Vento 350

[Muzz350]

"However I'd be sure to keep a flow-reducer in the right-side tip-end of the camshaft"
Yep, did that.
"if your weight is under 200-pounds"
only 154 lbs Bob
I discovered a problem when I installed the scrambler cam. Although when I did the figures on both cams the maximum lift for the scrambler cam occurs further from TDC than the Ventos, in reality as the cam on the vento is not symmetrical its actual max lift is further from TDC and the cam profile allows the valve to close partially as the piston gets closer to TDC but still allowing it to stay partially open for a long time ATDC.(The piston has large cut aways in the top to accept the valve) So although the figures imply there would be no problem fitting the scrambler cam the reality is the exhaust valve will touch the piston.
Muz

[DewCatTea-Bob]

" only 154 lbs "

____ That's fine, (same weight as myself [back in the day]).
I sort-of feel sorry for those of us who weigh over 100-kg,, as for them, nothing smaller than a 450 would be very fun to ride, (although if not in any rush to get somewhere, can still be fairly enjoyable).



" I discovered a problem when I installed the scrambler cam. "

____ There should be no real "problem" -(meaning that there's no actual PROBLEM)...
I guess I should've mentioned that you should have kept your job-progress more detail-updated as you progressed-along with your camshaft swap/installation job, (as it seems you've forgotten or overlooked a certain*detail which was brought-up earlier in this thread).
(* The relevant-point of which will be [rather indirectly] brought-up after I've finished with directly responding to your post-wording.)



" Although when I did the figures on both cams the maximum lift for the scrambler cam occurs further from TDC than the Ventos, in reality as the cam on the vento is not symmetrical its actual max lift is further from TDC and the cam profile allows the valve to close partially as the piston gets closer to TDC but still allowing it to stay partially open for a long time ATDC. "

____ Exactly what you are actually meaning to make a point of within that rather long extended sentence, is not coming-across very clearly,, as for one point, it seems you have stated that the max.lift-point of either cam.model is "further from TDC", which understandably leaves me somewhat confused as to your intended main-point.
__ That your Vento-cam is not symmetrical (as the Scrambler-cam is), is naturally due to the effort of such wild cams requiring that the valves be held open further (as well as longer) during the overlap-period,, and-so that effort actually makes it more difficult to make sure that the valve-heads don't over-occupy the allowed space provided within the piston's valve cut-away/pockets.
So therefore, the much milder valve-overlap effort done by the Scr.cam means that clearance between the valve-heads & the piston's pocket-floors, is much increased and less of a concern !



" (The piston has large cut aways in the top to accept the valve) "

____ Of-course, as those v.head-pockets have to be deep enough to allow clearance for both valves to be held open during the camshaft's intended valve overlap-period near that TDC.



" So although the figures imply there would be no problem fitting the scrambler cam "

____ By "the figures", I assume you mean the 'max.lift-figures', correct ?
Regardless of whether either the 'lift' figures or the valve-timing figures, those of the Scr.cam could only make any functional-compatibility issue LESS concerning (than that of the Vento-cam) !



" the reality is the exhaust valve will touch the piston. "

____ How exactly did you come-to such a conclusion, actually ?
__ If you have made the mistake of DISCOVERING that the ex.valve's head actually comes in contact with the piston's v.relief-pocket floor, then that's clearly a concrete sign that the Scr.camshaft has been installed out-of-time with the crankshaft !
____ And now that finally brings us back to the important detail which it seems you must've failed to take into consideration, (as it seems you've instead tried to place the blame for your issue, on the point of exactly where max.lift happens to occur)...

____ Earlier in this thread -( viewtopic.php?f=3&t=1302&start=30#p8839 ), it was noted that a Vento-cam (rather uniquely) did-not have it's keyway-slot located at the standard-location of most other cam.models, and thusly caused that slot to not be normally/properly aligned with overlap-TDC, (or so it seemed). _ And to counter-effect that strange relationship, the Vento-model's crankshaft bevel-gear made use of a somewhat uniquely altered timing-mark location.
__ So what now needs to be sorted-out, is the exact differences in keyway-slot locations between the two cam.models, and reset the camshaft-to-crankshaft bevel-gear timing, accordingly.
So could you please post a picture of both camshafts side-by-side, showing their respective keyway-slots, (so as to help determine their specific relationship) ? _ As it would be quite nice to actually SEE & compare such a location-difference confirmed, in any case.
And then we'll continue-on forth-ward from there.
__ So-far, all this may somewhat seem like it's going to possibly become some kind of a deal-breaker (of sorts), however I'm fairly confident that all will be simply ironed-out fairly easily !


