Repairing worn rocker pin holes in the head

[graeme]

Has anyone done this?
What did you do?
Bush the holes?
Fit oversize rocker pins and bore the original holes?

I've been chasing loud tappet noises and traced it to worn holes in the head of a Scrambler.

(I started this in the Oldham coupling thread of Kev's but it should have its own thread for future reference)

Graeme

[Jordan]

I'm thinking that, even if pin housings were worn, excessive noise wouldn't happen as long as tappet clearance is correct? I've had badly worn pins (at the bushes) that still ran quietly.
I guess it's possible, but I've never seen worn heads at the pin housings, and I've seen dozens of well-used ones.
Jordan

[graeme]

Hello Jordan,

I have seen lots of Desmo heads that were worn but not as much as this spring head. The desmo ones didn't make noise like this.
When I measure the shim clearance it measures 0.15 to 0.18mm, but if I lift the rocker up the gap increases to over .45mm.
I can see the rocker pin move up in the head and can see and hear oil being squeezed out of the head holes, both bevel side and cam bearing side.
The inlet is not too bad, but the exhaust is sloppy.

There will be slop in the rocker bush also for sure but the pin / head hole looks worse.

If the hole in the head was sloppy the pin could have been bouncing up and down for some time and making the hole larger and elongated.

I could lift the rocker as high as possible and shim to suit which would stop the noise but that doesn't seem to be the right way to do this.

Graeme

[machten]

The repairs I've seen done for this were done using bronze bushes. I think it was VeeTwo that did the repair. I know one of the fellas there had a jig that he used to convert 750 roundcase heads to desmo too. A friend of mine has the machinists old 750 Sport which he had "desmo-ed".

regards,

Kev

[DewCatTea-Bob]

[quote= graeme ...
" I can see the rocker pin move up in the head
the pin / head hole looks worse.
the pin could have been bouncing up and down for some time and making the hole larger and elongated. "

____ Is the black/rubber-block missing from it's slot within the valve-cover ? ...
__ I knew a fella who raced his 250Scr in off-road motocross-events in the late '60s, and he assumed that those rubber-pieces were intended for quieting rocker-noise,
and since he didn't care about any such noise,, then whilst checking valve-gear, he allowed them to fall-out & become lost. ...
Then after many hours of hard/hot competition-racing, he became more aware of the rocker-noise (after hearing OTHER Duke-engines running),, and later finally discovered that the exhaust-side rocker had become nearly seized to it's bushing & it to the rocker-pin. _ So evidently the pin had-sometime found it somewhat-EASIER to rotate within the head, apparently due-to oil not being captured by those missing rubber-blocks.
__ If ya look-at & take-note of the specific-placement of those blocks, it's fairly obvious that their intended-purpose is to catch & divert cam-lobe flung oil back-towards the oiling-hole within the top-front of the rocker-arm.
__ His plan for fixing-up the resulted elongated rocker-pin hole, was to drill-out the hole with a 1/2" drill-bit* (on a drill-press jig-stand), and-then ream-hone the enlarged-hole until a (used) rocker-bushing (which he had cut-in-two) could then be pressed-in. _ And in that way, he'd never have-to worry about such rocker-pin rotation-wear ever-again.
(* I had recommended that he first carefully drill-out the hole with a 7/16ths-bit, before-next trying his 1/2" drill-bit, [which he replied he'd try].)
__ I never witnessed his actual repair-work, but he claimed that even-though he had somewhat messed-up his repair-job, the final-result still worked-okay well-enough.
(At that time, he also installed sets of 10x13x13mm needle-bearings in-place of the stock rocker-bushings, [a somewhat-common engine-mod practiced back-then].)
__ In the late '70s, another local fella & myself bought-up all of his Ducati-collection, so I MAY-possibly have that same repaired cyl.head but, it was the OTHER-buyer who particularly wanted all his Scrambler-related parts, while I-myself only got most-of the street-model Duke-parts. _ I still have most-all of the cyl.heads I got from him, so I may someday take a peak inside them & see if any happen to-be that particular repaired-cyl.head.
The fellow-buyer who bought all his other Ducat-parts, ended-up trading them away at a swap-meet, and then-next I later saw many of those same parts listed on eBay by a seller in southern-Ill., back-in 2007. _ So some eBay-buyer may've ended-up with that repaired 250-Scr.head .


Hopeful-Cheers,
-Bob

[graeme]

Hi DCT Bob, yes the rubber blocks are in the rocker covers.
The bronze bush fix makes sense and would seem to be a sound long term repair, if done well.
This head, and the rest of the bike has (by the looks) had an unloved life, which I will restore when I have time and space.
But I've had it for a few months so I thought I'd get it running and have a bike that wasn't restored and I could use on dirty days.
Apart from this noise it goes well and I'm very happy with it.
I'd hate to do a bodge job and a future owner curse me, so maybe I'll do it now or put it away until I rebuild it later.

