Resurfacing rocker arms/ reconditioning cylinder heads and components

[graeme]

I have a Mk111 Comando that had the cylinder leaning forward and the head leaning to the right. Don't ever complain about Ducati manufacturing until you've restored an English bike.
(and I did put a Mikuni on it)

Graeme

[double diamond]

Aaron,
The 33/37 valves are Monza size. The SCR valves are made of better material. Most Monza/Sebring stock valves I’ve seen are usually pretty worn on the stems but the SCR valves hold up pretty well. You can regrind the valves if the stems are still OK and there’s enough material left after grinding to leave a margin at the perimeter of the valve head. If the valve perimeter comes to a sharp point after grinding, the valve should not be used. There was an article in Cycle World about race tuning a 250 Ducati in which they used a stock 36mm intake valve for the exhaust, claiming that the material used for intake and exhaust valves was the same. I would not use a Monza/Sebring intake for an exhaust valve. CW used it at 36mm diameter, not cut down to a smaller size. A new Ducati valve seat is machined so the valve seat contact area stands proud of the seat. If this raised valve contact ring is gone or a concentric seat can’t be ground to what remains of it, it’s time for a new seat. With most old Ducati heads, the valve contact ring has been flattened out or ground away on previous valve seat resurfacing. I’ve seen heads with seats that are simply rectangular in cross section which allows the relief cuts, but these seats don’t blend into the contour of the combustion chamber as well. Also, if the valve seat has been ground beyond the design limits, you won’t be able to adjust the valves to the proper clearance. Time for a new valve seat. Because of the Ducati design, if the seat is cut to this point you’ll end up sinking the valve into the seat and shrouding the valve to the point where it affects airflow. The seats on the head in your pics actually look pretty good so you might be able to leave those seat in if you use stock valve sizes. The intake port of that head has been worked on, so if it is a Monza head, it’s been ported or it’s a SCR or Diana head, both of which used 36mm intake valve.
Matt

[amartina75]

Thanks for your replies. I'll have to measure the valves again that came out of the head pictured but they are definitely longer then the stock scrambler valves that came out of my other head. They measured around 85.5mm. Maybe someone ground 2mm off the ends to make them fit the head. It did have a grey cam and 29mm intake port. I was hoping to reuse some parts like maybe the valves and one of my cams if possible.

The head in the pictures has the damaged squish band which is my main concern on that. I can set it up on a mill at work and recut it but I'm not sure what to shoot for as far as the geometry. I know it should be a 45deg angle and about 74mm where it meets the cylinder, That's not going to be possible. Will be closer to 76mm.

I'd really like to save the one grey cam I have. It is worn but not badly like my other one. I measured about 7 thou difference between lift from the edge to the center of the lobe. Can I polish out the wear and use it?

I found a picture of what the piston looks like for the Misano heads, totally different so no way to copy that double angle squish.

Thanks
Aaron

[double diamond]

I was thinking the SCR valves might be shorter than Monza valves since the SCR has lash caps and the Monza has screw adjusters. The SCR valve would have to be shorter to accommodate the lash cap. But this would also be affected by the geometry of the rocker arm and the profile of the cam, so I don’t know that this possible reason for the difference in valve length is true.
It would be extremely difficult to remove .007” off the cam profile by stoning/polishing, keep it square with the rocker pad and maintain a smooth opening ramp/peak/closing ramp. I have several cams in the same condition and have considered the possibilities but no solution yet.
Matt

[Eldert]

the camshafts for screw type adjust rockerarms have a bigger base circle .

lashcap type camshafts have a smaller base circle

Eldert

[bikester250]

Eldert,
Regarding the different base circles for cams with different rocker arms do you have the actual dimensions?
My Mach 1S has the screw adjuster type rockers even though a Mach 1 should have solid rockers and caps according to the parts books and everything I've read. I don't know if this is because my Mach 1S is an early production bike or if someone put these rockers in later.
Since I also don't know what cam is in the bike, I'd be interested in knowing if the cams I have are correct with respect to the base circle.
Regards,
Phil

[Eldert]

Hi Phil

i just measured a few camshafts base circles

screw type rockerarm 21 / 22.6 mm lash cap rockerarms 24 / 25 mm

Eldert

[double diamond]

Phil,
I just remembered I have some cam data recorded. Some measurements I made myself, others come from sources I’ve found on the web. The base circle measurements I have recorded show NC GT,Monza, Scrambler, Diana, Diana MkIII and Sebring base circles ~24.3-25. The Mark 3 and Mach 1 grey cam, curiously, is ~23. WC cams are all ~20-22. It appears that the NC/WC distinction must be recognized when making generalizations about base circles.
Matt

[amartina75]

I just measured the valves and cams that I have out of two different heads.
my 66 scrambler: valves measured 33/36 by 83.7 long. cam Base Circle 24.5 Ex lift 7.9, In. lift 8.0

My unknown head, which I think is also NC Scrambler: valves measured 32.75 by 84.72 and 37.0 by 85.3
looking at the ends of the valves it looks like a little material was removed, but no way 2mm was removed
the cam measured 24.5 BC lift 8/8.17

I don't have my GT head with me now sow I cant measure those parts.

I emailed a guy in town here that races Ducati singles I told him I'm looking for a cam. I think he has a white cam for me that is nice so I might have that figured out for one bike at least.

[amartina75]

Are all non Desmo solid rocker arms the same on singles? Same part number? I don't have a NC parts book just a WC
The one online only shows the adjustable ones.
Thanks