Old 1st November 2019, 08:29 PM #1
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gsxr valve stem damage cause?

HI Guys, currently working on a gsxr 750 and have found an odd problem on the engine, upon looking down the intakes i noticed what looked like notching on a valve and decided to instigate, i found 6 of 8 intake valves are scored around the valve, looks to me like someone turned it in a drill against a file. two valves are unharmed and they oddly both share a port with a damaged valve so im unsure of the cause,

The head will be replaced anyhow but id like to find out what caused this issue, i have attached an image for anyone who thinks they may have an idea. i would have assumed guides but its too low on the stem.



any help appreciated
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Old 1st November 2019, 09:23 PM #2
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Re: gsxr valve stem damage cause?

The scoring looks horizontal! If it was a mechanical issue like bad guides,you’d expect to see vertical wear....probably someone decoking them with a bit of rough stuff
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Old 1st November 2019, 09:29 PM #3
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Re: gsxr valve stem damage cause?

Originally Posted by DavyH
The scoring looks horizontal! If it was a mechanical issue like bad guides,you’d expect to see vertical wear....probably someone decoking them with a bit of rough stuff
thats what i was thinking, looks like someone took a drill and a strong wire brush to the valve stems, thing that gets me is they never touched 2 of them and did 6, i rubbed a flatblade across the scoring and it is very harsh, enough to convince me to replace anyway
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Old 1st November 2019, 09:44 PM #4
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Re: gsxr valve stem damage cause?

i found a nut down an intake on a cage one time, obviously dropped in sometime and never removed, damaged the valve stem something like that but it was only one valve as the nut couldnt jump anywhere else, wore the shit outta the nut too.
dunno what could have done it in your case, obviously replace but id be curious about it too.
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Old 1st November 2019, 09:53 PM #5
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Re: gsxr valve stem damage cause?

Originally Posted by allsorts&oddjobs
i found a nut down an intake on a cage one time, obviously dropped in sometime and never removed, damaged the valve stem something like that but it was only one valve as the nut couldnt jump anywhere else, wore the shit outta the nut too.
dunno what could have done it in your case, obviously replace but id be curious about it too.
i thought that too at first, odd one, has to be over vigorous cleaning, but who has the skills and tools to rebuild a head and do such a terrible job of cleaning valves, curious is exactly the word, im sure ill never know for certain what happened but it does bug me trying to work it out
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Old 1st November 2019, 10:31 PM #6
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Re: gsxr valve stem damage cause?

definitely a weird one Paul, be worth keeping one up on the shelf as a curio. lucky you found them, those could snap off the head of the valve and feck up uour day bigtime.
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Old 1st November 2019, 11:09 PM #7
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Re: gsxr valve stem damage cause?

Originally Posted by allsorts&oddjobs
definitely a weird one Paul, be worth keeping one up on the shelf as a curio. lucky you found them, those could snap off the head of the valve and feck up uour day bigtime.
true would have been a bad day indeed, was running like a bag of shite anyway so intended to ultrasonic carbs and do valves clearances. little did i know id be doing them on a different head
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Old 2nd November 2019, 09:22 AM #8
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Re: gsxr valve stem damage cause?

Maybe someone thought making lighter valves would make it go faster. And machined them with a blunt lathe.
The two good ones are replacements for the ones that broke.
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Old 2nd November 2019, 10:57 AM #9
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Re: gsxr valve stem damage cause?

Originally Posted by dukeNblade
Maybe someone thought making lighter valves would make it go faster. And machined them with a blunt lathe.
The two good ones are replacements for the ones that broke.
definitely possible but hope not
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Old 2nd November 2019, 11:10 AM #10
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Re: gsxr valve stem damage cause?

Originally Posted by dukeNblade
Maybe someone thought making lighter valves would make it go faster. And machined them with a blunt lathe.
That's what it looks like to me. I'm pretty sure a stock inlet valve stem on a gsxr 750 shouldn't reduce in diameter along its length. It looks like someone has butchered it in a lathe.
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Old 2nd November 2019, 11:16 AM #11
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Re: gsxr valve stem damage cause?

Originally Posted by Gixxer
That's what it looks like to me. I'm pretty sure a stock inlet valve stem on a gsxr 750 shouldn't reduce in diameter along its length. It looks like someone has butchered it in a lathe.
what gets me is why, not for performance gain obviously as the ports are stock
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Old 2nd November 2019, 12:51 PM #12
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Re: gsxr valve stem damage cause?

