Technical Camshaft specs

[nzbobc]

So, for fun, I thought I'd learn a little about camshafts and mine in particular. Pretty much everything I know about camshafts I just learned in the last few hours...

The previous owner had a new camshaft made and I just got the specs on it from the shop that built it. They are listed below in the pdf. The specs are based on 'checking heights' of .012" and .050".

I was wanting to compare this to the original but, if I understand this right, the 'valve clearance for timing check' given in Haynes is .025". So, I'm not able to make a direct comparison of overlap, duration, etc., right?

Any way of telling how my camshaft differs from the stock one? All I know is what the previous owner had listed in the add when I bought it: "Hi-lift cam/good low end torque."

The Haynes specs are for a 650cc, which is what I have.

On an aside, when you guys have talked of camshafts, you mentioned 35/75-75/35 110/290. I think I understand the last two numbers to be Intake Centerline and Duration. But what are the previous 4 numbers?

 

[Bambino]

Hi NZ,

The first four numbers refer to the angles from TDC and BDC where the inlet and exhaust valves effectively open and close. The attached image will explain it better than I can in words.

So to use your example, a 35/75 75/35 camshaft will open the inlet valve 35deg before TDC and close it 75deg after BDC (open for 290deg during the intake cycle). The exhaust valve opens 75deg before BDC and closes 35deg after TDC (open for 290deg during the exhaust cycle). There will 70deg of overlap when both valves are open.

Chris

 

[fiat500]

*Hijack of thread*, which I know is despised on some Forums.

I have been looking at the "Autobooks" specs for the 110F 500cc engine and the 126.A.000 594cc engines to compare standard camshaft specs. I don't have the book for the 652 engine which I am actually working on.:bang: (So later,cribbed it from Bob's data)

Using the system clearly described above, I can see that these two engines have different specifications;

20/50 50/20 (500)
26/56 66/16 (600)
18/53 72/24 (650)

To my untutored eyes this seems like two completely different camshafts. Presumably this evolved so that I suspect that there are likely to be more than two types of standard camshaft for the later 650 engine.

All the spare parts suppliers that I have seen list only one camshaft common to the range of engines although I am aware that there is a wide range of aftermarket cams available.

I have replaced the camshaft on my engine with a"standard" one as one cam was really badly worn. Lacking this sudden "insight" I didn't record the part number nor take any measurements.

I assume that a 500 camshaft on a 650 engine will work fine, but what sort of performance loss or potential, insidious damage would it cause?

PS. Just noticed the 650 specs are attached to this thread so will now check them.
If you've read this far I now realise that I have baffled myself and maybe the specifications above are all for the same camshaft but with different valve clearance specifications....:bang:

 

[timgarman]

Hi Bob

Just out of interestThe camshaft I took out of my 500-F to replace with a lightly ground one, has an inscription scratched into the flange. It reads:

Auckland Cams
4/13
GT30 (or it could be G730).

Auckland Cams still exist so I emailed them but no reply. Any idea what these numbers mean?

Tim

 

[nzbobc]

Hi Tim,

My camshaft had similar markings. One was essentially their job number and used it to look up cam card report for this shaft.

Coincidentally, the makers of my camshaft didn't respond to an email request for info but were responsive when I rang them up. May want to try giving them a bell.

Your car is looking great, BTW!

Cheers,

-bob

 

[timgarman]

Thanks Bob, will do that.

I'm loving the finishing touches stage (I think this stage actually goes on permanently).