Ducati 600 MONSTER

A crashed bike bought cheap for my partner to try getting back onto bikes ( as if anyone’s going to believe that! ), it also provided me with a 600 to play with. I hadn’t got my hands on one so far, so this was as good an opportunity as any. I was going to surprise her on her birthday, but just couldn’t wait that long to start riding it myself. So she got it early. It’s good fun to ride too, particularly around town. Kind of nice having a bike that WON’T wheelie past the speed limit in 1st. Well, for a little while anyway.

One of the "early" pre 98 600’s, it has the forged pistons that make the horrible slappy noise when cold, not that it gets much better when it warms up. Sounds like the insides are trying to get out, but we’ve been saying "they’re all like that" for so long that I have to believe myself. I had the chance to pull one apart recently to test the theory, and yes, there was nothing wrong with it. Just very short pistons with quite a bit of ( but not excessive ) piston to bore clearance. We replaced the pistons on that one with the cast pistons from a later model ( which supercede from the early ones anyway ) to make the owner happy. Slappy no more. That’s going to drive me nuts now every time I start ours.

These engines have the small valves left over from the Pantah range, being 33.5mm inlet, 30mm exhaust. The new 620 Monster has the 750’s 41mm/35mm valves, which would seriously help in the power production area. Fitting them to a 600, however, isn’t really an easy option, as the fully machined chamber shape is tailored toward the small valves. Certainly do-able, just not that easy. The new 620 also runs new cams, with 15 degrees less inlet duration, less lobe separation and about 0.5mm more lift. Of course, you can’t fit them as Ducati has changed the cam/head design very slightly ( 2 bearings instead of 3 ), but the changes point a direction to travel.

So my plan of attack with this ones was the usual cam timing mods, then replacing the cams with the cams from the 900 SS carb model. These cams were the std 900 cam from 906 Paso up until the ie model of 99. When I first started this report, I thought that, compared to the std 600/750 cams, they have very similar duration and more lift. Turns out the specs listed in the manuals are not correct. I came across some new specs – see the 900SS with Vee Two cams report – which I have updated the table below with. This new info would have changed my theory on fitting the 900SS cams no doubt, but I’d already tried it. The 900SS cams have quite a bit more duration on the inlet, which would have contributed to the result.

The only issue I could foresee was lift @ TDC, causing piston to valve clearance problems. The table below shows the cam differences. C/L refers to the mathematical lobe centreline, calculated from the opening and closing figures. It is an easy figure to use for comparing lobe positioning and cam timing settings, but has no physical or measurable quantity.

900 CARB

The first step was to run some dyno tests in the std configuration. The results are shown below. I must say I was surprised by the 50 Hp. I was expecting 45ish, but the log of previous runs at the dyno showed 2 distinct groups, with about half the bikes showing 45, the other half showing 50. This was regardless of mufflers, etc. The graph below shows std in green and some Megacycle mufflers fitted in red. The lambda trace shows the mufflers lean the mixture in the midrange, but not enough to be a problem. The top end could maybe do with a bigger main jet, but I wouldn’t get too excited about any of it really. It’s a pretty good result. At 90 km/h, the extra 4 hp works out to be about 12%, something you really notice. Which means this is the first mod for a 600M.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Once I’d managed to get that done ( involving two trips, after dealing with a muffler bolt that wouldn’t come undone – nothing like planning ahead ) I checked out how much piston to valve clearance we had, then set the cam timing based on this. The results are shown below. All std is green, cams dialed with std mufflers is blue, std with MEGACYCLE mufflers is purple, cams dialed with MEGACYCLE mufflers in red.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Perhaps a bit too confusing. Below shows the results with std mufflers, before in green, after in red. As you can see, a small improvement at the bottom, a small loss at the top. The change in lambda is minimal.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

With the Megacycle mufflers fitted, the change is similar. The top end loss is a little greater, but the main difference is the lambda trace. An increase in main jet and lifting the needle one notch would improve the lambda curve no doubt, but whether it would make any real difference, either road or dyno, would remain to be seen.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

On the road, with either std or aftermarket mufflers, the most noticeable changes are in the lower half of the rev range, such as getting away from the lights and response. I was a little surprised about the response thing, as generally 600’s are about as responsive as a big paddle in a shit pit. The top end loss was really not noticeable to me in my normal riding (only when I revved it out to check the top end performance), and is probably due to a couple of things. The std cam timing on this bike was out by about 5 degrees, but in the direction I normally change, so this may have some effect on the std output. I usually check how far I can go, then try that. So maybe ( well, obviously ) I went too far.

The second thing is that the small ports and valves probably lead to very high port velocities. This would somewhat compensate for the late inlet valve closing that these cams have. The std timing on my bike was the same as I have set 750 models to in the past, but they have larger valves and, obviously, a bigger engine. I can’t say I would expect all the 600’s to have std cam settings like this, as the bits on the 750’s are the same, and they’ve all been different.

So, overall, I can say that the cam timing changes had a small, but noticeable effect. The top end loss I have noticed ( I think ), but only when holding it open far longer than normal, and it is only 2 or so hp at 8000 rpm. The only thing I can’t judge is the consistency of the std cam settings. Whether it’s worth the money I’m not really sure of yet. Maybe a quick job with offset keys is more appropriate for the 600. I guess having an owner try it out would be the best test, but I don’t like disappointing people.

The final graph is some torque curves. Not all the RPM traces worked over the full range, but you get the idea. Red is cams dialed with std mufflers, blue is cams dialed with Megacycle mufflers, green is Megacycle mufflers with std cam settings. You can see the big lump in the middle of the curve and the slightly better top end the mufflers give, but you can really feel that below 3,000 RPM loss too. Not sure where that comes from, but it’s consistent with all runs and on the road. It certainly initially gets off the line better with the std mufflers, but you lose out in the usable mid range area you ride a bike like this in. Depends how loud you like it.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

The next stage is to be some 900 cams, but the results of this first step have led me to not expect too much. The problem with the 600 engine seems to be air flow, and nothing short of more valve area is going to help. That or more capacity, but both steps are a little more involved than playing with cam timing. Lifting the valves more without making them any bigger I cannot see having a great effect. Maybe the age-old response to the question of how to hot up a 600 is pretty spot on, but I’ve already owned a 900 and that made me ride like a real dickhead.

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