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Piston to valve clearance?

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Hello.  I've somewhat recently expanded my tool set to include a Bridgeport milling machine.  Already have a bit of tooling and work clamping stuff already.  Anyway, I recently had valve train issues with my 05 crf150f.  I've pulled it apart to replace valve guides, valves, etc.  I'm going with a slightly smaller cam than I had in there just because I've had continual valve train problems.  This last one was caused by aftermarket KW valve springs, combined with the large cam.  Literally snapped the top of the valve off.  I got lucky, and just bent the intake valve.  Anyway, going with a slightly smaller cam and now having the tools to do some real custom work, I'm wanting to use some clay and check the piston to valve clearance and maybe mill a little bit off the head or top of the cylinder.  I know the intake chases the piston and is fairly safe.  What is considered safe for the motors for the exhaust piston?  I guess a couple things to keep in mind on this.  I race this bike as a sumo setup, and I'm not beyond downshifting 3 gears going into the turn to slide it sideways.  Thanks for any advice or info!

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Some are comfortable with .040-.050" exhaust side piston to valve clearance...

From a lifetime of experience building engines I will add in that my comfort level is at .080" ....

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In many cases it is exhaust valve bounce that will kill you... Not exhaust valve float...

Cams can be huge and as long as they have safe accel and decel ramps at the beginning and end of the lobe, you will be safe...

The accel ramp serves as a way of preventing shock loading harmonics to the valvetrain... Gentle acceleration off seat ... Preceding higher rate acceleration of the lobe proper... Necessary for cam chain and valve spring longevity...

Next up is the decel ramp... In a world without inertia it would be a perfect setup for performance if a cam lobe was more like a rectangle... Instant open to full lift... Instant close after holding full lift for it's whole duration rating...Maximum time at full lift/full flow potential... Now back to the real world... The one with mass and inertia... The exhaust valve is held open as long as possible, followed by a fairly radical closing side of the lobe... The closing ramp portion is at the end... Sort of parachute that catches the semi free falling valve and gently let's it contact the seat... Instead of free fall until collision... Which induces bounce... Which is where the piston and exhaust valve shake hands with catastrophic results...

Decel ramps that are inadequate are also famous for popping heads off valves.... Along with a host of other undesirable effects...

So... You CAN have big lobes as long as you have good accel and decel ramps.... Evidenced by having more duration between the "off the seat" duration , and the "duration @ .040-.050" lift" ... The bigger the difference, the more gentle the accel and decel ramps...

Anyways... In my decades of experience with off road engines there has been one company that holds the record for aggressive profiles that have shock hardened springs so they shatter... Popped heads off of valves... Broken timing chains.... And turned more race engines into boat anchors and door stops than all the others combined....

But that's another story

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Thank you.  I appreciate the initial answer.  I very much intend to go with a safe number, so at minimum I'll go with your larger number.  I really appreciate that you took the time to explain all that.  I had already known a little bit about duration .vs lift, and knew there were at least some points about the lobe shape I didn't know.  I'm now pretty certain that it was indeed the cam's fault at not having a soft decel ramp, thus snapping the tip of the valve off.  That said, I just measured it  for the nominal diameter and lobe height compared with the new cam.  It's nominal diameter is large enough that it could be reground, so maybe after enjoying a reliable engine that doesn't make me pull it apart, I'll send off the old cam and have it modified so I can have a larger cam again that's also safe for the motor.

I'd be interested in what brand it is that you've had those experiences with.  If you're just not wanting to bad talk a brand on a public forum, you could PM me.

Again, thank you for the in-depth responses!

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Very glad to help out...

I will post it ...

Web Cam is single handedly the #1 destroyer of engines in my many moons of engine building... Personal and professional...

I am however quite happy running one of Terry Miller's profiles , ground by web cam, in my own 230... If it weren't for my faith in Terry, I would not...

I have shut down engines the moment I have fired them up on the dyno... The loud valvetrain noise making it seem as though I left a shim out during clearancing... Nope... Clearance good, ramps just that radical...

I'm all for power, but my enthusiasm wanes quite sharply when chasing a hp or 2 entails a short fuse on my beloved race engines longevity... Nope... No sale... I will find a pony or 2 somewhere else...

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3 hours ago, ygolohcysp said:

Hello.  I've somewhat recently expanded my tool set to include a Bridgeport milling machine.  Already have a bit of tooling and work clamping stuff already.  Anyway, I recently had valve train issues with my 05 crf150f.  I've pulled it apart to replace valve guides, valves, etc.  I'm going with a slightly smaller cam than I had in there just because I've had continual valve train problems.  This last one was caused by aftermarket KW valve springs, combined with the large cam.  Literally snapped the top of the valve off.  I got lucky, and just bent the intake valve.  Anyway, going with a slightly smaller cam and now having the tools to do some real custom work, I'm wanting to use some clay and check the piston to valve clearance and maybe mill a little bit off the head or top of the cylinder.  I know the intake chases the piston and is fairly safe.  What is considered safe for the motors for the exhaust piston?  I guess a couple things to keep in mind on this.  I race this bike as a sumo setup, and I'm not beyond downshifting 3 gears going into the turn to slide it sideways.  Thanks for any advice or info!

