GY6 valve lash started changing for some reason

[dadx3]

GY6 valve lash started changing for some reason on my scooter. I did the intake exhaust mods and carb jetting and this 125cc does 60mph but recently something happened wz hard to start and I checked compression and was below 100psi so I followed you guys guide on valve lash settings and mine were tight no lash so i adjusted to spec and compression went back to 160+ again started fine ran 100 miles perfect and gf called me I picked her up the dead scooter ran fine then seems no compression again cz of sound how its turning over. I'll check the valve lash again and I suppose it's off again hopefully will run again

Question: Sounds like something is moving like a timing chain or some flywheel key pin is bending cz there was no reason for the valves to be that far off the first time and now seems did again within 100 miles so I'm sure this has happened to someone before... and sure some other root cause is causing this valve lash I just hope you guys don't say it's the crank slipping but gotta be something cz came on all of sudden and not going away it seems with just a valve adjustment(s) IMO.

Thx in Advance,

Dad_X3

Oh my scoot has the GY6 QMI (125cc) 3.2k miles

[ltdhpp]

How long had it been since your last adjustment before the one you just did? Its not uncommon for the valves to tighten themselves up, some faster than others. Until you check it out again its hard to say what happened. It could have blown up if you didn't do something right.

[dyoung1167]

also, running too lean will cause higher temps on the valves and in turn they tend to tighten sooner.

[dadx3]

okay guys thx now you mention heat maybe lean she did do a long run prior to failure. hmmmm...

It was less than 100 miles since I adjusted valves and compression went from less than 80psi back up 160+ but weird how ride the crap outta this motor for over 3k miles and never checked lash or needed to adjust lash and now it's changing so often (I'm assuming till i get in there...) just weird why it's doing it now.

I can visualize a broken key on flywheel will only effect spark timing performance effects so that's not it.

Short of me screwing up (these valves are just like any other I've done kinda simple stuff) ---> it must be the timing chain IMO. I'll havta see an exploded view and see how it's attached at crank as well.

Do these timing chains stretch? Ever need adjustment on chain tension-er or something? What is the SOP lifetime duty cycle of these chains and do they need to be replaced at so many hours/miles?

I can visualize the lean idea to tighten up valves but I've ran this scooter historically way lean and used to shut down in hot traffic till I ended up put in a 115 main 38 pilot. Maybe since I recently adjusted the valves 100% and get to have 160 psi compression again ya it may need a 117.5 or 120 main now but just don't see as root cause to these valves tightening all of sudden. It must be the timing chain IMO.

I dig in tomorrow am and send pics if needed.

Thx Doods! Dad_X3

[dadx3]

Ya you were spot on... Lean issue and valve bent so lost compression then. It didn't hit the piston but tiny tiny bit left small nick... see image.





Might be a little lean on plug and is how failed as is valve images.





The cam is fine chain was fine I think I was tuning carb with valve out of adjustment end of summer and then when I adjusted valves I never tuned carb after and prety sure needed more fuel after valves were opened up to make compression and bike run. With .004" lash ran great for 80 miles till my gf went on long WOT and think was running too lean and I need min 117.5 or 120 main. I modified intake and exhaust wide open basically with 7$ BS muffler so these pics show me needed way more fuel WOT. I think got hot as hell bent/burnt valve and lucky didn't do worse IMO. I was wrong about timing chain... You guys were right about lean heat as I see it.

Thanks for the input. Maybe you can verify my cylinder and head marking orientation and let me know what 100% correct last should be intake exhaust in inches (") thx!








Dad_X3

[dadx3]

Okay i was google-ing gy6 bent exhaust valve and found this guys comments very interesting... The kid he was helping wz saying his exhaust valve was bent but ended up being intake in the end but dood had some good comments IMO. What you guys think of copy paste below?

First response he had:
Re: Bent exhaust valve again
by PGH on Thu Nov 03, 2011 2:46 am
When you were timing the crank to the cam, did you use the timing mark on the flywheel or actually verify TDC of the piston in relation to the marks on the flywheel?