Hopeful-Cheers,
-Bob

[graeme]

May I suggest measuring the Scr cam's timing with a degree wheel and dial gauge to be sure it is operating the valves as intended, for a Scr cam, ?
Perhaps the Spanish could have slightly different timing alignment marks?
I agree with Bob that a Scr cam should cause no valve clearance problems, compared to a higher performance cam.

Graeme

[DewCatTea-Bob]

" May I suggest measuring the Scr cam's timing with a degree wheel and dial gauge to be sure it is operating the valves as intended, for a Scr cam, ? "

____ That's of-course a reasonable check-job to consider but, first we should be assured of the particularly employed bevel-gear timing, (as that's quite likely all that's probably at fault).


" Perhaps the Spanish could have slightly different timing alignment marks? "

____ Why would you say "Perhaps" ? _ Have you TOO also forgotten already as well ?
As such fact has already been touched-on back on page-4, and you (of all readers) had to have been aware of it, since you-yourself also placed a post that same day (back on Dec.28th). viewtopic.php?f=3&t=1302&start=30#p8840
__ Well at least I-myself haven't forgotten that noteworthy revealed fact, (so I can help keep the forgetful amongst us, reminded).


Hopeful-Cheers,
-Bob

PS. I've finally finished (for now) my previous extended-post.

[Muzz350]

Hi Bob and Graeme
I can see you were able to decipher my previous post but for anyone who couldn’t I’ll elaborate.
Before installing the scrambler cam I first did a quick check of both cams to see where max lift occurred.
To calculate this point I did calculations for inlet & exhaust for both cams .
Example : 450 Scrambler Cam (Exhaust )
Duration : 60°+ 180°+ 32° = 272°
Max Lift (ML) occurs at: 272°÷ 2 = 136° (or lobe centre)
To find where ML occurs before TDC : 136° - 32° = 104°
• This figure assumes the Valve reaches ML exactly ½ way between the time it opens and the time it closes. ie: the cam profile is symmetrical. (The Reality is that the Vento isn’t)
The 2nd check was after installing the cam I turned the motor slowly by hand with no spark plug and watch the valves open and close as the piston came into view. It looked close but no sound of the valve hitting the piston.
The 3rd check was to start the engine but with a larger valve clearance & listen at low revs.I could hear something but it was hard to tell if it was just the noisy extra clearance.
The 4th check was to reduced the valve clearances to normal and try again. There was now a distinct clicking sound.
Conclusion: The exhaust valve was hitting the piston.
5th Check. Remove the cam and physically measure the point of ML using Vernier callipers ( not real accurate but good enough for the exercise)and mark each point with a white dot. Then place each cam side by side, aligning the keyway groove in each cam and check the difference. (photo with markers inserted in each groove to show vertical alignment in previous post.) There is a difference.
(I will note at this time the keyway groove in the bevel gear attached to the cam with piston at TDC is at 12 oclock and the only dot below is at six oclock & lines up with the dot on the bevel shaft gear )
Using the photo as a reference you can see that I can adjust the scrambler valve timing to match closely the Vento cam ML position by rotating it a few degrees anticlockwise but that may alter the valve timing from its original inlet 27, 75, ex 60, 32 and make it run better or worse? I have always had the option of playing around with the position of the Vento’s cam to alter the valve timing to see (by trial and error) if it would improve the performance in traffic but I believed swapping cams would eliminate the need for this. Now I have two cams that need to be adjusted instead of one?
Back to the drawing board or Degree wheel.
What a learning curve.
Muz

[DewCatTea-Bob]

____ Muz, I can tell by your post (& the pic you produced showing the cam profiles done with considerable intelligent-thought), that you must be independently capable of fairly-good deductive reasoning,, yet it seems you've still not addressed my offered concern/deduction which must be what's actually responsible for the mistiming of the installed Scr.cam.
__ Do you understand the reason for why I've requested that you post an overhead pic.shot of your two camshafts with their keyway-slots facing upward ?



" Conclusion: The exhaust valve was hitting the piston. "

____ Rather respectively, it was actually the piston that was hitting the ex.valve ! ... As the valve was not opening at that time, but rather was in the process of closing (when the advanced crankshaft forced the piston to come-up early and catch the valve before it had time to close as far as it should before the piston [normally] reaches TDC).
Since it's been revealed that (at least some) Vento-models employ a crankshaft bevel-gear with an oddly placed timing-dot, (which causes the crankshaft to be slightly over 17-degrees advanced relative to the normal tower-shaft location), it therefore stands-to-reason that the keyway-slot on the Vento-camshaft is also oddly located so as to have it's cam-lobes advanced (relative to the tower-shaft) as well.



