Rocker arm / head combination

[tunnelrider]

Hello everyone,

Question is - can I safely shim a 1980 rocker arm on a 1985 head to take up axial play?  I'm talking 0.28mm axial play, shim 0.20mm.  Has anyone done this and can give me advice on longevity?

Also I was hoping to know to re harden my original rocker arms if I grind them down?  They may be so worn they should be replaced.  See the photos, I was surprised to see the older version 1980 rockers have a noticeably thicker pad where the arm contacts the valve stem.  

Thanks,Dan.

[Tony Smith]

Hello everyone,

Question is - can I safely shim a 1980 rocker arm on a 1985 head to take up axial play?  I'm talking 0.28mm axial play, shim 0.20mm.  Has anyone done this and can give me advice on longevity?

I've not done that swap but given that early heads can be concerted to the later rockers by simply punching out the "pillow blocks" on the head, I see no reason why not.

CAVEAT - If you play "mix-n-match" with valve gear components make VERY sure that you have correct contact with the valve stem or your valve gear is apt to have very short life. There is somewhere on the web a very good tutorial on setting up rocker arms for VWs - the principle is the same.

Also I was hoping to know to re harden my original rocker arms if I grind them down?  They may be so worn they should be replaced.  See the photos, I was surprised to see the older version 1980 rockers have a noticeably thicker pad where the arm contacts the valve stem.  

No great secrets there but please use the correct machine (or pay someone who has the right machine to reface the valves. I used to own a "Wolf" valve and rocker grinding machine and the joy I felt in refacing my rockers was somewhat negatived by the cost of replacing the rocker arm bearings I destroyed through not thinking it through properly.

It is not something you do with an angle grinder or bench grinder.

If grinding a new profile on your rocker will reduce the pad greatly, consider having it welded up and then ground.

To harden there are a number of chemical processes readily available BUT they are all perhaps too expensive for a one-off - a good auto machining shop will have the equipment, or know a nearby business that does.

If you look back in the archives you will find a series of posts where I described hardening them myself - this is because I have a large tin of "Hardite" that I am still using. Hardite and like hardening compounds were once cheap and plentiful and a lot of home mechanics would do their own hardening. Sadly all the really good (cheap) hardening systems involve nasty chemicals like cyanide and and no longer generally available. The less potentially lethal hardening systems are significantly more expensive

[tunnelrider]

I've not done that swap but given that early heads can be concerted to the later rockers by simply punching out the "pillow blocks" on the head, I see no reason why not.

Yes I agree and just after I posted the question I found this from Bob Roller, in another thread:

"What is the rocker arm side play clearance ??

I have mine shimmed to about a .004 in., .1 mm clearance when cold ."

Which on his pre '85 R65's means he shim's them, if that's what he means by side play clearance, Bob? if you are reading this?

No great secrets there but please use the correct machine

Ha thanks for this detail in your post Tony, 'cause I was actually going to ask what tools are needed.  You see I don't even have a bench grinder yet (but could go and use one) and even was thinking a quick angle grind might do the job!  Yep, I had thought that doing it with the shaft in place to save the roller bearing from falling out was gonna be tricky to pull off.  Let alone the hardening. Lucky there's great advice from you guys on this site.

Tony, can you explain briefly what 'correct contact with the valve stem' means - you mean that it has to be in the middle of the pad as seen vertically?  What would happen if the contact is closer in to the heel, i.e. the arm is raised more than before?  They are centred ok looking along the bike length plane (or the horizontal) but I have to say the arms are raised a bit further than before, at tdc.  Just a brief description would be cool.
Thanks for your advice.    

[Bob_Roller]

I shimmed mine I think back in '83 or '84, I had a rocker arm bearing shell cracked out and let the needles out, I got a later version replacement rocker arm, it has a plastic plug in one end and had to be shimmed, it had an excessive gap, I think it was .060 in., 1.5 mm .

I had no idea what kind of a clearance I should have, so I went with .004 in. right around .1 mm .

The shims have been in there for 75,000 miles,  121,000 km  and do need replacing now .

One member here Barry found this somewhere, that BMW recommends no clearance, just enough for an oil film .

Hopefully he can expand on this .

[tunnelrider]

Thanks Bob, yeah I can see why you need shims there!  I've just put new plastic bushes in all my '85 rocker arms and there's no doubt they wear down over time.

I think no one should spend anymore of their valuable time replying on this as I've decided to stick with the original '85 rocker arms.  This was enforced, on further trialing the other cylinder the earlier rocker arms, of having just 0.2mm future lash adjustment on an intake valve before the adjuster could back out no further and I don't think this is enough for future seat or valve recession.  Maybe a hatchet job on the head reconcondition too... see what happens. I could just install the original arm on that valve I suppose, but might see how it goes using all the original gear. I haven't got time to get the rocker arm contact pads ground down and polished this turn, so she'll still be fairly noisy. But the axial play will be back to minimal with new plastic bushes.  Cheers.