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Adjustable pushrods - drilling needed?
Posted: Wed May 24, 2017 7:36 pm
by moppit
After removing the heads of the engine built by someone else I notice adjustable pushrods but with variable amounts of scoring on the stems. I thought things were a little rattly and had my suspicions... I'm assuming the previous builder should have drilled the heads to suit? Rods are 5/16 or 8mm diameter.
Is it just a case of drilling out with a pillar or cordless drill to give clearance? I plan to check none are bent before re-use. Is there a particular angle needed for the drilling? Heads are going to a machine shop for skimming so could get them to do but I'm guessing fairly easy DIY?
Posted: Thu May 25, 2017 6:31 am
by benjai
They really need to be slotted - easy job (with the heads off) using a dremel and an ebay burr... Link below shows what I mean - scroll to the bottom...
http://www.cobraclub.com/forum/showthre ... post510363
Posted: Thu May 25, 2017 8:43 am
by sidecar
Your 'slidey' tube of cardboard is an excellent idea, you are a genius Sir!
Posted: Thu May 25, 2017 8:45 am
by SimpleSimon
Check those push-rods are true if they have been making contact with the heads they are tubular and may be bent now, you can safely drill the holes out to 12/14mm but like mentioned better to custom elongate them so you only remove required material
Posted: Thu May 25, 2017 10:21 am
by sidecar
When setting up adjustables don't bother with poking about bits of bent wire under the circlip on the cam followers, just set each follower on its base circle then carefully adjust the pushrod so that there is no play in the valve train but at the same time there is no preload on the follower then turn the adjuster X number of flats on the nut, each flat is worth about 4 thou of preload so one full turn (6 flats) would be 24 thou. I run 5 flats.
Posted: Fri May 26, 2017 11:18 am
by moppit
Excellent stuff! Heads being skimmed at the moment for composite gaskets.
Anyone managed to find decent burrs/grinding dies for their dremel on Ebay?
Benjai - did you use an old head gasket when checking clearances?
Thanks all
Posted: Sat May 27, 2017 12:08 am
by unstable load
moppit wrote:Anyone managed to find decent burrs/grinding dies for their dremel on Ebay?
http://www.ebay.co.uk/sch/i.html?_nkw=d ... noapp=true
Posted: Sat May 27, 2017 7:31 am
by benjai
sidecar wrote:Your 'slidey' tube of cardboard is an excellent idea, you are a genius Sir!
Thankyou! I can't take credit for that idea though, I learned it from a wise old sage... I can't recall who though!... No wait... it was you!!!
moppit wrote:Excellent stuff! Heads being skimmed at the moment for composite gaskets.
Anyone managed to find decent burrs/grinding dies for their dremel on Ebay?
Benjai - did you use an old head gasket when checking clearances?
Thanks all
As posted above, any old carbide burrs will be fine for ally. I bought the second one on the list (follow the link above) and they've been fine for a couple of years. Not brilliant, but plenty good enough. It really helps to use some cutting fluid when using them in ally to stop the burr clogging (WD40 will do).
As for clearances - yes, I used the old composite head gaskets to check clearances (piston to valve). I didn't bother for pushrod clearances - i don't want things so tight that the head gasket thickness makes a difference...
HTH