Thanks, and all ideas or experience is always appreciated.

Graeme

ps, do you think it would much more damage if I rode it as it is for a while?

[DewCatTea-Bob]

[quote= graeme ...
" yes the rubber blocks are in the rocker covers. "

____ Well-then if they're original, they ought-to be rather stiff and uneasy to fall-out of their slots,, whereas if they're newer items, they ought-to be rather flexible and easy to slide-out of place. _ And if the later-conditions apply to them, then perhaps the originals had once been lost and then later replaced with those which you've found fitted in-place.
__ Otherwise, I suppose your-own suspected theory (of rather-loose original machine-work) is possibly probably-likelier.



" The bronze bush fix makes sense and would seem to be a sound long term repair, if done well. "

____ If done on a drill-press, the cyl.head should be locked-down in the platform-jig WHILST-also the drill-head has-been preloaded with a suitably-long 10mm-pin/rod set in place (while fed-down all-the-way inside the intended drill/working-position within the work-piece -[cyl.head pin-hole]),, so-as to help be sure that the intended drill-bit, (when-next loaded & set into the drill-head), will then already be properly aligned with the ORIGINAL hole-center, before the actual-drilling begins.
Cuz if that's not all properly done-right, then a new/SHARP*drill-bit will grab & pull the work-piece and-thus screw-up the hole-opening, (as I think such alignment-setting was the issue which my old-buddy had somewhat messed-up on, with his very-first drilling-step attempt).
(* A brand-new super-hardened drill-bit will even drill a hole (into a pre-established smaller-hole) within such relatively-soft alloy,, in a far-more CONTROLLABLE-manor,
when drill-spun in REVERSE !)
__ Of-course this-job can't be done on a mere table-top type drill-press, and-so only on a full-size 'drill-stand' can the drill-head be jacked-up & away from the work-piece, (that's held-down in it's platform-jig), high enough to swap-out the 10mm-rod & extended-length/reach drill-bits.



" do you think it would much more damage if I rode it as it is for a while? "

____ Can't say for-sure, as I-myself have never even heard-tale of any further-consequence (from running with elongated-holes which had exceeded any related thrush-hold).
But to get as bad as it seems to-have (according-to your description), I'd guess that it took a few thousand-miles,, and-so it's likely not going to make much-more difference to go a couple-hundred more.
__ But to help that cause, perhaps a fine oil-additive or Teflon-fluid would possibly significantly hold-off any further such wear.


Hopeful-Cheers,
DCT-Bob

[graeme]

Nice flexible rubber blocks that are not the originals.

graeme

[DewCatTea-Bob]

[quote= graeme ...
" Nice flexible rubber blocks that are not the originals. "

____ So-then someone had found the need to install the newer-blocks either because the original-rubbers had become rather non-flexible (which even-so actually still preform their intended-function well enough), or-else because it had been discovered that the originals had been found-missing...
And it pretty-much seems fairly-certain that you-yourself have discovered evidence of WHICH-possibility is most-likely the actual particular-case.
__ Over the decades of acquiring old Duke-heads, a notable number of them had those rubber-blocks missing from their valve-covers ! _ It seems that some-people are fairly apt to loose them, in their rush to get the valve-covers put-back in-place.
Also, in the majority of cases where the rubbers were still found within, many had become quite hardened*, especially in the 250Motocross-models, (* some to the point of busting-up into pieces, rather than flex) !
____ So did you also inspect & scrutinize the rocker-pins & bushings as well, for any signs of possible likewise renewment ?
As I'd suspect that the actual pins & bushings which had actually gone-through the process that elongated the pin-holes, would likely ALSO be somewhat worse-off than normal. _ So-thus if your pins & bushings all slide-through NICELY (as normal), and rather show no-signs of excess-wearing,, then they were probably also renewed at the same-time (as the rubber-blocks).
__ If you find that you have found enough evidence to conclude that the past/suspected cause of your discovered-issue has now actually-been addressed, then you can be more-so assured that further riding (with things left as they've become), ought-to be okay (for more than a few-hundred miles) without causing further-significant additional-wear.
Although I'd still keep a close-eye on the oil, however !


Hopeful-Cheers,
-Bob

[graeme]

An idea for a temporary "bodge" fix to prevent any more damage from sloppy holes and very noises tappet noise.
A small amount of Devcon (JB Weld) in the upper part of the head hole, an old oiled rocker pin inserted until the Devcon has gone hard, remove the old oily rocker and then reassemble the rockers etc.
The head has to be bushed later anyway and I wouldn't think Devcon (JBW) would hurt milling the holes out for an insert.
I know this is cheating but what do you lot think?

Graeme