Not a good weekend... 350 NC dis-assembly

[DewCatTea-Bob]

[quote= SebringMike ...
" I purchased a 76.5mm Omega piston from Nigel. "

____ Unless your previous piston was a 76.4mm 1st.overbore, then it seems you would've had to've had your cylinder bored-out rather than merely "honed".
__ Is the Omega-piston designed to fit n-c.350-engines, or has it's skirt-length been modified ?
Either way, it would be nice to see a picture of your Omega-piston !



" I provided the machinist the dimensions you suggested, and I'm waiting for him to respond regarding his ability to meet those dimensions. "

____ I sure wouldn't count-on any particular OD.dimension turning-out to be exactly perfect for best-possible fitment of the resulted bushing into the ks.casing-hole, especially since you went-ahead & had it's boss welded-up !



" I also have a new normal bushing (without the flange) as a backup. "

____ That's good, that-way you can try fitting it into your welded-up ks.hole and see how tight or loose it fit's, then measure it's exact OD.dimension and have your custom-bushing's OD adjusted accordingly.



" I had the kickstarter boss TIG welded, "

____ While of-course I wouldn't have recommended against going that extensive route,, I was left inclined to advise avoiding such unnecessary modification with it's uncertain outcome, (had you not ignored the continuation of this thread). _ Cuz after the welding-material has been added and-then partially removed by the clean-up aftermath, the otherwise straightforward fitment of a new bushing then likely becomes more complicated (and quite possibly additionally problematic).
__ How about posting a pic showing the resulted weld repair-work ?



" While it may not have been mechanically necessary, "

____ Now if you somehow manage to get the welded-up repair-work cleaned-up/machined to be pretty-much near identical to stock-form, then a rather regular modified-bushing will fulfill your replacement needs.
But had you not gone-ahead & jumped-forth with you weld-repair attempt,, I had intended to rather advise skipping-over that excessively-complex step and instead go-with the more elaborate modification-work that allows the fitting of the modified-bushing with the extra-thick brim-flange, as that repair-route would've adequately dealt with the common damage issue.
However now,, I guess we may be allowed a chance to learn how well the weld-material holds-up against the potential kick-back damage, compared to the stock casing-material.
____ What material are you inquiring to have your custom-bushing made of ?



" it also didn't cost much in time and effort to have it cosmetically repaired. "

____ That's quite an unexpected pleasant-surprise ! - (Providing the job is completely done with.)


Hopeful-Cheers,
-Bob

[SebringMike]

The piston was advertised as replacement for the 3 ring Borgo piston, suitable for Ducati NC 350s. I confirmed that it was suitable for my Sebring with Nigel... with the note to check the squish upon assembly.

http://www.laceyducati.com/ducati-parts/350-road-piston-765mm-p-589.html

A photo of the TIG work after cleaning it up. The weld shows two pores on the surface of the repair; I don't feel this is an issue when I get the improved bushing in place. The ID of the repair cleaned up very nicely.

I've asked the new bushing to be machined from bronze.

[DewCatTea-Bob]

____ Thanks for the posted pix Mike !

[quote= SebringMike ...
" The piston was advertised as replacement for the 3 ring Borgo piston, suitable for Ducati NC 350s. "

____ It may be a suitable fit but, it's comp.ratio is certainly higher than that of a stock Sebring-piston !
Were you informed of what it's CR is expected to be ? _ It looks to be at-least as high as that of a w-c.350-piston, (thus possibly over 9.5:1).
Such a high-dome 350-piston combined with the stock mild cam, will certainly necessitate use of the compression-release during kick-starting ! _ So if you had previously found the kicking-procedure to be tedious before, then you better be prepared for quite notably intensified kick-staring hardship with your new high-CR.piston !
__ The intense increase in kick-over hardship is-not experienced with w-c.350s that employ the same high-dome type piston because, those other 350-eng.models employ wilder cams that can't help but allow bleeding-off of the compression during the low eng.revs of kick-starting.
There's a couple changes you could possibly make to help insure that the resulting increase in kick-back likelihood & intensity becomes effectively countered...
For one, you could modify the stock AAU so as to have a wider range than it's normal 28-degrees. _ That-way you could possibly end-up with a static-timing of 0-degrees and-yet still retain the max.advance of 36-degrees before TDC. - (You'd just have to increase the AAU's 14-degree mechanical rotation-range an extra 4-degrees.)
For another helpful change, you could replace the stock mild cam with a wilder model such as a Scrambler-cam or Mark-III cam. _ (I much recommend that you replace the Sebring's stock Monza-cam with a Mark-III cam.model !)
If you don't bother to make either of these recommended changes, then you'll certainly run the risk of over-straining your ks.boss repair-work to a point that exceeds it's robusticity to remain in it's current repaired-state !
Of-course your preventative-steps (to avert the common [cosmetically severe] damage to the boss-edge of the kick-starter hole), will help inhibit the recurrence of similar damage to such an extensive degree (as your motor-case has already experienced). _ However during the times it takes you to learn to avoid the intensive kick-back episodes that can cause such damage,, it's still likely that something will give-way from a full-fledged kick-back, and-so you really ought-to care to take any steps that'll help avoid stress-testing your completed repair efforts !



