Roundcase cam specs

If you need technical information or help with your roundcase Ducati 750 engine - post your FAQs, comments & questions here.
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machten
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Roundcase cam specs

Post by machten » Wed Dec 22, 2010 7:25 pm

Hi all,

Myself a few other interested parties are currently dial gauging our cams on various Sport and GT 750s. This is a bit of an investigation to see the effect of cam timing on engine performance of some freshly rebuilt engines - including why some engines really "bark" through the contis, and some are more restrained despite everything else being "equal". We've done a Sport and a GT and have a number of each yet to do, and whilst I have VeeTwo and some other third party specs, I can't find any definitive original Ducati 750 springer camshaft specifications to compare against.

Does anyone know where to find them/know them/have them?

Kev

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Steve Foster
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Post by Steve Foster » Fri Dec 24, 2010 3:35 pm

Kev - I don't have the reference handy as I'm away over the Xmas break but I recall reading in Ian Falloon's 750 Bible that the cams on the last model of the GT (i.e. the last series in '74 and I assume those 40 put together for Oz in '78 as well) were slightly modified (steeper opening ramps I think) in order to partly compensate for the performance hit due to the more restrictive Lafranconis. I often wondered how they would work/sound with Contis.

I also understand that the cams in the GT and Sport were the same (although I don't know whether those mentioned above were also fitted to the last Sports produced) and I'd be very interested to hear the outcome of your investigations.

Regards,
Steve.
1974 Ducati 750 GT

machten
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Post by machten » Fri Dec 24, 2010 8:11 pm

Thanks Steve. A few lurkers on the other forum (who also lurk here) pointed me at the specs in the owners manual, viz:
The owners manual lists the specs Duccout provided, IO 65 btdc,IC 84 abdc and EO 74 bbdc,EC 58 atdc. The figures are with the valve clearance at .010 mm and the specs allow a + or - of 5 degrees.
and my reply...
DOH! Thanks guys. Clearly they are not using a cam checking clearance of 1mm as is usual. Those figures collate to a 0 clearance. Re two grinds, yes I understand that to be the case too. I'll need to check some more to get a good picture, but at this stage we have one grind with an extra 1.1 mm of lift on the inlet although exhaust is only a very marginal difference increase and inside our margin of error. Interestingly, that ain't the one that barks!

What we have found so far though, is that the cam alignment on the "barker" between front and rear cylinders is perfect (I'll check the actual timing compared to the figures you've provided later), whereas the sport cam aligment is 11 (crank) degrees out between front to rear cylinders. We'll definitely be looking at trying some offset woodruff keys on that one to see what difference it makes.
More news as we do some more over the next two or three weeks.

Kev

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Steve Foster
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Post by Steve Foster » Fri Dec 24, 2010 11:04 pm

Kev,
... some engines really "bark" through the contis, and some are more restrained despite everything else being "equal".
Have you tried swapping the Contis (or indeed the whole exhaust system including the headers and cross-over) between the "barking" and the "non-barking" bikes? If everything else about the engines really is equal then perhaps it's something that's not directly engine-related. Just a thought .....

--Steve.
1974 Ducati 750 GT

machten
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Post by machten » Sat Dec 25, 2010 2:32 am

Hiya Steve,

Phew! A few more notches out on the belt after Christmas dinner. Best wishes to all!
Have you tried swapping the Contis (or indeed the whole exhaust system including the headers and cross-over) between the "barking" and the "non-barking" bikes? If everything else about the engines really is equal then perhaps it's something that's not directly engine-related. Just a thought .....
Yep. Been there, done that. This is a theory that some of us that have owned bevels since the seventies want to test. Over the years we've changed pipes, rebored, new pistons, valves, seats, guides, etc. We all know how tune the carbs in our sleep. We're now at the point of looking at cam timing and squish because that's what we have left. The inspiration on the cams has been Peter Shearman's excellent work on the subject.

