0.09 mm (as stated in haynes manuel)
set exhaust to between 0.11 - 0.15 (same sorce)

runs beautifully for about 50 -60 miles then you get a slight tap which gets worse till ajusted

i do roughly 25 miles a day and i check most weekends the distance due to the amount of tapping it will incure in a week

camchain is prety clean and at correct tensionand the cam cog is clean with no broken teeth
any ideas
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[aero]

Taken from a 'tapetty' SR engine where the owner had , surprizingly, been chasing the valve adjustment. It did sound a bit rough as he pulled up.
https://i29.tinypic.com/jv10s0.jpg
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70's & 80's 4 stoke Yamaha Guru and professional workshop dweller.

[Billd]

I had an SR125 in about '88. I know it's a lot older than yours but I corcscrewed several valve stems just from red lining it too much. In fact, I still have a brand new valve somewhere from these days...

[nightshaddow]

there is another symptom.... it my not be related, thought i have a sneaking suspision it is

it has developed over the past few months a backfire, not a miss fire but a true back fire, it doesnt do it on tick over steady revs or high revs but when i throtle of or down shift it dont half pop.... normaly wen the revs get to 3000rpm wen slowing down,,,, any ideas
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[nightshaddow]

ok these are from the new tappet put in around 500 miles ago

https://img184.imageshack.us/img184/461/imag0011qt5.jpg

https://img519.imageshack.us/img519/9311/imag0012ln5.jpg

I am now on a new tappet 3rd one in 2 months plz help
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Pete.]

Bit of a toughie this one but I would suspect one of two things:

1) Poor oiling at the top-end, causing the follower to wear against the cam until it's got so loose it's hammering the adjuster down. Could be from a clogged strainer or more likely an oil passage up to the head is restricted. Only a strip-down would reveal the fault. The cam is probably scrap.

2.) You've suffered a bit of valve float causing a piston-valve strike and bent the valve a bit. The valve is slightly open causing loss of compression and too small a piston/valve clearance, and the piston is just clipping the valve at revs.

I prefer the 1st option, the 2nd is frankly unlikely on the SR engine.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[nightshaddow]

[aero]

Utter schisse! If you bent a valve even a thou or so it would stick in the valve guide and wreck the piston. Situtation two is that just the head gets bent a little in which case it wouldn't seal and the engine won't run!

These are either cheap crap adjusters from India or the clearence has been badly wrong. In either case you need to look at the cam and the other ends of rocker arms to what's going on.
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70's & 80's 4 stoke Yamaha Guru and professional workshop dweller.

[Pete.]

When you rebuilt the top-end, did you use any hylomar/instant gasket anywhere?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[aero]

Looking at that there is loads of oil up there.

The only other thing I can think of is - has someone wound on a standard 8mm nut on to the adjuster? The adjuster has a 1mm thread pitch, where as the 8mm nut has 1.25. The adjuster being a harder metal wins every time, leaving the lock nut in capable of locking.

Or has the adjuster lock nut simply not been tightened up enough?

Its odd that the engine runs fine but the lock nut comes undone on its own!
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70's & 80's 4 stoke Yamaha Guru and professional workshop dweller.

[nightshaddow]

ok firstly these are good genuine brand new tappets from yamaha i have one left after replacing it today,

second i use genuine engine gaskets again ordered from local bike shop

third yes always plenty of oil at the top end (latly i had to check the clearences every few days... these are no standard 8 mm nuts these are 10mm nuts suplyed with the tappets(at my request)

and finally as i stated earlyer in the thread when i have ajusted it up it runs absalutly perfectly for a few hundred miles till the tapping starts again,

i have been working on bikes and cars since i was about 5 with my dad but never have i seen anything like this, i have alot of people stumped with this if i can find a good stockinst i will rip the engine down and replace what needs
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Pete.]

The adjusters shold not wear with normal clearances. The few thou gap isn't enough for the adjuster to gain enough momentum to peen the end over - essentially they are "pressing" on the valve stem rather than "hitting" it. If the adjuster is wearing down there must be another reason for the clearance to increase, and that usually means the cam follower is worn out. This would be evidenced by you having to screw each new adjuster down a little further to attain the proper valve clearance. If this is happening I would check the follower and cam for wear.

If you have used any liquid gasket in any of your rebuilds I would check the oil strainer and ensure that the oil passage to the head is not partially blocked.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[nightshaddow]

this machine is coming off the road next week i will recheck the cam and rocker as well as the valves, if i still see no problems i will post more pics see if anyone can decifer the problem...... general intrest could it be down to valve springs no one seemed to mention this yet but i just hitting into space on this one, it been just over 1000 miles since the problem started so maybe the internal problem will be more pronounced
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Pete.]

I was going to suggest checking for a broken spring, but in my opinion it would have dropped the valve by now with that much rattling going on. It doesn't take much to sling the collets out. Good thinking though and it might yet be the cause.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[aero]

We replaced several top ends from these engines under warranty from new due to excessive wear on the cams.

Two springs breaking (inner and the outter)? Don't think so. Either will hold the valve tightly closed, you'd get problems as the revs build with one broken spring though.
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70's & 80's 4 stoke Yamaha Guru and professional workshop dweller.

[Trilby]

I think I may the same trouble. My bike has only just done 5000 miles....and I hear this constant tapping noise, but it only seems to happen on tick over. I have set the timing correctly and the tappets but it just seems to revert back to this god awful noise.
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TrIbZ

[Pete.]

[prawny1]

check the condition of the cam follower shaft and bush, if they are worn it wil lead to noisy top end and difficult to set valve clearence as the follower will be all over the place. anyone with experience of the a-series mini and metro will agree.

[smegballs]

on my 1998 SR 125 i have a similar thing going on, after setting the valves it starts tapping after around 200 miles, its only a very quite tap tho and only under load so i havent bothered with it to be honest, generally ive found the engine pretty bulletproof.

[nightshaddow]

true the engines are bullet proof but this machine is a backup and reliable as hell wen my other is being serviced or off road for repair,
but it is damaging itself and it is no quiet tap, latest symptom loosing power mid range loads of power and torque low and high but splutters mid range
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[craigT19]

get a compressoion check mate, sr's arnt as bullet proof as poeple think... they are terrible for dropping there exhaust valves.. the ones ive seen sound like a bag of spanners but do still run after the piston hits the valve because the gap at tdc is fairly big, the valves get rammed up damaging the collets and some times valve guids but ofter the rocker and cam gets damaged
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Bikes owned :- 2001 nsr125, 1999 zx6r, 2006 yzf-r1, 2009 xmax 250, 2012 yzf-r1, 2015 MT-07
Current bike : - 2016 MT-10
BCF member pops. sadly missed 1945-2003