Is the timing chain tight and tensioner working? A stretched chain will jump teeth.

Do you have an exhaust leak or are your running it without a muffler? The cold air rushing in behind the exhaust stroke can destroy your head or exhaust valve.

2nd message...
Re: Bent exhaust valve again
by PGH on Thu Nov 03, 2011 2:52 am
Everything I posted will still apply except valve damage to the intake valve can also be caused by intake leaks or lean jetting backfires through the carburetor.

Bring the piston to TDC and see if your flywheel agrees. If the Woodruff key is sheared or marks are off it can allow the piston to contact the valve.

• So my question is is my open muffler and cold air a posible root casue and I didn't know timing chain is attached to woodruff key and that potential issue?
  
  
• What do you guys think your best guess is with data so far what my root cause of this exhaust valve failure is? (review images above):
  

1. piston bent my valve? Via woodruff key issue? FYI: Timing chain and tensioner seemed all good and tight.

2. cold air in exhaust cz not running stock muffler bend valve? FYI: I'm running a 5$ BS muffler

3. Lean condition running 115 main 37.5 pilot (see ics above) seems little lean plug right?

4. Lean condition plus cold air not running stock muffler?

I'll check this TDC as guy mentions next time I'm at shop for this woodruff key as potential root casue and I didn't think that wz possible it could be root cause before but... live and learn ;D

Thx in Advance,

Dad_X3

[dyoung1167]

all i can say is he seems fairly knowledgeable except the timing mark. that is for spark timing and WILL be slightly off as spark occurs just prior to tdc and should never be used for tdc or adjusting valves.

[dyoung1167]

that said, it doesn't mean the key isn't sheared and is still worth looking at, just that the two will not agree.

[dadx3]

ya I don't see woodruff key shearing move make any effect on piston "bending" valve either I just looked at some vids on youtube and chain is attached to crank crank attached to piston and I just cannot visualize a that key slipping bending effecting only spark performance etc not mechanical... hmmmm....

I asumed the valve got too hot from lean and bent and touched the piston as per image.

I'm just exhausting (no pun intended) the potential root cause piston came up and hit the valve and "bent" it in that way... hmmmm...

What common conditions/failures do you guys know that will cause piston to come up and hit "bend" valve (exhaust).

Thx Dad_X3

[Fox]

The lash gets tight from the valves seating deeper and deeper into the valve seats. Excessive heat can make that happen sooner. When they seat in deeper the lash goes away and when the cam lobe comes around they open further than they would with a normal gap setting causing them to hit the piston.

Ps: I always use the T mark when adjusting the valves cause that is the point at which they are both closed. You can use the F mark cause that's when the spark sparks so they should both be closed there as well.

[jlee]

Nov 7, 2012 10:47:39 GMT -5 Fox said:

Ps: I always use the T mark when adjusting the valves cause that is the point at which they are both closed. You can use the F mark cause that's when the spark sparks so they should both be closed there as well.

I always use the "stick in the spark plug hole" method as I take the plug out to make it easy to turn the crank by hand.

[Moat]

Nov 6, 2012 19:08:08 GMT -5 dadx3 said:

What common conditions/failures do you guys know that will cause piston to come up and hit "bend" valve (exhaust).

1) Improper cam timing (chain skipped sprocket teeth, sprocket lost index)
2) Broken valve stem
3) Stuck valve (tight guide, insufficient lubrication, stem deposits, etc.)
4) Loose/dropped valve seat (intermittently holding valve open)
5) Valve float (from over-revving)
6) Dropped valve (lost keepers, spring retainer failure)
7) Crank/rod bearing/piston pin/piston failure
8) Setting valve lash waaay too tight - forcing valve to always be substantially open
9) Failure of that kickback, compression release thingy on some GY6 cams... maybe...?

BTW - If anything, your spark plug looks rich (chocolate brown to black)... not lean (white-ish, light grey).

[dadx3]

OMG, you guys rock!

Okay If I'm not running lean then piston came up and hit bent valve IMO... I got some investigating to do then and thanks for the "to do" list.

