Vento 350

[DewCatTea-Bob]

____ I've had some time to contemplate concerning the mystery of why the Vento-engine has such an oddly placed keyway-slot & timing-dot...
And while I've forgotten a minor detail (since I've slept & awakened), I should-not delay any longer a detail which could be of certain importance. ...
__ Muz seems to believe that his ex.valve was being (rather lightly) struck by the piston (and came-up with his-own theory as to why that occurred only with the Scr.cam), and it has really seemed that the LIKELY actual reason for that negative contact is due to retarded valve-timing (caused by the unique Vento crankshaft bevel-gear timing-mark location).
__ Well after working-out that the Scr.cam (when retarded the expected 17-degrees) has the ex.valve closing at 49-degrees ATDC (instead of the expected 32-degrees), it ought obviously occur (to one's thought-process) that that rather tame amount of retardation should-not be sufficient to leave the ex.valve out in the way of the piston. _ (As even a relatively mildly-wild Gray-cam leaves the ex.valve open that far after TDC !)
So this concern now brings-back a question I had asked early-on in this thread... Which was since the specific timing-dot location on the crankshaft bevel-gear was changed for/on the Vento-engine,, then llikewise, was the timing-dot location on the camshaft bevel-gear ALSO changed (away-from that of a regular/std.cam-gear) ??
I'm thinking that if the valve-timing was really retarded far enough to cause such collision-contact, then either perhaps the Vento-cam.gear also has it's timing-dot relocated, or the so-called "450 cam" is possibly not the expected 1968 w-c.Scr cam.model, (or even perhaps, either Muz was mistaken [about the actual cause of the noise which he had assumed was due-to piston/valve contact], or had possibly refit the upper bevel-gears out of correct time-alignment).
__ So anyhow in any case, I now think it's fairly important to check the timing-dot location on Muz's Vento camshaft-gear next time he has it off & out.


Hopeful-Cheers,
-Bob
PS. Hoping that nobody (who's really interested in this thread) has overlooked the past two (fastly overflowed) thread-pages.

[Jon Pegler]

I agree with Bob that Muz should remove his timing cover and move the lower timing gear one tooth to bring the upper timing gears into the normal position for a widecase single.
This would probably make checking the valve events with the other cam and a degree disc conform to the usual settings.

However, Bob raises an interesting point regarding the bevels used in the Spanish widecase machines.
The upper bevel gears of an Italian or a Spanish 350 widecase single are the same. Part no. 0608 29 600
The lower bevels sometimes have the different timing dot(s) as in Elderts photo.
The Mototrans parts books have the same parts number ( 0600 29 700 ) for the lower bevels on the Mototrans machines as the Italian widecase engines. Strange, since they obviously have different timing marks.
Perhaps it didn't matter too much as the Italians had ceased production of single by then.

Jon

[Harvey]

I don’t know if this ties in with this timing difference, but there was a cam that I got for a 450 desmo, Blue/Black that had the cam keyway cut 18* out. You had to advance it one tooth at the cam, to get the right timing. This was followed by a 12mm one that V2 did for me that also had the same fault, plus some inlet lobe phasing faults. We eventually sorted out the later one before it was sold, but there were a number of the earlier Blue/Black that were sold around the world with this keyway fault.

[Muzz350]

Thanks for the information and advice.
I was intending to reinstall the Scrambler cam and checking the valve timing and the timing marks top and bottom (and anything else I can check or confirm) and I will then adjust the timing marks, recheck everthing and see what happens. It's all valuable knowledge I will use again.
Muz

[DewCatTea-Bob]

By: Harvey...
" there was a cam that I got for a 450 desmo, Blue/Black "

____ I've heard-of a Blue&Black-camshaft for the 450 before but, I've never heard of a Blue&Black DESMO-cam,, are you sure that DESMO-cam wasn't actually 'Blue&White' ?


" that had the cam keyway cut 18* out. "

____ That would equal 36-degrees for/at the crankshaft.


" You had to advance it one tooth at the cam, to get the right timing. "

____ That's near 13-degrees of cam-gear advancement, which would then mean that that camshaft WAS retarded near 26-degrees from the crankshaft's TDC.position. ...
__ So 36 minus 26 yields a 10-degree discrepancy,, which if really actual, would indicate that an offset-key may've ALSO been involved (in order "to get the right timing") ? _ UNLESS perhaps you forgot to include that the lower bevel-gears were ALSO adjusted & reset as well. ...
Cuz by adjusting the upper AND lower bevel-gears a tooth or two, ya can then obtain advancement or retardation steps (between the cam & crank shafts), in 8.6-degree increments, (without including any use of offset-keys) !



