Bevel question

[DewCatTea-Bob]

[quote= lloydy1 ...
" I have placed an order for some more shims
which I will use under the OHC Bevel to withdraw it back up into the bearings. "

____ The same type of shims could RATHER be employed to (more easily !) withdraw the crankshaft bevel-gear away from the overly-tight meshing spot !
__ Of-course there are either of the two extreme-end* adjustment-ways able to relax & relieve any negative-clearance between the bevel-gears, (* other than backing-off BOTH the 'x' and 'y' axis-directions),, but whichever of those two ways should be chosen for the relief-task FIRSTLY, is the-ONE (& only way) which happens to be the one that's orientated to be movable in the required direction to better adjust the level of the related b.gear-teeth towards EVENly-level & flatly-mated* alignment with the corresponding tooth-level of the other bevel-gear, (* at the meshed point where the grind-mark patch-areas are located).
And if it happens to turn-out that THAT-way alone doesn't sufficiently relieve the negative-clearance fully (by the point when both tooth-levels are properly mated at the desired flush-level),, then at THAT point, ALSO relaxing the adjustment-setting of the OTHER bevel-gear, will be required as well, (so as to prevent the mated bevel-teeth from becoming conversely UNeven towards the opposite-direction [that they were previously miss-mated in when first beginning with the lash-adjustment job] ).
Or else-wise, if the wrong bevel-gear adjustment is solely chosen (for otherwise acceptable mesh-lash adjustment), then an even greater miss-mated/non-level step between the corresponding b.tooth-levels will then (more obviously) develop.
__ Whatever's the (likely limited) available-selection of shims for the job, it still may possibly not allow absolute perfection of precisely-level mating of the corresponding b.tooth-levels,, but with some trail & error (or fortunate luck), it should finally be able to get properly done fairly close enough.
For anyone to not bother with attempting to do-so as suggested & advised (and leave the corresponding grind-patch areas un-levelly miss-mated), would be hastily-done work for such fairly critical engine maintenance !


Hopeful-Cheers,
DCT-Bob
(This post re-edited, [for further improved wording-conception].)

[LaceyDucati]

Hello Dave,

As Bob describes it's necessary to obtain the correct alignment of the ground surfaces and the correct clearance between the gears. The only other things are as I mentioned before is to ensure that the shim stack below the circlip is snug so the gear shaft is pulled into the correct position and the bearing housing is correctly held down as otherwise you will get a false reading.

Also when the clearance is getting close to correct, 0.025mm can make a noticeable difference so 0.25mm is in bevel shimming a big move! Whatever, I received your order for shims and I will make sure get sufficient to ensure you can play for the rest of the week
Nigel

[lloydy1]

Hello Dave,

As Bob describes it's necessary to obtain the correct alignment of the ground surfaces and the correct clearance between the gears. The only other things are as I mentioned before is to ensure that the shim stack below the circlip is snug so the gear shaft is pulled into the correct position and the bearing housing is correctly held down as otherwise you will get a false reading.

Also when the clearance is getting close to correct, 0.025 can make a noticeable difference so 0.25mm is in bevel shimming is a big move! Whatever, I received your order for shims and I will make sure get sufficient to ensure you can play for the rest of the week
Nigel

Hi Nigel. I am learning all the time with this engine and with the fantastic, much appropriated assistance and advise from yourself, Bob and others I feel very humbled. Thank you very much. Dave.

[Jordan]

May I ask for clarification on this interesting topic?
From reading here and a previously posted thread on this topic, I thought I understood this:

Shimming should achieve zero running clearance with no binding. Due to tolerances, that might only be achievable at a certain point, but never should there be negative clearance.
Even with the above done as described, the gears may not be meshed correctly, due to the bevel gear teeth being helical. That produces convex and concave mating surfaces.
The best mesh is achieved using bluing compound and trial fits, to establish maximum tooth surface contact patch area.
The best mesh might result in the machine-ground outer surfaces of the mated gears NOT to be level with each other.
When best mesh is confirmed, a hand-ground (probably with a small angle grinder) spot across the edges of the mated gears can be done, to simplify future re-shimming. As long as there's zero clearance, no binding, and the hand-ground spot is perfectly matching, all is good.

Is all that correct?
I can't see the advantage of the hand-grinding, if matched machined-ground edges were the target.

