Hi Im making a TDC/Timing tool for a 2stroke engine By fitting a 5/16 unf bolt inside a spark plug. I need to know how much this bolt will extend by each complete
revolution in mm. thanks
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you are going about it the wrong way
get a longer bolt ...drill a hole down the middle of it ...put a long stroke dial indicator in the hole ...make clamp arrangement or something to hold the dial indicator in the bolt.
all the best.mark
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mark wrote:

No, spark plug hole in head is at an acute angle I dont have a dial gauge thanks but i just need to know how far a 5/16unf thread moves with each complete turn.
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PW

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PW wrote:

Well if you googled "5/16 unf thread" the first hit says it is 24 tpi. Can you work it out from there?
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Cliff Ray wrote:

No, im a completely stupid, thick ignorant fool. Thats why I asked on here hoping to find the answer,
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PW

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wrote:

If you're so dim you can't look up a bolt thread on Google how are you going to work out the maths for ignition timing versus bolt movement? Have you even considered that if the spark plug is at an angle that alters the vertical movement of the bolt? I'm guessing trigonometry would be way beyond you too. The words "to happen" and "accident waiting" spring to mind in no particular order.
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Dave Baker

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On Wed, 26 Nov 2008 12:49:03 -0800 (PST), ravensworth2674

Our trigonometrically challenged friend doesn't indicate the make and model of the engine, so I can't tell him which FM to R :-)
There has been sensible advice. A defensive/aggressive attitude might possibly blind one to the sense and helpfulness of said advice.
Mark Rand RTFM
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Provided the stroke is known and the flywheel easily accessible; All you need is: something to poke in the plug hole at approx. TDC., a tapemeasure, a scriber, and some very basic maths.
ttfn
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Roland Craven
Nr. Exeter, Devon, UK
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If the spark plug hole is at an acute angle, then one turn of the bolt will not result in 1 mm change in the direction of the stroke.
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brightside s9

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On Thu, 27 Nov 2008 09:02:36 +0000, brightside S9

Without Googling, I reckon one could work it out, in theory: from exactly TDC, if x turns of the bolt turns the crank y degrees (measured by some means) and the bolt pitch and crank throw are known, then the bolt angle could easily be calculated. However, the point of contact would move across the piston crown and the foregoing asumes that the piston crown is flat, which it usually isn't. It also assumes that TDC can be accurately found without a dial gauge, which I doubt.
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-Pip

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wrote:

Andrew, sorry to hear of your own probs.
I was musing like the giant Cyclops and wondering. I was scrapping my old records of 60 years back but realised that kids of 18 only got 6 weeks training to work on aircraft engines and airframes.
What has happened since? Here is a guy that can't even grasp that people have fed in information from 100's of sources. And he can't see it with 2 eyes
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wrote:

complete
...put a long

or
with each

24 tpi.

are you going

bolt
Andrew, sorry to hear of your own probs.
I was musing like the giant Cyclops and wondering. I was scrapping my old records of 60 years back but realised that kids of 18 only got 6 weeks training to work on aircraft engines and airframes.
What has happened since? Here is a guy that can't even grasp that people have fed in information from 100's of sources. And he can't see it with 2 eyes
It's nothing new Norm - stuck a mapping pen in it when I was five (*) so if I'm not used to it now I never will be <G>
AWEM
(*) and that's at least ... ten years ago <G>)
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ravensworth2674 wrote:

They got six weeks of training, but they would have been watched closely, given much further instruction until they were proven competent, and, unless my sources have mislead me, they would have had to face a sound beating from one of their superiors, if they screwed up, or did not pay close enough attention to what they were doing and/or learning.
Fear is a great motivator, if properly applied. Focuses the mind, as it were.
Cheers Trev
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Trev, What arrant nonsense is this? I am actually looking at my intake of 1948. None of them look in fear and as to a beating, you must be out of your tree. On the 12th September 1948, I was in a squarebashing intake prior to this photo of a training course lasting 6 weeks. Again, I can tell you that one of the lads who became one of my 'erks' is still in contact with me. Further, in Star News which is the Journal of RAF 31 Squadron Association, one of the 6 week wonders was guest of honour to his old sergeant's presentation of 50 years in the Freemasons. He presented his old boss with a model of the Spitfire SL 721 which is still airworthy. If you live in London, go into the Peel Room at the Met at Hendon. It was in honour of three crew which died there. WE put it there. We might have been half starved, overworked, underpaid and generally buggered about- but we were tough enough. We had lived through 6 years of total war from the age of 9 - and this was luxury in comparison.
Norman Atkinson.
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My earlier post deleted. Obviously, Trev has no intention to dare to reply- he wasn't there.
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On Sat, 29 Nov 2008 03:47:52 -0800 (PST), ravensworth2674

this is Usenet Norm, you can't delete a post once it's been downloaded :-) You can't cancel one where news servers don't accept cancels either.
Mark Rand RTFM
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Thanks Mark but everyone who did National Service is at least 70( I'm 78+) The accuracy of accounts from first hand is getting less and less.
What is accurate is 'RTFM', the RAF Tech Library - or all the RAF Technical Publications is still at my old unit-RAF Hendon. Now there's thing. I would expect that the answers to the original post are repeated and repeated- there and there.
Mumble, mumble
Norm- another 6 week wonder
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ravensworth2674 wrote:

On the contrary, I dare reply just fine.
I have not been spending much time on the newsgroups of late.
Regarding the training. I am basing my statements on what has been told to me by, among others, some of the old farts that spent time in either the RAF, or the RCAF, during the war years and postwar. I worked with several fellows that had spent time in the RCAF, prior to amalgamation, here in Canada, into the Canadain Armed Forces. That took place in 1968. Most, if not all those fellows, retired through the '80's.
Reading through the reminiscences of the folks that did their apprenticeships both before and after that time, adds a bit more of a perspective.
The monitoring and mentoring did go on long after the 6 weeks of training was completed. And I can see no reason for any of them to have lied to me about the real potential of getting a beating laid upon them by the Corporal, or by the LAC that was watching over them, if they screwed up. They told me it happened. Good enough for me.
As to the benefits of fear, I'll stand by that. Whether it's a fear of a beating (rare these days) or simply fear of failure (of which there seems not enough about) fear does focus ones mind. Being in the military, one of the few employers that maintains it's own prison system , there is the fear of that, also, if one screws up badly enough.
I still run across the odd apprentice tradesman that could use a sound beating. It might not cause them any good, but would improve my spirits a great deal.
Cheers Trev