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mac cam #766038
02/21/19 1:43 pm
02/21/19 1:43 pm
Joined: Feb 2006
Posts: 624
Ontario , Canada
R
RGSROB Offline OP
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RGSROB  Offline OP
BritBike Forum member
R

Joined: Feb 2006
Posts: 624
Ontario , Canada
Have just finished restoring a 51 mac. The original M17/5 cam and original followers were in rough shape .
I replaced the cam with a M17/7 and the later venom type followers. This bike is intended for normal road work and I wonder if this is the best cam.
I do also have an M17/6 cam available it appears to have more duration on the inlet but not as much lift as the m17/7

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Re: mac cam [Re: RGSROB] #766460
02/25/19 10:19 pm
02/25/19 10:19 pm
Joined: Dec 2018
Posts: 45
UK
P
Project ROTM Offline
BritBike Forum member
Project ROTM  Offline
BritBike Forum member
P

Joined: Dec 2018
Posts: 45
UK
Hi, I am building a '53 MAC.

I have drawn out the cam timing charts for a few cams, these don't take into account lift.

I will try and work out how to post them on here, but the can be found on my Facebook.

Project ROTM

I hope this helps.

Cheers,

Christian

Re: mac cam [Re: RGSROB] #766463
02/25/19 10:31 pm
02/25/19 10:31 pm
Joined: Jul 2016
Posts: 230
Australia
Joolstacho Offline
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Joolstacho  Offline
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Joined: Jul 2016
Posts: 230
Australia
Sounds useful. What clearance figure did you use? Cam timing figures from the factory are nearly always specified at larger than normal running clearances to account for the quietening ramps.
(I seem to remember a figure of 40 thou for Velo, but don't trust my suss memory!) If there's no clearance figure specified, or you use running clearances, the opening and closing position figures will be inaccurate.

Re: mac cam [Re: RGSROB] #766665
02/27/19 7:55 pm
02/27/19 7:55 pm
Joined: Feb 2006
Posts: 624
Ontario , Canada
R
RGSROB Offline OP
BritBike Forum member
RGSROB  Offline OP
BritBike Forum member
R

Joined: Feb 2006
Posts: 624
Ontario , Canada
Hi Guys, .030 seems to be the standard clearance for checking valve timing. On the m17/8 ,if you want to really dial it in they recommend .053 "on the inlet cannot remember the exhaust setting. I do think the M17/8 will be too much for a road going MAC.
I set the M17/7 using the .030 recommended for the early viper and used the figures quoted , Inlet open at 19 deg BTDC..
Bike did start up right away But had a few excessive smoke issues and a bit of a howl from the timing chest.
I just wondered if any one had actually tried the two cams I quoted.
I am going withe M17/7 to start with after I check the lube system over and adjust the idler mesh.
Bike is looking quite nice, bit non standard with flanged aluminium rims.


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