Which cam was in with the snapped valve?

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I have 2 230's both with Web cams and one is a Mike Coe 89a grind which is noisy as hell and the other is a TM 2.5 grind which is quiet as a church mouse.  I run KW valve springs and no issues at all.  Hate your having issues. 

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3 minutes ago, Titanman said:

I have 2 230's both with Web cams and one is a Mike Coe 89a grind which is noisy as hell and the other is a TM 2.5 grind which is quiet as a church mouse.  I run KW valve springs and no issues at all.  Hate your having issues. 

That sound like your rockers have been replaced with ball pein hammers...

Is exactly what it sounds like... Harsh impacts... The drum beat of the death march for a valvetrain/engine...

Or... Some like to think of it as the tick tick tick of an electric start time bomb...

I like to think of it as:

"Lightly used cam for immediate and discounted sale, all offers considered"

I know the air cooled fins add to the effect by radiating sound..  but , I don't care for it... 

tick... tick.... Tick.... TICK...

BOOM!

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Doesn't sound good at all even after multiple valve adjustments.  Everyone says noise is normal with some of the Web grinds.  This is the reason Im switching to another TM 2.5 grind in the 89a bike.  I cant tell the difference in the two performance wise both pull great just less noise with the 2.5.  

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8 minutes ago, stevethe said:

I am running the original 89A Web cam with the titanium retainers and heavier springs. Mine is quite.

I hate to add this in, but I have seen disturbing variations in cam profiles that are supposed to be one and the same...

One silent, next one loud as hell... But supposed to be identical... Doesn't build a lot of confidence ...

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I can add my experience.My first TM cam by web 1.0 Valve train noise I used my stock rockers. One lobe,rocker short life. My new TM Cam 2.5 with hard coat rockers same valve train noise. (all with stock springs) so far so good.Of course I wont know for sure till I pull apart for 69mm piston install. I will have to add this I would almost bet money.No one on this site pushes a built 230 harder the Stevethe.So if his hangs in there good for me.

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I don't really care what people run in their own equipment... I just give everyone the benefit of my own experience when I can...

 

Some are more comfortable "dancing in the mine field" than I am.... one second everything is wonderful... The next second nothing is wonderful...

I am a certified , incurable lover of engines... my comfort level doesn't extend to loud valvetrains on my 4 strokes....

Most failures blindsided you without warning... But if you hear loud valvetrain action... And you get a catastrophic failure at some point... You have no excuses... 

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HAAA Mixxer  If you hear a stock KTM 450/500 engine sounds like a cement mixer. Better to have your helmet before starting.JAAAA!

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28 minutes ago, bajatrailrider said:

I can add my experience.My first TM cam by web 1.0 Valve train noise I used my stock rockers. One lobe,rocker short life. My new TM Cam 2.5 with hard coat rockers same valve train noise. (all with stock springs) so far so good.Of course I wont know for sure till I pull apart for 69mm piston install. I will have to add this I would almost bet money.No one on this site pushes a built 230 harder the Stevethe.So if his hangs in there good for me.

I'm not sure as the OP is racing his in Supermoto and down shifting three gears at a time to back the bike in on pavement. Could be resulting in rev limiter bounce. Ouch!

But the original 89A cam has been around forever and has not known to be a thrasher. I haven't found too much issues with Web cams over the years. They seem to have a good understanding of opening and closing ramps except for:

The one issue I had with a Web torque cam in a Yamaha with stainless steel valves that require stiffer valve springs. Unheard of in a Yamaha shim and bucket set up but it happened. I think there was insufficient open and closing ramps on the intake cam for the heavy springs. 

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2 minutes ago, bajatrailrider said:

HAAA Mixxer  If you hear a stock KTM 450/500 engine sounds like a cement mixer. Better to have your helmet before starting.JAAAA!

Lol... I owned a KTM 450sx....

Completely understand...!!

Cement mixer is a perfect description!

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1 minute ago, mixxer said:

Lol... I owned a KTM 450sx....

Completely understand...!!

Cement mixer is a perfect description!

Brother I had two KTMs 525s in the fleet Rickety/boom/knock/bang

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I can add my experience.My first TM cam by web 1.0 Valve train noise I used my stock rockers. One lobe,rocker short life. My new TM Cam 2.5 with hard coat rockers same valve train noise. (all with stock springs) so far so good.Of course I wont know for sure till I pull apart for 69mm piston install. I will have to add this I would almost bet money.No one on this site pushes a built 230 harder the Stevethe.So if his hangs in there good for me.


" possibly" but maybe: "That you have ridden with"
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2 minutes ago, ygolohcysp said:

It was a Powroll cam.  It does have some numbers etched into it, but I'll have to look at it again to get those numbers.

It was a web cam then... Powroll... As well as many others... Use web for their cam making

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