Here is images of valve I took out have new one coming 7.90$ free shipping eBay.

Thanks Bros! I'll keep ya posted on root cause this week.

Best, Dad_X3

Attachments:

[dadx3]

Okay I messed up and moved my photobucket images so lost links above darnit...

I'll post a couple pertinent one s again cuz I'm not convinced this piston hit the valve to bend it. This image shows the piston after I took head off with cam and 3 holes lined up on the "T" mark and is top TDC. The chain was tight all good I just cannot visualize even if valves seated deeper which I think they did this summer thus making scooter stop running well and hard to start but as you stated deeper seated valves are further away from piston so when cam pushes further IMO will only be the difference and should not hit valve.







I'm not so sure the valve didn't just bend on it's own but since the plug u guys say plug shows more on rich side not lean so not make sense it got too hot and bent from the heat... Plus if you look at this image wouldn't the valve bend the other way if piston hit and bent it??? What you think?



I just read a Scootrdawg big bore kit instructions saying to adjust the .008" intake and .010" on exhaust. They also say some have better experience with even larger openings... So my .004" intake/exhaust (adjusted cold) specs i adjusted my valves seems pretty far off from this and would have my valves opening much more and much more risk to valve piston clearance(s).

Can we consider my valve adjustments (.004") might have been too tight and thus root cause for exhaust valve bending (hitting piston)?

Thanks in Advance,

Dad_X3

[dyoung1167]

the "t" mark should not be exact with the three holes on the sprocket lined up properly with the edge of the head, more like a tooth off (roughly). you can waste your time pulling the plastic peep plug n trying to get your face and a flashlight lined up for a glimpse or pull the plastic cover from the fan to use it to bring the engine around for the combustion cycle but i don't know why as you have to pull the valve cover and line up the holes anyway. if doing a 15min job in 45 is your thing be my guest, but if they both line up exact it's wrong!!!!!
the "T" mark should line up just prior to actual TDC then travel slightly past once TDC (when the valve sprocket holes lined up to the edge with the single larger hole up)

[dadx3]

Nov 19, 2012 16:01:45 GMT -5 dyoung1167 said:

the "t" mark should not be exact with the three holes on the sprocket lined up properly with the edge of the head, more like a tooth off (roughly). you can waste your time pulling the plastic peep plug n trying to get your face and a flashlight lined up for a glimpse or pull the plastic cover from the fan to use it to bring the engine around for the combustion cycle but i don't know why as you have to pull the valve cover and line up the holes anyway. if doing a 15min job in 45 is your thing be my guest, but if they both line up exact it's wrong!!!!!
the "T" mark should line up just prior to actual TDC then travel slightly past once TDC (when the valve sprocket holes lined up to the edge with the single larger hole up)

Okay thanks for info on this. I remember the T mark was about a tooth off as I remember as you mention and will pay close attention to this on re assembly valve lash adjustment to the cam holes not "T" mark. Thx!

I'm putting back together today and delayed prior to wait for some NCY titanium valve springs cuz I never really got a definitive root cause on this and I see some discolor on exhaust side of head and maybe when overheated those times last summer (till I put large enough main jet) damaged and weaken the exhaust spring. I say this cuz pretty sure I set valves right last time ran great 100 miles so how could valve suddenly hit piston unless that long ride she rode the weak exhaust spring didn't hold WOT top speed (60+MPH) or the open BS muffler exhaust burned the valve bent then hit piston a little to make that small mark you can see on piston.

What you guys think is root cause if you had to choose?

1. Weak overheated damaged exhaust OEM spring?

2. Open exhaust (cold air) burned exhaust valve?

There was someone said something about kickback mechanism on some cams as root cause I'll read up on question that too but anything you guys could help out before i set this all back up would be appreciated.

I can adjust .004" each intake exhaust is okay right? I wanna stay away from tight exhaust for sure and is .005" (thousands) on exhaust too much?