" This was followed by a 12mm one that V2 did for me that also had the same fault,
there were a number of the earlier Blue/Black that were sold around the world with this keyway fault. "

____ Well it would be quite informative to learn the story for why such a strange common (error?) occurrence was allowed to propregate-onward.


____ Thanks for your input ! _ As this revelation may possibly explain why Muz's ex.valve was still able to be caught by the piston when it WAS figured that the ex.valve was only retarded MERELY-just 17-degrees. _ (As NOW we can suspect that his Vento-cam may actually have it's k.slot located for yielding as much as ANOTHER 17-degrees of equivalent advanced crankshaft-rotation, [which could possibly mean that he may've actually had the Scr.cam installed (just-over) 34-degrees retarded].)


Dukaddy-Dukes,
-Bob

[DewCatTea-Bob]

By: Muzz350...
" I was intending to reinstall the Scrambler cam and checking the valve timing and the timing marks top and bottom (and anything else I can check or confirm) and I will then adjust the timing marks, recheck everthing and see what happens. "

____ Firstly,, I hope you will keep us rather more detailedly updated (closer to real-time), so that you can then be better directed to not miss any steps to be checked-out, before jumping-ahead & past.
____ I-myself had offered four different possibilities to cover the claim concerning possible ex.valve & piston contact, and Jon has indicated that the one about the Vento cam-gear timing-mark is not valid, while Harvey has offered another/new possibility -(that the keyway-slot in the Vento-cam may be "18" degrees off from the regular camshaft-TDC position [rather than the mere 8.6-degrees which I had figured]). _ This new possibility (if true), would then likewise require that the crankshaft also be set advanced still ANOTHER tooth at the crankshaft bevel-gear (which is about 17 ADDITIONAL degrees),, but this would then mean that your crankshaft bevel-gear would be unlike any of those shown in Eldert's picture, as IT's timing-dot would have to be altered by TWO teeth (rather than just the one tooth) !
If this is the actual case, then when you installed the Scr.cam (with all timing-dots aligned as would be expected done), the resulted valve-timing would then have the ex.valve closing at 66-degrees after TDC,, which STILL is not retarded enough to leave the ex.valve out in the piston's way far enough for any contact to occur !
So some further (more in depth) investigation needs to be checked in order to determine exactly what's-what with your suspected issue, (if still possible, cuz I now rather suspect that when you installed the Scr.cam, you also somehow got the upper tower-shaft out-of-time with the lower tower-shaft.)
__ Since it now seems that there's no getting-around setting-up a degree-wheel to check on a number of things,, then before removal of your Vento-cam, be sure to (once again) check the degree-point when the ex.valve becomes in-contact with it's seat.
Then after*that, without changing anything-else,, do so again with the Scr.cam installed, to check the ex.valve's closure-timing THEN.
(* But priorly-first... I gather that the reason you didn't provide the requested picture of the Scr.cam & Vento-cam side-by-side with their keyway-slots faced upward, is because you had [rather hastily] reinstalled your Vento-cam. _ But before installing the Scr.cam, I hope you'll then be able to post such a pic, so that the respective locations of their k.slots can then be compared.
Also before the camshaft installation, it would be good to see a picture of your Vento's cam gear [so that it can be confirmed that it's timing-dot is indeed directly-aligned with it's keyway-slot].)
__ If you choose to remove the cyl.head, and you still think that the Scr.cam is allowing the valve & piston contact as before,, then this time try setting a wad of soft clay on the piston's ex.valve pocket, to learn whether there's really no clearance for sure or not.


Hopeful-Cheers,
-Bob

[Harvey]

By: Harvey...
" there was a cam that I got for a 450 desmo, Blue/Black "

____ I've heard-of a Blue&Black-camshaft for the 450 before but, I've never heard of a Blue&Black DESMO-cam,, are you sure that DESMO-cam wasn't actually 'Blue&White' ?

