Rocker shaft bolt hole chamfers

[Dubmatix]

Hi all
I have been putting my rocker assemblies together today and noticed that all the shafts have chamfered bolt holes but only at one end (of each drilled hole). As the mounting blocks go over this anyway and the books seem not to mention it, i am thinking that it doesn't matter whether these chamfers go inside or outside if you know what i mean. It would seem sensible to have them outwards to ease the bolt through...maybe that's what it was done for to ease assembly, or is there another reason for this chamfer to be there?

Cheers

John

[Ol'fogasaurus]

Having not been there when the design was done, just a guess: usually chamfering a threaded hole is to accommodate the radius between the grip of the bolt (the unthreaded part of the bolt) and the head of the bolt, especially if there is no washer under the head of the bolt; the same for fully threaded bolts also. Since these bolts are in tension, the radius between the head and the shank of the bolt may be greater than an "in shear" style of bolt of the same diameter. I always called out a chamfer in this situation.

It also can aid in starting the bolt in the hole but probably not necessary on the bottom of the block.

Lee

[Dubmatix]

Cheers Ol Fog'. This hole is not threaded though but is clearanced for the mounting stud (not bolt as i put previously) as is the one in the block. I think i'll out the chamfers on the inside to aid alignment when being fitted onto the stud. (i said outside before cos i was thinking it was a bolt...but as its a stud, inside makes more sense...) phew got there in the end!

John

[Ol'fogasaurus]

With a stud, I would suspect that the direction is probably irrelevant. It is hard to tell with out being there or a picture. Glad things are working out.

Lee

[sideshow]

Uhhh, look at your head, the factory studs are slightly thicker near the boss than the shank. The rocker shaft & block are directional for a reason.

[Ol'fogasaurus]

Uhhh, look at your head, the factory studs are slightly thicker near the boss than the shank. The rocker shaft & block are directional for a reason.

Dubmatix I just checked some of my books as I don’t have a set of heads I can access easily and sideshow is correct, the rocker stand mounting stud does have a bossed area at the bottom of it, there should be a circular gasket added and it is put on dry.

A quote from the HP books: “How to Rebuild Your VOLKSWAGEN Air-Cooled Engine”:

“… Next mount the rocker arms. The pedestals have a cutout section that must face downward and away from the valve springs when installed. Also, one end of the pedestal is beveled. It should face outward and away from the center of the engine. After checking for correct orientation, install the washers and nuts. Completely loosen the valve adjustment before tightening the rocker assembles. Tighten them to 18 ft-lbs (2.5 kg-m)…”

A quote from the "Hot VW's special... All about VW Performance engines II" ,magazine:

”…once the heads have been properly torqued down, and the push rods have been installed, its time to install the rocker arm assemblies. If the adjusting screws are badl worn, replace them, along with the new 8mm nuts. The rocker arm stands should have the open slot facing “up”. Using a 8mm wave washer and nut, torque the rocker arm stands to 18 ft-lbs.”

Sorry I got lazy (unforgivable) and I forgot I had the books. The Haynes manual is kind of iffy in this area as well as the several others I have.

Lee

[Dubmatix]

That's logical Sideshow, not looked at the studs as i only noticed it as i was bagging the assemblies together after cleaning. It was the first time i noticed it was different.

Lee, the HP book (excellent book btw) refers to the pedestal (ie the block but not the shaft) and i have sussed out the right way round for those...flat face down, cutout is towards pushrod tubes so the clip clips in. But it doesn't mention the shaft...which got me wondering.

The second quote seems wrong to me about the pedestal orientation...as the first says away from valve springs (ie down) which is correct...and the second says up but anyway that's beside the point....maybe it's for a different engine type.

So in summary, the consensus is that chamfer of shaft holes goes towards the head for clearance of stud base and (not so much but usefully) ease of assembly.

Thanks for your suggestions on this as i didn't notice it on disassembly...must pay more attention!

Cheers

John

[sideshow]

About the pedestal block clocking, it is my observation that the opening from the factory was down. In the beetle engines it matters little (I always have the opening up), but in the type-4 if you plan on using the wire push rod tube retainers then the opening must be down.

[rwk2]

The chamfer is there so that the drill stays centered on the shaft in manufacturing, no other reason, that's why its only on 1 side, and assembly manuals make no mention of it. The larger dia. of the stud clears the hole due to the rocker shaft support spacing,and the hole is slightly larger. The chamfer must always be larger then the drill when you cross drill a shaft, if no chamfer is used a flat spot face must be used if you need any kind of accuracy.