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MG Midget and Sprite Technical - Shock absorber pinch bolt

The consensus on shock absorbers seems to be to keep any older Armstrong ones if possible and re-fill the oil. From my collection one of the better ones I want to use (front) has a sheared off pinch bolt a fair way down. I've used heat and Plusgas but it's stuck. I've tried drilling but the bolt shank seems quite hard and I've already broken two or three drill bits without making much impression. So, what is the best procedure? Should I get a new bit, something decent like a Dormer? What size? Start small and work up to tapping size? I get the feeling this could take hours. I have at least one other arm with bolt removed but I can't seem to separate the arm from the shock shaft.
Bill

Bill Bretherton

Bill

Why separate the arm from the shaft? If it doesn't leak, I would leave it well alone. IIRC I basically replaced the valve seals, gave everything inside a good clean out, and replaced the oil with Silkolene motorcycle fork oil of a slightly heavier grade.
Oggers

Bill,

IIRC those bolts are just standard UNF HT grade 5 or there abouts and shouldn't be an issue to drill out with a good quality HSS drill. If you have broken previous drills then maybe there are some remnants in there causing an issue for subsequent drills. Often when drilling out right hand threads a left hand twist drill is useful as if it catches it will unwind the thread. If there is and issue with drill bit remnants in there then I would be tempted to get a cheap diamond core drill off ebay or similar the size of the minor diameter, fill the hole with water or oil, clamp firmly to keep centred, and peck away at the bolt remains with that. Not something I've tried though as nothing so far has come to that. I've only used the core drills for glass, ceramics ,and the like.
David Billington

Cobalt drill bits are tougher than HSS and don't blunt anywhere near as quickly. When drilling out sheared bolts I always work up from smaller sizes and you need to be careful to get it absolutely central to the sheared bolt to avoid damaging the component thread. Use a centre punch to guide the start of the drill and drill slowly with plenty of oil to lubricate and stop the bit overheating and blunting.
Chris Hale

Oggers, the shock with the "good" arm has a jumpy action so needs attention. I didn't realise you can change the seals without removing the shaft - do you just remove the flat plate? I clearly don't fully understand the procedure.

David, the best drills I have are Dormer but are probably more worn than I realise - I find sharpening accurately difficult.

However, David/ Chris do you think a screw extractor such as Screwfix sell might work which may be better than a left hand drill? I'm always concerned they might snap leaving you with a bigger problem.
Bill Bretherton

Bill,

I have used easy outs in the past with no success but not broken one and know a few people who have used them and broken them in the part they were trying to remove resulting in a hardened steel piece in an otherwise softish drillable core. Your choice but they wouldn't be my choice.

Dormer should be good as far as I know unless they've sold the name on and are now crap, I don't know. For drill sharpening I have a Darex drill doctor and while I thought it wasn't good to start with once I'd learned to use it and its little foibles it is a very handy tool for sharpening drills and I find the split pointing feature useful especially for tough materials like stainless steel. The one I have is now about 16 years old and still on the original grinding wheel.
David Billington

David

I'm with you on the easy outs - drilling it is then.
Bill Bretherton

Bill

A jumpy action surely does not necessitate removing the arm - unless the seal is leaking of course. I have also read that removing the arms and refitting are a bit of a nightmare. You can certainly change (damper) valve seals without removing the shaft, and IIRC, I think they are actually O-rings. Damper assembly is behind the large hex head at the base of the unit. Again IRRC, the kit also contained springs and adjustment spacers to set the preload. I did not touch the seal at the arm, or anything else for that matter save giving cylinders and internals a good clean and replacing the oil.

One or two of mine (I did all 4) were also jumpy - certainly not smooth - but the action post "reconditioning" was firmer and very uniform throughout the operating arc thereafter. It certainly made a noticeable improvement in handling.
Oggers

In my experience, an easy out will work if you snapped the bolt while installing it so that everything is fresh. But, if it broke on removal of an old seized bolt, it is likely that the easy out will also break.

Charley
C R Huff

Thanks Oggers, that's useful information.

Charley, yes my instinct is to agree.
Bill Bretherton

This thread was discussed on 26/10/2016

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