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valve lash

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    Senior Member APOLLO's Avatar
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    Default valve lash

    What determines the amount of valve lash in a cam? When a cam maker is making a cam do the numbers that are programed predetermined? Thanks

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    Quote Originally Posted by APOLLO View Post
    What determines the amount of valve lash in a cam? When a cam maker is making a cam do the numbers that are programed predetermined? Thanks
    Depending on the lobe, the last sets the opening and closing points of the valve.
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    Default Yes...

    Quote Originally Posted by APOLLO View Post
    What determines the amount of valve lash in a cam? When a cam maker is making a cam do the numbers that are programed predetermined? Thanks
    Yes is a short answer. As Steel has said, it depends on the lobe design. Some cam grinders use a very aggressive "ramp", a steep ramp, that gets the lifter to the point of zero lash, (and the start of the valve "event"), very quickly. The grinder knows when he wants the event to start, and the aggressiveness of the ramp, so he says "lash" the valves at .xxx to keep the designed duration of the "event" accurate... Other grinders use a less aggressive ramp design in an effort to make things easier on the valvetrain components.. And as such, recommend the lash be tighter to once again, keep the advertized duration within their specs.... As you can see, if you run a tighter than spec'd lash you will increase the duration by making the valve event happen a few degrees sooner because the lobe will reach zero lash sooner and start the valve event. Usually a tighter than recommended setting, (.001, .002, .003) will give an engine a little more up top, but you will sacrifice a little down low. By the same token, a looser setting will be a real bear down low, but you'll give up a little up top... Anytime you're messing with the timing of a valve event be sure to recheck piston to valve clearance carefully. Just a few thousandths in a tighter lash can create an exhaust closing later, or an intake opening sooner, piston to valve collision during valve overlap... Sure, we're only talking a minute difference in duration, but sometimes things were already super close. So check it closely if you try "playing" with the settings...
    Ray
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    Senior Member stix818's Avatar
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    I've always wondered this also.. The last 3 cams that I have ran, duration @ .050" have been around 290 on INT and 305 to 310 on EX with moderate lift, .840/.800.. The lash on them have been .028" to .30" on EX and .030" to .032" on INT.. My new cam is 285/300, .873"/.823" and the lash is quite a bit tighter, .020"/.022" per the cam card.. I thought that was pretty interesting.. Obviously the ramp is a lot faster on the Intake which I would have thought the lash would be around the same as the others.. Should be interesting!!!!
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    Quote Originally Posted by stix818 View Post
    I've always wondered this also.. The last 3 cams that I have ran, duration @ .050" have been around 290 on INT and 305 to 310 on EX with moderate lift, .840/.800.. The lash on them have been .028" to .30" on EX and .030" to .032" on INT.. My new cam is 285/300, .873"/.823" and the lash is quite a bit tighter, .020"/.022" per the cam card.. I thought that was pretty interesting.. Obviously the ramp is a lot faster on the Intake which I would have thought the lash would be around the same as the others.. Should be interesting!!!!
    Some lobes are considered "tight lash" lobes, usually with lash <.020".
    One thing we can do with lash is change the relationship between the intake and ex lobe. I see all too often where a customer has a poor intake to ex flow ratio yet the split on their cam is only 4-5 degrees @ .05 in favor of the ex., when the cam really needs 10-12 or more to help the ex side. To validate this for the customer, I'll tell them to tighten the ex. lash a few thou and maybe even loosen the intake a few thou. Almost invariably they will come back and report a significant performance gain, either on the dyno or the track. Changing intake or ex lash independently will let us know what the engine needs.
    On my last 565 I did one final tune up to the ex ports before the engine went together which (expectedly) killed some of the flow. Unfortunately, I had already given Chris Straub some "final" flow numbers and the cam was already ground based on the original intake-to-exhaust flow ratios. Knowing that they were now different, when dyno testing I made some lash adjustments to the ex., tightening it to add some duration and make up for some of the lost flow. The last pull we did was nothing more than a .002 adjustment, ex. only, and it gained 10hp.
    "Lash is the best tuning tool you have in your tool box."
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    Quote Originally Posted by Moneypit View Post
    Yes is a short answer. As Steel has said, it depends on the lobe design. Some cam grinders use a very aggressive "ramp", a steep ramp, that gets the lifter to the point of zero lash, (and the start of the valve "event"), very quickly. The grinder knows when he wants the event to start, and the aggressiveness of the ramp, so he says "lash" the valves at .xxx to keep the designed duration of the "event" accurate... Other grinders use a less aggressive ramp design in an effort to make things easier on the valvetrain components.. And as such, recommend the lash be tighter to once again, keep the advertized duration within their specs.... As you can see, if you run a tighter than spec'd lash you will increase the duration by making the valve event happen a few degrees sooner because the lobe will reach zero lash sooner and start the valve event. Usually a tighter than recommended setting, (.001, .002, .003) will give an engine a little more up top, but you will sacrifice a little down low. By the same token, a looser setting will be a real bear down low, but you'll give up a little up top... Anytime you're messing with the timing of a valve event be sure to recheck piston to valve clearance carefully. Just a few thousandths in a tighter lash can create an exhaust closing later, or an intake opening sooner, piston to valve collision during valve overlap... Sure, we're only talking a minute difference in duration, but sometimes things were already super close. So check it closely if you try "playing" with the settings...
    Ray
    Most lobes are not designed from scratch per a customer's combination. Instead they're chosen from a library of lobes that are "close" and lash can be used to a certain extent, to help "tailor" the lobe more to the customer's specific needs but again. that's all "calculated" and in the end the engine will tell you what it wants. Lash adjustments or "lash loops" should be a part of every engine builder's or racer's testing/tuning program.
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    Senior Member bp298's Avatar
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    Quote Originally Posted by stix818 View Post
    I've always wondered this also.. The last 3 cams that I have ran, duration @ .050" have been around 290 on INT and 305 to 310 on EX with moderate lift, .840/.800.. The lash on them have been .028" to .30" on EX and .030" to .032" on INT.. My new cam is 285/300, .873"/.823" and the lash is quite a bit tighter, .020"/.022" per the cam card.. I thought that was pretty interesting.. Obviously the ramp is a lot faster on the Intake which I would have thought the lash would be around the same as the others.. Should be interesting!!!!
    kinda loose for the cams I've run. lifter type might also affect lash...

