Rocker cover thread repair

[ranton_rambler]

I have an oil leak from the inlet rocker cover on my 175, and having taken it apart today, I can see that the thread is damaged in one of the upper holes.
The bottom 3 holes appear to be blind but the top ones possibly break through into the drillings for the rocker spindles. Can anyone confirm?

Also, suggestions for repair….
I don’t really want to take the head off so I am considering either an in-situ Helicoil or maybe a slightly longer screw to grab any undamaged threads further down the hole.

Ian

IMG_9549.jpeg

[themoudie]

Aye Ian, it being a 175, I am unable to confirm whether the rocker cover cap screw drilling penetrates as far as the rocker spindle drilling.

An in-situ helicoil fitting would probably involve swarf, as the threaded hole will need to be enlarged to accommodate the helicoil, not a job I would do in situ. I would use an LED inspection light to light the hole and see what is revealed, or even if you are feeling flush, one of those endoscope cameras that you plug into your mobile phone and view on the screen. If you are a Luddite, like me that is not an option! The silver steel rocker spindle should be visible, if the hole breaks through to its drilling.

Measure, with a stiff copper wire, or a Vernier depth guage, the total depth of the hole and cut a 6mm cap screw to a length 2-3mm short of the hole depth, plus the thickness of the rocker cover casting and see if it grips. For these 6 mm cap screws, I use a quarter inch drive torque wrench set to 7.0 ft/lbs, or 9.0 Nm and have no problems with the cap screws loosening without a drop of nut lock. If the screw doen't grip, then I would time the engine up and whip the head off, afore helicoiling the hole.

I also use a small artist's brush to apply a thin film of Hylomar, Yamabond #4, or other non-setting RTV to the casting surfaces, before adding the gasket and assembling. Even so, I have some gaskets that after 15,000 miles are starting to weep oil through the gasket material after a good run. I may have to get the Capt.Tollies Creeping Crack Cure out that definitely cures the weeps, there are other sealants, but I haven't tried them.

Good health, BillR

[ranton_rambler]

I had a bit of time before dinner this evening, so cleaned the hole out as best as I could and shone a good LED torch down. The rocker spindle is visible but there is a small amount of good thread at the bottom of the hole. I have filed a longer screw to a custom length which appears to engage enough with the thread and should clamp the flange & gasket.

I don't normally use any sealant on these joints but will make an exception to give the gasket its best chance. I will just use a normal Allen Key and one finger to nip it up.

It will need a proper repair in due course but it's running well apart from the leak so I don't want to disturb too much before I do the Giro SW in September. After that I can take the head off.

Will update when back together and road-tested.

[themoudie]

Aye ranton, I too get that reluctance to disturb, if all is cushtie. At least you now know what lies afore you, after a good trip to and on the SW Giro.

All the best and good health, BillR

[Kreece]

I have found Timeserts to work great. They come in complete kits with a precision drill, taps, and an installation tool. They are a bit pricey the first time you buy a set, but the inserts are a good value purchased on their own. Every other motor I work on needs at least one, if not more.