" A photo of the TIG work after cleaning it up. "

____ It appears to've turned-out pretty-decent ! _ Hopefully it's actually accordingly stronger than stock as it's apparent increased-robustness seems to exhibit.
And hopefully all your finished repair-work will remain fully-intact as finally completed !



" The ID of the repair cleaned up very nicely. "

____ Have you tried checking the resulted ks.bushing-hole for fit-ability with the standard-bushing you already have ?
If so, does that std.bush slip-in/through it's retainer-hole, or is it rather a tight-fit,
(since after you've welded-up the hole's boss) ?



" I've asked the new bushing to be machined from bronze. "

____ What's your reasoning for choosing a relatively soft copper-alloy ?
I'd be more apt to suggest a less malleable copperless-alloy that's also stronger than the stock brass-alloy, such as stainless-steel or even something tougher yet (so long as it's not a brittle iron-alloy).


Hopeful-Cheers,
-Bob

[SebringMike]

Bob,
The bike wasn't running when I received it, so I have no concept of how easy/hard it was to start with the OEM piston. Having previously read the posts on your recommended starting procedure, I will need to work on perfecting the process to ensure successful starts. I've also contemplated installing the compression release device as (I believe) was available on the 1966+ 350s. Of course that assumes that those devices are suitable to be installed on my bike. Thoughts?

I have not tried installing the new (old style) bushing yet, as I haven't received it via mail yet. The original bushing is a snug fit into the newly repaired hole. I've assumed that the original bushing has worn, and therefore the new bushing will be even tighter in the case hole. Once I've received the two different style bushings, I will a) select the best choice and then b) determine if I will make the ID of the hole larger or (more likely) freeze the bushing and heat the case.

I selected bronze because it's (in my estimation) what the original bushing was made of. As I intend to use the bike for occasional rides, I believe that my wear-and-tear on the bike will be minimal; our riding season is very short, and I'm blessed with having several bikes to ride. I understand your recommendation, and as the new style bushing hasn't been machined yet, I'm still free to make that change.

Regards,
Mike

[DewCatTea-Bob]

[quote= SebringMike ...
" I've also contemplated installing the compression release device as (I believe) was available on the 1966+ 350s. Of course that assumes that those devices are suitable to be installed on my bike. Thoughts? "

____ I've never seen any stock 350-cylinder without a compression-release !
Doesn't your 350-cyl.head have an ex.valve-cover that's already equipped with it's-own cr.mechanism ?
If not, and-so you need to procure one,, then you'll need to get one from another n-c.350, as those employed on 350/450-w-c.models won't fit ! - (Assuming your n-c.Sebring still retains screw-adjuster type rocker-arms, and not w-c.type shim-adjusted rockers.)
__ While it's not too awfully difficult to get-by without a working comp.release with the stock 8.5:1-piston,, you're certainly apt to make much good-use of such, with that high-CR.piston you're going to be dealing with ! - (Assuming you'll be sticking with a cam.model that's milder than a Mark-III camshaft.)



