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UK Luke 72
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Location: Little Britain
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UK Luke 72
Samba Member
Joined: September 07, 2011
Posts: 2867
Location: Little Britain
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UK Luke 72
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Location: Little Britain
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mark tucker
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Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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 Posted: Fri Jun 23, 2017 11:15 am Post subject: Re: Yup- rocker geometry again |
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| the pushrods are normanly the same length....unless the base circle'a are different. with that said I routinely do not cut the pushrods the same length due to all the various factors involved. thus I can then if needed move them around to get the best adjuster location.I try to set up all my stuff with a max of 1/4 turn out from seated position. as for the inline stuff & half lift...the 1.1's do set up close to that...but not always and ...hear it comes....that are other factors that can alter this. |
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UK Luke 72
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Location: Little Britain
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mark tucker
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Location: SHALIMAR ,FLORIDA
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| Posted: Fri Jun 23, 2017 1:18 pm Post subject: Re: Yup- rocker geometry again |
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you can also get different thickness lash cappers fer fine tuneing.  |
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UK Luke 72
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Location: Little Britain
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oprn
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Joined: November 13, 2016
Posts: 12682
Location: Western Canada
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| Posted: Sat Jun 24, 2017 5:03 am Post subject: Re: Yup- rocker geometry again |
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A newby geometry question here.
Would you not want to set up the center line of the rocker shaft even with the lash surface of the valve at 1/2 lift? This would minimize the scuffing/valve stem side load encountered as the valve travels through it's range. With the rockers shimmed out away from the head and the adjusters with lots of threads showing on the valve side I suspect there would be more vertical movement of the adjusting screw tip on the end of the valve stem.
Or is it a compromise? |
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UK Luke 72
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Location: Little Britain
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| Posted: Sat Jun 24, 2017 5:42 am Post subject: Re: Yup- rocker geometry again |
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Yeah in some of the pics on page 1 you can see the adjusters vertical position relative to the valve stem, which at half lift is pretty good, that differs on mine slightly though as the cam profiles are split... Marginal but it makes a difference.
I'm certainly no expert but to me our valve train will always be a compromise, I fully appreciate the argument you want the rocker to be perpendicular to the valve at full lift as that's where it sees peak spring pressures but its only there for a very short period. It passes half lift twice every revolution. Thus, get it stable there and you've got it stable for the longest amount of time possible...
Yep, poke more adjuster out and get more 'wipe' on the rocker tip which IMO is not.how swivel feet should work.
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mark tucker
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Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Sat Jun 24, 2017 11:24 am Post subject: Re: Yup- rocker geometry again |
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| .005" from full lift also comes around 2 times....... |
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modok
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Joined: October 30, 2009
Posts: 26776
Location: Colorado Springs
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| Posted: Sat Jun 24, 2017 12:37 pm Post subject: Re: Yup- rocker geometry again |
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| oprn wrote: |
A newby geometry question here.
Would you not want to set up the center line of the rocker shaft even with the lash surface of the valve at 1/2 lift? |
yes, if using stock adjusters
If using the swivel feet, then the pivot point is the center of the swivel joint. |
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modok
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Location: Colorado Springs
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| Posted: Sat Jun 24, 2017 12:40 pm Post subject: Re: Yup- rocker geometry again |
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The valve stem can handle the scrub near full lift better than closed.
Why? because leverage.
The farther it is hung out of the guide the more it wobbles, more leverage the scrub has against the guide. If you look at it closely you can see this. |
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vwracerdave
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Joined: November 11, 2004
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Location: Deep in the 405
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| Posted: Sat Jun 24, 2017 2:10 pm Post subject: Re: Yup- rocker geometry again |
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| modok wrote: |
The valve stem can handle the scrub near full lift better than closed.
Why? because leverage.
The farther it is hung out of the guide the more it wobbles, more leverage the scrub has against the guide. If you look at it closely you can see this. |
I'll write this down in my notes. Something I never heard or considered.
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[email protected]
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| Posted: Sat Jun 24, 2017 2:14 pm Post subject: Re: Yup- rocker geometry again |
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Also, don't over think it.
If at half lift you are only off a little (like .020"), turn the valve adjuster in or out 1/2 turn to fix the alignment instead of spending hours getting the shims "exact".
Now that is done, figure out what length PR you need.
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oprn
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Joined: November 13, 2016
Posts: 12682
Location: Western Canada
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| Posted: Sat Jun 24, 2017 9:07 pm Post subject: Re: Yup- rocker geometry again |
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| modok wrote: |
The valve stem can handle the scrub near full lift better than closed.
Why? because leverage.
The farther it is hung out of the guide the more it wobbles, more leverage the scrub has against the guide. If you look at it closely you can see this. |
Makes perfect sense!
Back in the dark ages my automotive instructor told us that you want the tappet to contact the valve just a little off center horizontally to encourage the valve to rotate a little each time it opens. Is that still the case? |
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mark tucker
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Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Sun Jun 25, 2017 6:56 am Post subject: Re: Yup- rocker geometry again |
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| turn on the lights, it's nolonger the dark ages. springs are spiral wound and do a great job at rotating valves. I usualy try to set it up for best pushrod to tube clearance if there is a issue. |
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nsracing
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Joined: November 16, 2003
Posts: 9448
Location: NOVA
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| Posted: Sun Jun 25, 2017 9:32 am Post subject: Re: Yup- rocker geometry again |
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You will modify the rocker geometry to accomodate pushrod tubes?
I will just move the tubes out of the way if it rubs.  |
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modok
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Joined: October 30, 2009
Posts: 26776
Location: Colorado Springs
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| Posted: Sun Jun 25, 2017 2:14 pm Post subject: Re: Yup- rocker geometry again |
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| oprn wrote: |
| modok wrote: |
The valve stem can handle the scrub near full lift better than closed.
Why? because leverage.
The farther it is hung out of the guide the more it wobbles, more leverage the scrub has against the guide. If you look at it closely you can see this. |
Makes perfect sense!
Back in the dark ages my automotive instructor told us that you want the tappet to contact the valve just a little off center horizontally to encourage the valve to rotate a little each time it opens. Is that still the case? |
Sometimes it is true. We find that the valves rotate on their own usually, but only at certain RPMS. If the engine was for a generator, air compressor, boat.....some app that may spend all day at 3000 rpm, then I would probably maintain the way VW built it, with the loose keepers and offset rockers, and steel stem valves.
For most cars and HP engines, I would not worry at all, and lock the keepers and center the rockers. |
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oprn
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Location: Western Canada
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| Posted: Sun Jun 25, 2017 5:05 pm Post subject: Re: Yup- rocker geometry again |
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| Thanks modok! |
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