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61 Venom #768041
03/13/19 10:04 pm
03/13/19 10:04 pm
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
B
Brid Caveney Offline OP
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Brid Caveney  Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Hi guys -- We have a 61 Venom in for repairs. Just ordered a +0.020" "Hepolite" piston kit and valves for it from Grove Classics UK. Seems we've heard several opinions n a few questions we have. Any Velo officionado's here to give us firm answers? Supplier says to put 0.004" piston to bore clearance on it? What ring end gap? What final hone grit?
It had been set up at 0.002" with an Omega KRT squish style piston - and had partially seized. Exhaust valve had also been clouting the piston - as valve timing incorrect. Does the cam have any I/D markings on it (not down that far yet) so we can degree it?
Cheers,
Brid.

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Re: 61 Venom [Re: Brid Caveney] #768043
03/13/19 11:03 pm
03/13/19 11:03 pm
Joined: Jul 2016
Posts: 242
Australia
Joolstacho Offline
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Joined: Jul 2016
Posts: 242
Australia
2 thou clearance? no wonder it seized.

4 thou piston clearance is probably right, BUT it does depend on various factors; Alloy or Iron barrel? piston itself etc... (is it cam ground? split skirt? Comp ratio? etc).
Is it a 8.75:1 VM Clubman piston, or 8:1 VM split skirt piston?
Cam should have M17/8 engraved on it if it's a VM cam.
Hone: 400-525 grit at 30-60 degree angle.

Do yourself a favour... get a copy of 'Norm's Technicalities' by Norm Trigg, from the Velocette Owners Club of Australia. It'll tell you all you need to know.
It's worth much more than it's weight in gold for Velo guru info.

Re: 61 Venom [Re: Joolstacho] #768069
03/14/19 4:46 am
03/14/19 4:46 am
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
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Brid Caveney Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Iron barrel --- piston on its way from UK - and just sold as a Hepolite, from factory part numbers - so just assuming it's a replica of the original, and same compression? We'll get to the cam tomorrow - and hopefully find out what it is. 400 - 525 grit sounds a bit fine for (what we're assuming is) cast iron rings? We are just rebuilding a 69 Rocket 3 engine - and that barrel was done with 280 grit - using cast rings. Not arguing - but last 'old timer Brit' we talked to said to do the Velo barrel with 150 grit! Compression wise -- It had an 0.048" compression plate - plus 2 paper gaskets on the cylinder base when we stripped it. Assuming that was there from the factory -- though most talk I've seen is of 0.031" and 0.010" plates. Be nice having anything to add to the factory manuals we have - but time is not on our side with getting the job done. The owner (79yrs old) has a couple of rallies he wants to ride it in - first week in April -- so, we have to push on.
Thanks for the reply.

Re: 61 Venom [Re: Brid Caveney] #768084
03/14/19 10:07 am
03/14/19 10:07 am
Joined: Dec 2004
Posts: 9,883
Scotland
kommando Online content
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Posts: 9,883
Scotland
The grit is determined by the rings fitted so Grove would be the best one to ask as they should know which are fitted. You would expect the rings to be cast iron and so a rough grit being needed with 150 being rough but you need that confirming. The Wassells Hepolites for the T120 have different manufacturers rings fitted both by Wassells and the dealers as an example. Omega's are made from a low expansion alloy so need tighter clearances that cast pistons but 2 thou sounds risky.

Re: 61 Venom [Re: Brid Caveney] #768099
03/14/19 1:15 pm
03/14/19 1:15 pm
Joined: Feb 2006
Posts: 629
Ontario , Canada
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RGSROB Offline
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Joined: Feb 2006
Posts: 629
Ontario , Canada
Hepolite piston , solid skirt in an iron barrel = .0057/.006" clearance at base of piston.
omega( low expansion alloy )with an iron barrel = .0045"/.005 clearance.
regards
Rob

Re: 61 Venom [Re: Brid Caveney] #768100
03/14/19 1:36 pm
03/14/19 1:36 pm
Joined: Apr 2005
Posts: 1,769
Mississauga, Ontario.
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Adam M. Offline
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Adam M.  Offline
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Joined: Apr 2005
Posts: 1,769
Mississauga, Ontario.
Sorry for the off topic, but average cast iron piston rings in Rocket 3 cylinders will not last for long, you need to use Goetze rings ( cast iron with a spring in oil ring ).

