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More cam weirdness
http://ducatittandf1.com/viewtopic.php?f=24&t=11511		 Page 1 of 2
Author:  jr91 [ Thu Feb 23, 2017 11:49 pm ]
Post subject:  More cam weirdness
Years ago I was lucky enough to inherit (at a price!) my friend's '86 750F1 race bike. It has 40mm Dellorto's and reportedly big valves, manifolds, ports etc. It was apparently quite a hot rod, built by Ian Gowanloch back in the day.

When I got around to pulling the engine apart to see what was inside, this is what I found...

Horizontal

Image

Vertical

Image

From what I can see (without having measured anything yet), the camshafts look the same (aside from the holes drilled in the lobe). According to bikeboy's cam page (http://www.bikeboy.org/duccamspec.html) these are different cams, with the horizontal being a ?F1 Montjuic (assuming the OP marking on my cam is equivalent to the PO marking on the cam spec page) and the vertical being NCR7.

The cam spec page shows different timing, duration, overlap for these two cams but I notice that the Montjuic is measured at 0.2mm valve opening and the NCR is measured at 1mm valve opening.

My question is...are these essentially the same cam with the different measured numbers as a result of taking the measurements at different opening?
Are they able to be used together? (Clearly they can I guess because the bike was running (and running well) years ago).

Can anyone shed some light??
Author:  618F1 [ Fri Feb 24, 2017 1:35 am ]
Post subject:  Re: More cam weirdness
Wierd is right. But I don't think you can answer your concerns until you set up the degree wheel and dial indicator to take your own measurements. It will be interesting to see a side-by-side comparison of the duration and lift of these two cams once the lobe centers are close. Who knows, maybe they aren't so different, although the NCRs seem to be easier to live with. I have found three or more degrees duration difference on "same"-spec sets, such as for the 900SS. Maybe this is the "hot" setup. Please let us know what you find. MikeV

PS: it seems the .020 measurements have inflated the duration claims, since few in the hot rod world use less than .040 as a start point for that measurement.
Author:  jr91 [ Fri Feb 24, 2017 6:52 am ]
Post subject:  Re: More cam weirdness
Thx for the reply Mike.

Part of the problem is that the engine has undergone a complete rebuild with new 90mm Pistal pistons installed. This means I need to measure the squish and adjust as necessary before I'll be able to install the valves/cams. And then I've also now got adjustable cam pulleys so I have to work out the cam timing so I can measure valve to piston clearances to,see if I need bigger valve pockets on the piston. I've never done all this high tech stuff myself before so it's a slow process! Hopefully I'll get to the degree wheel soon(ish)
Author:  jr91 [ Fri Feb 24, 2017 11:15 pm ]
Post subject:  Re: More cam weirdness
Ok the numbers are in...

First ever attempt at dialling cams of any description on any vehicle and this is what I have come up with

Horizontal cam (marked OP)
Inlet Open 46° BTDC
Close 78° ABDC
Duration 304°
Lobe Centre (calculated) 110° ATDC
Lobe Centre (measured) 115° ATDC
Lift 11.2mm

Exhaust Open 74° BBDC
Close 54° ATDC
Duration 308°
Lobe Centre (calculated) 80° ABDC
Lobe Centre (Measured) 84° ABDC
Lift 10.5mm
Overlap 100°

Vertical cam (marked NCR 7)
Inlet Open 39° BTDC
Close 80° ABDC
Duration 300°
Lobe Centre (calculated) 111° ATDC
Lobe Centre (measured) 115° ATDC
Lift 11.2mm

Exhaust Open 63° BBDC
Close 60° ATDC
Duration 303°
Lobe Centre (calculated) 88.5°
Lobe Centre (measured) 91°
Lift 10.4mm
Overlap 99°

These values were more or less repeatable and seemed reliable when taken (keeping in mind my novice status!). On the basis of these numbers I would suggest that the NCR 7 cam and the Montjuic P cam are the same with perhaps the Montjuic a few degrees longer in duration. Any thoughts?