Originally Posted by sharpbikes
what gets me is why, not for performance gain obviously as the ports are stock
Lightened valves reduce the workload on the cams,which reduces workload on the rest of the motor....so technically it is a performance gain....if done correctly
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Old 2nd November 2019, 02:27 PM #13
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Re: gsxr valve stem damage cause?

Originally Posted by DavyH
Lightened valves reduce the workload on the cams,which reduces workload on the rest of the motor....so technically it is a performance gain....if done correctly
dont understand why someone would go to the effort of stripping to do valves and not doing anything else, then again carbs seem butchered too
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Old 2nd November 2019, 05:35 PM #14
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Re: gsxr valve stem damage cause?

Originally Posted by DavyH
Lightened valves reduce the workload on the cams,which reduces workload on the rest of the motor....so technically it is a performance gain....if done correctly
Also improves flow.
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Old 2nd November 2019, 06:52 PM #15
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Re: gsxr valve stem damage cause?

Originally Posted by joe williams
Also improves flow.
It does, if the inlets are ported and polished and flowed to make use of the tiny extra percentage of air flow, but on a stock head it's fucking ridiculous.
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Old 2nd November 2019, 07:02 PM #16
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Re: gsxr valve stem damage cause?

Originally Posted by Gixxer
It does, if the inlets are ported and polished and flowed to make use of the tiny extra percentage of air flow, but on a stock head it's fucking ridiculous.
exactly what im thinking.
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Old 2nd November 2019, 07:44 PM #17
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Re: gsxr valve stem damage cause?

Originally Posted by sharpbikes
exactly what im thinking.
I'm guessing someone bought those valves from a dickhead on ebay, and inserted them into this head, thinking he'd double the horsepower. The cunt was probably from Cork.
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Old 2nd November 2019, 08:17 PM #18
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Re: gsxr valve stem damage cause?

Originally Posted by Gixxer
I'm guessing someone bought those valves from a dickhead on ebay, and inserted them into this head, thinking he'd double the horsepower. The cunt was probably from Cork.
If trimming the valve doubles horsepower, wouldn't cutting that bit out altogether give you infinity horsepower?
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Old 2nd November 2019, 09:00 PM #19
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Re: gsxr valve stem damage cause?

He should have used these
https://imgur.com/RiRjovw
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Old 2nd November 2019, 09:38 PM #20
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Re: gsxr valve stem damage cause?

Originally Posted by johnpclynch
If trimming the valve doubles horsepower, wouldn't cutting that bit out altogether give you infinity horsepower?
now you might just have something there, free flow valving, what can go wrong
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Old 2nd November 2019, 09:58 PM #21
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Re: gsxr valve stem damage cause?

Originally Posted by SoulX
He should have used these
https://imgur.com/RiRjovw


I'm guessing the cunt who did that to the valves in the OP would fit something similar.
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Old 3rd November 2019, 09:05 AM #22
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Re: gsxr valve stem damage cause?

It's a strange one for sure
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Old 4th November 2019, 08:13 AM #23
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Re: gsxr valve stem damage cause?

Originally Posted by Gixxer
It does, if the inlets are ported and polished and flowed to make use of the tiny extra percentage of air flow, but on a stock head it's fucking ridiculous.
Pointless gain alright , but thats the idea behind them. Suppose it all adds up with a ported head.
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Old 12th November 2019, 05:08 PM #24
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Re: gsxr valve stem damage cause?

having bought another head for the bike and upon lapping in the valves i found the valves do narrow between the top of the stem and the valve itself, when the old head is removed ill check diameters to be sure but i assume at this point it was overly vigorous cleaning of the valves
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Old 12th November 2019, 05:25 PM #25
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Re: gsxr valve stem damage cause?

During WW2 forced laborers in German factories used various means of sabotage including grinding a slot in the valve stems of engines so they would fail after a few hours running causing utter destruction of the engine.
Have you considered the possibility that someone is trying to scupper your plans for world domination?
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Old 12th November 2019, 05:31 PM #26
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Re: gsxr valve stem damage cause?

Originally Posted by SoulX
During WW2 forced laborers in German factories used various means of sabotage including grinding a slot in the valve stems of engines so they would fail after a few hours running causing utter destruction of the engine.
Have you considered the possibility that someone is trying to scupper your plans for world domination?
that explains it all, need to release the slaves
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