The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: olev on 29.09. 2009 12:38

Title: cam profiles
Post by: olev on 29.09. 2009 12:38
Hi Folks,
Can someone tell me if the opening ramp on a 356 cam is the same profile as the closing ramp.
I've just had my cam ground and nitrided. The lobes are not symetrical. The closing ramp on the lobe seems steeper.
and I don't remember what they looked like before they went in.
I had a look at the cam curves on 'atlantic green' and managed to confuse myself.
Anyone??, cheers
Title: Re: cam profiles
Post by: Josh Cox on 29.09. 2009 13:20
Nitrided, planning on flying to the moon are we ?  *smiley4*
Title: Re: cam profiles
Post by: dpaddock on 29.09. 2009 14:48
Looking at the "atlantic green", I can't see any noticeable difference. But you can make your own trace and check this out.
Why, pray tell, did you have the cam reground?

Title: Re: cam profiles
Post by: olev on 29.09. 2009 21:50
There was a significent lip worn on the top of the cam.
The gentleman reground the cam to the same profile (i hope) and removed the lip.
Metal is also taken off the base of the cam so the lift is the same. The difference in size is taken up by tappet adjustment.
Nitriding is just the modern version of case hardening.
The whole thing costs less than a new one and should be better.
Unfortunately David, I don't have another cam to trace, hence the inquiry.
and Josh, one day you might use some of this technology when you upgrade to a cessna (or victa?)
Title: Re: cam profiles
Post by: dpaddock on 30.09. 2009 16:38
I regret I was imprecise in my "trace" remark.
What I mean is for you to obtain a lift/duration trace such as the one you see from "atlantic green". You do this with a degree wheel and a dial indicator on the rocker tips. It's quite simple and you'll get a direct comparison with the trace published by "atlantic green".
It's this curve that's important, not the profile of the cam.

Title: Re: cam profiles
Post by: RichardL on 30.09. 2009 19:27
Just tossing in here. Since Olev could not tell from the Atlantic Green curves if the closing ramp was the same at the opening ramp, I thought, maybe, make a photocopy on vellum of the trace and lay it over face down. If they are the same there should be no difference between the original trace viewed from the front and the photocopy viewed through the transparency.

Richard L.