" I have not tried installing the new (old style) bushing yet,
The original bushing is a snug fit into the newly repaired hole. I've assumed that the original bushing has worn, and therefore the new bushing will be even tighter in the case hole. "

____ You should closely 'mike' them both for comparison. _ I doubt you'll find the used-one's OD being any greater than a half-thousandth less.
These stock (rim/lip-less) bushings need to fit very-tight within their receptacle-hole, or-else they become worked-inward and eventually get ground-away by 1st.gear !
__ I much doubt that a standard/non-oversize bushing will still fit as tight as it ought-to, (especially since there's a chance that the welding-work has warped the otherwise-perfect circumference of the hole). _ So your custom-bushing ought rather be made near-around 2-thousandths wider than your new/stock-bushing.



" Once I've received the two different style bushings, I will
select the best choice "

____ Well that would have-to be the custom-one with the built-in rim-lip !



" then
determine if I will make the ID of the hole larger "

____ I'd advise avoiding getting-started with such an attempt, (unless the hole-circumference is already skewed-up from the welding-work).



" or (more likely) freeze the bushing and heat the case. "

____ That involved process need-not be necessary with a std.bushing,, however an over-sized version ought-to, and I'd recommend placing the over-sized bushing onto it's ks.shaft and leave them both placed together in the freezer (at-least over-night prior to insertion of the bushing into it's case-hole).



" I selected bronze because it's (in my estimation) what the original bushing was made of. "

____ I'm fairly-sure that the stock material is more of a brass-type alloy, however both bronze & brass are metal-alloys which may possibly include a widely varied range of different mixed metals with copper being the prime base metal ! _ I'd be inclined to avoid such relatively weak & malleable copper-alloys.
__ Ducati had chosen the bushing-alloy which they did, no-doubt just because it's been a standard-practice to form ordinary bushings from an alloy that's preferable for non-directly lubricated relatively-light load-bearing surfaces. _ But then they apparently had no-idea that their cheap (poorly designed) bushing and it's surrounding area would ever become subjected to such excessive detrimental forces as those created from the occasional severe kick-back ! _ So with that fairly likely deleterious-circumstance now finally taken into consideration,, a rather non-standard bushing-material that's more apt to hold-up against such occasional overly-excessive pressures, is certainly called-for ! _ As this afterthought-factor has revealed itself to be considerably more important than the antiseizing-factor that's the standard prime-consideration for normally preferring soft-alloys for bushing-material. _ And besides,, even made from the hardest material available, it's extremely unlikely that there'd ever be any chance of the ks.shaft becoming seized-up within such a custom-bushing ! - (Assuming of-course that it's ID has sufficient clearance over the ks.shaft-tip's OD.)



" I believe that my wear-and-tear on the bike will be minimal; "

____ That's good-reason to substitute the original bushing-material that's meant to absorb accumulated wear-&-tear type wear (to save the casing's material from wear), and rather make-use of a stronger metal for the custom-bushing that's thusly more apt to stand-up against the greater enemy !
And even your expected minimal wear&-tear can't possibly cut-down the amount of the full effect of even a single fateful severe kick-back episode !



" I understand your recommendation, and as the new style bushing hasn't been machined yet, I'm still free to make that change. "

____ I suggest that you actually do.
__ Do you fully realize that besides preference for a stronger material, you also still have the option of making your custom-bushing with a thicker rim-lip ?



____ Have you developed any serious consideration concerning the use of a less mild cam.model or the cutting-back of the advance-lead of the static-ign.timing ?


Hopeful-Cheers,
DCT-Bob

[SebringMike]

Bob,
My bike was never equipped with a compression release device. Valve covers are identical (intake and exhaust), with no setup for CR, and no lever on the handlebars. Yes, the bike has screw type rocker arms. I'll keep my eyes on Ebay and the like for a CR assembly from a NC 350.

I've not contemplated the milder cam, and probably won't proceed (at this time) with the change. As I stated in an earlier email, my budget is well blown on this project, and I'm trying to control discretionary expenditures. My plan is to complete the bike, and ride it for a while. Once I've put some miles on it, I can then make the decision whether to keep it as-is, or upgrade. From a purely economic standpoint, it sounds like adjusting the timing is a better, but possibly more complex solution.

Regarding the kick-starter bushing... my (old) understanding was that the thickness of the new "flange" would be identical to the shim currently installed on the kick-starter. Now having looked at the parts breakdown, are you suggesting that both the shim and the washer can be replaced with the "flange"; ie 1mm thick washer+0.5mm thick shim? And if that's what you are saying... it's all clear to me now on why I should proceed with the stainless steel bushing.