" Then place each cam side by side, aligning the keyway groove in each cam and check the difference. (photo with markers inserted in each groove to show vertical alignment in previous post.) "

____ It would've been fairly helpful if you had made note of that detailed-detail below your posted-pic ! _ Also it would've helped to notice that fact if you had included w.keys inserted in their key-slots, so that we'd then obviously realize that significant detail (of having placed both camshafts so that their respective key-slots are both faced directly downward). ...
Now not only can the obvious difference in cam-lobe profiles be noticed, but we can also realize that the particular location of the cam-lobes on your Vento-camshaft must be relatively slightly advanced (as seen next to the regular/standard Scr.cam),, which is a significant point.
STILL however, it would be nice to directly see the relative positions of the keyway-slots of both camshafts shown in a picture with the shafts side-by-side (as better described in my previous-post), so that we can then confirm that YOUR Lento-cam is actually predisposed to be advanced.



" There is a difference. "

____ So seems to be the case... In that it's (likely) meant to be 'advanced' with respect to the tower-shaft,, while the std.Scrambler-cam is meant to be set in a regular/standard relationship with the tower-shaft !



" the keyway groove in the bevel gear attached to the cam with piston at TDC is at 12 oclock and the only dot below is at six oclock & lines up with the dot on the bevel shaft gear ) "

____ Of-course that's as normal (with either camshaft). _ But it should be realized that (apparently) the slot-location on the Vento-camshaft must cause it to be advanced, (just as the Vento bevel-gear on the crankshaft causes the crankshaft to also be advanced). _ So when installing a regular/standard camshaft (which is not held in an advanced position), THEN the Vento crankshaft also has to be set UN-advanced, as well !


" Using the photo as a reference you can see that I can adjust the scrambler valve timing to match closely the Vento cam ML position by rotating it a few degrees anticlockwise "

____ It's not actually the max.lift point which necessarily needs to match, but rather more specifically, it's the overlap-center point that's of utmost concern to have properly timed to the crankshaft !
Exactly how were you thinking of accomplishing that adjustment,, by simply mis-aligning the camshaft-gear by one tooth, or what ?



" but that may alter the valve timing from its original inlet 27, 75, ex 60, 32 and make it run better or worse? "

____ It's fairly strange that you'd realize such as that, yet have seemingly failed to realize that which I've been trying to make clearly-understood about the Vento bevel-gear on the crankshaft being preset to position the crankshaft in an advanced reference to the tower-shaft (so as to directly compensate for the advanced Vento-cam).
__ As you've had it, your crankshaft has been left set 17-degrees too advanced relative to the tower-shaft & Scr.cam,, so if you simply reset the cam-gear one-tooth advanced forth-ward away-from the normal bevel-gear timing-dot alignment, then that would advance the Scr.cam by nearly 26-degrees, which would thusly put the camshaft in an advanced relationship to the tower-shaft, just as the crankshaft already is. _ So-thus the crankshaft & camshaft would then be set closer together timing-wise, and the ex.valve would thus-then be much further-closed & well out of the way of the piston as it reaches TDC.
However the resulted Scr.cam valve-timing would then be 8.6-degrees advanced away-from it's intended factory-specs, (thus providing an altered valve-timing of: 36BT-66AB & 69BB-23AT) which may-not be very good for a 250 but should provide a 350 (with a restrictive muffler) with increased low-end torque/power (which would be quite good for hill-climbing or carrying a passenger in stop&go-traffic, [but would actually lower the engine's overall power-output, since the top-RPM power would suffer relatively more loss than the low-end gains] ).



" I have always had the option of playing around with the position of the Vento’s cam to alter the valve timing "

____ Not really, as that cam-model is really TOO wild to play with it's set valve-timing, although there may be the possibility of advancing it (by just 8.6-degrees) so as to POSSBLY obtain slightly improved low-end torque/power.
But that fairly questionable change would then of-course also require resetting the bevel-gear down-inside at the bottom-end as well.



" to see (by trial and error) if it would improve the performance in traffic "

____ While resetting the Vento-cam could possibly provide a very slight improvement (by advancing only), it wouldn't be by an amount that I think you'd notice.



" but I believed swapping cams would eliminate the need for this. "

____ That's a fair certainty, and a much better option !



" Now I have two cams that need to be adjusted instead of one? "

____ Assuming that you've set all the timing-mark/dots in perfect alignment, then it's not the Scr.cam that needs to be adjusted, but rather the CRANKshaft ! _ Unless of-course you don't really wish to also get down-into dealing with the lower-bevel/timing-gears at the bottom-end, AND are willing to try-out the Scr.cam with it set 8.6-degrees advanced (so as to experience the EXTRA low-end torque that the [already rather torque-ish] Scr.cam would then [additionally] provide).