Re: 61 Venom [Re: kommando] #768104
03/14/19 3:23 pm
03/14/19 3:23 pm
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
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Brid Caveney Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Kommando - Grove owner is on holiday (and not available it seems) and lady I spoke to couldn't answer the questions about the pistons/rings - so we are a bit stymied there. Need to put it to bed though - as need to get the bore done as soon as we get the new piston - to have a chance of completing the job on time.
Adam M -- the A75 has Grant compression rings and Emgo 2 piece oil rings (for some reason - the Grant 3 piece oil rings weren't correct for the JCC pistons)

Re: 61 Venom [Re: Brid Caveney] #768142
03/14/19 11:18 pm
03/14/19 11:18 pm
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
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Brid Caveney Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Camshaft has no markings on it at all - but according the the marks on the gears - the last perps had the timing 3 teeth out . Only question is cam positioning according to the picture in the factory manual we have?[img][IMG]http://i68.tinypic.com/260zoyh.jpg[/img][/img] [Linked Image] Any thoughts folks?
Cheers,
Brid

Last edited by Brid Caveney; 03/14/19 11:20 pm.
Re: 61 Venom [Re: Brid Caveney] #768143
03/14/19 11:19 pm
03/14/19 11:19 pm
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
B
Brid Caveney Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Pic with cam -- is it correct? [Linked Image] The con rod is on the downstroke - just before BDC

Last edited by Brid Caveney; 03/14/19 11:25 pm.
Re: 61 Venom [Re: Brid Caveney] #768188
03/15/19 7:10 pm
03/15/19 7:10 pm
Joined: Mar 2012
Posts: 197
Draper, Utah
F
Fullminator Offline
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Joined: Mar 2012
Posts: 197
Draper, Utah
Brid, keep in mind that Velocette cams are pressed into the gear wheel that drives them, that is they are pressed in with no hard locating pin or keyway. So, seeing a gear wheel such as yours, that is off on the timing marks could be a factor of the pressed in job being off a little bit. Checking valve opening and closing positions with a degree wheel is the only sure way to make it correct.
Fullminator

Re: 61 Venom [Re: Fullminator] #768275
03/16/19 5:14 pm
03/16/19 5:14 pm
Joined: Aug 2011
Posts: 77
Austin, Texas, USA
B
Brid Caveney Offline OP
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Joined: Aug 2011
Posts: 77
Austin, Texas, USA
Fullminator - thanks for that thought. Thanks to the help of a well known Velo guru - we've ascertained it is an M17/8 cam, and it appears the centre line through the exhaust lobe/cam spindle corresponds with the timing mark on the gear. Once we get the barrel and head back on, we'll degree the cam, and check the exact figures.

Re: 61 Venom [Re: Brid Caveney] #768665
03/20/19 1:09 am
03/20/19 1:09 am
Joined: Mar 2017
Posts: 21
Iowa
9
99cyclone Offline
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Joined: Mar 2017
Posts: 21
Iowa
That looks to be a Venom cam (M17/8). The MSS cam (M17/7) looks very different. The Venom lobes are much wider.


Buells and Brit Bikes
Re: 61 Venom [Re: Brid Caveney] #768786
03/21/19 7:29 am
03/21/19 7:29 am
Joined: Oct 2015
Posts: 67
Western Australia
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barry2 Offline
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Joined: Oct 2015
Posts: 67
Western Australia
Hi Mates
it the valve timing is right in the last photo, the cams look 90 degrees out, also I think the Velos have hunting teeth, they take a few turns to line up again after rotation also I rebored an 500cc Alloy cylinder/ Omega piston w/- 4 thou clearance that was spot on
Barry

Re: 61 Venom [Re: Brid Caveney] #768787
03/21/19 7:31 am
03/21/19 7:31 am
Joined: Oct 2015
Posts: 67
Western Australia
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barry2 Offline
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Joined: Oct 2015
Posts: 67
Western Australia
and that bush on the idler shaft should be firmly in the timing cover ( i would think)
Barry


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