" that had the cam keyway cut 18* out. "

____ That would equal 36-degrees for/at the crankshaft.

" You had to advance it one tooth at the cam, to get the right timing. "

____ That's near 13-degrees of cam-gear advancement, which would then mean that that camshaft WAS retarded near 26-degrees from the crankshaft's TDC.position. ...
__ So 36 minus 26 yields a 10-degree discrepancy,, which if really actual, would indicate that an offset-key may've ALSO been involved (in order "to get the right timing") ? _ UNLESS perhaps you forgot to include that the lower bevel-gears were ALSO adjusted & reset as well. ...
Cuz by adjusting the upper AND lower bevel-gears a tooth or two, ya can then obtain advancement or retardation steps (between the cam & crank shafts), in 8.6-degree increments, (without including any use of offset-keys) !

" This was followed by a 12mm one that V2 did for me that also had the same fault,
there were a number of the earlier Blue/Black that were sold around the world with this keyway fault. "

____ Well it would be quite informative to learn the story for why such a strange common (error?) occurrence was allowed to propregate-onward.


____ Thanks for your input ! _ As this revelation may possibly explain why Muz's ex.valve was still able to be caught by the piston when it WAS figured that the ex.valve was only retarded MERELY-just 17-degrees. _ (As NOW we can suspect that his Vento-cam may actually have it's k.slot located for yielding as much as ANOTHER 17-degrees of equivalent advanced crankshaft-rotation, [which could possibly mean that he may've actually had the Scr.cam installed (just-over) 34-degrees retarded].)


Dukaddy-Dukes,
-Bob

Well Bob it was 20 years ago , but the memory of that development is fairly clear, and I am going off the original correspondence that I had with Brook Henry at the time. It was always referred to as a Blue/Black cam, and I said 18*, one tooth out then, and have no reason to suspect that it was not.

This was over the space of three cams, the first was from Phil Hitchcock, that I suspect was a copy of an original cam. This cam was fitted to the timing marks and run. It was realised from the blowback that it was retarded. It was checked and found the 18* discrepancy. Retimed one tooth to run ok.

The second cam that Brook did for me had the same 18* problem,(that was probably still programed into the grinder), but also a phasing difference, in the inlet opening and closing lobes. So that the clearance changed from zero to 0.045" and back to zero through its travel. We corresponded and I sent all the valve gear to him, and we finally got the final V2 cam that was perfect.

What I was looking at mainly Bob, is that I have a good recollection that the first cam was a Spanish cam, that was copied. Phil may have a better recollection of where that cam was from, but reading of the Vento problem, it seemed to match up.

[graeme]

", but also a phasing difference, in the inlet opening and closing lobes. So that the clearance changed from zero to 0.045" and back to zero through its travel"

I have found this on "some" Desmo cams but not all. And some worse than others, which I assumed was poor machining.
I've relieved, lapped, the closing lobes to achieve a constant clearance through the rotation.

Are you saying that the Spanish made Desmo cams and engines?
I wasn't aware they made Desmo engines?

Graeme

[DewCatTea-Bob]

____ Graeme, you have gone-ahead & done something which I-myself (somewhat reluctantly) refrained myself from doing further. _ And that is, to get more involved with any stuff that Harvey had brought-up concerning DESMO-cams.
__ I held myself back because I figured that this (rather nonDESMO) thread may quite possibly get taken-over with pages of 'DESMO' related issues, and that would not be very-good for two sensible reasons...
1st, THIS-thread has already become so excessively-extended that it's no-longer possible to jump DIRECTLY to most of it's pages, & 2nd, any particularly interesting stuff about DESMO-cams shouldn't be allowed to become left berried so deeply within another thread which had been originally established with no obvious direct relationship to DESMO-engines. - (Please let me know if anyone doesn't agree with my [good?] reasoning.)
__ So therefore, I'm next going to start another appropriately titled thread so as to divert any further discussions concerning DESMO-camshafts (& possible other related desmo-stuff), away-from this thread & to the intended new-thread.
So please look for that new-thread and redirect any further-content concerning DESMO-engines forward to THAT new-thread. - Here follows a handy link... viewtopic.php?f=3&t=1364


Forward-Cheers,
-Bob

[graeme]

Bob, I agree on both counts.
Apologies Muz.
Graeme