[LaceyDucati]

Hello Jordan

Yes you seem to be mostly correct in what you have summarised. However the tightest mesh can occur anywhere, as the variation of clearance is a feature of poor gear concentricity. This varies slightly from one set to another and is not from my experience down to wear more manufacture. The variation is invariably only a few thou and in practice equates to fractions of a degree, so is immaterial. This variation is the reason I only take timing figures in the first rotations leading away from all the dots lined up (or the position they are arranged). This way you are always measuring with the same teeth in mesh for consistancy.

The "hand" ground marks are on the gears from the factory. On Italian gears they are always there but not always clearly visible due to minor surface corrosion or light carbon deposits. If you examine them closely with an eye glass they are usually clearly visible. Sometimes when I chemically clean components that are stained from carbon deposits, it is quite a surprise to see how bright these ground surfaces become against the rest of the gear. The gears were most likely set on a jig at the factory and the area in question then leveled by a small grinder. These ground surfaces then being used to set the gears on assembly of the gears in the engine. You cannot work off the machined surfaces.

Although you could perform this grinding to a set of "unmatched" gears after you had set them via blue, you would need to completely strip and clean the components exposed to the grinding. I have done this myself as it can help in the future.

Regard Nigel

[DewCatTea-Bob]

May I ask for clarification on this interesting topic?
From reading here and a previously posted thread on this topic, I thought I understood this:

Shimming should achieve zero running clearance with no binding. Due to tolerances, that might only be achievable at a certain point, but never should there be negative clearance.
Even with the above done as described, the gears may not be meshed correctly, due to the bevel gear teeth being helical. That produces convex and concave mating surfaces.
The best mesh is achieved using bluing compound and trial fits, to establish maximum tooth surface contact patch area.
The best mesh might result in the machine-ground outer surfaces of the mated gears NOT to be level with each other.
When best mesh is confirmed, a hand-ground (probably with a small angle grinder) spot across the edges of the mated gears can be done, to simplify future re-shimming. As long as there's zero clearance, no binding, and the hand-ground spot is perfectly matching, all is good.

Is all that correct?
I can't see the advantage of the hand-grinding, if matched machined-ground edges were the target.

" May I ask for clarification on this interesting topic? "

____ But of-course you "May", Jordan,, (as well as anyone-else !) !
__ Once again Jordan, you have proven your well above average value to our web.site ! _ Thanks a lot for bothering to submit your quite relevant post to this thread !



" Shimming should achieve zero running clearance with no binding.
Due to tolerances, that might only be achievable at a certain point, but never should there be negative clearance. "

____ Good point... Such occurrence may be possible but ought be rare, and should be concerning rather quite minute amounts of such clearance run-out variances. _ So if one were to happen to discover such a b.gear-meshing discrepancy (likely only during highly detailed shimming-work), I'd then say that the (rather unexpected) non-consistent clearance-limits ought-to be set to be split-up towards 75% slop & 25% negative-clearance (with the neg.clearance being set under .0005"), as such a small amount of neg.clearance ought-to wear-away during the following engine break-in period.
If it's ever found that such unlikely run-out clearance-variation much exceeds .002" (in it's total-range), then I'd suggest replacement of the parts in question, (although the engine should still run well enough with slightly over double that amount).
(In all my experience with resetting bevel-gears, I never found any such varying-clearance case that required ANY warranted concern ! _ I merely made-sure that no binding-effect could be detected.)



" The best mesh might result in the machine-ground outer surfaces of the mated gears NOT to be level with each other. "

____ Yes that circumstance could possibly be a possibility, but somewhat unlikely with all the related parts not being suspect. _ In order for such miss-mating of the grind-patch level-matching to actually be preferred as "best mesh", I'd pretty-much suspect that there's something wrong with at-least one of the related parts which are being worked with,, or else, it could be suspected that the factory-worker who grind-marked the particular factory-matched bevel-pair, had just happened to not have bothered to fully set-up the particular bevel-pair correctly, before going-ahead with grinding his patch-area of grind-marks.
It's anyone's guess as to what the case may actually be, (for such grind-level miss-mating to actually be preferred as a better mesh circumstance). _ I really don't think anyone ought-to be concerned about ever running-into such a case of such unlikely circumstance.



" When best mesh is confirmed, a hand-ground
spot across the edges of the mated gears can be done, "

____ Such second-guessing above the expertise of the factory-worker could possibly actually be superior work to prefer to follow,, however only someone with high mechanical-skills and much experience with bevel-gear setting, should be considered competent enough to do such involved work.
This degree of work is really not necessary in the vast-majority of bevel-gear resetting jobs.



