Forum

[stinkwheel]

I'm old school and don't use a torque wrench much.
Except! Steel studs into alloy! It's oh so easy to overdo it. Steel on steel you have plenty of leeway but not steel into alloy. On fact, strictly speaking, you shouldn't do steel to alloy, there should be an insert.
You'd never find a alloy thread on anything really critical like an airframe.

They don't help by using very fine pitch threads, compounding the issue by using worn machining to cut them, there is very poor penetration of the thread into the alloy. You can wind the cylinder head studs right out out of some of the iron barrel bullets before they even come close to being tight. The worst one is the little stud that holds the barrel down on the right hand side just above the tappet cover. I routinely fit an insert to these.

I think it would be hard to pick a worse thread to screw into fairly low quality alloy than a cycle thread. My local engineer was horrified that's what they were using when I asked him to make some slightly over-length gearbox studs with a square end on for me.

[PeteF]

Agreed SW.
The two times I've had an RE barrel off I helicoiled them (which is better) but inserts would be even better.

[Presto]

PF says things about ‘… an airframe’.

But a Bullet doesn’t fly and this arrangement (however ‘wrong’) has been used in 10,000s of Enfield engines that are still going as well today as the day they were made.

The question is ‘Why did such a savvy company as RE persist with threads into alloy?’ Does anyone have an informed answer? Because they must be one.

[Presto]

BTW – I have in the past tested cylinder numerous studs to destruction but have never had one pull the thread from the casting.

Just a bit of ‘anecdotal’ – only put up here to be short down in flames!!

[Cranky]

[/quote]
So how come RR issue a 10 page document listing a torque figure for virtually every fastener on the car?
http://rrtechnical.info/sy/tsd2476/18.pdf

Well because I am so old I am quoting RR school from 50 years ago.

[stinkwheel]

PF says things about ‘… an airframe’.

But a Bullet doesn’t fly and this arrangement (however ‘wrong’) has been used in 10,000s of Enfield engines that are still going as well today as the day they were made.

The question is ‘Why did such a savvy company as RE persist with threads into alloy?’ Does anyone have an informed answer? Because they must be one.

Threading into alloy is done on pretty much all automotive engines.

I don't know why they picked the thread pitches they did though. Surely the "done thing" from the RE era was Whitworth or BS on engine parts and cycle thread on cycle parts?

I have a picture in my head of Indian enfield workers handing down their hereditary and increasingly worn thread 3/8" BSCy tap from father to son.

I've wound a cylinder head stud out of my 350 bullet before it was even tight enough to put a torque-wrench on them, just two fingers on a ratchet socket. And yes, I DO use a torque wrench on cylinder head studs, I feel for stretch too but if it's incapable of tightening down without winding the thread out of the alloy, that's something that needs fixing.

On the last one I built, I got some of our hosts EN8 studs and they wouldn't screw in at all. I checked the pitch by holding the old and new studs against one another and they were the same but the depth of thread cut onto the original studs and into the alloy was so shallow, the properly cut ones wouldn't go in. The threads on the stud still had square tops, no points. I had to get a bottoming tap and go down the holes again, it took proper curls of swarf out, then the new studs fitted.

[PeteF]

Why just thread the alloy?
It's the cheapest option that works on initial assemble. The problems start on subsequent diamantling and assembly.

[Presto]

I am still unconvinced that Enfield’s persistent use of BSC into alloy was a ‘cheapskate’ option - given the fact that the hallmark of Enfield engine design was always heft with a tendency to ‘over-engineer’ every component. They weren’t ignorant – and were very used to repeated dismantling of their engines.

Or was this trend a similar aberration to the notorious alloy centrestand?

[stinkwheel]

I didn't say it was a cheapskate option so much. They used cycle thread on motorbikes because they were set up for making bicycles. Even BSA moved onto BSF when they entered the 1960's.

They were probably ok when properly cut too but that went right out of the window on Indian machines. My BSC taps and dies generally get a good workout if I ever buy new bits.

Mind you, it's not just Enfield that make some questionable decisions. The main bolts that hold the mainstand bracket on my VFR750 is M10 extra fine into the alloy of the crankcase. You can imagine my amusement as two of them came out with all the alloy still in the thread.

[Adrian]

BSA and Triumph moved to UNC and UNF from the 1969 season.

A.