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E: Engine Valve split collets

Robert Watson

Well Known and Active Website User
VOC Member
Can anyone tell me positively what the angle is (or included angle for a pair) of the splits collets on the top end of the valve stems. Trev? Ian Savage? Anyone?

Thanks

Robert
 

delboy

Well Known and Active Website User
VOC Member
Can anyone tell me positively what the angle is (or included angle for a pair) of the splits collets on the top end of the valve stems. Trev? Ian Savage? Anyone?

Thanks

Robert
Roberto,
I put the digtal angl-o-meter on a selection of collets and it looks like 28 degrees + - on the post-war ones. -Not 30, as I was expecting. [That would be typical PEI]
Do I recall the collet and circlip idea was blagged from JAP though?
Cheers, Delboy.
 

Vincent Brake

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VOC Member
Hi Robert, sorry not the ones you asked for, just silly me. I made up some spring washers, (mm whats the damm thing called: ET37) with 1,5 mm less spring compression. we measured several and came up with 28,0 degr. its in it for 30T km. see drawing
 

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oexing

Well Known and Active Website User
VOC Member
When planning for new spring caps why not do the perfect job with split collets with three grooves ?? So the valve can rotate whenever it wants to as the collets don´t lock the stem. There must be hundreds of these stupid wire clips orbiting the moon from trying to fit them. Can´t see why they came up with these, standard split collets were easily avaliable even then and no different or more expensive to do - but a hassle to do or undo the wire clips. I have three groove collets in all engines I do since decades .
Certainly you cannot turn the grooves in the lathe safely with carbide tipped tools, too hard , so I grind them either with air grinder on the tool post, or with hf spindle - easy and slow with cutting oil and diamond file profiled stone, 2.70 mm pitch.
Three weeks ago had to do 36 grooves for the old Ford V 6 , so for a Vincent twin this would be only 12 to do. Type is Mk-8H (TRW) , for 8 mm stems - 5/16 " for those on remote islands - standard since many decades and perfect. They are 1 € each in my country,, so look around at VW, BMW Ford etc. for 8 mm stems, used are allright as well.
Spares Co. valve collets : "Split the pair and remove tang one pair per valve" - - - in 2021 they must be joking . . . . .

Vic
valve collets MK8-H

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P1080045.JPG


P1090396.JPG
 

vibrac

Well Known and Active Website User
VOC Member
Having used an eight and a half ton Jack this year to sequentially release 4 valves on a classic bike held by grooved collets (after breaking a vale compressor- they had been there a few years:() I am a little more inclined to like the Vincent method, one can curse the flying spring clips and you need horny thumbs, but I dont see a lot wrong with splitting a collet pair to ensure they are a matching pair, After all when I lost a grooved collet on the same job (as easy to do as a spring clip) and contemplated making one I was told make them as a pair and then split them....
NB I did find it at the bottom of a Burman Gearbox spares box (dont ask!).
 

Michael Vane-Hunt

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VOC Member
These were with a box of Vincent stuff I bought at John McDougal's estate sale. Anyone know if they are anything to do with Vincents? John was known for coming up with modifications.20210325_094730.jpg20210325_094646.jpg
 

oexing

Well Known and Active Website User
VOC Member
Now when referring to your experiences with these collets, what type of grooved valves were they , single groove or three groove ? The single groove type is found on XT SR valves or Guzzis. These grip the stem, no rotation with these possible. How come I never in decades had your troubles when working on that type of collets ? My guess, just a reflection of poor engineering - or fitting by the mechanic ? Same goes with collet pairs that have to be split before use - another reflection of poor engineering, never ever have seen some of these in all my life here. The three grooves types are standard in most serious European car engines for decades, down to 5 mm stems in modern four valve cars as well - for a reason . . . .
The one groove collets may be suitable for standard Vincent valves instead of the wire circlip, possibly just a little bit of grinding the old groove for the new collets to do.

Vic
 

vibrac

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VOC Member
They were single groove and as far as I know assembled by no less than the McCandless brothers of northern Ireland (They who invented the featherbed) 50 or so years ago, to a pair Douglas 90+ heads. As I say the release of said collets needed a hydralic jack mounted on a milling machine bed with the head held on the valve tulip and tube above the spring to a crossbar and then as the bar bent under the strain a blow from a mallet loosened them. An action repeated 4 times!
Let this serve as a warning to those who would stray from the joys of Vincent Engineering :D

1616748203527.png1616748389708.png
 

oexing

Well Known and Active Website User
VOC Member
Thanks Tim, for the photos, my guess the spring cap was the reason for this defect. They did not get collets with correct taper for the spring cap, or the stem groove did not match the collet shape - or the spring cap was too soft brass or alu. The single groove types come in several different types, see my photo. But I would not pick them as that type of collets leave a gap and squeeze the stem - unlike the three groove precision No. 22 MK8-H collets with no gap. So their perfect taper spreads all loads evenly and should go well with alu caps. Anyway, either types are produced and installed in millions of engines without problems. In your case I can imagine that the collets digged into the soft spring cap at the top edge to form a substantial ridge that prevented easy disassembly - my theory. The printed sample of collets is in a TRW book , more than 20 forms in there - but definitely no combo with a tiny wire clip.

Vic
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vibrac

Well Known and Active Website User
VOC Member
Thanks Tim, for the photos, my guess the spring cap was the reason for this defect. They did not get collets with correct taper for the spring cap, or the stem groove did not match the collet shape - or the spring cap was too soft brass or alu. The single groove types come in several different types, see my photo. But I would not pick them as that type of collets leave a gap and squeeze the stem - unlike the three groove precision No. 22 MK8-H collets with no gap. So their perfect taper spreads all loads evenly and should go well with alu caps. Anyway, either types are produced and installed in millions of engines without problems. In your case I can imagine that the collets digged into the soft spring cap at the top edge to form a substantial ridge that prevented easy disassembly - my theory. The printed sample of collets is in a TRW book , more than 20 forms in there - but definitely no combo with a tiny wire clip.

Vic
Yes very strange -the spring cap was steel and I think I can trust one of my Hero's Freddie Dixon* to get the angles right. Perhaps it was just the years it had sat there...

"Freddie did not just ride an HRD to a TT victory (1927) and have unbroken Brooklands car records he also helped develop the post war Douglas engine after Douglas asked him to sort their initial mistakes
 

oexing

Well Known and Active Website User
VOC Member
Anyway, even just looking at single groove stems and collets I found a few subtle details in various types so one has to check all fits very closely to avoid defects as you have experienced. A taper of 28 or 30 degrees is not difficult to handle for quick disassembly , slimmer tapers of 5 to 6 (10 to 12 deg.) degrees like on gearbox sprockets or flywheels need substantial pullers to crack them open . So really there was something quite wrong on your bike, like near enough fits but not really right - with slowly growing defects from this in that joint. So in the end I will remain faithful to the three groove non-gap collets like on most serious modern engines since decades, free for the valve to rotate for reliable good sealing on the valve seat.

Vic
 

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