" As long as there's zero clearance, no binding, and the hand-ground spot is perfectly matching, all is good. "

____ INDEED so !



" Is all that correct? "

____ I-myself really have no argument with any of it, (but just a little concern of some of it's likeliness to be really concerned with).



" I can't see the advantage of the hand-grinding, if matched machined-ground edges were the target. "

____ Well the 'machined' tooth-levels are-not the actual 'target' (for checking for perfect mating), as it's a fair possibility that THOSE outer levels may-not flatly line-up with perfectly mated bevel-gears.
That's why the grind-mark patch-areas are considerably more useful for the bevel-gear mating task.


Enlightening-Cheers,
-Bob

[machten]

" The best mesh might result in the machine-ground outer surfaces of the mated gears NOT to be level with each other. "

____ Yes that circumstance could possibly be a possibility, but fairly quite unlikely with all the related parts not being suspect. _ In order for such miss-mating of the grind-patch level-matching to actually be preferred as "best mesh", I'd pretty-much suspect that there's something wrong with at-least one of the related parts which are being worked with,, or else, it could be suspected that the factory-worker who grind-marked the particular factory-matched bevel-pair, had just happened to not have bothered to fully set-up the particular bevel-pair correctly, before going-ahead with grinding his patch-area of grind-marks.
It's anyone's guess as to what the case may actually be, (for such grind-level miss-mating to actually be preferred as a better mesh circumstance). _ I really don't think anyone ought-to be concerned about ever running-into such a case of such unlikely circumstance.

I've seen this that Jordan states in a few cases where bevel gears have not been shimmed correctly in the past and the mating surfaces have have worn such that the best mating surfaces to eliminate lash were not the best original mating surfaces. That being said, I agree with DCT Bob that, in the absence of extremeis, "I really don't think anyone ought-to be concerned about ever running-into such a case of such unlikely circumstance."

Kev

[DewCatTea-Bob]

[quote= machten ...

" The best mesh might result in the machine-ground outer surfaces of the mated gears NOT to be level with each other. "

" I've seen this that Jordan states in a few cases where bevel gears have not been shimmed correctly in the past and the mating surfaces have have worn such that the best mating surfaces to eliminate lash were not the best original mating surfaces.

____ I believe I correctly understand what the thoughts of your chosen-wording actually means to convey Kev, (although if I actually got it right, then it could stand some rewording).
We all need to be more careful/thoughtful when choosing our stated post-wording, as we can too often find ourselves having to ASSUME what another post-writer had meant to convey with their statements ! ...
__ For instance, I'm NOW thinking that Jordan may've also thought the same-thing as I had when I first/PREVIOUSLY read the submitted sentence (above in the blueish-color)...
I had originally ASSUMED that the writer of that sentence had just happened to pick the compounded-word: "machine-ground" in place of the wording that Nigel or I happened to choose for representing the factory-done 'grinding-level' made with a hand-held grinding-tool (rather than the outer machining-work originally rather done by 'machine'.
But NOW when I read that possibly carefully-chosen compound-word without the inspired bias-thinking concerning the bevel-level alignment-matching that I thought Jordan was meaning to have addressed & contended with,, if the writer was actually meaning exactly what he had stated (rather than the grind-mark patch-area), then in THAT case, everything stated within all the post-wordings makes fairly perfectly-fine sense and-so there's actually no conflict (between that which the writer was meaning to convey and that-other-of-which Nigel & myself were meaning to convey), to be contended with, (as I [and seemingly others as well], had gathered/assumed that Jordan had meant to have addressed & un-conflicted) !
__ Does this make good-sense to everyone now ?
If not, then have a look-read at lloydy 1/Dave's pic which I've re-posted (at the bottom of my post at the top of this page), and see if my inserted-wording below it helps to clear-up all this (possible) misunderstanding.


Hopeful-Cheers,
-Bob

[ducwiz]

fyi: http://i.minus.com/1391624674/4PCa4S5GXenbbTcMEAipDw/d8gmyql9spk4P/mesh_job.pdf

[nalimugmug]

I used the attached article to set up my bevel gears

http://www.bevelheaven.com/duc-mags-CamDrive-index.htm

Thanks to bevelheaven

Hope this helps