Mike

[DewCatTea-Bob]

[quote= SebringMike ...
" I've not contemplated the milder cam, "

____ I hope "milder" was a typo for 'wilder', cuz otherwise it seems you don't understand how a wilder-cam reduces the compression-ratio during kick-starting.
Would you like to have me elaborate the explanation ?



" and probably won't proceed (at this time) with the change "

____ Then you will discover for yourself (as I-myself already have) how hard it is to kick-over the engine with a high-top piston combined with the overly mild valve-timing of the stock camshaft.



" it sounds like adjusting the timing is a better, but possibly more complex solution. "

____ Yes indeed retarding the static-timing (only) is the best way to cut the chance of kick-back episodes !
And doing so is-not so complex to accomplish, as you just have-to do some grinding-work on parts of the AAU.mechanism. ...
The width-thickness of the AAU's stop-tabs can get-by with their inside-surface ground-away 50 ~ 70%, and the narrow corresponding area-section of the flyweights can also have at-least the same amount of material/space removed,, so as to allow for increased advance-range, (thus allow for a less advanced static-timing starting-point [yet still attain the stock max.advance setting]).



" Regarding the kick-starter bushing... my (old) understanding was that the thickness of the new "flange" would be identical to the shim currently installed on the kick-starter. "

____ To state same with clarifying wording...
Concerning the custom-bushing,, the thickness of it's 'rim-lip' -("flange", if-ya-will) would-be near same as that of the 'thrust-washer' -("shim", if-ya-will) that fit's over the tip-end of the ks.shaft (between it & the normal-bushing).
Assuming this was indeed your initial "understanding", then you had understood quite correctly !



" Now having looked at the parts breakdown, are you suggesting that both the shim and the washer can be replaced with the "flange"; "

____ No. _ (I've previously given explanation for the actual source of the optional extra space, within a prior-post back in March. _ So it seems I then failed to explain it clearly enough for you.)
__ Let's detail/cover the relevant parts-breakdown...
While I no-longer recall the exact thicknesses of all the space-taking pieces which fit-over the ks.shaft, there are four pieces which come into play,, and they are: the 'thrust-washer'; the large-OD/plate-washer (which helps hold the ks.return-spring in place); the long spacer-tube/sleeve; and, the (outermost) shim-washer.
To rather easily acquire space for beefing-up the strength of the custom-bushing,, the simplest way is to add an included "flange" (to the outer-side of the bushing) which has a thickness-dimension near equivalent to that of the 'thrust-washer' (which thusly gets replaced).
(This is the rather straight-forward method I've employed for over a half-dozen busted n-c.case-ks.holes that ended-up with either regular brass, or hardened aluminum-alloy, or treated steel custom-bushings.)
Because the resulted thickness of the included flange is somewhat petite, a stronger than brass material is most preferred.
__ However in order to create more additional space for a thicker more-robust flange/rim-lip, it's possible to make it .5 ~ 1mm thicker by subtracting an equal amount from the spacer-tube/sleeve. _ You'd just need to make-sure to evenly grind-off the same amount of material away-from the inner-end of that spacer-tubing, is all.
This-way, the custom-bushing can then be made considerably stronger and more robust (to help hold-up against severe kick-back episodes that are known to damage the casing-boss of the ks.bushing-hole) !
(This further increased extreme-measure was only ever employed just one-time by me and also made out-of carbon-treated nickel-steel, intended for an unusual extremely-damaged ks.bushing-hole, [which probably should've been welded-up like yours, but wasn't].)
__ Considering that you're intending to take your risk-changes with the high-comp.piston (that's more apt to cause more intense kick-back episodes), I suggest you consider taking-advantage of every robustifying advantage available for a custom-bushing.



" ie 1mm thick washer+0.5mm thick shim? "

____ Which is which ? _ There should only be just one 'thrust-washer', which I had thought was 1mm-thick but you had stated that yours was .5mm.



" And if that's what you are saying... "

____ I'm not sure what you're referring-to exactly.
__ Back-before, I had previously mentioned that the thrust-washer's purpose could still be fulfilled well enough with a .2 or .1mm shim-stock that's normally intended for the bevel-gear shimming, even-though I believe it's unnecessary,, (I had never meant to suggest substituting a thrust-washer/shim as thick as .5mm).