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    Quote Originally Posted by bp298 View Post
    kinda loose for the cams I've run. lifter type might also affect lash...
    With the Lunati it had the intake and exhaust lash reversed.. The EX was tighter than the intake which I found unusual at the time.. I called them up and they could only tell that it was a cam design directly from WJ.. I said ok and ran it that way.. But I agree, it was a lot looser than I have ever ran.. But it's still together and in my oldman's Blue boat as a back up motor..
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    Quote Originally Posted by Moneypit View Post
    Yes is a short answer. As Steel has said, it depends on the lobe design. Some cam grinders use a very aggressive "ramp", a steep ramp, that gets the lifter to the point of zero lash, (and the start of the valve "event"), very quickly. The grinder knows when he wants the event to start, and the aggressiveness of the ramp, so he says "lash" the valves at .xxx to keep the designed duration of the "event" accurate... Other grinders use a less aggressive ramp design in an effort to make things easier on the valvetrain components.. And as such, recommend the lash be tighter to once again, keep the advertized duration within their specs.... As you can see, if you run a tighter than spec'd lash you will increase the duration by making the valve event happen a few degrees sooner because the lobe will reach zero lash sooner and start the valve event. Usually a tighter than recommended setting, (.001, .002, .003) will give an engine a little more up top, but you will sacrifice a little down low. By the same token, a looser setting will be a real bear down low, but you'll give up a little up top... Anytime you're messing with the timing of a valve event be sure to recheck piston to valve clearance carefully. Just a few thousandths in a tighter lash can create an exhaust closing later, or an intake opening sooner, piston to valve collision during valve overlap... Sure, we're only talking a minute difference in duration, but sometimes things were already super close. So check it closely if you try "playing" with the settings...
    Ray


    The bottom portion where you loosen and tighten for the lower and upper end is what my engine build explained to me a long time ago. I guess a person would never play with the lash like that unless your at the track to help back it up with numbers unless its that noticeable. Don't know! Might have to play now just to see!
    As for the top portion of the page. That is what I was looking for. all you guys have so much good info I just keep making copy's of all of this info. Thanks a lot guys....I'm sure I'll have more questions later. Troy

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    Default "Seat of the pants"

    Quote Originally Posted by APOLLO View Post
    The bottom portion where you loosen and tighten for the lower and upper end is what my engine build explained to me a long time ago. I guess a person would never play with the lash like that unless your at the track to help back it up with numbers unless its that noticeable. Don't know! Might have to play now just to see!
    As for the top portion of the page. That is what I was looking for. all you guys have so much good info I just keep making copy's of all of this info. Thanks a lot guys....I'm sure I'll have more questions later. Troy
    Well Troy, you might be able to "feel" a difference in the seat of your pants... If a motor seems to fall off, or the boat noses over before you think it should, you can try tightening the lash a couple of thou and see how that feels.. BUT, as I said, messing with the valve "event" timing can create piston to valve clearance issues, so unless you KNOW you have plenty of room to play, DON"T!!!
    Ray
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    Quote Originally Posted by Moneypit View Post
    Well Troy, you might be able to "feel" a difference in the seat of your pants... If a motor seems to fall off, or the boat noses over before you think it should, you can try tightening the lash a couple of thou and see how that feels.. BUT, as I said, messing with the valve "event" timing can create piston to valve clearance issues, so unless you KNOW you have plenty of room to play, DON"T!!!
    Ray
    You'd have to be running p/v clearances really tight in the first place to have a real problem by adjusting lash a few thou. You're looking at about 1* duration for every .002" lash.
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    Default Yes, but....

    Quote Originally Posted by steelcomp View Post
    You'd have to be running p/v clearances really tight in the first place to have a real problem by adjusting lash a few thou. You're looking at about 1* duration for every .002" lash.
    Yes Scott I agree, but since I have no idea what, or how, his deal is set up now, I erred on the caution side and suggested he be sure....
    Ray
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    valve lash is something that I have have always tried to learn more about , like when it comes time to setting it on an engine that you don't know what cam is in it . I have always thought it best to be a little tight rather than too loose . maybe the guys that work with cam design can help here but if your lash is more than whats in the clearance ramps doesn't the follower get slammed into the opening ramp and the valve seat get hammered without the slower set down of the closing side clearance ramp ? maybe loosen a little to see whats happens to the power or rpm , but if you need less duration get another cam .
    Quote Originally Posted by gn7 If your ran a cammer your odds of finishing WERE ZERO.

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    Default lash

    With so many combinations out there, the best way to design a cam is come close, then put her on a dyno. Make changes to lash, timing fuel... till it's optimised. then take thos enumbers and make another cam and do this again, and agiain till you've eeked out every hp and tq you can find.b Few of us have this capability.

    then reality would set, in. What if i went bigger cubes, heads... It's a never ending quest.

    Jerry

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