" Back to the drawing board or Degree wheel. "

____ I believe it's certain that the drawing-board has already been laid-out for you, it's just a matter of you comprehending most-all of what I've written-out for you.
__ If there's ANY sentence I've posted which you'd like to have clarified, then PLEASE ask,, and I'll then try to reword it in another way so that it's intended point may be better understood.



" What a learning curve. "

____ It's actually all really quite simple,, and you'll realize so, once you've fully grasped exactly what-all you're involved with (with this camshaft/tower-shaft/crankshaft-timing issue).


Hopeful-Cheers,
DCT-Bob

[graeme]

Are offset keys available for singles? (3mm)
I know they are for the Pantah family of engines. (4mm)
If so you could get the cam timing closer by moving one tooth and using offset keys.

Graeme

[DewCatTea-Bob]

" Are offset keys available for singles? (3mm) "

____ I've never gotten my hands on any but I've seen them pictured in a cycle-mag, and I believe they offered a 1mm-offset.


" If so you could get the cam timing closer by moving one tooth and using offset keys. "

____ Of-course that's true and-so could possibly avoid the trouble of getting involved with the resetting of the crankshaft bevel-gear.
However their offset-effect is also fairly limited at exactly solving valve-timing issues, as I think the 1mm-offset only provides about a 7 or 8 degree change (which results with about a 15-degree alteration, at the crankshaft).
So-then offsets of less than 1mm would be of more use.



____ I've been thinking of the (rather simpler) option of leaving the crankshaft bevel-gear left in it's position required for the (rather oddly positioned) Vento-cam, and I think it would possibly be worthwhile to go-ahead & try-out the engine with the Scr.cam advanced 8.6-degrees (from it's normal/intended v.timing),, as that may provide Muz with even more of a radical change from mere high-end power to (more relatively vastly) improved low-end torque. _ And such an extra-radical change in valve-timing would be most beneficial with a muffler which doesn't let the exhaust-gas pass straight-through.
__ Then if Muz finds that he doesn't care-for the trade-off of losing so much high-end power,, he could THEN bother with going-ahead & getting-down/into dealing with the crankshaft bevel-gear, to reset the valve-timing to that which is actually intended by the w-c.Scr-cam.

____ For further improved comprehension, I offer the following way of keeping all this camshaft-to-crankshaft timing in proper prospective...
__ Normally it's logically natural to consider that the CRANKSHAFT is the 'master' of reference for all engine timing concerns, and if ya happen to be somebody who has no trouble at all with reference to that logical-state, then that's fine (as that's how it ought to be).
However for others with trouble keeping everything in clear logical-order (in regards to cam-timing though the tower-shaft to the crankshaft),, it can actually be better for keeping those shafts in proper prospective by considering the tower-shaft as the 'master' point of reference.
__ So then in the (odd) case of the Vento-engine, we know that it's crankshaft has been advanced (by one tooth, due to it's oddly-marked bevel-gear) in relation to the tower-shaft.
And-so in like-kind, the Vento-camshaft has also been (compensatingly) advanced in relation to the tower-shaft.
So if a camshaft with a regular/standard placed keyway-slot is substituted, then THAT camshaft is then going to be time-set normally along-with the tower-shaft,, BUT yet the crankshaft is still left advanced away-from the tower-shaft (& camshaft) ! _ (So that then also has to be dealt with.)
__ So with this tower-shaft as the master-point of reference thinking, it's then easier to keep what's-what all in clearer prospective. _ And if THIS prospective indeed helps ya -(whoever) keep what's going-on all straightened-out, then it may now be easier to comprehend & retain all that which I've already posted.
____ I realize that what has added to the likely confusion, is that ya'd normally expect that there must be some logical-reason behind the peculiar (effectively retarded) Vento tower-shaft setup, and-so ya thus naturally expect that there's some related fact that's left to be realized within all ya'r contemplation... But that's just subdiffuse -(misleading confusion), as there's actually no other good reason for the mysterious oddness.
__ So-thus I'm left to conclude that the mere reason behind this Vento-oddness is due to the keyway-slot in the Vento-camshaft having been accidentally mis-located. _ Although I suppose that there could've been some-other reason for it,, but in any case, it's not relevantly important to get sorted-out.


Hopeful-Cheers,
-Bob

[graeme]

The 3 and 4mm I was referring to is the width of the key way. I have used them in belt engines and they are sold in degrees of offset.
Graeme

[DewCatTea-Bob]

" The 3 and 4mm I was referring to is the width of the key way."

____ Yes, of-course ! _ I don't know why you felt the need to make that point, (so I'll guess)...
When I stated "1mm-offset", that was naturally meant to allow assuming that the 3mm-wide key would thus-then be only 2mm-thick just at it's offset-point.
____ A 3mm-thick key that's 'offset' only .5mm, would be of more-useful use in Muz's presented case.


Dukaddy-Dukes,
-Bob