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  #11  
Old 02/01/2012, 10:42 PM
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Originally Posted by Brian Catt View Post
OK, here's one for the technical bods, if a siamese system is used, will it need to be double the size of two single pipes?
On any two stroke seperate exhaust systems are more efficient than a siamese one, but if a siamese one is used the front pipes into the expansion chamber/silencer need to be of equal length not one short & one long as on the roadsters. The length of the exhaust system is critical so it may be advisable to design in an adjustable tail pipe that can be slid in or out to tune the system for optiman performance.
As for tuning the Villiers 2T (or 3T) the problem is the closeness of the cylinders resulting in a very narrow transfer port on the inner side of cylinders.
It also gives rise to overheating due to sparse finning. Tuning is therefore restricted to reshaping the outer transfer port & the inlet & exhaust ports, crankshaft & crankcase stuffers & heads. It is possible to fit 4T heads on the 2T barrels thus giving a central plug & higher comp ratio (8.75:1 as standard higher if skimmed). A larger carb should also help, but on a bigger manifold.
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  #12  
Old 03/01/2012, 08:45 PM
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Originally Posted by riflegreen View Post
I forgot the exhausts Adrian , yes they did have short stubs , marginally quieter than an MDS with a megga .

Also have vague idea of a pair of high pipes floating about , if I remember rightly they looked similar to the Mayfield exhausts .

Chris
Cheers for that Chris. Ernie Tull campaigned a 2T with high pipes in the mid eighties in Pre65 Club events, I remember seeing him at the Classicfest, Donnington park about '85, but can't remember seeing much of him, or it, after this time. Perhaps that one had survived from the factory and your memory for Ernie to ride.
Thanks too, Brian, for the question but I shall avoid a siamese system, if only based on Villiers advise to Bert, which he duly ignored. I see JW has stepped in to claim the title of "technical bod" and seems to have answered you quite comprehensively. I wonder what Primary compression ratio might result once all those crankshaft and crankcase stuffers have been applied?
Mayfield and CZ are two options worthy of consideration Marcelle, thankyou. I'm sure whatever we eventually end up with, it will be a compromise between a classic look, efficiency and the shear practicality of where it might fit. A very good friend of mine has supplied plans for the geometry based upon information gleaned from Rob Carricks tuning book involving lots of calculations. As to whether it could be made to fit the SA's contours or what the result might look like is another matter.
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  #13  
Old 04/01/2012, 01:15 AM
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Default g/box

Hi adrian, did you have any joy in the end with info on a c/ratio box, or are you stuck with the standard cluster.
Is there any chance any of the A series g/box parts might be adapted? just a thought. dave.
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  #14  
Old 09/01/2012, 02:43 AM
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Hi Dave, apparently there are wider ratio gears available as JW pointed out, but not closer ratio. I haven't spent any time assessing whether the A series gears are interchangeable, but at first glance they don't appear to be so, the gears are individually wider as is the box so it looks unlikely. It's not a major concern though because apart from first gear the ratios are not much different to the A series box that I run in the Hawkstone. I only use first for getting off the line and even then not all the time, in wet conditions it'll take second OK, so that was most of last season.!
On another matter, I took the bottom loop off yesterday and had a pleasant surprise. It turns out that Mr Blobit the welder was indeed Mr Blobit the Brazer, so not too much harm done there then. It's definitely going to need new bushes as I think those in there are the originals!
Have assembled the crank into the cases this weekend so at last some assembly work has started and we also managed to get Robs built into the left side case too, so some progress made at last.
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  #15  
Old 09/01/2012, 10:59 AM
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Default 25SA scrambler fork bushes.

Hi Adrian, Good luck with the Hawkstone Twin. I hope to see you out on it this season.
Are there any decent fork rubber bushes about at the moment as the good ones seem to have been replaced with really stiff unyeilding ones that are no good for trials. They may be ok for scrambles but not for you as you are so light. Probably ok for a Tri-Greeves.
I do hope that you avoid the seizing problems that the twin suffered from, good idea to have a word with Simon Bateman as to clearances...John.
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  #16  
Old 09/01/2012, 10:59 PM
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Originally Posted by John Pattinson View Post
Hi Adrian, Good luck with the Hawkstone Twin. I hope to see you out on it this season.
Are there any decent fork rubber bushes about at the moment as the good ones seem to have been replaced with really stiff unyeilding ones that are no good for trials. They may be ok for scrambles but not for you as you are so light. Probably ok for a Tri-Greeves.
I do hope that you avoid the seizing problems that the twin suffered from, good idea to have a word with Simon Bateman as to clearances...John.
Hi John, it's good to hear from you. Will try to get it out for this season but it will be later on, possibly.
I've not found a problem with the recent front Bushes, I fitted the first pair of Scramble grade(50 Shore hardness) from the last batch made and they've been fine, even for my light weight. They are also available in a softer grade(45 Shore hardness). I do confess to making sure that the shocks I fit, damp on the return only, if they damp both ways then, for sure, the combination is too hard, but I've always found this to be the case. I'm not sure if you'll approve, but I usually sort clearances in the bore by inducing a seizure, then dressing the high spots off of the piston. To date, with the single, I've only had to do it once on each occasion. I wonder if I'll be that lucky with the twin?
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  #17  
Old 03/02/2012, 09:06 PM
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[QUOTE=dave higgins;9441]Yeah, it looks like good clean bike to start from, apart from the link arm mod, by mr blobit the welder..
QUOTE]

Sadly, Mr Blobit the "welder" has left an indelible mark upon the bottom loop, which must now be replaced with a new tubular section. Initially I thought it had been brazed, but when it came to removing the offending item, John Fryatt tells me that brass had only been flowed on top of Mr Bolbit's handiwork. It's either replacing the tubular section, or finding another loop!
Onwards and upwards is the saying, or is it one step forward and two back. Never mind, on the plus side we've discovered one 3T Barrel from a fellow enthsiast, so all we need now is a mating half and we shall definitely be taking one step forward.
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  #18  
Old 06/02/2012, 10:16 AM
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Adrian - I hear I might be the transport medium for said 3T barrell! Didn't realise you knew my old pal Porky! Going round to see him on Wednesday and no doubt get conned into something Greeves-related!

Rob
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  #19  
Old 06/02/2012, 01:00 PM
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Default Bottom loop

Sorry Adrian, I had got behind with my Forum reading, not realising you were on look-out, too, for a bottom loop.
I still have the one I had mentioned to "our" Rob, before he said he was after a complete set of forks.
The loop can be your's, if you can settle with Rob? I was gifting it to him in exchange for parts I have taken from his 9E unit.
John
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  #20  
Old 06/02/2012, 10:54 PM
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Originally Posted by Rob View Post
Adrian - I hear I might be the transport medium for said 3T barrell! Didn't realise you knew my old pal Porky! Going round to see him on Wednesday and no doubt get conned into something Greeves-related!

Rob
Hi Rob, I didn't, until he phoned last week. He seems a damned nice chap and we were able to do a swap that suits us both, hence you being commandeered into transporting the barrel to me. It's really good of you and most appreciated. Will your transport take the additional weight!
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