Note I have adjustable cam pulleys but have not yet set valve timing precisely...only close enough to get some measurements without things getting tangled up inside.
Author:  brad black [ Sat Feb 25, 2017 6:17 am ]
Post subject:  Re: More cam weirdness
i calc the c/l as OP 106/100 and 7 110.5/91.5. advance the 7 4.5 degrees and you get 106/96. the separation comes out at 103 and 101, so quite possibly they are the same cam.

you could also check the timing at every mm of lift, that will give you a better idea of what the actual lobe looks like and if they are really the same.
Author:  flattop900 [ Sat Feb 25, 2017 11:05 am ]
Post subject:  Re: More cam weirdness
Hi jr...
Did you start measuring @ .040 ?
Regards...
Flattop
Author:  618F1 [ Sat Feb 25, 2017 12:12 pm ]
Post subject:  Re: More cam weirdness
Really interesting! Thanks so much for posting this. I also get 106 LC on the M cam intake.

These are almost close enough to be just manufacturing-tolerance differences on the "same" grind. Or, maybe some age on a component? I have actually seen a five degree duration difference in a set of matching cams. I have the same question about starting lift; 020, or 030, or ".040"?

With NCR 7s and 90mm RAM pistons my F1 just kissed the piston with the exhaust valve with the intake lobe centers set at 106 degrees (my first go in 2003, with the info I had then). Later I changed to 103-104 degrees, and it still pulls well over 10,000 RPM.

MikeV
Author:  jr91 [ Sat Feb 25, 2017 5:55 pm ]
Post subject:  Re: More cam weirdness
Thanks for the feedback gentlemen.

Also thanks for the correction Brad. I can see where and how the errors were made and put it down to me being a cam degreeing newb.

All measurements were taken at 1mm lift (0.04"). Whilst the differences in duration between the two cams could be due to manufacturing tolerances, I'm thinking it could equally as likely be due to my measurement tolerances ie accuracy of my technique and equipment. I will recheck everything...the first time took me hours mainly because of working out what to do and how to do it. The next time should be much quicker now that I've got the theory right and it's more familiar.

I haven't formally measured squish or valve to piston clearances yet but I can't feel any interference when turning by hand. I'm thinking .95 to 1.05mm squish and 1.5mm valve to piston clearance. Any comments or suggestions on these numbers?

I will also measure each mm of lift and graph it out to get a good picture of the lobe profile as suggested. I assume this will pick up if the ramp up and ramp down are not symmetrical. My calculated lobe Centre seemed to be consistently a few degrees different to the measured point of maximum lift.

When setting the cam should the setting be relative to the lobe centre (as calculated by opening and closing points) or set to the point of maximum lift? Am I on the right way of thinking here? Does it even matter?

Thanks for your help!!
Author:  brad black [ Sat Feb 25, 2017 6:58 pm ]
Post subject:  Re: More cam weirdness
jr91 wrote:
I haven't formally measured squish or valve to piston clearances yet but I can't feel any interference when turning by hand. I'm thinking .95 to 1.05mm squish and 1.5mm valve to piston clearance. Any comments or suggestions on these numbers?

I will also measure each mm of lift and graph it out to get a good picture of the lobe profile as suggested. I assume this will pick up if the ramp up and ramp down are not symmetrical. My calculated lobe Centre seemed to be consistently a few degrees different to the measured point of maximum lift.

When setting the cam should the setting be relative to the lobe centre (as calculated by opening and closing points) or set to the point of maximum lift? Am I on the right way of thinking here? Does it even matter?



i use 0.90 - 0.95 for squish cause i like it tight, and 1.5mm for p-v. unless it's a pain to get 1.5 with the cam setting i want, as a comprimise i might go down to 1.2 or so and see if it's noisy or it stops.

only a symetrical cam will have the calc centreline (a mean number with no basis in physical reality) equal to the max lift point. irrelevant imo, i never even look at max lift.

you go by calc centreline or max lift. it's just a convention. choose one, stick with it and don't even check the other. calc c/l is just easier imo and it's what most use, so that way you can compare.
Author:  618F1 [ Sat Feb 25, 2017 7:50 pm ]
Post subject:  Re: More cam weirdness
JR. The squish and V-to-P seem to be reasonable targets. You could choose to leave the OP cam where it is, and move the NCR V cam forward 5 degrees. Based on my limited experience, I would not retard the H cam. At least the "lobe centers" of both cams would be close/equal, and they would act similar. Then, see how it runs. MikeV
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