Regards,

Kev

machten
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Post by machten » Mon Jun 06, 2011 7:55 pm

Just to tidy this post up, we have now dialled a 74 GT, a 73 Sport and A 74 Sport. We found that the cam alignment on the "barker" (the GT) between front and rear cylinders is perfect. The GT is also using a different cam grind to the Sports with Inlet/Exhaust ML points at approximately 101 ATDC/117 BTDC. The Sport cams are detailed below.

Note: We know that GT cam was changed at some time, so this is not saying that all GT's have this cam (or even any - it may be aftermarket). We'll be dialling my GT later on, so that might provide some more info.

The 73 Sport cam aligment was out 11 (crank) degrees between front to rear cylinders, with the front retarded 6 and the rear too advanced by 5 degrees. This is pretty close to Ducati's stated +/- 5 degrees accuracy, but the worst possible spread. We fitted a +6 degree offset woodruff key to the front camshaft and a -6 degree to the rear (they only come in 2, 4, and 6 degree offsets). Result - now has the crisp exhaust "barking" and performance noticably improved.

The The 74 Sport cam aligment was out 10 (crank) degrees between front to rear cylinders, with the front retarded 6 and the rear too advanced by 4 degrees. Once again, this is close to Ducati's stated +/- 5 degrees accuracy, but the worst possible spread. We fitted a +6 degree offset woodruff key to the front camshaft and a -4 degree to the rear. Result - now has the crisp exhaust "barking" and performance noticably improved.

Here's how my Sport cam timing finished up after the modifications. All figures are with 0.1mm valve clearances. I can't rule out some measurement errors along the way - it's most prone to error on the extremeties of the opening and closing ramps (ie. at and around 0mm of lift), but I was as diligent as I could be.

To interpret..

Opens "n" and Closes "n" --- n = number of mm of cam lift measured at the valve. "0" is when it just either starts moving (opens) or stops moving (closes) the valve.
ML = maximum lift of cam
ML 1 = the first point where maximum lift is acheived.
ML 2 = The second point where maximum lift is acheived (ie. there is a small circular arc at the top of the cam)
ML = (ML 1 + ML 2)/2 = the centre of the maximum lift arc on the cam
I/E Lobe offset = number of degrees between Inlet ML and Exhaust ML on each cam

The rest is standard cam terminolgy.

Image

For my Sport with such a timing difference, I'd put this modification as right up there with fitting Dyna ignition, and well worth the effort. (most of which is dialling it in the first place, fitting the keys is easy.)

Anyway, food for thought if you're wondering why other roundcases might sound and perform better than yours.

Kev
Last edited by machten on Tue Jun 07, 2011 6:32 pm, edited 2 times in total.

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Steve Foster
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Post by Steve Foster » Tue Jun 07, 2011 4:18 am

Hi Kev,

Awesome piece of investigative work there. (I would like to nominate you for a "Nob[ev]el Prize".) While I understand in principle what you have done, I would like to know more about how you actually did it. You mention that
We'll be dialling my GT later on, so that might provide some more info.
Is there any possibility that you or one of your cohort of long time bevel owners could document the process by taking a series of snaps, or perhaps even a video that could be posted on Youtube?

Are any "special" tools required? Is more than one pair of hands needed at any stage?

Cheers,
Steve.
1974 Ducati 750 GT

machten
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Post by machten » Tue Jun 07, 2011 7:28 pm

I would like to nominate you for a "Nob[ev]el Prize".
Oh, very droll, Steve! :-D
EDIT: And I should be clear, there's 3 others involved in this little bit of fun, so I neither take all the credit for any good, nor all the responsibility for any errors! ;)
Is there any possibility that you or one of your cohort of long time bevel owners could document the process by taking a series of snaps, or perhaps even a video that could be posted on Youtube?
Yes, for sure. I regret not doing that now, but the excitement/anticipation was too much at the time (pretty sad, eh?). Also, this might have diverted someone from attending to the important duty of ensuring appropriate workshop team hydration.