Thx in Advance,

Dad_X3

[ce]

I adjust intake to .004 and exhaust to .006, in some engines it will clack for a while, if I can't stand the noise I'll tighten the exhaust down to .005, but never more, since it wil eventually tighten on it's own. The intake never sems to move.

It looks like you burned through the exhaust header gasket from all that carbon on the head, that would have been a big leak right at the exhaust port, and that may be what smoked your valve.

115 is a pretty big jet unless you're running a lot of air in there with it, you may do better to mount a 'velocity stack' between the filter and the carb to constrict the flow of air a little and get a more balanced burn.

[dadx3]

Dec 17, 2012 15:21:57 GMT -5 ce said:

I adjust intake to .004 and exhaust to .006, in some engines it will clack for a while, if I can't stand the noise I'll tighten the exhaust down to .005, but never more, since it wil eventually tighten on it's own. The intake never sems to move.

It looks like you burned through the exhaust header gasket from all that carbon on the head, that would have been a big leak right at the exhaust port, and that may be what smoked your valve.

115 is a pretty big jet unless you're running a lot of air in there with it, you may do better to mount a 'velocity stack' between the filter and the carb to constrict the flow of air a little and get a more balanced burn.

Sweet great info I agree and will look at my custom intake is pretty much velocity already with large tubing and UNI filter at end I'll send pic later. I think you may be onto the exhaust leak maybe. I have new header gaskets brought in from eBay. I still may leave in the 115 main cz this 125cc moves pretty good over 60 MPH and have CDI to install with 4 degree advance too after install this head with new valve and HD springs. Then do some real WOT cut ign coast pull plug checks.

Thx keep ya posted

Dad_X3

[Deleted]

It takes practice to get those adjustments right, it's as much about having a "feel" for it than the actual specifications but even after having done it several times I've put it all back together just to have it be off again!
Oh, once or twice I've had it clattering not two minutes after it's all back together.

In that time I have learned, ignoring small details usually spells frustration...
1. The engine needs to be COLD and I mean let it sit overnight, valve lash MUST be adjusted on a COLD engine.
2. I use .004 both intake and exhaust because I have never had a problem them tightening they always loosen on me.
3. First order of operation is to CHECK the lash before loosening ANYTHING, just in case one or the other is correct.
3. It took the MOST practice to get the exact amount of "tightness" on the nut correct, if it's not tight enough it will work itself loose and obviously too tight is no good but that is only because it could strip something... Therefore, tight enough is past too loose and before something strips, tighter is better but again too tight and we're in trouble.
4. I like to drag the feeler back and forth slowly while tightening, it is best when there is some drag, doing this gives me that practice that is how I develop a "feel."
5. A LOT of times the lash will change AS I'm tightening giving it that final twist, it is a real pain trying to hold the bolt while tightening the nut and holding the feeler in place, special tools my butt, I use a needle nose vise grip to hold the bolt and a tiny open end wrench for the nut, the trick is to keep that vise grip STEADY.
6. ALWAYS check the lash one last time before putting everything back together, be ready to do it over, check and double check.
7. Up to you if you want to do this because of the risk but after everything is complete and before I put it all back together I will run the engine for a few seconds with the valve cover off just to see if I hear obvious noise, only a few seconds because she'll spew oil and etc, just to see if I hear anything terribly wrong, then shut her down and re-assemble.

One other thing to always check is those dang upper and lower plastic/metal timing chain guides, the two black pieces, the upper one rests against the tensioner and guides the chain, IF this guide is gone and the chain rides against the tensioner you can expect trouble in 100 miles or less thou oddly enough the engine will run dandy for a bit.

[dadx3]

Dec 18, 2012 1:44:45 GMT -5 @8307c4 said:

It takes practice to get those adjustments right, it's as much about having a "feel" for it than the actual specifications but even after having done it several times I've put it all back together just to have it be off again!
Oh, once or twice I've had it clattering not two minutes after it's all back together.

