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914World.com _ 914World Garage _ tolerance when cutting pushrods..... margin for error
Posted by: mike373 Aug 8 2007, 04:44 PM
Ok..... So, I did the rocker geometry, and got my adjustable pushrod dialed in and locked. It has the same exact ball ends as the ones im using (manton chromoly).... so there will be no guessing with regards to radius of the ends. I took everything to my machinist, and he said that because his lathe bit was on the dull side.... from cutting flywheels.... that he could only get them within .008 or .010 from the adjustable pushrod I gave him. MY QUESTION.... What is acceptable tolerance....or margin for error.... before the geometry starts getting affected. I took these to a couple other machine shops, who said they could get it within .005 . This is crazy making.
Mike
Posted by: mike373 Aug 9 2007, 12:04 AM
Ok..... So, I did the rocker geometry, and got my adjustable pushrod dialed in and locked. It has the same exact ball ends as the ones im using (manton chromoly).... so there will be no guessing with regards to radius of the ends. I took everything to my machinist, and he said that because his lathe bit was on the dull side.... from cutting flywheels.... that he could only get them within .008 or .010 from the adjustable pushrod I gave him. MY QUESTION.... What is acceptable tolerance....or margin for error.... before the geometry starts getting affected. I took these to a couple other machine shops, who said they could get it within .005 . This is crazy making.
Mike
No one....Eh???
Posted by: orange914 Aug 9 2007, 12:09 AM
Ok..... So, I did the rocker geometry, and got my adjustable pushrod dialed in and locked. It has the same exact ball ends as the ones im using (manton chromoly).... so there will be no guessing with regards to radius of the ends. I took everything to my machinist, and he said that because his lathe bit was on the dull side.... from cutting flywheels.... that he could only get them within .008 or .010 from the adjustable pushrod I gave him. MY QUESTION.... What is acceptable tolerance....or margin for error.... before the geometry starts getting affected. I took these to a couple other machine shops, who said they could get it within .005 . This is crazy making.
Mike
No one....Eh???
mike
have you posted ? on jakes site? i'll be doing this soon on my 2056. the chromoly came as a set of 8, right? keep us posted
mike
Posted by: Jake Raby Aug 9 2007, 12:20 AM
+/- .001
If you don't use insane accuracy there is no reason to do the geometry process at all..
Remember that any pushrod length variation will be multiplied by the rocker arm ratio, so that .005 will net you .008 or so of a variance and that can lose you .020 valve lift or compromise the geometry completely.
Posted by: Joe Ricard Aug 9 2007, 11:40 AM
Just a clarification question on your kits Jake. Do the push rods come cut or do we have to do this step ourselves.
Posted by: mike373 Aug 9 2007, 05:15 PM
Found a great machinist in Santee, Ca. He will get the pushrods within .001 . Yipee!
Ballistic Machine and Fabrication 619-562-8750 if anyone is interested.
Mike
Posted by: davep Aug 9 2007, 06:33 PM
Just a dumb question here, since I have yet to order a kit, do the ball ends all measure the exact same so that when installed into the newly cut tubes the finished pushrods will all be the same length, or do you have to carefully measure them also to ensure the tubes are not cut too short.
Being anal, I'd assume the latter, and err on the long side, fit the end, measure total length, and adjust as necessary to get a perfect length on each one.
Posted by: George H. Aug 9 2007, 06:35 PM
Just a clarification question on your kits Jake. Do the push rods come cut or do we have to do this step ourselves.
Joe,
you cut them yourself
Posted by: Joe Ricard Aug 10 2007, 10:31 AM
Damn it.
Something to not look forward to when I order a kit.
Maybe I should get better tools.
Yea that's it get more and better tools. Brilliant!!!!!!!
Posted by: Borderline Aug 10 2007, 10:57 AM
I don't know if I understand what you're doing. You set up one valve/pushrod and are now going to have all 8 pushrods machined to that length? I did each one individually on mine. They aren't all the same! especially if you're trying to get within .001"
Posted by: orange914 Aug 10 2007, 03:42 PM
I don't know if I understand what you're doing. You set up one valve/pushrod and are now going to have all 8 pushrods machined to that length? I did each one individually on mine. They aren't all the same! especially if you're trying to get within .001"
i'll be doing this shortly also. the feed back i've got from various experianced builders is this:
you can do each and every one BUT if you arent PRECISE to each (and you probably wont be) i've been told it's good to do just (1) exhaust and (1) intake. from there have exhaust and intakes done as sets.
the basic idea is to adjust geometry to new cam base/lift. unless you really are anal on each one you could go backwards.
feedback?
mike
Posted by: JPB Aug 10 2007, 08:00 PM
There are afew steps to be taken and all tubes are custome cut to length. I think Jake has the info you need to do the job correctly and it might take a tool also. He has mentioned this in his Fourth Dimension shows. 
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