Compression release

[Teckhardt]

Is the compression release on the 450 just as simple as a pin pushing down the exhaust valve? Is the cover with the release pin the only difference?

Could you put a compression release valve cover on any bike or vica versa - remove the compression release valve cover and put a plain one on?

Just curious how it works.

[DewCatTea-Bob]

" Is the compression release on the 450 just as simple as a pin pushing down the exhaust valve? Is the cover with the release pin the only difference?
Could you put a compression release valve cover on any bike or vica versa - remove the compression release valve cover and put a plain one on? "

____ Yes to all ! _ Its all about as simple as you have figured.
However, both valve-cover types will only exchange between just the 175, 200, 250, 350, & 450 models, (not "any bike")! _ Also, that type of comp.release will not function on a DESMO-head -(when it's exhaust closing-rocker is set to the factory-specified clearance, of zero).
____ Something that I highly recommend doing before installing one of those C.R.-covers onto a head, is to get-rid of the five stock 16mm-screws and replace with longer screws, after re-threading the three lowest screw-holes to their bottoms!
It's then possible to use 25mm long screws within those 3 lower positions, while the two upper locations (above the rocker-pins), can only accept 18m-screws.
Such modification will help to keep the compression-release from over-stressing the few threads which the short stock-screws are only able reach.


DUCATIly,
-Bob

[Teckhardt]

Good to know.

I saw these on Ebay and got to thinking about how it works.

http://cgi.ebay.com/ebaymotors/Ducati-4 ... ccessories

[DewCatTea-Bob]

" Is the compression release on the 450 just as simple as a pin pushing down the exhaust valve? "

____ I'd better point-out that the release-pin itself is a tad longer on the models which don't have screw-adjustable rocker-arms -(as the narrowcase Sebring has), and, that the pin actually opens the valve by pushing directly on the rocker-arm -(which then pushes the valve).

-Bob

[Thevin]

So, Bob what about the other type of release like on the side near the spark plug (like a R/T), is there any advantage or disadvantage between the two set up's.

[Eldert]

beware , there are 2 types of valve covers with compression release

there is the 350 Sebring N.C. type . this compression release is for screw adjuster type rockerarms

and there is the scrambler type for solid type rockerarms

they do differ !!!!

Eldert

[DewCatTea-Bob]

" So, Bob what about the other type of release like on the side near the spark plug (like a R/T), is there any advantage or disadvantage between the two set up's. "

____ Well Thevin, I figure that you're referring to the combustion-chamber c.release mechanism(that's located on the opposite side as the spark-plug), which the 450R/T & 350-Road models have.
I'd say the main advantage that such a c.release has is that it doesn't put any stress on the small & weak alloy-threads of the valve-cover's 5 screw-holes!
And I'd say that it's main disadvantage is that it adds another point where air-pressure can (eventually) find to leak-out through, (when it's seal gets sufficiently worn).
__ There's two models of that type of c.release...
The R/T's uses threads which are the same as for a 10mm spark-plug, (which is nice for converting to dual-ignition!). _ While the Mototrans version has courser threads and other parts which are not interchangeable with the Italian c.release-mechanism.
It's only my opinion that these type of c.release-mechanism cause a bit of a disconcerting blemish to the otherwise fine appearance of the unique styling-lines of Ducati's great looking OHC-single cylinder!

____ Concerning Eldert's point/warning about the Sebring having a different type of c.release than the wide-case models employ...
While the valve-cover itself is not to be blamed, the mechanism that screws into it is indeed slightly different, and enough so that some of the mechanism's parts are not interchangeable.
The main difference, (as I had stated previously), is the length of the pin which gets pressed against the rocker-arm. ...
__ I recall well a day in 1973 when I first discovered the difference, after realizing that there was something wrong as I tried to fit an exhaust valve-cover from a 350SCR onto a Monza-head... The cover just would not fit flush to the head!
The problem turned-out to be that the pin was too long, as it made contact with the rocker well before the cover could be properly mounted in place!
I had to fix that problem by disassembling the mechanism and grinding-down the pin's length until it was short enough to allow the cover to fit flatly in it's place against the head.
__ Now the only question is, would the shorter pin in a Sebring type c.release-mechanism still be sufficiently long enough to be able to press against a non screw-adjustable type rocker-arm!?
While ya would think that it must not be long enough, (since Ducati bothered to design the newer type mechanism), I suspect that the older/Sebring type c.release-mechanism would still do the job in that case as well,, because at the point when the release of pressure has occurred in a properly adjusted stock Sebring set-up, there's still a considerable amount of unneeded travel left in the cable-lever & hand-lever.
While I don't really recall ever trying a Sebring type c.release-mechanism on a head with the one-piece type rocker-arms, I do suspect that I probably had completed such a matching of parts, and I definitely do not recall there being any problem with that particular combination not working.
__ Since it seems that Eldert has some first-hand knowledge of these two valve-cover type c.release-mechanisms, then perhaps he can shed some more light on this last interchangeability question. (Since I myself do not currently have easy access to both set-ups.)

DUCATIly,
Bob

[Teckhardt]

However, both valve-cover types will only exchange between just the 175, 200, 250, 350, & 450 models, (not "any bike")!

Why do some valve covers have a "bump" on them and some do not?

[DewCatTea-Bob]

" Why do some valve covers have a "bump" on them and some do not? "

____ Starting for 1965, when the need for a compression-release for the 350 required the modification of the old-style fully finned covers,, Ducati apparently couldn't justify the continued production of both types of covers (the original & the newer modified version), and so from then onward, they only mass produced the modified version which could then be used for ALL covers regardless of the fact that only a relatively small number would require the extra machine-work needed for the compression-release mechanism.
__ Thus whenever you see a valve-cover with that added "bump" / boss in the center of the fins, you will know that the cover is from a 1965 or newer DUKE!


DUKE-Cheers,
DCT-Bob

[Wally Anderson]

I had a stroke last year and would like some help when starting my 250 bitsa cafe racer. I bought a c/r valve cover from Tom Bailey on Ebay but haven't been able to find any clear pictures on how to pull the c/r lever down to have the pin push on the exhaust rocker. I bought a c/r realease lever for the bar and a cable from Eurotrash. Does any of you have a picture of the cable set up at or hear the valve on your bike you could E-mail to me ?
Cheers,
Wally Anderson
ducmotorcycles@aol.com
State College, Pa.
65 250 bitsa
06 Sport Classic (for sale)