20 replies to this topic

[Cooperman]

I think it was a kind-of fad going back a long time. I never remember the thin-flange 'S' blocks having a problem and BMC Competitions never increased these bolt sizes on their ultra-competitive works rally cars.

 

Now, if you want a good bolt thread mod it is to Heli-Coil every threaded hole into any aluminium parts such as the clutch cover bolt holes, gearbox ends, drive output cover bolt holes. This prevents fatigue of the threads on engines which are regularly stripped.

[Spider]

Could vizard have meant as a mod for the thin flange early s blocks

 

I have read that book that it was in, but a long while back, it may have been in regards to all thin flange blocks, but even these don't leak if assembled correctly.

 

<Edit: Got me thinking, so I picked up David's early book to check what he was on about and it was in regards to the early Thin Flange S Blocks. There was also a brief mention of it in his later book.

 

Let's face it. If there was to be an Oil leak due to the flange flexing, then going to bigger fasteners won't stop the block flange flexing. Also, considering what it's bolted up to - an almost equally thin strip of cast aluminium - which would be more likely to flex?

 

Thinking this through a bit further, I'd say there's more likelyhood of leaks if going to a bigger fastener as there's a temptation to do them up tighter, which would more likely than not distort the gearbox flange and so create a leak. If they are not to be done up any tighter than the original 1/4" screws, then why bother going to the bigger fastener? >

Edited by Moke Spider, 30 December 2015 - 07:26 PM.

[Ivor Badger]

Well I fitted the 5/16" cap screws because it kept breaking the front middle 1/4" screw on a thin flange block.

 

£15 seems a lot for a handful of 5/16 cap screws.

Edited by Ivor Badger, 30 December 2015 - 08:33 PM.

[tiger99]

£15 is a lot, considering that cap screws are almost all at least 10.9 grade (except stainless, best avoided in structural applications), otherwise the head would split, so you can buy them easily, unlike hex heads which you have to check are at least 8.8, because they could be mild steel. Any nut and bolt stockist will be able to supply 1/4" or 5/16" UNF caphead setscrews. Try Google. You should get a lot for £15.

 

I am with Cooperman on Helicoiling threads in ali. Very worthwhile in most places including Mini transmissions, including the infamous drain plug, which may need some jigging to get it bored, tapped and the helicoil aligned accurately. In my opinion it is also usually beneficial in cast iron, base of cylinder head studs for instance, or the engine steady bolt holes. But get very good expert advice before messing with main bearing or big end bolt holes.

[Cooperman]

On aero engines where parts are of aluminium alloy it is mandated that thread wire inserts are fitted in all bolt holes. But of course, in a vehicle production environment cost is as important as good engineering practice - maybe more so.

It is less important where studs are fitted as it is the reversal of loads which occur in repeated tightening and loosening that cause thread form fatigue.

Edited by Cooperman, 01 January 2016 - 12:08 AM.

[tiger99]

Agreed, a stud may be often fitted for ever, as may a thread insert. Not so for a bolt, which needs to be undone sometimes.

But on certain A series engines you need to replace the head studs from time to time. Only if they are tightened to the higher of the two specified torques. Can't remember the actual numbers.

I got one back from the reconditioners and duly torqued it up correctly after a few runs. Several studs snapped. I did not get any more engine work done there!

Never had a K series apart, but I would expect that the long through bolts would need thread inserts, unless the bearing ladder is steel.

Bolting is a very interesting subject, and it is not always done correctly.

Edited by tiger99, 01 January 2016 - 10:13 PM.