Now having done the process a few times, we're a lot better and quicker at it, so we're in a better place to do it, so I'll document it with some photos when I do the GT.
Are any "special" tools required?
All you need is a dial indicator, a piston stop for accurately determining TDC, and a timing wheel (with handles for turning the crank).
Is more than one pair of hands needed at any stage?
It is easier with 2 people because it can be a bit fiddly getting the dial gauge in position so that you can read it as you turn the crank if you're doing it on your own. Having said that, I did a second check on my Sport that way.

I've got the single up on the bench for some work at the mo, but I'll get onto the GT later in June, I think.


Kev

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Re: Roundcase cam specs

Post by jonduke74 » Sat Apr 29, 2017 10:48 pm

Hi I would be really interested in learning more about cam timing for my 1974 750 GT and checking to see if they are different and how to correct them.

Also another question, would I benefit much from swapping my cams for a “road race” Springer cams, I have been told:
“more mid to top end power still ok for road use”

My concern is by swapping these cams I would no longer have my “stock” cams to go back to?

How will they affect the low range as in idle and around town?

How would this modification affect the rest of the motor, like the bottom end?

Do not need more speed; a bit more pull around mid would be good for the hilly bits around New Zealand?

My 1974 750 GT has high compression pistons (about 9.0 compression) and 32 mm Carbs (blended into the 30mm heads).

Thanks John NZ

wdietz186
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Re: Roundcase cam specs

Post by wdietz186 » Sun Apr 30, 2017 8:26 am

I would start with checking and correcting the timing of the cams you have. Considering the assembly differences of the engines of the time you might find a performance boost by bringing the timing into spec. I've been meaning to do my GT for a long time but stuff keeps getting in the way. It's really not that difficult to check but do remember that the crank turns CLOCKWISE when viewed from the left side. On most every other bike on the road the crank turns anticlockwise, so you will get really weird readings unless you pay attention.

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Re: Roundcase cam specs

Post by Macdesmo » Thu May 04, 2017 2:13 pm

I believe that Machten, Ken, has regrettably passed away.
Ian

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Steve Foster
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Re: Roundcase cam specs

Post by Steve Foster » Fri May 05, 2017 8:27 pm

Hi Macdesmo/Ian and others,
That is incredibly sad news. What a knowledgeable and generous person Kev was.
Steve
1974 Ducati 750 GT

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abmartin
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Re: Roundcase cam specs

Post by abmartin » Sat May 06, 2017 5:16 am

Condolences from Canada. Always sad to lose such a devoted guy.

Bruce
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Fredericton, NB
Canada

jonduke74
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Re: Roundcase cam specs

Post by jonduke74 » Sat May 13, 2017 4:09 am

wdietz186 wrote:
Sun Apr 30, 2017 8:26 am
I would start with checking and correcting the timing of the cams you have. Considering the assembly differences of the engines of the time you might find a performance boost by bringing the timing into spec. I've been meaning to do my GT for a long time but stuff keeps getting in the way. It's really not that difficult to check but do remember that the crank turns CLOCKWISE when viewed from the left side. On most every other bike on the road the crank turns anticlockwise, so you will get really weird readings unless you pay attention.
Ok this sounds like my next best move, the only problem is that I have no information on how to do this, I feel that I would be capable as I like to do most of the maintenance on my old Duke. Where could I get specs and procedure for this type of work on the cams?
Best Regards John

wdietz186
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Re: Roundcase cam specs

Post by wdietz186 » Sat May 13, 2017 7:06 pm

There is nothing Ducati specific out there that I know of. You will need a degree wheel,a dial indicator,and a way to turn the crank in small increments. The basics are covered in many hot rod books and cam manufacturers catalogs. These will explain what is supposed to happen, when and why. The big difference is the engines they are talking about are pushrod actuated valve gear not overhead cam and the timing specs are usually stated at a certain lift figure. The stated Ducati timing events are at running clearance and the lift points are actual and not stated for a certain amount of lift, meaning they don't allow for the opening/closing ramps. MegaCycle explains it in their catalog as does Comp cams. Read all you can to get an idea of what you are checking, it is very easy to confuse yourself. Every time I get into it I have to re-educate myself. Adjusting the cams will require disassembly of at least the top bevel/camshaft to access the cam key to install an off set item.

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