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Rocker bearing studs

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Rocker bearing studs
Started at 09:59am on the 3rd February, 2018 by stinkwheel
stinkwheel Subject: Rocker bearing studs
On a classic engine 500 bullet, 4 of the rocker bearing studs are black and 4 of them are silver. I see the parts list shows some as "ground diameter" and some as standard. Oddly the ground ones are 10p more expensive.

I'll confess I have absolutely no idea in what way they are different to one another, why there are two different types and where each type should be fitted.

The ones I have are rusty as hell (basket case motor, these were in the bottom of a bucket) so I was going to make some new ones. I am going to incorporate some way of removing at least two of them with the rocker cover still on to allow removal of the inlet cover from the taller 612 engine. Probaby a flat just above the bottom thread but maybe a flat on the top threads.

I'm off to pick up some EN8 bar now.

So the question. In what way are "ground" studs different to normal ones, why and where should they be fitted?
Posted: 09:59am 3rd February, 2018
scotty Subject: Rocker bearing studs
Hi i think they fit diagonally on the rocker boxes as an alignment tool to keep both parts of box square. Same idea is used on crankcases.
Posted: 10:31am 3rd February, 2018
Blown265 Subject: Rocker bearing studs
I just checked some early photos of my '06 500 Classic (the bike had 500 miles on it when I bought it, and was completely standard), and as Scotty mentioned, the two stud types are diagonal to each other. Regards Paul.
Posted: 12:54pm 3rd February, 2018
ric Subject: Rocker bearing studs
Think of the black pair as locating pins (which is what they are). Check for fit in the rocker blocks to hopefully find which diagonally opposite holes give the tightest fit and screw them into their corresponding holes in the head. Then fit the remaining studs in the remaining holes :)
Posted: 01:36pm 3rd February, 2018
Barry N Subject: Rocker bearing studs
Just in case you aren't aware, the rocker block studs are notorious for stripping their threads in the head, so go easy on the nuts! (about 5ft/lbs is recommended, I believe - especially with Samrat alloy blocks). Also, if going with the Samrat rockers, it is advisable to drill out the oil feed holes in the blocks to 3mm, to lighten the load on the oil pump spindle, especially with the high-capacity pumps.
Posted: 01:51pm 3rd February, 2018
stinkwheel Subject: Rocker bearing studs
Cheers for the info. Just had a measure and yes, the "ground" ones are 0.3mm wider than the standard ones. A shame because one of the reasons I wanted to make my own is so I have a decently cut thread. I suspect shallow, poorly cut Indian threads are partly responsible for their tendancy to strip. I do have a 1/4BSF insert kit on hand for just such eventualities in any case.

I'm now wondering if I could make these too though (oh for a lathe, somewhere to keep it and the knowledge to use it eh?). The ground ones are 6.8mm. Nearest imperial size is 17/64" which is way too oddball to get in bar stock. I could probably shave enough off a bit of 7mm using a pillar drill and abrasive paper to get a split 1/4BSF die on the end.

I'll be using undrilled, balanced samrat rockers with their o-rings in place in conjunction with our hosts scavenge side pressure relief valve. Had this setup on my 350 for 30k miles now without issues.
Posted: 06:02pm 3rd February, 2018
Alan R Subject: Rocker bearing studs
Hi STINKWHEEL------From what I can remember the last time I had my rocker covers off the larger ones act as "Fitted bolts" to accurately locate the position of the rockers whilst the other, smaller ones are just for compression only use......So therefore one large one is fitted next to one small one in pairs.........I have a fully equipped Machine Shop, 40 + years in repairs and restoration etc........send me your bits ( or Engineering Drawings showing what you want to achieve ) and I'll get them done for you ----OR ----try Paul, our Bullet Whispering friend as he is similarly endowed, so to speak. LoL !!!..........ps}--EN8 whilst a good, all-round general purpose steel might not be up to the tensile forces generated by the clamping nuts.....Why not buy some slightly oversize long series Metric bolts with the 8.8 rating ( High tensile steel ), remove the head and threaded portion and have the blank section turned to the sizes you need ??......
Posted: 02:56am 5th February, 2018
stinkwheel Subject: Rocker bearing studs
Thanks for the kind offer. I'll see how i get on at home, I like to do as much as I can myself. I did do a fair bit of research before selecting EN8 but follow through my thinking.

EN8 rolled bar has a tensile strength of 6-800N/mm^2. The standard tightening torque for a bullet rocker nut is 10ft/lb yes? So looking at torque tables for 1/4 BSF fasteners, that implies it's a grade R stud which has a tensile strength of 690 to 850N/mm^2 (hell I hate converting imperial and metric, you get tied in knots). So pretty much in the same ballpark. I certainly wouldn't want to be tightening them more than that and if I go with much higher tensile, there is then the risk of undertightening the fastener and it coming undone.

Interestingly, our hosts use EN8 for their cylinder head studs.
Posted: 12:48pm 5th February, 2018
Alan R Subject: Rocker bearing studs
Hi matey !!---------- As a practical type of person I'm always finally guided by the saying}-- "Proof of the pudding ----" etc.... So that's all good info you have there then and EN8 it will be.....Incidentally, wearing my other hat as a 5" gauge live steam locomotive builder I use EN8 but in BDMS form for axles...In the 0.750" dia. I need it measures up on average at -0.002" and concentric.....With my axleboxes reamed to 0.750" true that gives me a nice oil clearance of 2 thou....Works a treat..

As mentioned those studs can easily strip from out of the cyl. head---- I've done an insert or two but it's quite cramped in there.......I like your idea of putting some spanner flats on the bottom of those studs for easy removal......Nice bit of "Outside the (rocker) box" thinking there !!
Posted: 01:10pm 5th February, 2018

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