" it's all clear to me now on why I should proceed with the stainless steel bushing. "

____ Yes, that would probably be near*best, if you're sticking-with the thinner-flange design for your custom-bushing ! _ (* Although there's no-doubt some-odd super steel-alloy that would be even stronger for the intended job.)
__ In my previous-post when I asked if you were fully aware of the option to make your custom-bushing's rim-lip thicker, I was just checking to make-sure that you were still aware of all your possible custom-bushing options.
Since you (unlike myself), have bothered to fully-repair the damaged casing-boss,, your case may-not have as much need for your custom-bushing to employ both strengthening options -(of a thicker rim-lip and a stronger construction-material). _ However you really ought-to consider what-all's at-stake before you possibly decide to dismiss either bushing-robustifying option.



____ All this increased-detail stuff (and more) would've come-up and been covered long-ago, if you hadn't ignored continuation of this thread back when it was still active nearly 2-months prior.


Hopeful-Cheers,
-Bob

[ecurbruce]

Bob says;
 I hope "milder" was a typo for 'wilder', cuz otherwise it seems you don't understand how a wilder-cam reduces the compression-ratio during kick-starting. 
Would you like to have me elaborate the explanation ? 

Hi Bob, I would enjoy hearing (reading) your detailed explanation of how a wilder cam reduces the compression ratio. ..

Bruce.

[DewCatTea-Bob]

[quote= ecurbruce ...
" I would enjoy hearing (reading) your detailed explanation of how a wilder cam reduces the compression ratio. .. "

____ As you have your post worded Bruce, one would think they're no-doubt going to be entertained by some concocted fish-tale with a BS.explanation of the impossible.
But actually of-course, there's no-way any camshaft could reduce (or increase) the actual-mechanical compression-ratio dimensionally-created by the displacement of the piston within the cylinder-chamber's physical-capacity !
However, the active-max.compression resulting within the combustion-chamber can actually vary-around a fairly significant amount, depending on a number of operating factors besides that caused by a particular camshaft's valve-timing.
__ Naturally the best way to trap maximum intake-charge within the cylinder at all RPMs, would be if the camshaft could somehow control the intake-valve to open & close just like a reed-valve would, (which would have the valve open whenever the air-pressure within the cylinder is less than the atmospheric-pressure and instantly-closed as soon as the cyl.pressure begins to exceed the pressure opposite the valve-seat) ! _ But unfortunately the mechanical valve-timing of the OHC.setup can't similarly provide such valve-control extremes at both the highest and lowest RPM.ranges. _ So we have to be stuck with valve-timing that best traps the intake-charge, either during low-RPM or high-RPM, (or some compromise in-between).
So a mild-extreme would have the intake-valve closing near 180-degrees before TDC, which would trap pretty-much the entire cylinder-capacity to become compressed at TDC,, thus-then resulting with the maximum-possible compression-ratio (as the 'CR' is normally calculated), but only at the lowest RPM.range (such as when 'kick-starting') !
Conversely, a wild-extreme would have the in.valve closing nearer 90-degrees before TDC, which is helpful to allow more high-velocity intake-charge to get a chance to attempt improved partial-filling of the available cyl.capacity near the highest RPM.range (such as when red-lining).
But (with such otherwise appropriately-considerate late in.valve-closing) during the low kick-starting RPMs, there's then insufficient intake-charge momentum to fight it's way into the cylinder against the air-volume within that's (then*) tending to be expelled past the still open in.valve (* because-of the pressure being exerted by the rising piston). _ So thus-then some of the air that would've otherwise been kept trapped, instead gets a chance to escape,, thusly lowering the resulting active compression-ratio !
__ So ya see, that's the manner in which a wild-cam effectively lowers the actually-resulting compression-ratio during kick-starting RPMs !
____ I hope that's "detailed" clear enough, cuz I don't think I can explain it much better.


Enlightening-Cheers,
D.Bob

[ecurbruce]

Thanks, Bob, that's exactly what I'd hoped to hear from you, in that detail.
I should have included on the end of my wording "during kick starting...".
No other motive was intended

Thanks, Bruce