F cam reprofiling

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T Batnes
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F cam reprofiling

Postby T Batnes » Sun Feb 03, 2019 9:01 pm

Hi, can a fairly good F-cam (W/NG) be welded/ground to say a Franklin P2 profile? Or will it need too much material to be added, as it is more "pointy" than a A6/664 cam?
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: F cam reprofiling

Postby david.anderson » Mon Feb 04, 2019 5:51 am

The model F cam has a 1.5” base circle, the later cam has a 1” base circle. The P2 is the 1954HS mk1 cam which is 1” base circle.
By the time the cam is ground back to 1” base circle there will not be any problem with the pointy lobe.
Further Franklin recently built up an old regrind of the A6/664 VH 1.5” cam that had been ground back to 1.2”. I had them restore it with stellite weld to the original 1.5” base circle and they ground back pitted shafts, hard chromed and reground to original shaft size.
So it is just a matter of specifying that you want the model F cam ground back to 1” base circle and P2 profile, which is an excellent choice.
David

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Re: F cam reprofiling

Postby T Batnes » Mon Feb 04, 2019 8:03 am

Ok, great! Just the info I need. When grinding the base circle down to 1", then I must use the longer push rods, yes?
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: F cam reprofiling

Postby david.anderson » Tue Feb 05, 2019 3:44 am

Yes, longer pushrods are required
David

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Re: F cam reprofiling

Postby T Batnes » Tue Feb 05, 2019 11:38 am

Contacted Franklin Cam Services in NZ, and they can indeed reprofile the "F" cam to either a single lobe or keeping it as a twin lobe cam with their "P2" profile. They need the lifters as well, for hard chrome and grinding. They will not reduce the original base circle diameter, so pushrods can be the same as before. Wondering if they then can get enough lift from it..? I would think that 0,40-0,42" lift should be ideal. They can also supply a kit with suitable conical valve springs, collars and retainers. Not bad. Now, I must go and find the hammer and put it to my piggy bank.
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: F cam reprofiling

Postby david.anderson » Tue Feb 05, 2019 9:21 pm

I do not know why Franklin stated that they would not reduce the base circle dia to 1” as they have done that before for me. To maintain the 1.5” base circle will result in the casing having to be modified as the larger lobe will hit the case. I would also suspect the followers may also hit the casing with the extra lift. I suggest a mock up to verify before having the cam reground. And the original 54HSmk1 cam has a base circle of slightly less than 1”.
With regard to followers, what are you using, the twin lobe or single lobe follower. The twin lobe follower can be used on the single lobe cam (at a higher wear rate) but it will not give as much lift as the later HS single lobe follower. The twin lobe follower will however give the same valve timing as the HS follower.
With a HS single lobe follower the lift at the valve is .418” whereas with a VH single lobe follower the lift at the valve is .390”. The lift measured direct on the lobe is .455”
David

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Re: F cam reprofiling

Postby nevhunter » Tue Feb 05, 2019 11:50 pm

With pivoting cam followers the shape of the cam has to be non symmetrical to get anything near optimum lift rates. For serious tuning and minimising valve spring loadings for use at higher RPMs, it's necessary. I had some Art Senior Cams once but gave them away to some clubman racer way back. NO cam that I have looked at so far, fills me with Awe. The shape is usually two part circles with tangential straight sides. That is a great compromise and once you have a master cam you just make copies so getting it right has ongoing benefit . I wonder if roller cams like the speedway JAP's have been made? Other engines use them but they are heavier more expensive and you are stuck with a predetermined radius. Tweaking of the shape of the followers has always been an option for fine tuning an Ariel single. Just going for wild timings can make it into a pretty unpleasant bike to ride generally You need inlet length /diameter and exhaust pipe similarly as well as having a decent designed muffler, that doesn't rob you of power, and flow the ports. You don't need a monster sized exhaust port.
High lift on a large base cam will cause fouling of the crankcase at full lift.. IF you are mucking about with the pushrod lengths you must get it right or the ex lifter won't work and your adjusters will be on the limit Its quite easy to remove the ends and make new tubes from chrome molly thin section tube. Machine the ends to an interference fit and press them on. Nev

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Re: F cam reprofiling

Postby T Batnes » Wed Feb 06, 2019 12:21 am

I am using a twin lobe cam and followers.
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: F cam reprofiling

Postby david.anderson » Wed Feb 06, 2019 8:10 am

With the VH twin lobe follower the lift at the valve will be .390” but the valve timing will be the same as with a HS follower ie
inl 15 btdc 54abdc ex 38bbdc 31 atdc measured at .050 lift overlap 46 degrees and duration 249deg LSA 101.5.
David

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Re: F cam reprofiling

Postby T Batnes » Wed Feb 06, 2019 9:41 am

That is for a Franklin P2 cam, single lobe David?
Nev; dimensions for the pipes to use for push rods, do you have them at hand?
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.


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