In that time I have learned, ignoring small details usually spells frustration...
1. The engine needs to be COLD and I mean let it sit overnight, valve lash MUST be adjusted on a COLD engine.
2. I use .004 both intake and exhaust because I have never had a problem them tightening they always loosen on me.
3. First order of operation is to CHECK the lash before loosening ANYTHING, just in case one or the other is correct.
3. It took the MOST practice to get the exact amount of "tightness" on the nut correct, if it's not tight enough it will work itself loose and obviously too tight is no good but that is only because it could strip something... Therefore, tight enough is past too loose and before something strips, tighter is better but again too tight and we're in trouble.
4. I like to drag the feeler back and forth slowly while tightening, it is best when there is some drag, doing this gives me that practice that is how I develop a "feel."
5. A LOT of times the lash will change AS I'm tightening giving it that final twist, it is a real pain trying to hold the bolt while tightening the nut and holding the feeler in place, special tools my butt, I use a needle nose vise grip to hold the bolt and a tiny open end wrench for the nut, the trick is to keep that vise grip STEADY.
6. ALWAYS check the lash one last time before putting everything back together, be ready to do it over, check and double check.
7. Up to you if you want to do this because of the risk but after everything is complete and before I put it all back together I will run the engine for a few seconds with the valve cover off just to see if I hear obvious noise, only a few seconds because she'll spew oil and etc, just to see if I hear anything terribly wrong, then shut her down and re-assemble.

One other thing to always check is those dang upper and lower plastic/metal timing chain guides, the two black pieces, the upper one rests against the tensioner and guides the chain, IF this guide is gone and the chain rides against the tensioner you can expect trouble in 100 miles or less thou oddly enough the engine will run dandy for a bit.

This is great write up cz sounds exactly what i just performed and I could not believe how much different feel .004 and .006" so I follow you and your right up 100%... cept I did exhaust at .006 just because fraid of it tighten up but seems I need to remove head and have valve job done. The new exhaust valve seems fine but and the orig OEM intake valve not hold compression. Valve spits oil out on my "ring/valve" test. FYI: I took the intake valve out to put the new springs so not sure why messed up but musta needed valve grind job and i probably shodda done planned this with new valve but I figured those springs hold those valves pretty tight esp new ones giver er a try. Live and learn... I'll pull head and send to machine shop tomorrow.

Can I have them grind my old intake valve or do i have to buy a new valve like I did for exhaust? Intake valve looks okay and I can print the OEM pages valve grind angle(s) specs from OEM service manual and I have a very good motorcycle machine shop avail. Gonna check eBay prices new head assy with free shipping maybe way to go this time and I can fix this one back up later.

Thx for help Mang!

dad_X3

[dadx3]

Hey and another thing is the intake valve seat a sleeve and comes out of head cuz mine is loose and may be root cause as I'm thinking now I'm home that sleeve is not supposed to move and my issue!!!!! I'll go back to shop tomorrow and confirm take pictures...

Dad_X3

[buford1488]

the valve seat is pressed in. and no the seat ring should not be moving if that is what you mean..again its a ring that is pressed in. if that is moving do not attemp to run it...you need to have that repaired or buy a new head.............buford

[dadx3]

Dec 19, 2012 11:14:40 GMT -5 buford1488 said:

the valve seat is pressed in. and no the seat ring should not be moving if that is what you mean..again its a ring that is pressed in. if that is moving do not attemp to run it...you need to have that repaired or buy a new head.............buford

Yes thx makes perfect sense I Google d and don't see any removable valve sleeve and my issue gonna fix ASAP and get this scooter back up soon!

I wonder if/how much grief I've been exposed too from this loose valve sleeve? Hmmmm... I like root causes and fixing this sleeve excites me

Thx Gin!!! ;D

Dad_X3

[buford1488]

depending on the ring's and size if you don't have a machine shop to make them yourself you would have to shop around and they aren't cheap. then get it pressed in perfectly then cut the seat to 45% for the valve i do three angle cut's when i do heads. if you want to experiment you should get a old head first. i think it would be less money for ya to just get a new head. just my opinon. i dont think that its been loose long. because it would deff be a big issue.